ML20140C484

Effects of Inhibitors & Poisons on Performance of Passive Autocatalytic Recombiners (Pars) for Combustible Gas Control in Alwrs

ML20140C484
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Issue date:	05/22/1997
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ML20140C472	List: ML20140C484 NSD-NRC-97-5167, Forwards EPRI Rept, Effects of Inhibitors & Poisons on Performance of Passive Autocatalytic Recombiners (Pars) for Combustible Gas Control in Alwrs, Requested by NRC Staff During Hydrogen Control Meeting on 970520
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NUDOCS 9706090288
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Text

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I EFFECTS OF INHIBITORS AND POISONS i

ON THE PERFORMANCE OF i

PASSIVE AUTOCATALYTIC RECOMBINERS (PARS)

FOR COMBUSTIBLE GAS CONTROL IN ALWRs 4

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May 22,1997 l

Prepared by the EPRI ALWR Program i

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3412 Hillview Avenue, Palo Alto CA 94303 3

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aEsteaJeEik EFFECTS OFINHIBITORS AND POISONS ON THE PERFORMANCE OF PASSIVE AUTOCATALYTIC RECOMBINERS (PARS)

FOR COMBUSTIBLE GAS CONTROL IN ALWRs l

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May 22,1997 J

Prepared by the EPRI ALWR Program 1

Electric Power Research Institute 3412 Hillview Avenue, Palo Alto CA 94303

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SUMMARY

This report summarizes available quantitative and qualitative information to assess the effects of potential deactivators (chemical poisons and physical inhibitors) on the performance of passive autocatalytic recombiners (PARS) being proposed for control of hydrogen in AP600 design basis accidents (DBAs). PARS are required to perform their safety function not only after exposure to potential contaminants during operation, but also in an accident environment that may contain various gases or aerosols that are potentially poisonous to the palladium or platinum PAR catalyst elements.

The report begins by providing a technical understanding (based on established chemical / catalyst principles) of the mechanisms that can reduce recombination in PARS. It then reviews the amounts of the chemical species that can be present during a PWR accident. Since the function of PARS in a DBA is to control an amount of hydrogen produced by a slightly damaged core, the main focus of the report is on fission products from gap releases, principally iodine. However, the information and data also address poisons released from a beyond-design-basis damaged core accident. This provides added assurance that even such levels of contaminants would not degrade a PAR's recombination capacity to the extent that I

it could not perform its safety function in a DBA. Finally, the report summarizes existing test data on the effects of suspected inhibitors and poisons on the types and forms of catalysts in PARS. The sources of test data include (1) model recombination tests conducted several years ago by PAR developers and recently by EPRI/EdF/CEA and (2) benchtop laboratory recombination tests conducted many years ago on palladium and platinum catalyst pellet-bed filters subjected to a wide range of chemicals in the hydrogen / air feed stream. Among the potential poisons investigated by these test programs were substances known from chemical principles to have some poisonous effect on noble metal catalysts. These include iodine, methyl iodide, chlorine, bromine, sulfur, tellurium, and seleniu.m.

The conclusions of this study are although existing information and data do not identify any contaminant

=

expected to be present in a containment during operation to significantly degrade the performance of a PAR in an accident, a surveillance program is needed in which PAR elements are periodically removed from service and their hydrogen recombination capacity checked of all the contaminants released during accidents. halogen gases have the most deleterious effect on PAR performance on the basis of PAR model tests in the presence of gaseous iodine supplemented with data from laboratory benchtop tests on the effects of iodine, methyl iodide, and hydrogen iodide on the efficiency of fixed-bed catalyst devices, it is estimated that halogens released in a DBA (intact core) would, result in minimal reduction ii

l.'

in PAR recombination efficiency and that even significant levels of halogens l

resulting from early in-vessel core damage would reduce PAR efficiency by no more than about 15 percent.

regardless of their chemical composition, blockage or chemical poisoning by aerosols introduced into the containment atmosphere in an accident will not i

have large effects on PARS because (1) a large fraction of aerosols will settle out i

or be scrubbed out of the atmosphere before they have a chance to reach PARS through diffusion or convection, (2) the large majority of aerosols that do reach functioning PARS are expected to be carried vertically through the one-centimeter-wide open flow channels without contacting the catalyst element surfaces at the walls of the channels, and (3) particulates managing to reach catalyst sites are much less reactive than poisonous gases. This conclusion has been confirmed by two types of tests: PAR tests with aerosols from burning cables and laboratory benchtop tests of pellet-bed catalysts with a wide variety of chemical aerosols.

Review of all currently available data on the effects of potential poisons on PAR performance indicates that for an AP600 under DBA conditions, a minimal reduction in PAR recombination capacity is expected, so that an assumption of a 10 percent reduction factor observed when sulfur-bearing cable insulation was burned immediately below a PAR is sufficent to cover both DBA fission products and a cable fire.

Even if the accident were to progress beyond a DBA to substantial in-vessel damage, PAR recombination capacity would be reduced by no more than 25%,

which is sufficent to address both the 15% reduction in efficiency observed for an NIS PAR model exposed to a conservatively large mass of elemental iodine vapor and, separately, the 10 percent reduction observed in a cable fire test.

(Even this poisoning from iodine would burn off in a DBA from the catalytic heat generated from recombining a mixture with 3 vol % of hydrogen.)

Furthermore preliminary information from the ongoing H2 PAR test program in France, which is generating test data on one type of PAR subject to simulated fission products from a PWR severe accident, indicates no significant reduction in PAR performance. It is therefore likely that further evaluation of this data will show that the 25% PAR capacity reduction factor suggested by this report is overly conservative.

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.n TABLE OF CONTENTS

SUMMARY

.......................................................................................................................................ii S ECTION 1. B ACKG RO UND AND PURPO SE.................................................................................. 1 SECTION 2. HOW PARS AND CATALYSTS WORK........................................................................ 4 2.1 HOW PARS FUNCTION................................................

........................................................4 2.2 HOW NOBLE METAL CATALYSIS WORK..........:.......................................................................... 4 SEGON 3. DEACITVATION OF CATALYSTS............................................................................... 7 3.1 CATALYST DEAC11VA110N MECHANISMS................................................................................. 7 3.2 DEACTIVA110N BY INHIBITORS.................................................

...........................................7 Fouling During Operation................................................................................................... 7 Wetting.............................................................................

........................................10 Fouling Dunng an Accid en t........................................................................................ 11 3.3 DEACTIVA110N BY POISONS...................................................

.....................13 3.4 HOW DEACTIVATORS REACH PAR CATALYST........................................................................... 15 InactivePAR.............................................................................................................15 Functioning PAR............................................................................................................ 15 SECTION 4. COMBUSTIBLE GAS RELEASES AND REGULATORY LIMITS...................................16 4.1 DESIGN B ASIS ACCIDENTS.........................................................................

......................16 4.2 S EVERE A CCIDENTS........................................................................................................... 17 SECTION 5. POTENTIAL PAR POISONS IN NUCLEAR PLANT ACCIDENTS...............................18 5.1 FISSION PRODUCT RELEASES..................................................................................................... 18 i

5.2 CHEMICAL FORM OF FISSION PRODUCT RELEASE....................................................................... 19 i

5.3 NON-FISSION PRODUCT MATERIALS RELEASES........................................................................... 22 1

5.4 FISSION PRODUCT AND NON-FISSION PRODUCT MA1ERIALS THAT ARE PO1ENTIAL POISONS................. 23 i

5.5 AMOUNIS OF POTENTIAL POISON FISSION PRODUCIS RELEASED...................................................... 23 Design B asis Accid en t......................................................................................................... 23 Damage.1 Core..........................................................................................................24 4

5.6 TRANSPORT AND DEPOSITION OF AEROSOLS TO PARS.................................................................. 24 4

i 5.7

SUMMARY

.............................................................................................................................25 SECTION 6.

SUMMARY

OF TEST DATA ON THE EFFECTS OF POTENTIAL DEACTIVATORS ON N O B LE METAL CATA LYSTS.......................................................................................................... 26 6.1 NIS PAR M ODEL TESIS............................................................................................................ 27 Ba t telle Iodine Results..................................................................................................... 27 Battelle Fire Exposure Tests................................................................................................ 30 i

6.2 EPRI /EDF/CEA PAR MODEL TES15......................................................................................... 30 6.3 IPSN H2 PAR SIEMENS PAR AEROSOL TESIS............................................................................... 32 6.4 LABORATORY TESTS ON FIXED BED PELLET CATALYS15.................................................................... 32 6.5 WARRANTY LEVEL OF HALOGENS FOR POISON RESISTANCE OF CATALYST PELLE15............................... 34

6.6 CONCLUSION

S.........................................................................................................

........... 34 S ECTI ON 7. REFEREN CES............................................................................................................. 3 5

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APPENDIX. LABORATORY TESTS ON POISONING OF FIXED BED CATALYSTS.....

A-1. BACKGROUND AND OBJECTIVES........................~ ~...........................

A-2. POTENTIAL POISONS SELECTED FOR TESTING.................................

40 A-3. DEdCRIPTION OF TESTS..........................................

..... 42 Test Arrangement..................................

Application of Gaseous Poisons....................................................................... 42 Application of Liquid Poisons..........~....~........................~................................ 43

... 43 Application of Particulate Poisons........................

. 44 A-4. APPLICABILITY OF TEST RESUL'IS TO PARS...................... m.

...... 44

...m.

A-5. TEST RESULTS AND COMPARISONS WITH AP600 POISON LOADINGSm....

..... 46 Halogen Test Results.............

...................................................................46 Fixed Quantity Non-Halogen Test Results.........

. 47 A-e. REFERENCES.... ~................. ~..... ~.. ~ ~..... ~ ~.. ~. ~ ~.... -

.-~. 49

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TABLE OF FIGURES FIGURE 1.

NISPARUNIT..............................................................................

... 1 FIGURE 2.

SIEMENS PAR UNIT..................................

....... 2 FIGURE 3.

HYDROGEN DEPLETION CURVES FOR NIS PAR MODEL WITHOUT (SOUD CURVE) AN)

(DATA POINTS) IODINE (REF.15)..................................................

.. 28 FIGURE 4.

RECOVERY OF FIXED-BED CATALYST FROM TWO VOLUMES OF LODINE AS TEMPERATURE IN CREASES (REF. 19)...............................................................

I FIGURE 5.

HYDROGEN DEPLETION CURVES FOR NIS PAR MODEL WTniOUT (SOUD CURVE) AND W (DATA POINTS) EXPOSURE TO CASLE FIRE (REF.15)..........

.... 31 FIGURE A-1.

SNE FIXED-BED HYDROGEN RECOMBINER TEST LOOP................

... 50 FIGURE A-2.

TEST SECTION OF SNE TEST LOOP...

.. 51 FIGURE A-3.

MEASURED RECOMBINAT10N EFFICIENCY FOR INCREASING PELLET BED DEPDi (UNPOIS FIGURE A-4.

SNE RESULTS FOR IODINE IN SPRAY FORM IN A 2.25-IN.-DEEP BED (PALLADIUM AND PLATINUM)..................................~.......................................................53 FIGURE A-5.

SNE RESULTS FOR GASEOUS IODINEIN A 2.2S-IN.-DEEP BED (PALLADIUM AND PLATINUM).. 54 FIGURE A-6.

SNE RESUL15 FOR METHYL IODIDE IN A 2.25-IN.-DEEP BED (PALLADIUM)....................... 55 FIGURE A-7.

SNE RESULTS FOR METHYL IODIDE IN A 2.25-IN.-DEEP BED (PALLADIUM)........................ 56 FIGURE A-8.

SNE RESULTS FOR BROMINEIN A 2.25 IN.-DEEP BED (PALLADIUM AND PLATINUM).......... 57 FIGURE A-9.

SNE RESULT 5 FOR GASEOUS AND HIGH VOLATIUTY TESTS ON PALLADIUM AND PLATINUM CATALYSIS................................................................................................58 FIGURE A-10. SNE RESULTS FOR SOLUTION POISONS ON A PALLADIUM CATALYST............................. 59 FIGURE A-11. SNE RESULTS FOR SOLUTION POISONS ON PLATINUM CATALYST. ~....................... 60 TABLE OF TABLES TABLE 1.

PWR RELEASES INTO CONTAINMENT..................................................................19 TABLE 2.

FWR FISSION-PRODUCT CHEMICAL SPECIES......................................................... 20 TABLE 3.

PWR NON-PISSION-PRODUCT CHEMICAL SPECIES....~............................................... 22 TABLE 4.

MASS OF HALOGENS RELEASED TO AP600 CONTAINMENT............................................ 23 TABLE 5.

TEST PROGRAMS ADDRESSING THE EFFECIS OF POISONS ON PARS AND CATALYSTS............... 26 TABLE A-1.

MISCELLANEOUS POTENTIAL POISONS TESTED AND THEIR CHEMICAL FORM....................... 41 TABLE A-2.

AP600 PAR HALOGEN POISON LOADING................................

..... 45 TABLE A-3.

SNE TFST RESULTS APPUED TO AP600 POISON LOADING.......................................... 47 y

Section 1 BACKGROUND AND PURPOSE Passive autocatalytic recombiners (PARS) have been proposed as an efficient, reliable, and cost-effective means for controlling combustible gases in the event of a design basis or severe accident in advanced light water reactors (ALWRs)(Refs. I through 4). In general terms, PARS are stainless steel sheet metal boxes open at the top and bottom and containing many vertical flat catalytic cartridges or plates with open gas flow channels between them. In the flow channels, the recombinable gases diffuse to the palladium-or platinum-coated surfaces of the cartridges or plates, where the catalytic action converts hydrogen and oxygen into water vapor. PAR 2

units from two suppliers are shown in Figs.1 and 2.

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Catalyst Cartridges in) #%.

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91 cm 91 cm Figure 1 NIS PAR Unit 2 In addition to these two PAR types from Germany (Refs. 5 and 6), EPRIis aware of two other commercial designs of PARS, one from Canada (Ref. 7) and the other from Switzerland (Ref. 8). All four designs share the common features of open flow channels between either pellet-filled metal screen cartridges or stainless steel plates. The pellets or plates are coated with either palladium or platinum. Because these four designs are similar, some of the conclusions and observations of this study may be applicable to all of them. However, because the resistance of catalyst systems to poisons is expected to depend on the details of how the catalyst is deposited onto the carrier material, not all of the results in this report may apply to PAR types different from the ones for which data are available.

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Testing has shown that the recombination rate or capacity of PARS increases with increasing concentrations of combustible gases (in terms of percent by volume) and is not retarded by steam or inert gases. However,it is recognized that the recombination efficiency of PARS can be diminished by the presence of contaminants (pollutants) in the containment atmosphere. Contaminants can act as recombination deactivators. which can be either physical inhibitors (blocking the combustible gas from reaching the catalyst) or chemical poisons (reacting with and deactivating the catalyst atoms). It is possible that when the PAR needs to perform its function during an accident, a contaminant may already have been deposited on the catalyst from exposure to a polluted atmosphere during normal plant operation (for example, from paint or welding fumes present during an outage) or a contaminant may be present in the atmosphere as a result of the accident (for example, from fission products released from a damaged reactor core).

PARS must be demonstrated to be capable of performing their design function during or after a postulated plant accident. For control of combustible gases in a design basis accident, PARS must be safety-grade and demonstration of function is called environmental qualification. For control of combustible gases in a severe accident, PARS may be non-safety-grade and demonstration of functionability is called survivability. For both applications, functionability must be demonstrated under environmental service conditions in which the PAR is required to function.

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These environments include pressure, temperature, humidity, radiation, and chemicals.

This report addresses the potential effects of deactivators on the functionality of PARS in design basis accidents in PWRs generally and the AP600 specifically. The i

effects include wetness as a potential physical inhibitor and chemical substances as potential inhibitors or poisons. The approach is to compile existing information and data as a basis for establishing a generic bounding value of a deactivation reduction factor for design e.nd qualification of DBA PAR systems. The reduction factor should be adequate to account for the potential effects of all inhibitors and poisons that may be present and may be able to reach PARS before or during DBAs.

The approach combines qualitative information based on established chemical and physical principles with quantitative information from testing of catalyst systems subjected to a wide range of inhibitors and poisons. The sources of test data include (1) tests on PARS conducted by two suppliers over the past several years, (2) tests on the same two types of PARS conducted recently in France by EPRI/EdF/CEA, and (3) tests on catalyst pellet-bed filters conducted in a laboratory about 25 years ago. An additional important source of test data comes from an IPSN/CEA program in which one type of PAR (supplied by Siemens) has been subjected to simulated fission product aerosols while recombining a hydrogen / air atmosphere. Here we briefly describe the tests and give the preliminary result. A final report by IPSN is i

expected to be available by the end of the year.

Section 2 explains how PARS and catalysts work and Section 3 is a technical discussion of the mechanisms by which metallic catalysts can be inhibited or poisoned. Section 4 quantifies the amounts of hydrogen that have to be controlled and Section 5 identifies the substances in PWR containments that are potential PAR deactivators. Section 6 and the Appendix summarize the available test data.

4 PARS can be used to control combustible gases in both PWR and BWR ALWRs. The former (AP600 or System 80+) are not inerted and the latter (ABWR and SBWR) are inerted with nitrogen. Although much of the information in this report applies to PAR applications in both PWRs and BWRs and thus to all four ALWR designs, a quantitative application is made only to non-inerted AP600 conditions.

Although there are no PARS installed in US operating plants, some plants may find it technically and economically beneficial to replace certain existing complex recombiner systems for design basis combustible gas control with simple PARS. The treatment of the effects of inhibitors and poisons in this ALWR report is to a large extent applicable to the design and qualification of PAR systems in operating plants.

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Section 2 HOW PARS AND CATAIYSTS WORK i

2.1 How PARS Function A PAR is a passive molecular diffusion filter in contrast to the active fixed-bed particle filter configuration used in many industrial catalyst applications. With a PAR,instead of the gases being actively pumped through a fixed bed of catalyst-coated pellets, gases are driven upwards passively (no electric power or moving parts) by buoyancy forces through vertical open flow channels with hydrogen / oxygen molecules reaching the catalyst by diffusion.

In the Siemens design (Fig. 2), the platinum' catalyst is flame deposited along with a ceramic material onto the surface of the thin (0.12 mm) stainless steel plates. The ceramic material provides some degree of porosity to increase the catalyst surface area.

In the NIS design (Fig.1), the carrier material is the porous ceramic, sintered alumina (aluminum oxide). The spherical pellets have diameters in the range of 4 to 6 mm. The sintering gives a very porous structure with a high fraction of open porosity. The thickness of the palladium-impregnated shell is 500 m (microns).

According to the manufacturer, due to the high reaction rate of hydrogen and oxygen, the depth needed for the catalytic action is only 50

m. Therefore the greater impregnation depth is available as a reserve in the event that a portion of the inner surface of the active layer is blocked or poisoned. It is estimated that the total available reactive surface of an NIS PAR device is more than a million square meters (Ref. 2).

Vertical convection driven by catalytic recombination draws gases from the containment atmosphere into the unit from below. Heated gases and water vapor exhaust at the top of the unit and mix with the containment atmosphere via natural and PAR-induced convection. If the PAR is wet from spray or condensed steam, startup can be delayed while the heat of recombination dries the water on the catalyst. Initial wetness can be reduced by adding a hydrophobic coating on the catalyst elements. The metallic catalyst material is not consumed as it functions and is not subject to long-term aging degradation. However, as discussed further in Section 3, periodic surveillance is needed to detect any potential functional degradation due to buildup of contaminants during operation.

2.2 How Noble Metal Catalysts Work A catalyst is a substance that promotes a chemical reaction without itself being altered or consumed. It is often comprised of a noble metal thinly dispersed on an 4

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ei inert, high specific surface area, metallic or ceramic substrate or " carrier." The active, microscopic, catalyzing sites on the surface of the carrier collect reactants, which are essentially ionized then reacted to new molecules, releasing or absorbing heat in the process.

The use of catalysts for purifying gases of undesired traces of hydrogen or oxygen is a standard process in the chemical and automotive industries. Normally, oxygen and hydrogen recombine by rapid burning only at elevated temperatures (greater than about 600 C). However,in the presence of catalytic materials such as the platinum group, this " catalytic burning" occurs even at temperatures below 0 C. Adsorption of the oxygen and hydrogen molecules occurs on the surface of the catalytic metal because of the attractive forces of the atoms or molecules on the catalyst surface.

The catalytic process can be summarized by the following steps (Ref. 9):

(1) diffusion of the reactants (oxygen and hydrogen) to the catalyst; (2) reaction with the catalyst (chemisorption) to give adsorbed O and H; (3) reaction of the intermediates to give the product (O + 2H = 2H O [ water vapor]

2 2

2

+ heat); this reaction is called " catalytic combustion" (4) desorption of the product; and (5) diffusion of the product away from the catalyst.

A reactant must get to the active catalyst sites before it can react. At temperatures above 170 K hydrogen atoms are adsorbed on the catalyst surface. After reaction 1

with oxygen atoms, the product, steam molecules, must get away from the catalyst before more reactant will be able to react. Since the catalyst does not itself take part in the reaction, it is not used up and is available for further recombination.

However, any solvents or contaminants that form stable compounds with the catalyst will poison it. The exothermic heat of the oxygen / hydrogen reaction can raise the temperature of the catalyst surface to more than 1000 C, which raises the temperature of the flowing gas about 80 C for each one percent by volume of hydrogen recombined. This heat of recombination can dissociate or " burn off" many poison compounds that are not highly stable.

Presently a wide variety of standard catalyst materials is available for many uses.

The application in other industries that comes closest to the use of a catalyst for depletion of hydrogen in reactor containments is gas purification (Refs.10 and 11).

This application uses noble metals (platinum or palladium) deposited onto alumina (aluminum oxide pellets as carriers). The production gases flow through a fixed bed of the catalyst. Applications include the removal of hydrogen and other gaseous impurities in the production of pure air and the removal of traces of oxygen and other impurities in the manufacture of pure hydrogen (so-called "deoxo" processes, Ref.12). This recombination proceeds even at room temperature.

Another application of catalyst-coated pellets in a fixed-bed configuration is in the off-gas systems of some BWRs. Filter-type catalytic recombination is used to reduce gas volumes as well as minimize the potential for localized rapid burning prior to 5

1

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l the off-gases passing through charcoal filters in most plants. According to a 1981

. PRI report, "No sign of degradation of the catalyst material has appeared, even after five years of operation." (Ref.13)

As discussed above, in one PAR design (by NIS) the catalytic element consists of the same type of pellets as in fixed-bed applications - palladium-coated aluminum oxide spheres. This design depends on diffusion for the gas molecules to travel from the free flow area to the catalyst sites on the surface and in the pores of the pellets i

within the cartridges. The pellets near the cartridge covers provide a measure of protection against inhibitors or poisons - molecules of the gases to be recombined i

will diffuse to the pellets within the cartridge, which are less exposed to

{

contaminants.

l In the Siemens plate design, the plate surface is immediately accessible to gas molecules in the flow channels. However, much of the catalyst surface is protected within the porous structure of the catalyst system.

Therefore, regardless of the form of catalyst system employed, all PARS have a certain amount of active catalyst surface area available. Each accessible atom on the surface of an active catalyst surface area is called an " active site." As discussed in the next section, the phenomenon of reduction of PAR recombination efficiency due to poisoning involves a competition for these active sites between the target reactants (H and 0 ) and reactive contaminants in the atmosphere.

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i Section 3 7

DEACTIVATION OF CATALYSTS This section is a general discussion of how inhibitors and poisons can deactivate noble metal catalysts.

3.1 Catalyst Deactivation Mechanisms The following three mechanisms could potentially have a negative influence on PAR catalyst efficiency:

I j

. Direct mechanical blockage of the active catalyst surface by solid or liquid aerosols and/or gases such that access of the reactants (oxygen and hydrogen) to the active j

sites on the catalyst particles on the carrier material is reduced or even j

eliminated.

Deactivation of the catalyst material from its chemical reaction or chemisorption with impurities in the surrounding atmosphere (i.e., chemical reduction).

Reactions of the carrier material with components of the surrounding j

atmosphere causing a gross change of the surface or porosity structure and thus causing a mechanical blockage of active catalyst particles located inside or on the

. surface of the carrier.

The first may be viewed as an inhibitor, while the last two are poisons. The first two mechanisms are generally reversible under the influence of increased temperatures.

This is true, except if the entire surface of the catalyst would be blocked, or for some chemical reactions like total oxidation. Reaction areas will form at non-blocked locations and will grow as they " burn the surface free." The third mechanism, blockage of the catalyst due to the formation of products from reactions with the l

carrier material, will not occur because of the non-corrosive nature of the carrier

. materials (stainless steel or ceramics).

In the following two subsections, we discuss potential deactivation by inhibitors and j

poisons, respectively.

i 3.2 Deactivation by Inhibitors i

The three known mechanisms involving potential inhibitors of catalytic action in PARS are fouling during operation, wetting, and fouling during an accident.

3.2.1 Fouling During Operation. It is conceivable that contaminants like dust, dirt, paint spray, or deposited lubricant vapors could build up after very long periods under operating conditions and inhibit catalysis by direct mechanical blockage of the 7

active catalyst surface. For example, the cause for poor performance in one of the many full-scale PAR tests in the Battelle model containment (Ref.14) was traced by post-test examination to be due to the depositing of greases on the surface of the catalysts. In nuclear plants, the usual precautions of covering the devices during nearby maintenance activities should and will be followed. Nevertheless, a j

preventive maintenance program similar to the one described in the following i

paragraphs is proposed. This surveillance will assure that the capacity of PARS is

)

not degraded by long-term crud buildup, nor by other aging mechanisms.

The traditional process of environmental qualification addresses the potential for aging degradation of material properties due to exposure to operating levels of temperature and radiation. For example, aging can significantly affect the i

properties of polymeric materials such as 0-rings in mechanical components.

i Thermal and radiation aging effects are addressed mainly by the formal testing and/or analysis procedures established in industry standards for qualifying safety-related equipment.

i Some PARS are constructed entirely of metal and ceramics. The physical properties of such materials do not change significantly under long term exposure to containment operating environments such as temperature and radiation.

Therefore, such PARS have no known significant aging mechanisms other than the i

physical / chemical aging mechanisms of inhibitors / poisons being addressed here.

i This means that the potential effects of deactivators aside, a PAR constructed entirely of metal and ceramics is expected to have a qualified service life equal to the design life of the plant - 60 years for an ALWR.

For PARS with hydrophobic coating on the catalyst pellets, the non-metallic polymeric coating could be degraded after long-time thermal and radiation aging under operating conditions such that the wetproofness or recombination efficiency of the catalyst is degraded. One or both of two approaches can be used to address these aging mechanisms. The first is to include 60-year-equivalent accelerated thermal and radiation aging as part of qualification testing. The second is to perform periodic surveillance testing of PARS to ensure that all actual plant aging effects are addressed. Surveillance testing, a form of on-going qualification allowed by industry standards, has the advantage of addressing at the same time not only the thermal and radiation aging addressed by traditional qualification practices, but also the aging degradation mechanism of physical / chemical fouling of the catalyst due to settling or plateout of contaminants that might be present in the atmosphere of the containment during its operating life. There is no acceptable way to simulate or accelerate this aging mechanism as a part of an up front artificial qualification aging program. Therefore, periodic surveillance testing is needed for PARS both with and without a hydrophobic coating, even if accelerated thermal and radiation aging is included in qualification tests.

It is important to note that physical / chemical fouling is not expected to have a significant degrading effect on PAR catalysts. First of all, the fouling will be 8

s minimal because of the normal precautions taken to keep the containment environment clean. For example, a PAR unit would be covered with plastic sheets to protect it from inadvertent coating from maintenance activities like nearby painting or welding.

Secondly, even if a PAR were to be subjected to an atmosphere highly contaminated with particulates (such as might be produced by a fire in the containment), testing has shown that the recombination capacity of a PAR is not significantly diminished.

As described later in this document, in three separate test programs, PAR models were exposed to the vapors and soot produced by burning of cables and oils directly below the intake region. The amounts of burn products deposited were much greater than could be expected to reach a PAR in an actual fire. After the heavy deposition of burn products, the models functioned during subsequent recombination tests with little degradation from pre-exposure to a fire.

Nevertheless, to address the small possibility of buildup of foreign materials enough to reduce the depletion rate of a PAR, a preventive maintenance program should be carried out. The program would consist of periodic visual inspection of all catalyst elements, supported by sampling surveillance tests (benchtop performance tests of catalyst specimens removed from selected PAR devices). This surveillance would be applied periodically during normal operational periods of the plant and should be performed after completion

' any outage activities that could be a source of contamination. If some abnormal event such as a fire would occur, any PARS exposed to the burn products would be subject to an even more rigorous examination and performance check before being retumed to service.

Periodic surveillance tests should be made on specimens removed from selected PAR devices. Each benchtop performance test would use one catalyst cartridge or plate from a PAR device. The specimens would be placed in a standard laboratory performance test apparatus. The specimen container in the test apparatus would include a gas flow channel on one or both sides of the cartridge specimen. A controlled flow of air containing a known quantity of hydrogen would flow through

)

the specimen container. A measured recombination response parameter after a specified time from start of gas flow would indicate whether any degradation of catalytic reaction (in comparison with baseline tests of new specimens) has taken place. The parameter could be the temperature increase of gas within the specimen, or the temperature or hydrogen concentration of the gas exiting the test specimen.

At first the periodic tests would be performed on sample catalytic elements removed from PARS at every refueling outage. If, as expected, no significant degradation is observed, the test intervals could be increased.

Acceptance criteria for the surveillance tests will be specified in the environmental qualification report for the PAR.

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3.2.2 Wetting. PARS would most likely be wet when called upon to function during a postulated accident that releases combustible gases to the containment volume.

. Because AP600's do not have emergency containment cooling sprays, the wetting would come only from condensation of moisture or steam in the atmosphere. For 1

PAR applications in plants with sprays, despite spray covers provided with the i

PARS, some additional water could reach the catalyst elements. Therefore, water must be viewed as a potential inhibitor of recombination by direct mechanical blockage of the active catalyst surface. Although hydrogen or oxygen molecules do i

diffuse through water and can reach a wetted catalyst site to be recombined, the i

}.

diffusion rate is so much less in water than in gases that recombination is virtually eliminated on a fully wetted catalytic surface.

i Testing (Refs.15 and 16) has shown that once a PAR device starts up, its efficiency is essentially the same whether or not it was wet prior to startup. However, testing has also shown that startup of the PAR is delayed as expected by the presence of water on the catalytic elements. Full efficiency of the PAR is reached only after complete evaporation or boiloff of wetness. Evidently, once even a small area of catalyst sheds water or dries off, the heat of recombination from the local area is sufficient to lead to eventual dryout of all catalyst surfaces and to startup of the PAR.

The delay time for startup increases with increasing amount of water, decreases with increasing concentrations of combustible gas in the atmosphere, and is different for differing PAR catalyst systems.2 Therefore, as part of a demonstration of functionability.of PARS for a paricular plant application, the effect of wetness on startup must be addressed. For use in a DBA, for which combustible gas buildup from radiolysis of water occurs very slowly (several weeks to build up even uncontrolled gases to a combustible level of about 5 vol %), delay times may be as long as many hours or even several days without compromising safety.

For PAR catalyst elements that include a hydrophobic coating, surveillance testing would be relied upon to ensure that aging due to operating temperature, radiation, or chemical contamination does not degrade the wetproofing function of the coating to an unacceptable extent. For such PAR specimens, after a recombination 8 Each PAR design differs with regard to wetproofness. For example, to prevett water from collecting in the pores of the catalyst pellets and minimize water buildup between pellets, pellets in the NIS PAR design are coated with a thin layer of hydrophobic polymeric material. Tests have shown (Refs.15

. and 16) that this hydrophobic coating suffices to keep startup delays acceptably short and that there

' is no effect on NIS PAR recombination efficiency with or without a hydrophobic coating on the pellets.

However, qualification of a PAR incorporating a hydrophobic coating must demonstrate that the wetproofing function of the coating can not be unacceptably degraded by damage from recombination heating or by radiation. _ On the other hand, the basic design of the Siemens design does not include any hydrophobic coating, depending instead on the inherent water shedding capability of the vertically oriented stainless steel plates to lead to an acceptably short delay time when wetted. Startup capability of Siemens PARS has been enhanced by adding a narrow strip of palladium along the bottom edge of each catalyst plate. Testing has confirmed (Ref.16) the adequacy of wet startup delay for Siemens PARS under a wide range of containment accident conditions. If desired, a hydrophobic coating can also be added to the Siemens catalytic plates.

10

4 d

surveillance test is conducted on a dry specimen as described above, the specimen would be dipped in water and weighed to check whether the coating is maintaining its waterproofing function. If the weight of water retained is greater than it would be in the new condition, a recombination test of a wetted specimen would be run to i

confirm that the change in waterproofing ability does not have an unacceptable effect on startup time for the PAR specimen.

Because of their inherent ability to start up in the wet condition as demonstrated in generic performance testing, PAR catalyst elements designed to start up without a 3

hydrophobic coating would require a surveillance test only in the dry condition.

In summary, once a PAR starts up, initial wetness does not have a significant effect on recombination capacity. However, because initial wetness inhibits initial recombination and delays full functioning of PARS, this mechanism must be addressed in the design and qualification of the PAR combustible gas control system for a particular application. Results for wet startup from existing test programs (such as Refs.15 and 16) can be cited for addressing the effects of wetness on startup and recombination, or wet startup testing can be included in plant-specific i

qualification programs. The effects of wetness on PAR perfonnance will not be addressed further in this report.

3.2.3 Fouling During an Accident. The periodic surveillance testing described above ensures that, in the event of an accident, a PAR's ability to perform its safety related function during or after an accident has not been compromised by thermal, radiation, or chemical aging mechanisms. We now address the possibility that substances that can reach and pass through a PAR during an accident may deactivate the catalyst. As indicated in Section 3.1, this deactivation can occur via mechanical l

blockage of catalyst sites by inhibitors or via chemical reactions of poisons with the catalyst. The following paragraphs address the possibility of mechanical blockage 2

during an accident. The next subsection addresses the possibility of chemical poisoning.

It is conceivable that liquid or solid aerosols that become suspended in the containment environment during an accident can plate out on the catalyst elements and block active catalyst sites. Recombination in the PAR itself sets up forced convection currents that circulate a substantial fraction of the containment atmosphere along with suspended particles through the PAR. Hydrogen reaches catalyst sites by diffusion or turbulent motion transverse to the gas flow direction.

The heavy solid (and liquid) aerosols do not move to the sides of the flow channel i

nearly as much as the reactants. With the relatively wide open channel gas flow pattern used for the PAR (diffusion rather than fixed-bed filter), aerosols are not led directly over the catalyst surface and, in the pellet cartridge design, there is no pressure drop that would induce aerosols to enter the slots in the cartridge. Indeed, the exiting from the slots of steam produced by recombination further impedes the ability of aerosols to reach the pellets. The result of all these mechanisms is little or no effect.on catalyst efficiency by blockage.

11

4 In terms of their ability to block catalyst sites, liquid aerosols have no worse a potential for blocking than water. In this regard, liquid aerosols are addressed along with wetness as discussed above. The potential chemical poisoning effects of liquid aerosols are treated in the following subsection.

There are three sources of information that can be used to address the ability of solid aerosols to block catalyst sites.

One is the same evidence discussed above with regard to PARS having little reduction in recombination efficiency after exposure to a lot of smoke and soot from cable and oil fires - it is reasonable to assume that the solid aerosols from a cable and oil fire directly below the PAR exceed any core / fission-product solid aerosols dispersed in a containment, even for a severely damaged core.

The second is that blockage effects from solid aerosols are present whenever a test of potential chemical poisoning by solid aerosols is performed. Therefore, the results of chemical poisoning experiments on catalysts discussed later in this report inherently cover blockage effects of solid aerosols as well.

The third body of evidence that solid aerosols do not dramatically inhibit recombination in a PAR is the study of aerosol deposition performed as a part of the PAR qualification study reported in Appendix E of Ref. 2. A theoretical study of aerosol deposition was performed to address the concern that deposition of aerosols during a severe accident might act as inhibitors, blocking access of combustible gas j

molecules to the catalytic surfaces. The study examined the extent to which typical accident aerosols based on current accident source terms, including those from core / concrete interaction, are deposited as a film on flat p!ates with the same dimensions as the catalyst cartridges in an NIS PAR. Since the plates served as simplified representations of the screened-in catalyst cartridges, the analysis applies also to the plate element of a Siemens PAR. Conservative assumptions were employed in selecting various parameters for the analysis, which had at its center an expression for the turbulent deposition of aerosols involving the Reynolds number, Stokes friction coefficient, and Schmidt number of the flow through the free channel between the catalyst cartridges. For example, the film is assumed to be as thin as possible (the thickness of one aerosol particle diameter), so that the film coverage is a maximum. Also, no credit was taken for the resistance to deposition that occurs as the heated product of recombination (steam vapor) expands away from the plate surface. Even with such conservative assumptions, the analysis estimated that the maximum coverage of the plates would be less than 0.2% during the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of an accident. The first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> should be the focus of concern because after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> the suspended aerosol concentration is very small and high hydrogen generation is most unlikely. Such a small coverage implies that the aerosol effect on the efficiency of the recombiner would be very small.

12

'On the basis of the three factors described above, we conclude that mechanical blockage of catalyst sites by solid and liquid aerosols is not a significant degradation mechanism for PARS.

3.3 Deactivation by Poisons In simplest terms, poisoning can occur when contaminating chemicals react with atoms of the metallic catalyst, so these atoms are no longer available for adsorption i

followed by recombination of hydrogen and oxygen molecules. For a region of a catalyst system reached by a potential poison, the degree of poisoning (reduction in recombination rate) is proportional to the fraction of catalyst atoms deactivated.

j Depending on how stable the product of the contaminant / catalyst reaction is, the poisoning can be relatively permanent (irreversible) or temporary (reversible, for

. example, by dissociation of the poison products by heating or upon removal of the j

poison from the feedstream under actual reaction conditions, Ref.17).

The science of catalysis is mature (it dates back to the discovery of the hydrogen catalyst properties of platinum in Germany by J. W. Doebereiner in the early part of -

the nineteenth century) and has become a standard process application in the chemical and automotive industries. Therefore, the literature is rich on the subject of catalytic poisoning, but needs to be consulted anew for each evolutionary application such as for PARS in nuclear plants.

To examine the potential effects of poisons on PAR performance, we first consulted the literature to identify known poison substances for noble metal catalysts. The results of this search are presented in the following paragraphs. The next question addressed is which of the known or potential poisons are expected to be present in the containment after the initiation of a postulated nuclear plant accident. This is covered in the next section of this report.

According to Maxted (Ref.18), " poisons are usually strongly adsorbed species which, even if they are present in traces only, tend by virtue of their strong bonding to a catalyst... to accumulate in the adsorbed phase in the course of the adsorption-desorption equilibrium at the catalyst surface, which, by reason of this obstructive occupation by the poison, is rendered no longer free for its normal participation in the adsorption and catalysis of less strongly held potential reaction species."

Further, "The common catalyst poisons fall into the following main classes:

13

(a) Molecules containing elements of the periodic groups Vb and VIb, namely:

Group Vb Group V1b N

O P

S As Se Sb Te j

including (except in the case of nitrogen) the free elements.

(b) Compounds of a large number of catalytically toxic metals [especially lead]

(c) Molecules containing multiple bonds, such as carbon monoxide, cyanogen compounds and even, to some degree, strongly adsorbed molecules such as benzene."

In general, physical and chemical forms are important to the, degree of poisoning.

Solid or liquid aerosols containing a potentially poisonous element are much less effective as a poison than the elemental form (the aerosol form is not as reactive and cannot diffuse to the catalyst as readily as the vapor elemental form). In general, gaseous forms of an element are more effective poisons than solids or liquids. With gases, the more reduced chemical compounds are more effective as poisons because they are more efficient at chemisorption on the catalyst. For example, H S 2

(hydrogen sulfide) would be more effective than SO (sulfur dioxide). Organic gases 2

such as methyl iodide are more reactive than elemental iodine vapor.

A well known poison group is the halogens - iodine, bromine, and chlorine (Refs.

19 and 20). For these elements, poisoning is temporary and reversible (results of testing in Ref.19 are summarized in Section 6.1.1).

Ref.15 states " Catalyzer poisons for the catalyzers of the H oxidation on metals of 2

the platinum group that are covered here are compounds with S, Se, Te, P, As and halogens as well as CO in higher concentrations which cause a deactivation through solid chemisorption."

Still another form of poisoning is known as " coking," in which coke (elemental carbon) in carbon-bearing gases is deposited on the surface of a catalyst, blocking the reaction of the recombinants. Coking is a complex process - an entire chapter of Ref. 21 is devoted to its description. The only known source of carbon-bearing gases in a reactor containment accident without core / concrete interaction is a fire. In this report, the potential effects of coking are addressed by citing the results of tests in which PARS were exposed to the smoke and soot from electrical cable fires prior to recombination performance tests.

In summary, the extensive body of literature on noble metal catalysts and their susceptibility to chemical poisoning that has been consulted in this study leads to 14

the conclusions that (a) catalyst poisoning mechanisms are understood (the elements most effective as poisons have been identified and gaseous forms of those elements are known to be much more effective as poisons than solid and liquid forms) and (b) there is no known " terminator" poisonous substance that can completely incapacitate substantial amounts of noble metal catalysts "in a single bound" (the ability of any chemical substance to significantly poison noble metal catalysts depends on the substance's ability to be transported to widely distributed catalyst sites, to be reactive enough to deactivate catalyst sites, and to be plentiful enough to react with all or mostly all the catalyst atoms).

3.4 How Deactivators Reach PAR Catalyst To act as an inhibitor or poison, a substance must reach the surface of the catalytic element in a PAR. Mechanisms for substances reaching the catalyst are different when the PAR is inactive and when it is functioning.

3.4.1 Inactive PAR. During normal plant operation, there is essentially no hydrogen or other recombinable gases in the containment atmosphere, so the PAR is in a standby mode. With the PAR inactive, no gases are flowing through the open channels between the PAR elements (plates or pellet cartridges). Since the plates are oriented vertically, gravity does not act to foul the surface with dust or other aerosols that might be put in the atmosphere during maintenance activities.

The surfaces of the pellet cartridges are also vertical, limiting buildup of particulates by gravity. To an extent, the pellet surfaces are protected against particulate buildup by the sheet metal in the vertical slotted cartridge cover and by adjacent pellets.

Thus, during normal plant operation, contaminants reach the catalyst surfaces of a PAR only by diffusion in the quiescent atmosphere surrounding the catalyst elements.

3.4.2 Functioning PAR. When the PAR is functioning during an accident that releases hydrogen into the containment atmosphere, contaminants, including potential inhibitors and poisons, are drawn into and circulated through the PARS.

Hydrogen molecules, which are the lightest, diffuse to the catalyst surfaces most readily. While oxygen is much heavier, some ten times the amount needed is in the air already present at the catalyst sites. Other potentially poisonous gases, like iodine and carbon monoxide, diffuse to the catalyst surfaces at a lower rate than hydrogen. Because any liquid or solid aerosols that may be entrained in the atmosphere at the location of the PAR have orders of magnitude less diffusivity than gases and because turbulence is limited, essentially all of them are carried through the flow channels without affecting the PAR catalyst. The ability of poisons to be transported to PARS and to deposit on PAR catalyst surfaces is discussed further in Section 5.6.

l 15

p.

Section 4 COMBUSTIBLE GAS RELEASES AND REGULATORY LIMITS i

For any type of postulated accident in a nuclear power plant, hydrogen is generated by the following three mechanisms: (1) metal-water reaction involving the fuel cladding and the reactor coolant,(2) radiolytic decomposition of the reactor coolant, and (3) corrosion of metals. The mechanism of hydrogen generation that dominates depends on the level of core damage. For a relatively undamaged core as in a design basis accident, radiolysis and corrosion are the dominant contributors. For a highly damaged core as in a severe accident, metal-water reaction is the dominant contributor.

The Code of Federal Regulations (Refs. 22 and 23) specifies the generated and released quantities of hydrogen in PWRs required to be considered. Regulations (Ref. 22) require combustible gas control (CGC) systems to prevent volume average concentrations in a DBA from reaching combustible levels of 5 vol % for hydrogen in a non-inerted containment (in order to account for uncertainties in measurement capability, the actual limit is set at 4 vol %). For PWRs, post-TMI regulations (Ref. 23) require that hydrogen burns or detonations during a severe accident not compromise containment integrity, nor the ability of the plant to be 1

brought to a safe shutdown condition. Detonation is prevented by the requirement that the average hydrogen concentration be less than 10 vol % (dry).

PARS alone can be deployed to control DBA hydrogen in PWRs (typically two full-size PAR units are sufficient to do the job with a large margin). For control of severe accident hydrogen in PWRs both PARS alone (Ref. 25) and PARS supplemented with igniters (Ref.1) have been proposed. The CGC system of the

]

current AP600 design includes two PARS for control of DBA hydrogen and many distributed igniters for control of severe accident hydrogen.

The following subsections address the amounts of combustible gases released for different accidents.

4.1 Design Basis Accidents During and following a design basis loss of coolant accident, relatively small amounts of hydrogen and oxygen can be released to the containment of a nuclear power plant. Since a design basis accident involves a cooled core and mostly undamaged fuel cladding, regulations (Ref. 22) mandate the conservative assumption of a hydrogen generation from reaction of up to 5% of the active fuel clad material with the coolant water. The release to the containment is assumed to 1

be virtually instantaneous.

16

l For a 600-MWe AP600, this regulatory assumption corresponds to a release of 31.75 l

kg of hydrogen into a 45,900 m containment volume, which leads to an average 8

hydrogen concentration of 0.74 vol %. Additional hydrogen is produced by radiolysis of water in the coolant and sump at the rate of about 0.4 kg/hr (average for first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> after shutdown). Thus, the rate of increase of hydrogen is slow, about 0.01 %/hr (Ref. 2).

For DBAs in PWRs, PARS can keep hydrogen levels below the regulatory limit of 4 vol % by having a combined recombination rate that exceeds the rates given above for radiolytic generation and release of hydrogen.

4.2 Severe Accidents For severe accidents in PWRs for which an active CGC system is needed, the system has to control not only radiolytic hydrogen, but also the much greater amounts produced by metal-water reaction of 100% of the active fuel clad materialin a degraded core (Ref. 23).

For an AP600, this regulatory assumption corresponds to a release of 635 kg of 3

hydrogen into a 45,900 m containment volume, which leads to an undepleted average hydrogen concentration of about 13 vol %. Thus, the DBA PARS are supplemented with igniters to meet the volume average regulatory limit of 10 vol % hydrogen in all compartments.

l l

17

Section 5 POTENTIAL PAR POISONS IN NUCLEAR PLANT ACCIDENTS This section identifies the chemical constituents, amounts, and physical forms of potential PAR poisons that may exist after an accident in PWR containments.

5.1 Fission Product Releases A major source of chemical contaminants / poisons in the containment atmosphere during an accident is fission products released from overheating of and damage to the clad and fuel. As is the case for hydrogen generation in an accident discussed in the previous section, the amount of fission product releases depends strongly on the assumed level of core damage.8 Fission products comprise the " accident source term" for light water reactors. The source term being used for design of ALWRs is the revised source term described in NUREG-1465 (Ref. 24). NUREG-1465 is being used as the main basis for specifying the chemicals, amounts, and physical forms of fission products that should be addressed as possible poisons to the PAR catalyst (Ref. 26).

1 Table 1.1 of NUREG-1465 identifies the following five release phases for a severe accident: coolant activity release, gap activity release, early in-vessel release, ex-vessel release, and late in-vessel release. The fractions of core inventory of each of several radionuclide groups released into PWR containments are listed in Table 3.13 of NUREG-1465, which is reproduced in Table 1 (the gap release column includes coolant activity release).

As discussed in the previous section, the regulations on combustible gas control in 10CFR50.44 (Ref. 22) require the assumption of metal-water reaction generation of hydrogen corresponding to a core with slight fuel damage; i.e. decomposition of less than 5% of the fuel cladding. This assumption is consistent with the first two phases of release of fission products in Table 1.1 of NURFG-1465, viz., coolant activity release and gap activity release associated with fuel cladding failure, but no fuel melting. This leads to the releases into containment given by the gap release column in Table 3.13 of NUREG-1465 (see Table 1). This source of fission product release will be termed the " intact core release" in the remainder of this report.

3 Another possible source of contammants released into the containment may be the result of decomposition of non-metallies by radiation effects; e.g., chlorine and sulfur compounds or acids from cable jacket and insulation decomposition. As discussed in Section 3.2.3, this possible source is addressed by the testmg of PARS exposed to the almost complete decomposition of cable materials bumed directly below PAR models prior to recombination testing in Germany and France. Still another source (for an ex-vessel severe accident only) is the carbon monoxide from core / concrete interaction.

Since this report focuses on PARS in a DBA, test results for PARS subject to carbon monoxide are not included.

18 p

Table 1. PWR Releases Into Containment (taken from Tables 3.13 and 3.8 of NUREG-1465, Ref. 24 -- values shown are fractions of core inventory)

Radionuclide Elements Gap Early Late Group in Group Release In-Vessel Ex-Vessel In-Vessel Noble Gases Xe,Kr 0.06 0.95 0

0 i

Halogens I,Br 0.05 0.35 0.25 0.1 kikali Metals Cs,Rb 0.05 0.25 0.35 0.1 Tellurium group Te,Sb,Se 0

0.05 0.25 0.005 Barium,.

Ba,Sr 0

0.02 0.1 0

Strontium i

Noble Metals Ru,Rh, 0

0.0025 0.0025 0

Pd, Mo, Tc, Co Cerium group Ce, Pu, Np 0

0.0005 0.005 0

Lanthanides La, Zr, Nd, 0

0.0002 0.005 0

Eu,Nb, Pm, Pr, Sm,Y, Cm,Am According to NUREG-1465, the releases in the "early in-vessel" column of Table 1 are based on " severe core damage accidents involving major fuel damage but without reactor vessel failure or core-concrete interactions". Assumption of this release for the qualification of PARS for DBAs would conflict with the guidance in Regulatory Guide 1.89 (Ref. 27) that safety related equipment be qualified to demonstrate "that it can perform its safety function under environmental service conditions in which it will be required to function" - the function of PARS is to control hydrogen from an intact core release. If hydrogen consistent with the early in-vessel column of Table 1 were present, the amount of hydrogen produced in a severe accident, not a DBA, would need to be controlled (in the AP600 design, severe accident hydrogen is controlled by igniters). The sum of releases in the gap release and early in-vessel columns of Table 1 will be termed the " damaged core release" in the remainder of this report. Although the report evaluates the effects on PAR performance of fission products from both an intact core release and a damaged core release, it is important to recognize that the latter release is inconsistent with the amount of hydrogen that the PARS are required to control in a DBA.

5.2 Chemical Form of Fission Product Releases All fission product elements in Table 1 are released as vapors from a damaged core during an accident. Most of these vapors will react resulting in a number of different chemical forms. For example, according to an ORNL paper on tellurium 19

i.

I i

J behavior in containment under LWR conditions (Ref. 28), most of the tellurium in the core will be held up by oxidation with the Zircaloy cladding. After Zircaloy oxidation, the tellurium would be released as the solid tin telluride (SnTe). Tin

~

telluride oxidation could lead to the formation of SnO and TeO, with both being 2

2 more thermodynamically stable than tin telluride.

l Table 2 lists the chemical forms expected under the low oxygen potential accident conditions in a PWR (Refs. 29-32). Low oxygen potential conditions are consistent with the damaged core accident terminated in-vessel noted above. Not all the listed species will necessarily be present, and many, even if present, would exist in very small quantities. Also shown in Table 2 is the physical form (gas or particulate) of each species as it is transported into containment.

t It is noteworthy that the only materials in the table that are gaseous are the noble gases and iodine compounds (HI,1, and CH 1). The remaining materials are solid 2

3 aerosols at typical containment temperatures. This is important because as discussed previously the ability of aerosols to be transported to the catalyst, and thus

' act as poisons, is limited and any solid aerosols that do reach the catalyst are much less chemically reactive than gases.

i Table 2. PWR Fission-Product Chemical Species Element Chemical Form Physical Form Comments Noble Gases Xe Xe Gaseous Kr Kr Gaseous Halogens I

Csl Particulate Similar compounds for Br I

HI Gaseous I

1 Gaseous 2

I-CH1 Gaseous j

3 I

FeI Particulate Also, Nil and CrI l

2 2

2 Alkali Metals Cs CsOH Particulate Similar compounds for Rb Cs Csl Particulate Cs CsBO Particulate 3

Cs Cs UO Particulate 2

4

- Cs Cs2 moo, Particulate j

Cs Cs ZrO Particulate 2

3 Cs Cs CrO Particulate 2

3 20

l :'

Table 2. PWR Fission-Product Chemical Species (continued)

Element Chemical Form Physical Form Comments Telhtrium Group Te SnTe Particulate Similar compounds for Sb and Se Te TeO Particulate 2

Te CdTe Particulate Te ZrTe Particulate 2

Te Sb Te3 Particulate 2

Te Fete Particulate 2

Te

Nite, Particulate Te Cs2Te Particulate Te Cs TeO Particulate 2

3 Barium, strontium Ba Ba0 Particulate Ba BaZrO Particulate 3

Ba BaUO Particulate 3

Sr Sr0 Particulate Sr SrZrO Particulate 3

Sr SrUO Particulate 3

Noble Metals Mo Mo Particulate Mo moo Particulate 2

Mo Ca moo.

Particulate 2

Ru Ru Particulate Liquid solution with Rh, Pd, Te, and Ni Cerium Group Ce Ce O Particulate 2 3 Pu PuO Particulate 2

Np NpO Particulate 2

Lanthanides La La O Particulate Similar oxides for Y, Nb, 2 3 Pr, Nd, Pm, Sm, Eu, Am, Cm, and Nb i

I 21

5.3 Non-Fission Product Materials Releases As well as fission products, non-fission-product materials are released as vapors from a damaged core during an accident (Ref. 24). These materials, made up of fuel, clad, control rod, burnable poison, and structural materials, will react in the vapor phase resulting in a number of different chemical forms such as those listed in i

Table 3. The released mass of non-Cssion-product material can be somewhat higher than the released mass of fission product material, and the mass ratio is of the order of 1.5:1 (Ref. 31).

Table 3. PWR Non-Fission-Product Chemical Species Element

- Chemical Form Physical Form Comments Zr Zr Particulate Zr.

ZrO Particulate 2

U UO2 Particulate Fe Fe Particulate Fe Fe30 Particulate Ni Ni Particulate Ni NiO Partictlate Requires somewhat high oxygen potential Cr Cr O Particulate 2 3 Mn MnO Particulate Ag Ag Particulate In In Particulate In In 0 -

Particulate Depends on oxygen potential 2 3 Cd Cd Particulate Cd Cd 0 Particulate Depends on oxygen potential 2

B H BO Particulate 3

3 B-BC Particulate Liquid solution with Fe, Ni, Cr Al Al O Particulate Al-Zr-O metallic alloy, liquid 2 3 above 1625*K, Al O -ZrO 2 3 2

eutectic, liquid above 2125'K j

Gd Gd 0 -

Particulate j

2 3 22

5.4 Fission Product and Non-Fission Product Materials that are Potential Poisons To identify the. subset of fission product elements that, according to chemical principles, are suspect poisons, we compare the list of fission product elements from NUREG-1465 with the elements identified by the literature search in Section 2 as being potential poisons to noble mettJ catalysts. This comparison gives only the halogens (I, Br) and the tellurium group (Te, Sb, Se) as the NUREG-1465 elements that are suspect poisons. However, of the fission product chemical species formed i

in the containment and listed in Table 2, only iodine, hydrogen iodide, bromine, and methyl iodide (or bromide) are in the gaseous form and hence are suspect poisons.

None of the non-fission-product chemical species identified in Table 3 match the suspect poisons identified in Section 2, and besides, all are in particulate form.

Therefore, non-fission products produced in an accident are eliminated as potential l

poisons to PAR performance.

4 Sulfur, produced by decomposition of certain cable materials,is also identified as a potential poison.

5.5 Amounts of Potential Poison Fission Products Released Design releases into the AP600 containment for the halogens and tellurium group are given in Table 4.

Table 4. Mass of Halogens Released to AP600 Containment Intact Core (DBA)

Damaged Core j

Core Gap Total Mass Gap + Early Total Mass Inventory Release Released In-vessel Released i

(kg)

Fraction (kg)

Release Fraction (kg) 18.37 0.05 0.933 0.40 7.47 5.5.1 Desien Basis Accident. From Table 4 the assumed halogen release for a DBA is 933 g (91% iodine and 9% bromine). For simplicity, we will assume that the poisoning effect of all fission product halogens can be represented by assuming an equal amount of iodine. According to NUREG-1465 (Ref. 24), of the total assumed 933 g of iodine, five percent will be released into the containment as gaseous forms of iodine, and a small amount (0.15 %) as organic iodides, such as methyl iodide, CH I. The bulk of iodine released is in the form of particulate, mainly CsI.

3 However, in the aqueous environment of the containment, much of the Cs1 is expected to dissolve in water or plate out on wet surfaces as ionic iodine. Some of this dissolved or plated iodine may re-evolve as elemental gaseous iodine, but only 1

23 i

if pH control of the water is not maintained at a value of 7 or higher. Assuming pH control, the amount of gaseous inorganic iodine released into containment is 0.05 x 933 = 46.7g and the amount of organic (methyl) iodide released is 0.0015 x 933 = 1.4 g.

5.5.2 Damaged Core. From Table 3 the assumed halogen mass released for a damaged core is 7470g (91% iodine and 9% bromine). For simplicity, we again assume that the poisoning effect of all fission product halogens can be represented by assuming an equal amount of iodine. Of the total assumed 7,470 g of iodine, the gaseous forms are taken as comprising no more than 5% and iodine in organic form no greater than 0.15%. Therefore the quantities released into containment are 0.05 x 7470 = 373 g of gaseous inorganic iodine and 0.0015 x 7470 = 11.2 g of organic (methyl) iodide.

5.6 Transport and Deposition of Aerosols to PARS LWRs are designed to remove the accident fission products from the containment atmosphere relatively quickly in order to limit the amount which could leak from containment. The fission product removal system varies depending upon the plant type. Typical operating PWRs, for example, use containment spray systems for fission product removal. AP600, on the other hand, relies on natural aerosol removal processes which are enhanced in passive plant designs by the convection heat transfer which occurs in containment. The following discussion treats the AP600 design, for which natural removal is somewhat slower than spray removal.

As noted above, most of the fission product and non-fission product materials are in solid aerosol form. There are several mitigating factors for suspect poisons which are aerosol. First, the residence time for aerosol in the containment atmosphere is 5

limited. For AP600, the suspended mass of aerosol peaks at about 3 g/m at about 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after the initiating event, and drops by over an order of magnitude by 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> (Ref. 33) due to plateout and sedimentation. Second, based on the low gas velocity through the PAR, laminar flow conditions exist (the flow rate of gas through a typical PAR with a 1-4 vol % hydrogen concentration is expected to be in the range of 20 to 50 cm/s with a PAR channel width of about 1 cm, leading to a Reynolds Number of ~500). Of the particulates that manage to reach the PAR, the large majority are expected to pass through the flow channels without reaching the catalyst sites on the PAR elements because of the low diffusivity of the particulates in the laminar flow. This together with the fact that the PAR is hotter than the flowing gas (and thus heat transfer is from the PAR wall to the gas) suggests that little if any aerosol is expected to deposit in the PAR. Even under turbulent conditions, an analysis indicates that less than 0.2% of the PAR wall surface would be covered by aerosol (see Section 3.2.3). Finally, even aerosol which does deposit on a surface will not readily react with the surface due to limited contact area and relative chemical stability of solids.

24

5.7 Summary l

In summary, the literature was searched first to identify the known mechanisms for physical inhibition or chemical poisoning of noble metal catalysts. These were matched with potential inhibitors and poisons that could reasonably be expected to be present during accident conditions in a nuclear plant. This matching process identified only halogens, sulfur, and the tellurium group (plus carbon monoxide for a failed vessel severe accident) as potential PAR poisons. Although elements in the tellurium group could be poisons, these elements appear only in chemical compounds that are particulates, which are ineffective as deactivators for several reasons explained in this section. It is important to note that in all of the sources of information on catalyst poisons found in the literature, there were no data or information to point to a particular substance or mechanism in the amounts expected in a nuclear plant accident as having the ability to completely or almost completely compromise the recombination capacity of a PAR.

The following section examines available data from catalyst poisoning tests performed specifically for application to hydrogen controlin nuclear plant accidents.

The above estimates of the amounts of halogens released to the atmosphere in DBA and damaged core scenarios will be used to relate results of the tests to AP600 accident conditions.

l

L i.

Section 6

SUMMARY

OF TEST DATA ON THE EFFECTS OF POTENTIAL DEACTIVATORS ON NOBLE METAL CATALYSTS In this section we summarize the pertinent results on the effects of potential i

chemical deactivators for palladium and platinum catalysts from.the several test programs listed in Table 5. As discussed in Section 3, although water is a i

deactivator / inhibitor for initial startup, it does not significantly affect recombination capacity, and hence will not be discussed in this section. Also, although the effects of i

the carbon monoxide that may be produced by concrete / core interaction in a severe accident have been examined in more than one test program, those results are not covered here because carbon monoxide is not released during a DBA (or even l.

during early in-vessel release).

l Three of the four test programs in Table 5 were conducted on either NIS or Siemens PARS or PAR models. The fourth examined the effects of many chemicals on palladium and platinum catalysts in a fixed bed pellet configuration, which, as discussed below, is more susceptible to poisoning than the diffusion filter 2

configuration of PARS.

Table 5. Test Programs Addressing the Effects of Poisons on PARS and Catalysts Test Programs References Potential Deactivators RWE NIS PAR Model Tests Battelle Tests (Ref.15)

I, coke EPRI/EdF NIS/Siemens CEA KALI Tests (Ref.

S, coke PAR Model Tests 16)

Siemens PAR Aerosol Tests IPSN H2 PAR Tests Many fission product (Ref. 34) materials, including I, Te, Sb, and Se Southern Nuclear SNE Report (Ref. 35, Many industrial and fission Engineering Laboratory Tests see Appendix) product materials, including on Fixed Bed Pellet Catalysts I, S, Cl, Te, and Se After summarizing the results of the test programs in Table 5, this section discusses another source of information about the effects of chemicals as poisons to catalysts.

- The information consists of the concentrations of various applied chemicals for which the manufacturer of the pelletized catalyst used in the NIS PAR guarantees the rated performance of the catalyst over a stated lifetime.

1 l

26

6.1 NIS PAR ModelTests The PAR developer, RWE, and supplier, NIS Ingenieurgesellschaft, conducted some performance tests themselves and had other tests conducted by Battelle Frankfurt.

Results from this program pertinent to chemical inhibitors and poisons are summarized in the following paragraphs.

6.1.1 Battelle Iodine Results In the Battelle tests (Ref.15), three grams of solid crystalline iodine were heated in a plate five centimeters below an NIS PAR one-tenth-size segment model in a test compartment volume of 10 m. If the sublimed elemental iodine vapor were allowed to diffuse into the open volume (and not plated onto the PAR) the concentration would have been 0.3 g/m'. The equivalent value for an AP600 DBA is 933 g/45,900 m = 0.02 g/m' or 7470 g/45,900 m = 0.16 g/m' for a damaged core. Therefore, the Battelle test is a conservative representation of an AP600 condition (especially since the vapor plume was directed immediately into the PAR model).

The hydrogen concentration depletion history measured in the Battelle test vessel showed about a 15 percent reduction in PAR recombination efficiency (see Fig. 3 -

the solid curve is the empirical fit through data at reference conditions and the data points show the effect of exposure to the iodine). Note that from 1.1 hrs to 2.35 hrs, the unpoisoned PAR reduced the concentration from 3.6 vol % to 1.4 vol % (a change of 2.2 vol %), while the PAR model exposed to iodine reduced the hydrogen concentration from 3.6 vol % to 1.9 vol % (a change of 1.7 vol %). The percentage difference in hydrogen removed with and without iodine was (1.7 - 1.4)/2.2 = 0.14 or about 15 %.

The literature also contains experiments investigating the influence of iodine on the efficiency of precious metal catalyst materials. These experiments have been performed by leading the gas stream directly through a bed of catalyst particles (Ref.19). The experiments examined the effects of iodine concentration and temperature on the recombination effectiveness of palladium-coated aluminum oxide pellets. The pellets were packed in a 2-liter volume container heated from the outside. A hydrogen-air-steam mixture was led via a gas heater into the container.

Iodine was vaporized in an electric furnace and added with nitrogen via heated pipes to the gas stream, which flowed continuously through the test device. The concentrations of hydrogen and iodine were measured in front of and behind the catalyst. Figure 4 shows the reduction in recombination efficiency as a function of the inlet temperature of the gas mixture with two amounts of iodine added to the gas stream (although the two iodine loadings were not quantified in the reference, they were sufficient to reduce total recombination efficiency at 100 C between 50 and 70%). It is seen that the poisoning effect of iodine disappears when temperature is increased to about 200 C. Since the temperature of the gas in the flow channels of a PAR has been observed to increase about 80 C for each 1 vol % H recombined, the 2

effect of iodine as a poison would disappear (i.e. the iodine would burn off) when H2 concentration in a containment reached somewhere between 2 and 3 vol % (the 27

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Hydrogen Depletion Curves for NIS PAR Model Without (Solid Curve) and With (Data Points) Iodine (Ref.15) 6

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efficiency of a PAR with no poisoning is about 85%). Therefore, the effects of iodine l

poisoning are expected to be completely eliminited for a hydrogen concentrations l

exceeding 3%, well below the flammability limit designated by safety regulations.

l t

6.1.2 Battelle Fire Exposure Tests.

An NIS PAR model was directly exposed to the l

fumes from burning hydrocarbon oil, various cables, and silicon oil immediately beneath the model. It was observed that the cartridges were heavily coated with oily film and soot after removal from the half-hour fire, prior to hydrogen depletion performance testing. The contamination included a significant level of hydrocarbons that condensed on the initially cool catalyst pellets, allowing the

)

formation of coke (pure carbon) as a potential inhibitor of catalytic action. This exposure and contamination was viewed as being much worse than would be expected in an actual accidant in which the fire is not nearly as close to a PAR and for which burn produc'.s would be much more diluted than in these tests. (Of course, if a fire occur.ed during plant operation or during an outage, the shut down plant would not be restarted without examination and surveillance testing of the PAR cartridges, repiacing or cleaning them as necessary.)

Results from one of the fire tests, burning silicon oil and silicone cable insulation (T = 116 C, P = 1.91,50% steam), are shown in Fig. 5. Deposition of burn products had no measurable effect on recombination rate.

6.2 EPRI/EdF/CEA PAR Model Tests Although a substantial amount of PAR testing was done by developers, EPRI in collaboration with EdF recently generated supplemental performance data in a PAR model test program at CEA in France (Ref.16). The testing was performed on models of both NIS and Siemens PARS and the test conditions were selected to expand the PAR database, particularly with respect to test conditions that would cover US plant conditions and US regulatory requirements.

In addition to addressing the effects of initial wetness on PAR startup discussed earlier, the EPRI/EdF/CEA program included tests with exposure to cable fire products and to carbon monoxide. Because previous testing by the developers had l

established the effect of iodine on PAR depletion rate as discussed above, iodine testing was not repeated in this program.

)

l l

Although, as discussed above, PAR testing by developers included exposure to the l

burn products of cable fires, additknal cable burn tests were conducted because j

sulfur had been identified as a pe'.ential poison to noble metal catalysts, and a common cable jacket material in US plants, chlorosulfonated polyethylene (CSPE),

j contains sulfur. An acetylene torch was used to burn a length of cable with a CSPE jacket immediately below the PAR models. The models were wetted prior to the exposure to allow the formation of such acids as sulfuric and sulfurous acid. Also, 30

12 10 5

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Hydrogen Depletion Curves for NIS PAR Model Without (Solid Curve) and With (Data Points) Exposure to Cable Fire (Ref.15)

as in the previous tests by developers, these tests addressed the possibility of coking from pure carbon soot deposited onto the catalyst surfaces.

Indeed, a greater poisoning effect was measured from exposure to burning a cable containing sulfur than was observed in the previous developer tests on burn products from cable not containing sulfur. For a test with PWR conditions (oxygen rich), the exposure to fire reduced PAR recombination rate by about 10 percent.

6.3 IPSN H2 PAR Siemens PAR Aerosol Tests l

Because EdF is exploring the feasibility of using PARS for hydrogen control in beyond design basis accidents in French PWRs (Ref. 36), test programs in France are being conducted to demonstrate the performance of PARS under accident environments.

Two programs are examining the effects of potential deactivators on PAR performance.

One, performed in the same KALI test facility used for the EPRI/EdF PAR model tests discussed above, has shown that Siemens PARS function adequately in the presence of containment sprays containing soda and boric acid (Ref. 36).

Another test program is being conducted in the "H2 PAR" facility at the Cadarache research center by the French nuclear regulatory agency IPSN (Ref. 34). These tests subject a PAR to a hydrogen / air atmosphere simulating a severe accident. Simulated 8

fission product aerosols are released into the test facility (7.6 m plastic tent) by an induction furnace heated to 2900 C for 15 minutes. Within the furnace,24 chemical elements are being used to simulate a reactor core inventory. Among these elements are all of the elements in Groups 2,3, and 4 of the radionuclide groups in NUREG-1465, including many of the elements that are candidate poisons: iodine, tellurium, selenium, and antimony (Group 1, the stable noble gases xenon and krypton, is not included because these gases are not suspect poisons). Hydrogen is released into the tent as soon as the aerosols have been injected. An initial series of recombination tests using Siemens PARS has been completed. Preliminary information obtained informally indicates that the capacity of the Siemens PAR in the tests was not significantly affected by the French PWR simulated aerosols. Final results to be reported this year are expected to confirm the conservativeness of the conclusions about PAR poisoning reached in this report.

6.4 Laboratory Tests on Fixed Bed Pellet Catalysts About 25 years ago, an extensive series of benchtop laboratory testing was conducted to examine the effects of potential chemical poisons on the recombination officiencies of pelletized platinum and palladium catalysts. Conducted by Southern Nuclear Engineering (SNE), the tests (Ref. 35) were part of a feasibility study of forced flow through fixed-bed catalytic devices located inside a containment as a means of centrolling hydrogen produced in postulated accidents in PWRs and BWRs. Although the envisioned internal catalytic recombiners were never developed, the test data was cited in 1978 in the licensing application for use of an external. catalytic recombiner manufactured by Air Products for combustible gas 32 i

l control in a BWR (Ref. 37). This resulted in NRC approval of the only catalytic recombiner used for accident combustible gas controlin the US. The Air Products recombiner is installed at the WNP-2 plant of the Washington Public Power Supply l

System.

l Two of the several types of catalysts investigated by SNE were of a pellet type similar to the catalysts in the NIS PAR, except that the pellets were cylindrical, not spherical.

One type had a ceramic substrate coated with palladium and the other had an alumina substrate coated with platinum. Both substrates had porous surfaces similar to that of the NIS catalyst.

Both catalyst types were subjected in the SNE tests to a large array of substances that could be airborne in the catalyst's environment both during various plant operating modes (power operation, refueling, etc.) and under accident conditions. The substances included the following, identified above as being suspect poisons expected to be released to the containment atmosphere during an accident: halogens (elemental, methyl iodide, hydrogen iodide, and bromine), tellurium oxide, selenium oxide, sulfur (elemental and sulfur dioxide), and carbon monoxide. Also examined were compounds of chlorine, lead, rubidium, and cesium.

]

The tests were conducted by passing a gas stream containing a measured quantity of hydrogen at a pre-set temperature through 7/8-inch-diameter catalyst pellet beds.

l l

The bed thicknesses tested were 1 inch and 2.25 inches. The effect of various poisons injected into the gas stream was measured by the hydrogen removal efficiency (ratio of hydrogen concentration change in one pass through the catalyst bed to that in the entrance stream).

1 The most pertinent SNE test data for the two catalysts have been compiled and are presented in the appendix. The data showed that the halogen gases were by far the most deleterious to palladium and platinum performance, with methyl iodide being the most deleterious per unit mass of the halogen forms exammed. Comparison of l

the results with fission product mass loadings in the AP600 shows that reductions from both methyl iodide and the much greater amounts of gaseous iodine present in an AP600 containment are less than ten percent even for the conservative assumption of a damaged core. Thus the SNE results for gaseous iodine are consistent with the Battelle iodine results in Section 6.1.1.

l l

SNE tests with a wide variety of gaseous and aerosol non-halogen chemicals selected l

on the basis that they could be present in a containment during operation or during l

an accident showed reductions of 20 percent or less in fixed-bed catalyst efficiencies from each chemical.' These effects are expected to be much less for a PAR, for which

' An exception was elemental sulfur, for which a loading of 700 g/ft' reduced the efficiency of platinum by 80%, with a barely measurable reduction on palladium efficiency. However, the large poisoning effect of sulfur on platinum is not applicable to PARS because the only ;ource of sulfur in a containment is decomposition of sulfur-containing cable insulation material and this potential source was address directly by the exposure of PARS to cable bum in the EPRl/EdF tests (see Section 6.2),

33

little of the aerosols and gases heavier than hydrogen traveling up through the open channels would reach the catalyst surfaces and for which testing has shown a backup reserve of catalyst (most of the heatup and recombination occurs in the lower third of the catalyst elements).

6.5 Warranty Level of Halogens for Poison Resistance of Catalyst Pellets A useful source of information on the effects of chemical poisons on catalysts is the product guarantee provided by the fabricator, Degussa, of the catalyst pellets used in the NIS PAR (Ref. 38). The warranty states the levels of various contaminants in an atmosphere for which a catalyst is guaranteed to operate at rated capacity for a lifetime of 3 years.

Of special interest for the current study is the level cited for gaseous halogens (including fluorine, chlorine, bromine, and iodine). The warranty states that the halogens may not exceed 500 ppm. The level of halogens calculated for an AP600 containment atmosphere of air, hydrogen, and steam with a volume of 45,900 m at S

a temperature of 424 K and a pressure of 2.2 bars is 0.6 ppm for a DBA and 5 ppm for a damaged core - much less than the level for manufacturer guaranteed functioning at rated capacity.

6.6 Conclusion Review of all test data available to EPRI on the effects of potential poisons on PAR performance indicates that for the conditions expected to be present in an AP600 under DBA conditions, a minimal reduction in PAR recombination capacity would be expected. Therefore, an assumption of a 10 percent reduction factor (based on results of a test in which sulfur-bearing cable insulation was burned immediately below a PAR) is sufficent to cover both DBA fission products and a cable fire.

Even if the accident were to progress beyond a design basis accident to substantial in-vessel damage, PAR recombination capacity would be reduced by no more than 25%,

which is sufficent to address both the 15 % reduction in efficiency observed for an NIS PAR model exposed to a conservatively large mass of elemental iodine vapor and, separately, the 10 percent reduction observed for PARS in cable fire tests.

i 34 l

l'

]

)

i Section 7 i

REFERENCES 1.

" Advanced Light Water Reactor Utility Requirements Document," Volume Ill Utility Requirements for Passive Plants, EPRI Report NP 6780-L, Rev. 7, l

December 1995, Chapter 5, Section 6.5.

2.

" Qualification of PARS for Combustible Gas Control in ALWR Containments,"

EPRI ALWR Program Report, April 8,1993.

3.

U. Wolff and G. Sliter, " Passive Autocatalytic Recombiners for Combustible Gas Control in Advanced Light Water Reactors," Fourth International Topical Meeting on Nuclear Thermal Hydraulics, Operation, and Safety, Taipei, Taiwan, April 1994.

1 4.

G. Sliter, U. Wolff, H. Zimmer, D. Gluntz, and J. Thompson, " Passive Autocatalytic Recombiners for Combustible Gas Control in SBWR Advanced Light Water Reactors, ANS ARS '94, International Topical Meeting on Advanced Reactor Safety, Pittsburgh, Pennsylvania, April 1994.

5.

"NIS Catalyst Module for Hydrogen Removal in Containment Atmosphere," NIS Ingenieurgesellschaft MBH, August 1992.

6.

R. Heck, W. Heinrich, and V. Scholten, " Igniters and Recombiners for Hydrogen Reduction Following Severe Accidents," Siemens Service Report No.14, September 1991.

7.

W. Dewit et al., " Hydrogen Recombiner Development at AECL," OECD Workshop on the Implementation of Hydrogen Mitigation Techniques, Winnipeg, Manitoba, Canada, May 13-15,1996.

8.

F. Ferroni and A. Chakraborty, " Design Comparison of Devices for the Catalytic Removal of Hydrogen," Int. Conf. on Nuclear Containment, University of Cambridge, UK, September 1996.

9.

Thomas, C. L., Catalytic Processes and Proven Catalysts. Academic Press, 1970.

l l

i

10. Kohl, A. L. and F. C. Riesenfeld, Gas Purification. Fourth Edition, Gulf l

Publishing Company,1985.

11. Muller, H., et al., " Catalytic Purification of Off-flow Gases Containing CKW using Precious Metal Catalysts," paper by DeGussa AG and Hoechst AG at Achema Conference,1991.

l l

35

12. Engelhard Industries, Inc, Chemical Division. Bulletin El-4419A.9.

13. C.A. Negin, L.O. Kenworthy, and G. Worku, "BWR Off-Gas Systems -

Operating Experience and Planning Study," Final Report NP-1839, May 1981.

14. Behrens, U., "Experimentelle Untersuchungen zum Verhalten des vom NIS entwickelten Katalysator-Moduls im 1:1-Massstab bei verschiedenen Systemzustanden im Modell-Containment (Experimental Investigations of the Behavior of the NIS-Developed Catalyst Module in Full Scale under Various System Conditions in the Model-Containment)," Batelle Institute Report, June 1991 (PROPRIETARY).

15. Behrens, U. et al., "Experimentelle Untersuchungen zum Verhalten des von NIS entwickelten Katalysator-Modell-moduls bei verschiedenen Systemzustanden und Anordnungen (ExperimentalInvestigations of the Behavior of the NIS-Developed Catalyst Model Module under Various System Conditions and Arrangements)," Batelle Institute, Volume I (Report) and Volume II (Test Data), March 1991 (PROPRIETARY).

16. " Generic Model Tests of Passive Autocatalytic Recombiners (PARS) for Combustible Gas Control in Nuclear Power Plants," Vols.1,2, and 3, EPRl/EdF/CEA Final Report TR-107517, June 1997.

17. L. L. Hegedus and R. W. McCabe, Catalyst Poisoning. Marcel Dekker, Include., New York and Basel.

18. E. B. Maxted, "The Poisoning of Metallic Catalysts," in Advances in Catalysis and Related Subjects. Volume III, edited by W. G. Frankenburg, V. I Komarewsky, and E. K. Rideal, Academic Press Inc., New York, N.Y.,1951.

19. Berndt, M., D. Ksinsik, and D. Durrwachter, "Einfluss verschiedener Verunreinigungen auf die Wirksamkeit von Edelmetallkatalysatoren" (Influence of Different Poisons on the Effectiveness of Precious Metal Catalysts)," Chemie-Technik,9(1980) 63.

20. A. K. Chakraborty, " Poisoning of Catalytic Recombiners Due to Radioactive Release of Sulphur and Halides During Core-Melt Accidents," and "The Influence of Catalyst Poisons and the Measures to Maintain the Functionability of Catalysts for the Removal of Hydrogen During a Core-Meltdown Accident,"

i GRS Final Report, GRS-A-2235, December 1994.

21. D. L. Trimm, " Poisoning of Metallic Catalysts," Chapter 4 of Deactivation and Poisoning of Catalysts. edited by J. Oudar and H. Wise, Marcel Dekker, Include.,

New York and Basel,1985.

l 36

. 22. U.S. Code of Federal Regulations,10CFR50.44, " Standards for Combustible Gas Control System in Light-Water Power Reactors."

23. U.S. Code of Federal Regulations,10CFR50.34(f), " Additional TMI-Related Requirements".

24. NUREG-1465, " Accident Source Terms for Light-Water Nuclear Power Plants," US NRC Final Report, February 1995.

. 25. ' J. Snoeck, C. Solaro, and PAR. Moeyaert, "First Experience with Installation of Passive Autocatalytic Recombiners," OECD Workshop on the Implementation of Hydrogen Mitigation Techniques, Winnipeg, Manitoba, Canada, May 13-15, 1996.

26. Letter from T. T. Martin, NRC, to N. J. Liparulo, Westinghouse, "AP600

. Use of Passive Autocatalytic Recombiners (PARS) for Design Basis Hydrogen Control," April 1,1997.

27. Regulatory Guide 1.89, Rev.1, " Environmental Qualification of Certain Electric Equipment Important to Safety for Nuclear Power Plants," US NRC, June 1984.

28. E. C. Beahm, " Tellurium Behavior in Containment under Light Water Reactor Accident Conditions," Oak Ridge National Laboratory Report, NUREG/CR-4338, February 1986.

29. R. R. Hobbins, D. A. Petti, and D. L. Hagrman, " Fission Product Release from Fuel Under Severe Accident Conditions," Nuclear Tecnology, Vol.

101,p.270,1993.

30. R. R. Hobbins, D. A. Petti, D. J. Osetek, and D. L. Hagrman, " Review of Experimental Results on Light Water Reactor Core Melt Progression,"

l l

Nuclear Technology, Vol. 95, p. 287,1991.

' 31. D. A. Petti, R. R. Hobbins, and D. L. Hagrman, "The Composition of Aerosols Generated During A Severe Reactor Accident: Experimental l.

fResults from the Power Burst Facility Severe Fuel Damage Test 1-4,"

i Nuclear Technology, Vol.105, p. 334,1994.

i i

32. Handbook of Chemistry and Physics,45th Edition, Chemical Rubber Company,1964.

33. "AP600 Containment Aerosol Calculation Results," Polestar Applied LTechnology, Inc., Calculation PSAT0902H.03, April 10,1997.

j i

~

j l

37 j

V i

j

\\-

l

34. E. Studer and P. Rongier, "The H2 PAR Facility for Hydrogen Research,"

OECD Workshop on the Implementation of Hydrogen Mitigation 2

Techniques, Winnipeg, Manitoba, Canada, May 13-15, 1996.

35. G. M. Brown, et al., " Catalytic hydrogen Recombiner Development Program, Post-LOCA Conditions Investigation," SNE-100NP, Southern Nuclear Engineering Inc., December 1971.

36. S. Guieu, "EDF Analysis of Hydrogen Problem on Present NPPs," OECD j

Workshop on the Implementation of Hydrogen Mitigation Techniques,

. Winnipeg, Manitoba, Canada, May 13-15, 1996.

j

37. " Air Products Post LOCA Recombiner Test Summary," prepared by Air Products for Washington Public Power Supply System, Report No. APCI-78-8, July 1978.

38. " Guaranteed Conditions for Catalytic Recombination by Degussa Catalysts," product warranty of Degussa (fabricator of NIS PAR catalyst) i 4

t i

I i

l i

l i

38 l

APPENDIX A LABORATORY TESTS ON POISONING OF FIXED BED CATALYSTS A.1 Background and Objectives During the first decade of commercial nuclear power in the US, catalytic recombination was investigated as a means of controlling hydrogen produced in postulated accidents in PWRs. A feasibility study used benchtop laboratory tests to examine the effects of potential poisons and gamma irradiation on the recombination efficiencies of platinum and palladium catalysts. Early testing had i

been conducted by Combustion Engineering (Ref. A-1). A subsequent two-year laboratory study conducted by Southern Nuclear Engineering (SNE) for several utilities including Consolidated Edison was summarized in Ref. A-2, but detailed results in the files of SNE were not published in the open literature. EPRI recognized the value of these results for assessing the effects of chemical poisons on PARS and executed a consulting agreement with Gilbert M. Brown, who managed 1

the CE tests and directed the SNE test program, to describe the SNE testing and provide EPRI with selected test data relevant to the effects of potential poisons on catalyst systems similar to those in PARS. These test data and conclusions based on them are presented in this appendix.5 Since the test data were intended to be used to assist in the design of combustible gas control devices in nuclear plants, the testing was performed with quality assurance practices appropriate for applications in nuclear plants in the late 1960's. For use today, the results can be viewed as having at least research quality and as providing an understanding of PAR catalyst vulnerability to a wide range of potentially poisonous chemical substances.

SNE first performed preliminary scoping tests on approximately a dozen types of commercial catalyst types with different catalyst materials and physical forms. The objective was to identify catalyst types whose performance and cost were suitable for use in nuclear plant applications. Two of the types selected for further testing were pelletized catalysts consisting of cylindrical pellets. The catalyst pellets designated as SN-15 in the original program had a ceramic substrate coated with palladium and had diameters of approximately 1/8 inch and lengths between 1/8 and 3/16 inch.

The other pellets, designated as SN-18, had an alumina substrate coated with 8 The SNE program also examined the effects of gamma radiation on recombination. Comparisen of temperature rises in beds of palladium-and platinum-coated ceramic pellets with a continuous stream of a 3.0 vol% hydrogen-air mixture at temperatures between 120 and 160*F showed that irradiation of the catalysts with over 100 Megarads of gamma irradiation from a Cobalt-60 source had no effect on hydrogen removal efficiency. This was expected because of the high radiation damage resistance of metals and ceramics to gamma irradiation.

l l

39 r

1 i

i j

platinum and had diameters of approximately 1/8 inch and lengths ranging from 1/8 to 1/4 inch. Although both pellet types were commercial catalysts with exact composition proprietary to the manufacturers, both substrates had porous surfaces with pores providing very large surface areas per unit weight. Test data for these two catalysts, referred to henceforth as palladium (SN-15) or platinum (SN-18) were compiled and are presented in this appendix.

Both catalyst types were subjected to an array of substances that could be airborne in the catalyst's environment both during various plant operating modes ( power operation, refueling, etc.) and under LOCA conditions. The objectives of this appendix is to assess whether (and to what degree) the recombination performance of the two catalyst types were degraded by these substances and draw conclusions to the extent possible regarding these substances' poisoning effects on catalytic elements in PARS.

We next discuss how potentially poisonous substances were selected, we then describe the tests, and finally we give the results and conclusions.

A.2 Potential Poisons Selected for Testing The chemical substances examined in the tests were selected from both industrial substances and known post-LOCA fission products. All the substances except halogens that were examined in one stage of the SNE test program are listed in Table A-1. All substances known from practical experience to be present in significant amounts in a reactor containment were included as a potential poison, even if there was no reason to suspect that it could affect catalyst activity. The industrial substances included common plant chemicals used for example in sprays for iodine trappii in painting, as cleaning solvents, for filter testing, from welding fumes, and four a plant laboratories. The fission products were, selected based on regulatory guida e in TID-14844 (Ref. A-3) and other then-current information (Ref. A-4), whict entified the many substances that could be released in significant quantities from a. actor core during a LOCA or a severe accident, and hence could threaten the activity of a catalyst being used for combustible gas control.

Halogens were examined in a second stage of the SNE test program because (1) they were already expected to be poisonous and (2) there was some concern that they would permanently contaminate the test equipment (this did not happen). The halogens tested were elemental iodine, hydrogen iodide, methyl iodide, and bromine.

In the past 30 years, substantial information has been developed updating our knowledge about LWR accidents and the released fission products. Partly motivated by the ALWR program, a revised source term has been developed based on current understanding of light water reactor accidents and fission product behavior. A i

review of the revised radionuclides in Table 3.8 of NUREG-1465 (Ref. A-5) shows l

that, although a few elements have been added to the list in TID-14844, none of the 40

added elements appear in significant enough quantities or can be expected to poison noble metal catalysts. The conclusion is that the fission product substances identified for inclusion in the SNE test program (see Table A-1 and the list of halogens above) are, to our best knowledge today, representative of potential catalyst poisons released in a typical operating plant or advanced plant LOCA or severe accident.

Table A-1. Miscellaneous potential poisons tested (exclusive of halogens) and their chemical form

• Gases High Solution poisons Low volatility volatilityliquids solids and liquids Acetylene Acetone H O (14,000 gm/cu ft)

S 2

SO NHOH Pb(NO )2 Te (as TeO )

2 3

2 CO

CCl, Alcohol (8,000 gm/cu ft)

Mo (as moo )

3 Freon-12 Hydrazine

CuSO, Cs (as Cs CO )

2 3

NH "

H 0 (30% solution)

CCl,(22,500 gm/cu ft)

Rb (as Rb CO )

3 2 2 2

3 Oil (450 gm/cu ft SeO (in NaOH solution)

RuO, 2

increments)

H 0 (4,000 gm/cu ft)

(517 gm/cu ft) 2 2 Cs CO, Hg (liquid) 2 RbCl H BO 3

3 Na S O 22 3 NaOH H BO /NaOH/NA S 0 3

3 22 3 Nacl TeO2 FeCl3 ZnCl2 SnCl 2 NaVO3

'Unless otherwise shown, poison added in a quantity equivalent to about 700 gm/cu ft of catalyst pellet. Standard test conditions were: 1-in.-deep, 7/8-in.-diameter catalyst bed; 2% H -air mixture; 1.2 CFM and 170-180 F inlet temperature.

2

" Background only.

l l

41 I

A.3 Description of Tests i

1 A.3.1 Test Arrangement. The tests were conducted by passing a gas stream containing a measured quantity of hydrogen through a catalyst pellet bed (see schematic diagram of test apparatus and catalyst specimen in Figs. A-1 and A-2). The test specimen was a 7/8-inch-diameter bed of palladium-coated pellets (SN-15) or platinum-coated pellets (SN-18). The effect of various poisons injected into the gas stream was measured by the hydrogen removal efficiency (ratio of hydrogen concentration change in one pass through the catalyst bed to that in the entrance stream).

Initial testing was conducted to select the catalyst bed depth to be used in the program. Measured effluent concentrations for an inlet stream of 2 vol % hydrogen into unpoisoned platinum and palladium specimens of various depths are shown in Fig. A-3. On the basis of this data, a 2.25-in. bed depth was selected for most of the tests to ensure a baseline unpoisoned efficiency of essentially 100% for both catalyst materials. It is important to recognize that this depth is significantly less than that of the fixed-bed recombiners envisioned for plant use at the time of this study. The depth for the test had to be reduced to this small dimension so that the degree by which a potential poison reduces recombination efficiency could be measured. The measurement techniques used for these tests were most accurate for removal efficiencies in the range of 10 to 90%, so the pellet bed depth was chosen to give efficiencies in this range for the hydrogen concentrations and amounts of poisons used in the tests. If pellet bed depths representative of the envisioned fixed bed plant recombiners were used, scoping test results showed that the bed efficiency would be 100%, or close to 100%, for all test conditions. This means that any results or conclusions based on the efficiencies measured in 2.25-in.-deep beds are conservative (err on the safe side) with respect to efficiencies of the greater bed depths that were envisioned for use in a plant fixed bed filter configuration.

(Results of some tests, conducted on 1-in.-deep beds, were even more conservative.)

A similar consideration applies to PARS - test measurements have shown that the vast majority of recombination takes place over the lower third of the height of a PAR element (cartridge or plate). Therefore, even if the entire element was poisoned to some degree, the portion of hydrogen not recombined as it passed along the lower third of the catalyst elements could be recombined as it reached the upper two-thirds of the catalyst elements, which will have a reserve of unpoisoned catalyst available.

The quantity of substances applied to the specimen in each SNE test was established j

as follows. For the potential industrial poisons conservative estimates of the mass of each substance that could be present in a containment atmosphere were made.

For the fission products it was assumed that a 3200 Mwt PWR core was operated to fission product equilibrium, the fractions of core inventory of each product according to TID-14844 were released to the containment as an aerosol, and some plateout limited the amount of aerosol that could reach the recombiner. The quantity.of substances applied in a test was arrived by using the same unit poison 42 I

i

loading (ratio of total mass of expected poisons in the containment atmosphere to recombiner catalyst volume) in the tests as for the plant situation. It was assumed that four cubic feet of catalyst would be used in a typical containment. This approach led to a range of nominal test quantities which, for most of the substances was bounded conservatively by a loading of 700 grams per cubic foot of catalyst.

Therefore this amount was applied to the specimens in most of the tests (see Table A-1), allowing a direct comparison of the relative poisoning effect for a given loading. As indicated in the table, greater amounts were applied for a few substances.

To pass a stream of well-characterized gas through the catalyst bed, air from a j

compressor was metered first into a 2-inch diameter pipe and mixed with a separately metered stream of hydrogen. The air-hydrogen mixture was passed through a heated pipe and then through the upper portion of the test rig shown in Fig. A-1. The feed gas mixture temperature was set by adjusting power to an inline cartridge or pipe heater. The feed flow rate was set by using an ASME-specification orifice.

As the air-hydrogen mixture flowed downward in the test rig, its path narrowed through a conical section of pipe and entered a 7/8-inch inside diameter stainless steel tube which held the catalyst bed test specimen (see Fig. A-2). Readouts from a series of sheathed thermocouples penetrating the wall of the catalyst holder provided local bed temperature data. (As indicated in Fig. A-2, seven thermocouples were installed -- only five of them are shown in Fig. A-1.) Thermocouple locations were measured relative to a fixed screen, mounted on a lip rolled into the tube holder below the catalyst bed. Gas sampling lines in the exit stream below the catalyst bed and in the inlet stream above were connected to a Hays hydrogen analyzer by a valve arrangement that allowed the sampling location to be selected.

Values of concentration measured by the analyzer were checked by calculated concentration based on measured temperatures of the inlet and outlet streams with the knowledge that a reaction of 1 vol. % of hydrogen in air causes the temperature to rise by about 150 F.

A poison injection nozzle penetrated the flow-tube wall immediately above the conical section, approximately 14 inches above the catalyst support screen (see Figure A-2). A 3/8-inch-diameter orifice constriction located immediately below the point of poison injection was used to create a local region of high air velocity to assure thorough mixing of the inlet feed with the injected poison.

A3.2 Application of Gaseous Substances. Potentially poisonous substances normally in a gaseous state at room temperature were metered into the test rig from j

high-pressure tanks at known flow rates for a period of roughly 30 minutes.

l A33 Applicatien of Liquid Substances. Poisons that exist as liquids or solutions with relatively low boiling points were placed in a glass test tube connected to the test rig, with air or nitrogen passed over the material to sweep it, as vapor, into the 43

j test rig. In most cases, heat was applied (by such means as warming the test tubes) to speed up the poison vaporization. For most liquids about 700 grams per cubic foot of catalyst was added over a period of roughly 30 to 60 minutes.

i A.3.4 Application of Particulates_. Potential poisons that would be carried into the catalyst either entrained as particles or as a solution in water droplets in the gas stream were also tested. For these tests, the poisons were injected by using an aspirator-type spray (fog) nozzle with nitrogen as a driver gas. A mist containing the poison was injected downward toward the catalyst. Except as noted below,5 cc of liquid containing 5 gm of poison per 100 cc of water was used. Hydrogen peroxide (30% solution), water, alcohol, and carbon tetrachloride were injected directly (not in solution) in quantities of 5 cc each. Since poisons were generally added sequentially, visible amounts of various materials accumulated on the catalyst surface.

Low volatility solid poisons were vaporized from a zirconium " boat" that was electrically heated to 1400-1800 F. The boat was located about 12 inches above the catalyst support screen. The quantities of these poisons again corresponded to i

700 gm per cubic foot of catalyst (it should be pointed out that any of the poisons that plated out on the inside walls of the test section did not reach the catalyst).

To maximize the amount of potential poisons reaching the catalyst, no up-stream trapping devices, such as filters or adsorbers, were used. Feed temperatures were not affected by the addition of poisons, because their quantity and rate of additions were small (this was confirmed by bed inlet temperature monitoring (see Fig. A-2).

)

A.4 Applicability of Test Results to PARS We now address the question of how the results regarding the effects of poisons on the pelletized fixed bed filter catalyst systems modeled in the SNE program apply to catalyst pellets in the diffusion filter configuration in PARS. Note that, although the SNE test specimens included both palladium and platinum catalysts, they were both of the pelletized form, so that comparison of results with those for pelletized PARS (such as NIS PARS) are more directly applicable than for plate-type PARS (such as Siemens PARS).

An important difference between the two configurations is that the poisons are more likely to have a greater effect in the fixed bed configuration, in which the pellets are directly in the path of the poison-laden gases passing through the filter.

This contrasts to the lesser effect to be expected for the PAR diffusion filter in which l

the light hydrogen atoms readily reach the catalyst surfaces due to their high diffusivity, while the poisons, which are heavier in both gaseous and liquid / solid forms, tend to flow by the catalyst with low (gaseous) or very low (liquid / solid) difusivity. This difference applies to both the pellet-type and the plate-type PAR.

On the basis of this difference, we conclude that, for gaseous poisons, the reduction in hydrogen removal efficiencies observed in these tests with a pellet bed lead to reasonable, but conservative estimates of the reductions that a like amount of 44 l

1..

je e

poison would have on pellet or plate catalyst elements in a PAR configuration. On the other hand, for aerosols, the vast majority of which flow through a PA.R without reaching the catalyst surface, the pellet bed test results cannot be used to estimate the levels to which PARS would be poisoned by equal amounts of poison -

the effects of acrosol poisoning on pellet beds is expected to be dramatically less on PAR elements.

For these reasons, we are able relate the SNE test results with PAR performance quantitatively for gaseous poisons, but for aerosols, only qualitative conclusions can be drawn.

For gaseous poisons, we use the same definition of above (ratio of mass of poison to catalyst volume).' poison loading as descr It must be recognized however that using the same definition for poison loading for the fixed bed filter configuration as for the PAR diffusion filter configuration is an approximate but conservative assumption. The assumption would only be completely valid if all of the gaseous flow through a PAR was able to reach all of the volume of the pellets as it does in the fixed-bed configuration. Since reaching the catalyst pellets in a PAR relies on diffusion, not as much of the heavier-gas poisons like iodine reaches the catalyst pellets as the hydrogen gas. Therefore, although mass per unit volume of catalyst is a reasonable definition of gaseous poison loading for both PARS and fixed beds, its use gives a somewhat conservative result for PARS.

The PAR halogen poison loadings for an AP600 are given in Table A-2 (based on halogen release masses from Section 5.6 and volume of catalyst in the two AP600 PARS equal to 0.1584 m' or 5.59 ft. These are the AP600 halogen poison loading 8

parameters equivalent to the SNE test halogen poison loading parameters.

Table A-2. AP600 PAR Halogen Poison Loading DBA Damaged Core Poison Mass Poison Loading Poison Mass Poison Loading (g)

(g/ft3)

(g)

(g/ft3)

Iodine (all 46.7 9.4 373 66.8 halogens)

Methyl 1.4 0.25 11.2 2.0 iodide l

i l

• This measure of unit poison loading assumes that the effective noble metal catalyst area or loading is similar in the benchtop test pellets as in the PAR pellets. This assumption is reasonable because both l

pellets are of a standard type typically used in industrial applications. The concentration measured by the analyzer is a more accurate value.

45

t.-

1 l

l A.5 Test Results and Comparisons with AP600 Poison Loadings As mentioned previously, the poisoning tests were performed in two stages. The first stage (" fixed quantity non-halogen tests") addressed many industrial substances i

and known post-LOCA fission products with a fixed quantity of each potential poison applied. The second stage of testing (" variable quantity halogen tests")

addressed halogens only, and measured poisoning effects for each halogen (iodine, bromine, and methyl iodide) as a function of poison loading and various gas temperatures and flow conditions. First, the results of the second stage halogen testing will be treated quantitatively with respect to the AP600, and then the results i

of the first stage non-halogen tests will be treated more qualitatively.

l A.5.1 Halogen Test Results.The halogens iodine and bromine, including the organic form methyl iodide, were tested using the test rig and injection procedures described above.

In one series of tests, elemental iodine dissolved in ethyl or isopropyl alcohol was spray injected into a stream of 2% hydrogen in air at an inlet temperature of about 200 F. Each increment of concentrated solution added to the stream corresponded to about 10 gm per cubic foot of the 2.25-in.-deep catalyst bed. For this liquid aerosol application of iodine, substantial reductions in efficiency are observed for poison loadings of several hundred grams per cubic foot.

In another series of tests, the gaseous form of elemental iodine was introduced with a sweep gas was passed over iodine crystals to transport iodine vapor into the test -

bed. The rate of iodine addition was adjusted by varying the temperature of the iodine container and the sweep gas flow. Results of gaseous iodine tests are shown in Fig. A-5.

. Methyliodide was also tested and found to be the most deleterious poison encountered in the program on an equal mass loading basis. Results for palladium and platinum are shown in Figures A-6 and A-7, respectively.

Poisoning effects of hydrogen iodide were also tested. The hydrogen iodide was dissolved in water to form a 50% (by weight) solution, which was heated and the vapors swept over a 1-in.-deep catalyst bed. At a cumulative loading of 710 gm per cubic foot, the hydrogen removal efficiency of palladium (SN-15) was reduced to 39% and that of platinum (SN-18) was reduced to 21%. This is roughly the same degree of poisoning as observed for elemental iodine. Therefore, comparisons with iodine from the AP600 will be made on the basis of elemental iodine.

Finally, poisoning of a 2.25-in.-deep bed by bromine was tested. For these tests, the l

high vapor pressure of bromine made it difficult to regulate the rate of addition, which led to large scatter in the results (see Fig. A-8). With bromine, the efficiency 46

for palladium was reduced more than for platinum - the opposite result from poison tests with iodine compounds. However, comparison with the results for elemental iodine in Fig. A-4 show that the range of poisoned efficiencies observed for bromine are roughly the same as for iodine. In any event, as noted above, we will treat the smaller AP600 bromine releases as equivalent iodine poisoning, so that these results for bromine will not be used.

To determine how the measured SNE cfficiency reduction curves discussed above relate to AP600 conditions, we enter the curves with the poison mass loadings given i

in Table A-2. Results of this process for both gaseous iodine (actually all AP600 halogen releases treated as iodine) and for methyl iodide are given in Table A-3.

Table A-3. SNE Test Results applied to AP600 Poison Loading Poisoned Efficiency of a 2.25-in.-deep Bed (%)*

Palladium Platinum Test Condition Figure DBA Damaged DBA Damaged Core Core i

Iodine Spray A-4 92 90 88 72 Iodine Gas A-5 98 95 98 95 Methyl Iodide A-6, A-7 99 98 99 93

' Values correspond to the lower of measurements taken either by the hydrogen analyzer or by the change in inlet to outlet temperature.

To compare the results in this table with the results for an iodine poisoning test of a NIS PAR model (Section 6.1.1), we calculate the mass poison loading in the Battelle 8

3 3

test to be 3 g/0.001 m of catalyst or 3000 g/m = 85 g/ft. This value is about 20%

more than the iodine loading for the damaged core assumption in Table A-2. From the palladium curve in Figure A-5, we obtain a reduction in efficiency for iodine gas of 6 % for the Battelle iodine loading, in rough agreement with the 15 % reduction in efficiency measured in the Battelle test.

A.5.2 Fixed Ouantity Non-Halogen Test Results. For this stage of testing, a certain quantity of each chemical substance (see Table A-1) was added to the test stream one after another with the hydrogen gas mixture stream continually flowing through a l

1-in.-deep catalyst bed. Once in a while, after several chemicals had be added i

sequentially, the flow would be stopped and testing in a given series would be resumed later (e.g. after lunch or the next day). When this occurred, " restart" would consist simply of restarting the gas flow, measuring the removal efficiency with no poison in the gas stream, and then adding the next chemical. Prior to restart, the inner surface of the holder tube would be cleaned of plated materials, but neither l

I l

47 i

the catalyst pellets, nor the lower screen supporting the pellets was cleaned (materials accumulated on the pellets would sometimes be visible).

Results for the high volatility liquids and solution poisons in Table A-1 are given in Figures A-9, A-10, and A-11. As indicated by the " stair step" plots in these figures, the testing was performed in a number of series of sequential additions of chemicals. Each series started with an " initial" measurement of an unpoisoned pellet bed. The initial measurement of each series gave values of removal efficiency between 92 and 97%, which is an indication of the measurement scatter and accuracy observed for all the measurements.

It can be seen that there is also a degree of scatter between a measurement made before and after " restart." Part of this is measurement scatter and part may be any changes induced in the highly contaminated ("gunked up") bed during shutdown and startup (this change was particularly large toward recovery in the restart measurement shown in Fig. A-11).

The results in these figures show that, in general, each added chemical produced an increase of poisoning (reduction in removal efficiency) between 1 and 10 percentage points (on an absolute scale of 100% removal). Since a cumulative effect is being measured (except for the first chemical applied to a fresh catalyst), it is not possible to differentiate among permanent poisoning from previously applied chemicals, permanent or temporary poisoning caused by the chemical being added, or the ability of an added chemical to clean off accumulated chemicals that might be affecting recombination. Nevertheless, the increment from one application to another gives an indication of the poisoning capability of the newly applied chem.ical. Alcohol produced an increased efficiency of about 1% for palladium (Fig.

A-10) and about 9% for platinum (Fig. A-11) - alcohol evidently reacts exothermically to increase the basic catalytic reaction or is effective in cleaning off the catalyst so that its efficiency is improved. As indicated in Fig. A-9, a few other gaseous or volatile substances also improve removal efficiency by a small amount.

For palladium, none of the added chemicals caused a decrease in removal efficiency of more than 10 percentage points. For platinum, only two chemicals caused a greater decrease - a 15-point drop due to SeO (about a 20% decrease) and an 18-point 2

drop due to H O (about a 30% decrease). The latter result is not applicable to PARS 2 2 because hydrogen peroxide is not present in containments in significant amounts.

Results for the seven low volatility solids in Table A-1 were not plotted as above for the other potential poisons in the table. Also, unlike the other substances, these seven were applied individually to a clean 1-in.-deep catalyst bed, all with 700 grams l

per cubic foot (excepting ruthenium oxide with 517 grams per cubic foot). The l

measured reduction in efficiency of the palladium catalyst (SN-15) was barely L

measurable (less than one percent) for all seven substances. For the platinum catalyst, only sulfur and tellurium oxide had significant effects - sulfur reduced the efficiency by as much as 80 percent and tellurium oxide by 13 percent. Before 48

1 discussing the results for tellurium further in the following paragraph, we note that the substantial poisoning of platinum observed for sulfur in these tests is not applicable to PARS because the only source of sulfur in a containment is decomposition of sulfur-containing cable insulation material and this potential source was address directly by the exposure of both types of PARS to cable burn in the EPRI/EdF tests (see Section 6.2). The sulfur poison mass loading in the cable burn tests was at most 4 grams per cubic foot, much less than the 700 grams per cubic foot loading in the SNE tests.

j Of particular interest are the results of these tests regarding tellurium - a suspected poison that is released from a core in substantial amounts. In Section 3 we concluded that since all forms of tellurium are solid aerosols, they either are removed from the containment atmosphere before they have a chance to reach the PARS or they flow through the PAR flow channels without diffusing to the catalyst surfaces. Therefore, tellurium is not expected to be a significant poison, even for a degraded core assumption. The results in Figs. A-9, A-10, and A-11 and the result for vaporized tellurium oxide described in the previous paragraph confirm this conclusion in that 700 g/ft' of tellurium oxide produces no more than about a thirteen percent reduction in efficiency even though the aerosols were led directly onto the fixed-bed pellets. The tellurium group poison loading for an AP600 degraded core is 2050 g (84% tellurium,11% selenium, and 5% antimony) divided by 5.59 ft' or 366 g/ft' - about half the loading in the SNE tests. Thus, even for a shallew fixed-bed recombiner, the amount of tellurium in an AP600 containment with a damaged core (even if it could reach the recombiner) would have only a small (less than 10%) effect on efficiency.

References A-1 G. M. Brown, et al., " Catalytic hydrogen Recombiner Development Program, Post-LOCA Conditions Investigation," SNE-100NP, Southern Nuclear Engineering Inc., December 1971.

A-2 C. T. Sawyer and F. M. Stern, " Final Report: Investigation of Catalytic Recombination of Radiolytic Oxygen and Hydrogen," USAEC Report CEND-529, Combustion Engineering, Inc., March 1,1965.

A-3 J. J. DiNunno, et al, " Calculation of Distance Factors for Power and Test Reactor Sites," TID-14844, Atomic Energy Commission, March 1962.

A-4 H. N. Culver, " Maximum Credible Accident Exposures at Reactor Site Boundaries," Nuclear Safety. 2(1) pp 83-96, September 1960.

l A-5 NUREG-1465, " Accident Source Terms for Light-Water Nuclear Power Plants " US NRC Final Report, February 1995.

l A-6 AP600 Safety Analysis Report 49

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ALWR

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i EFFECTS OF INHIBITORS AND POISONS i

ON THE PERFORMANCE OF l

PASSIVE AUTOCATALYTIC RECOMBINERS (PARS)

FOR COMBUSTIBLE GAS CONTROL IN ALWRs i

i

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5

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May 22,1997 i

i Prepared by the EPRI ALWR Program i

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Electric Power Research Institute 3412 Hillview Avenue, Palo Alto CA 94303 4

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ALWR j

' A D V ' A N C E D '

2 i

t IGHT Waft R REACTOR i

EFFECTS OF INHIBITORS AND POISONS ON THE PERFORMANCE OF l

PASSIVE AUTOCATALYTIC RECOMBINERS (PARS)

FOR COMBUSTIBLE GAS CONTROL IN ALWRs May 22,1997 Prepared by the EPRI ALWR Program Electric Power Research Institute 3412 Hillview Avenue, Palo Alto CA 94303

l

SUMMARY

This report summarizes available quantitative and qualitative information to assess the effects of potential deactivators (chemical poisons and physical inhibitors) on the performance of passive autocatalytic recombiners (PARS) being proposed for control of hydrogen in AP600 design basis accidents (DBAs). PARS are required to perform their safety function not only after exposure to potential contaminants during operation, but also in an accident environment that may contain various gases or aerosols that are potentially poisonous to the palladium or platinum PAR catalyst elements.

The report begins by providing a technical understanding (based on established chemical / catalyst principles) of the mechanisms that can reduce recombination in 1

PARS. It then reviews the amounts of the chemical species that can be present during a PWR accident. Since the function of PARS in a DBA is to control an amount of hydrogen produced by a slightly damaged core, the main focus of the report is on fission products from gap releases, principally iodine. However, the information and data also address poisons released from a beyond-design-basis damaged core accident. This provides added assurance that even such levels of

(

contaminants would not degrade a PAR's recombination capacity to the extent that it could not perform its safety function in a DBA. Finally, the report summarizes i

existing test data on the effects of suspected inhibitors and poisons on the types and forms of catalysts in PARS. The sources of test data include (1) model recombination l

tests conducted several years ago by PAR developers and recently by EPRI/EdF/CEA and (2) benchtop laboratory recomb nation tests conducted many years ago on palladium and platinum catalyst pellet-bed filters subjected to a wide range of chemicals in the hydrogen / air feed stream. Among the potential poisons investigated by these test programs were substances known from chemical principles to have some poisonous effect on noble metal catalysts. These include iodine, methyl iodide, chlorine, bromine, sulfur, tellurium, and selenium.

The conclusions of this study are although existing information and data do not identify any contaminant e

expected to be present in a containment during operation to significantly degrade the performance of a PAR in an accident, a surveillance program is needed in which PAR elements are periodically removed from service and their hydrogen j

recombination capacity checked of all the contaminants released during accidents. halogen gases have the most deleterious effect on PAR performance l

l-on the basis of PAR model tests in the presence of gaseous iodine supplemented with data from laboratory benchtop tests on the effects of iodine, methyl iodide, and hydrogen iodide on the efficiency of fixed-bed catalyst devices, it is estimated that halogens released in a DBA (intact core) would, result in minimal reduction ii 1

v o

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l in PAR recombination efficiency and that even significant_ levels of halogens resulting from early in-vessel core damage would reduce PAR efficiency by no more than about 15 percent.

i

. regardless of their chemical composition, blockage or chemical poisoning by i

4 U

aerosols introduced into the containment atmosphere in an accident will not have large effects on PARS because (1) a large fraction of aerosols will settle out or be scrubbed out of the atmosphere before they have a chance to reach PARS through diffusion or convection, (2) the large majority of aerosols that do reach j

functioning PARS are expected to be carried vertically through the one-i-

centimeter-wide open flow channels without contacting the catalyst element l

surfaces at the walls of the channels, and (3) particulates managing to reach

)

E catalyst sites are much less reactive than poisonous gases. This conclusion has i

been confirmed by two types of tests:. PAR tests with aerosols from burning j'

cables and laboratory benchtop tests of pellet-bed catalysts with a wide variety of 1

i

' chemical aerosols.

)

l

. Review of all currently available data on the effects of potential poisons on PAR performance indicates that for an AP600 under DBA conditions, a minimal reduction in PAR recombination capacity is expected, so that an assumption of a 10 percent reduction factor observed when sulfur-bearing cable insulation was burned immediately below a PAR is sufficent to cover both DBA fission products i

and a cable fire.

4.

j-Even if the accident. were to progress beyond a DBA to substantial in-vessel i

damage, PAR recombination capacity would be reduced by no more than 25%,

j i

which is sufficent to address both the 15% reduction in efficiency observed for an NIS PAR model exposed to a conservatively large mass of elemental iodine -

l

vapor and, separately, the 10 percent reduction observed in a cable fire test.

(Even this poisoning from iodine would burn off in a DBA from the catalytic i

heat generated from recombining a mixture with 3 vol % of hydrogen.)

p Furthermore, preliminary information from the ongoing H2 PAR test program in France, which is generating test data on one type of PAR subject to simulated fission products from a PWR severe accident, indicates no significant reduction in PAR

- performance. It is therefore likely that further evaluation of this data will show that the 25% PAR capacity reduction factor suggested by this report is overly conservative.

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i TABLE OF CONTENTS 1

l i

SUMMARY

.......................................................................................................................................ii S EGO N 1. BACKG ROUND AND PURPO SE.................................................................................. 1 SEG ON 2. HOW PARS AND CATALYSTS WORK...................................................................... 4 2.1 H OW PARS FUNCTION......................................................................................................... 4 2.2 HOW NOBLE METAL CATALYSIS WORK.................................................................................... 4 S EG ON 3. DEAQVATION OF CATALYSTS............................................................................... 7 3.1 CATALYST DEACITVADON MECHANISMS................................................................................ 7 3.2 DEACUVADON BY INHIBITORS...............................................................................................7 Fouling Dunng Operation.................................................................................................. 7 Wetting.......................................................................................................................10 Fouling Dunng an Accident............................................................

...................................11 j

3.3 DEACHVADON BY POISONS................................................................................................. 13 3.4 HOW DEACUVATORS REACH PAR CATALYST...................................................................... 15 In ac tive PAR.............................................................................................................15 Functioning PAR...................................................................................................... 15 SEGON 4. COMBUSTIBLE GAS RELEASES AND REGULATORY LIMITS...................................16 4.1 DESIGN BASIS ACCIDENTS....................................................

............................................16 4.2 SEVERE ACCIDENTS..................................................................................................... 17 SECTION 5. POTENTIAL PAR POISONS IN NUCLEAR PLANT ACCIDENTS...............................18 5.1 FISSION PRODUCT RELEASES..................................

.....................................................18 5.2 CHEMICAL FORM OF FISSION PRODUCT RELEASE......................................................................19 5.3 NON-FISSION PRODUCr MATERIALS RELEASES.......................................................................... 22 5.4 FISSION PRODUCT AND NON-FISSION PRODUCT MATERIAIS THAT ARE POTENHAL POISONS................. 23 5.5 AMOUNTS OF POTENHAL POISON FISSION PRODUCTS RELEASED................................................ 23 Design Basis Accident.

...................................................................................23 Dama ged Core................................................................

... 24 4

5.6 TRANSPORT AND DEPOSIBON OF AEROSOIS TO PARS.................................

............................24 5.7

SUMMARY

.....................................................................................................................25 l

SEGON 6.

SUMMARY

OF TEST DATA ON THE EFFECTS OF POTENTIAL DEACTIVATORS ON i

N O B LE METAL CATA LYSTS.......................................................................................................... 26 6.1 NIS PAR M ODEL TESTS...................................................................................................... 27 Bat telle Iodine Results................................................................................................. 27 Battelle Fire Exposure Tests........................................................................................... 30 6.2 EPRI/EDF/CEA PAR MODELTESTS..............................

..................................................30 6.3 IPSN H2 PAR SIEMENS PAR AEROSOL TESTS...................................................................... 32 6.4 LABORATORY TESTS ON FD:ED BED PELLET CATALYSIS...............................................................32 6.5 WARRANTY LEVEL OF HALOGENS FOR POISON RESISTANCE OF CATALYST PELLETS............................... 34

6.6 CONCLUSION

S..............................................................................................

.......................34 S ECTI O N 7. REFEREN CES............................................................................................................. 3 5 4

.IV

APPENDIX. LABORATORY TESTS ON POISONING OF FIXED BED CATALYSTS........................ 39 A -1. B ACKGROUND AND OBJECTIVES.................................................................................. 39 A-2. POTENDAL POISONS SELECTED FOR TESENG................................................................. 40 A-3. DESCRIFDON OF TESTS...........................

..................42 Test Arran gement.....................................................

... 42 Application of Gaseous Poisons...............

.............................................................. 43 Application of Liquid Poisons................................

...............................................43 Application of Particulate Poisons...

..................................................................44 A-4. APPUCABIUTY OF TEST RESULT 5 To PARS......

..................44 A-5. TEST RESULTS AND COMPARISONS Wmi AP600 POISON LOADINGS.......................................... 46 I :alogen Tes t Results............................................................................................ 46 Fixed Quantity Non-Halogen Test Results........................................................... 47 A-6. REFERENCES..............

............................................................49 TABLE OF FIGURES FIGURE 1.

NIS PAR UNIT.........

..................................................................................1 FIGURE 2.

SIEMENS PAR UNIT...............

..........................2 FIGURE 3.

HYDROGEN DEPLETION CURVES FOR NIS PAR MODEL WTTHOUT (SOUD CURVE) AND Wmi (DATA POINTS) IODINE (REF.15)....................................

..........................28 FIGURE 4.

RECOVERY OF FIXED-BED CATALYST FROM TWO VOLUMES OF IODINE AS TEMPERATURE INCREASES (REF.19)...................

... 29 FIGURE 5.

HYDROGEN DEPLEDON CURVES FOR NIS PAR MODEL Wm!OUT(SOUD CURVE) AND Wmi (DATA POINTS) EXPOSURE TO CABLE FIRE (REF.15)....

.31 FIGURE A-1.

SNE FIXED-BED HYDROGEN RECOMBINER TEST LOOP............

....... 50 FIGURE A-2.

TESTSECTION OF SNE TEST LOOP.................

...........................51 FIGURE A-3.

MEASURED RECOMBINATION EFFICIENCY FOR INCREASING PELLET BED DEI"TH (UNPOISONED). 52 FIGURE A-4.

SNE RESULTS FOR IODINE IN SPRAY FORM IN A 2.25-IN.-DEEP BED (PALLADIUM AND PLATINUM )...................................

.............................53 FIGURE A-5.

SNE RESULTS FOR GASEOUS IODINE IN A 2.25-IN.-DEEP BED (PALLADIUM AND PLAUNUM)... 54 FIGURE A-6.

SNE RESUL15 FOR METHYL IODIDE IN A 2.25-IN.-DEEP BED (PALLADIUM)....................... 55 FIGURE A-7.

SNE RESULTS FOR MEHiYL IODIDE IN A 2.25-IN.-DEEP BED (PALLADIUM).........

.............. 56 FIGURE A-8.

SNE RESULTS FOR BROMINE IN A 2.25-IN.-DEEP BED (PALLADIUM AND PLATINUM)........... 57 FIGURE A-9.

SNE RESULTS FOR GASEOUS AND HIGH VOLATIU1Y TESTS ON PALLADIUM AND PLAUNUM CATALYSTS.......................

......................................................58 FIGURE A-10. SNE RESULTS FOR SOLUDON POISONS ON A PALLADIUM CATALYST............................ 59 FIGURE A-11. SNE RESULTS FOR SOLUTION POISONS ON PLATINUM CATALYST.............................. 60 TABLE OF TABLES

~ TABLE 1.

PWR RELEASES INTO CONTAINMENT.................................

.....................19 TABLE 2.

PWR PISSION-PRODUCT CHEMICAL SPECIES.................................................... 20 TABLE 3.

PWR NON-FISSION-PRODUCT CHEMICAL SPECIES.............................................. 22 TABLE 4.

MASS OF HALOGENS RELEASED TO AP600 CONTAINMENT..................................... 23 TABLE 5.

TEST PROGRAMS ADDRESSING THE EFFECIS OF POISONS ON PARS AND CATALYSTS............... 26 TABLE A-1.

MISCELLANEOUS POTENHAL POISONS TESTED AND THEIR CHEMICAL FORM................... 41 TABLE A-2.

AP600 PAR HALOGEN POISON 14ADING...................

..........................................45 TABLE A-3.

SNE TEST RESULTs APPUED TO AP600 POISON LOADING..................

..................47 v

Section 1 BACKGROUND AND PURPOSE l

Passive autocatalytic recombiners (PARS) have been proposed as an efficient, reliable, and cost-effective means for controlling combustible gases in the event of a design basis or severe accident in advanced light water reactors (ALWRs)(Refs. I through 4). In general terms, PARS are stainless steel sheet metal boxes open at the top and bottom and containing many vertical flat catalytic cartridges or plates with open gas flow channels between them. In the flow channels, the recombinable gases i

diffuse to the palladium-or platinum-coated surfaces of the cartridges or plates, where the catalytic action converts hydrogen and oxygen into water vapor. PAR 2

units from two suppliers are shown in Figs.1 and 2.

z..

V Db.,

Catalyst Cartridges 5

'5

$@)CSh f[-

4 k; c k ".m!p hh snsk N

6 cm(Chimney) s c

20 cm 91 cm 91 cm Figure 1 NIS PAR Unit 8 In addition to these two PAR types from Germany (Refs. 5 and 6), EPRIis aware of two other commercial designs of PARS, one from Canada (Ref. 7) and the other from Switzerland (Ref. 8). All four designs share the common features of open flow channels between either pellet-filled metal screen cartridges or stainless steel plates. The pellets or plates are coated with either palladium or platinum. Because these four designs are similar, some of the conclusions and observations of this study may be applicable to all of them. However, because the resistance of catalyst systems to poisons is expected to depend on the details of how the catalyst is deposited onto the carrier material, not all of the results in this report may apply to PAR types different from the ones for which data are available.

1

100 cm 4

5 Deflector Plate Removable j

Grill 100 cm i

Catalyst Plate 1

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Inspection Cover Catalyst Insert l

Figure 2 Siemens PAR Unit i

Testing has shown that the recombination rate or capacity of PARS increases with j

increasing concentrations of combustible gases (in terms of percent by volume) and is not retarded by steam or inert gases. However,it is recognized that the j

recombination efficiency of PARS can be diminished by the presence of

^

contaminants (pollutants) in the containment atmosphere. Contaminants can act as recombination deactivators. which can be either physical inhibitors (blocking the combustible gas from reaching the catalyst) or chemical poisons (reacting with and deactivating the catalyst atoms). It is possible that when the PAR needs to perform its function during an accident, a contaminant may already have been deposited on the catalyst from exposure to a polluted atmosphere during normal plant operation I

(for example, from paint or welding fumes present during an outage) or a j

contaminant may be present in the atmosphere as a result of the accident (for example, from fission products released from a damaged reactor core).

PARS must be demonstrated to be capable of performing their design function during or after a postulated plant accident. For control of combustible gases in a design basis accident, PARS must be safety-grade and demonstration of function is l

called environmental qualification. For control of combustible gases in a severe accident, PARS may be non-safety grade and demonstration of functionability is called survivability. For both applications, functionability must be demonstrated under environmental service conditions in which the PAR is required to function.

2

I l

These environments include pressure, temperature, humidity, radiation, and chemicals.

This report addresses the potential effects of deactivators on the functionality of l

PARS in design basis accidents in PWRs generally and the AP600 specifically. The l

effects include wetness as a potential physical inhibitor and chemical substances as l

potential inhibitors or poisons. The approach is to compile existing information l

and data as a basis for establishing a generic bounding value of a deactivation l

reduction factor for design and qualification of DBA PAR systems. The reduction l

factor should be adequate to account for the potential effects of all inhibitors and I

poisons that may be present and may be able to reach PARS before or during DBAs.

l The approach combines qualitative information based on established chemical and l

physical principles with quantitative information from testing of catalyst systems subjected to a wide range of inhibitors and poisons. The sources of test data include (1) tests on PARS conducted by two suppliers over the past several years, (2) tests on the same two types of PARS conducted recently in France by EPRI/EdF/CEA, and (3) tests on catalyst pellet-bed filters conducted in a laboratory about 25 years ago. An additional important source of test data comes from an IPSN/CEA program in which one type of PAR (supplied by Siemens) has been subjected to simulated fission product aerosols while recombining a hydrogen / air atmosphere. Here we briefly describe the tests and give the preliminary result. A final report by IPSN is l

expected to be available by the end of the year.

Section 2 explains how PARS and catalysts work and Section 3 is a technical discussion of the mechanisms by which metallic catalysts can be inhibited or poisoned. Section 4 quantifies the amounts of hydrogen that have to be controlled and Section 5 identifies the substances in PWR containments that are potential PAR deactivators. Section 6 and the Appendix summarize the available test data.

PARS can be used to control combustible gases in both PWR and BWR ALWRs. The former (AP600 or System 80+) are not inerted and the latter (ABWR and SBWR) are inerted with nitrogen. Although much of the information in this report applies to PAR applications in both PWRs and BWRs end thus to all four ALWR designs, a quantitative application is made only to non-inerted AP600 conditions.

Although there are no PARS installed in US operating plants, some plants may find l

it technically and economically beneficial to replace certain existing complex recombiner systems for design basis combustible gas control with simple PARS. The treatment of the effects of inhibitors and poisons in this ALWR report is to a large j

extent applicable to the design and qualification of PAR systems in operating plants.

l l

3 l

Section 2 l

i.

HOW PARS AND CATALYSTS WORK j

l 2.1 How PARS Function i

l A PAR is a passive molecular diffusion filter in contrast to the active fixed-bed

- particle filter configuration used in many industrial. catalyst applications. With a c

PAR,instead of the gases being actively pumped through a fixed bed of catalyst-coated pellets, gases are driven upwards passively (no electric power or moving i

parts) by buoyancy forces through vertical open flow channels, with

.i hydrogen / oxygen molecules reaching the catalyst by diffusion.

l f

In the Siemens design (Fig. 2), the platinum' catalyst is flame deposited along with a ceramic material onto the surface of the thin (0.12 mm) stainless steel plates. The ceramic material provides some degree of porosity to increase the catalyst surface l

area.

i In the NIS design (Fig.1), the carrier material is the porous ceramic, sintered i

alumina (aluminum oxide). The spherical pellets have diameters in the range of 4 i

L to' 6 mm. The sintering gives a very porous structure with a high fraction of open porosity. The thickness of the palladium-impregnated shell is 500 m (microns).

[

According to the manufacturer, due to the high reaction rate of hydrogen'and

~

oxygen, the depth needed for the catalytic action is only 50

m. Therefore the greater q

impregnation depth is available as a reserve in the event that a portion of the imier l

2 surface of the active layer is blocked or poisoned. It is estimated that the total available reactive surface of an NIS PAR device is more than a million square i

meters (Ref. 2).

j Vertical convection'drh en by catalytic recombination draws gases from the containment atmosphere into the unit from below. Heated gases and water vapor exhaust at the top of the unit and mix with the containment atmosphere via natural and PAR-induced convection. If the PAR is wet from i

spray or condensed steam, startup can be delayed while the heat of recombination dries the water on the catalyst. Initial wetness can be reduced i

by adding a hydrophobic coating on the catalyst elements. The metallic

~

. catalyst material is not consumed as it functions and is not subject to long-

- term aging degradation. - However, as discussed further in Section 3, periodic surveillance is needed to detect any potential functional degradation due to

' buildup of contaminants during operation.-

i 2.2 How Noble Metal Catalysts Work j

i A' catalyst is a substance that promotes a chemical reaction without itself being altered or consumed. It is often comprised of a noble metal thinly dispersed on an i

4 i

l

_.~.,__

inert, high specific surface area, metallic or ceramic substrate or " carrier." The active, microscopic, catt.lyzing sites on the surface of the carrier collect reactants, which are essentially ionized then reacted to new molecules, releasing or absorbing heat in the process.

The use of catalysts for purifying gases of undesired traces of hydrogen or oxygen is a standard process in the chemical and automotive industries. Normally, oxygen and hydrogen recombine by rapid burning only at elevated temperatures (greater than about 600 C). However, in the presence of catalytic materials such as the platinum group, this " catalytic burning" occurs even at temperatures below 0 C. Adsorption of the oxygen and hydrogen molecules occurs on the surface of the catalytic metal because of the attractive forces of the atoms or molecules on the catalyst surface.

The catalytic process can be summarized by the following steps (Ref. 9):

(1) diffusion of the reactants (oxygen and hydrogen) to the catalyst; (2) reaction with the catalyst (chemisorption) to give adsorbed O and H; (3) reaction of the intermediates to give the product (0 + 2H = 2H O [ water vapor]

2 2

2

+ heat); this reaction is called " catalytic combustion" (4) desorption of the product; and (5) diffusion of the product away from the catalyst.

A reactant must get to the active catalyst sites before it can react. At temperatures above 170 K hydrogen atoms are adsorbed on the catalyst surface. After reaction with oxygen atoms, the product, steam molecules, must get away from the catalyst before more reactant will be able to react. Since the catalyst does not itself take part in the reaction, it is not used up and is available for further recombination.

However, any solvents or contaminants that form stable compounds with the catalyst will poison it. The exothermic heat of the oxygen / hydrogen reaction can raise the temperature of the catalyst surface to more than 1000 C, which raises the temperature of the flowing gas about 80 C for each one percent by volume of hydrogen recombined. This heat of recombination can dissociate or " burn off" many poison compounds that are not highly stable.

Presently a wide variety of standard catalyst materials is available for many uses.

The applicatim in other industries that comes closest to the use of a catalyst for depletion of hydrogen in reactor containments is gas purification (Refs.10 and 11).

This application uses noble metals (platinum or palladium) deposited onto alumina (aluminum oxide pellets as carriers). The production gases flow through a fixed bed of the catalyst. Applications include the removal of hydrogen and other gaseous impurities in the production of pure air and the removal of traces of oxygen and other impurities in the manufacture of pure hydrogen (so-called "deoxo" processes, Ref.12). This recombination proceeds even at room temperature.

Another application of catalyst-coated pellets in a fixed-bed configuration is in the off-gas systems of some BWRs. Filter-type catalytic recombination is used to reduce gas volumes as well as minimize the potential for localized rapid burning prior to 5

i l

the off-gases passing through charcoal filters in most plants. According to a 1981 EPRI report, "No sign of degradation of the catalyst material has appeared, even after

' five years of operation." (Ref.13)

~

As discussed above, in one PAR design (by NIS) the catalytic element consists of the same type of pellets as in fixed-bed applications - palladium-coated aluminum 1

oxide spheres. This design depends on diffusion for the gas molecules to travel from the free flow area to the catalyst sites on the surface and in the pores of the pellets within the cartridges. The pellets near the cartridge covers provide a measure of j

. protection against inhibitors or poisons -- molecules of the gases to be recombined will diffuse to the pellets within the cartridge, which are less exposed to contaminants.

. In the Siemens plate design, the plate surface is immediately accessible to gas molecules in the flow channels. However, much of the catalyst surface is protected within the porous structure of the catalyst system.

i

. Therefore, regardless of the form of catalyst system employed, all PARS have a certain amount of active catalyst surface area available. Each accessible atom on the surface of an active catalyst surface area is called an " active site." As discussed in the next section, the phenomenon of reduction of PAR recombination efficiency due to poisoning involves a competition for these active sites between the target reactants (H and 0 ) and reactive contaminants in the atmosphere.

2 2

6

s l

l I

Section 3

' DEACTIVATION OF CATAINSTS l

This section is a general discussion of how inhibitors and poisons can deactivate noble metal catalysts.

l 3.1 Catalyst Deactivation Mechanisms The following three mechanisms could potentially have a negative influence on PAR catalyst efficiency:

- Direct mechanical blockage of the active catalyst surface by solid or liquid aerosols and/or gases such that access of the reactants (oxygen and hydrogen) to the active sites on the catalyst particles on the carrier material is reduced or even eliminated.

. Deactivation of the catalyst material from its chemical reaction or chemisorption with impurities in the surrounding atmosphere (i.e., chemical reduction).

- Reactions of the carrier material with components of the surrounding atmosphere causing a gross change of the surface or porosity structure and thus causing a mechanical blockage of active catalyst particles located inside or on the surface of the carrier.

The first may be viewed as an inhibitor, while the last two are poisons. The first two mechanisms are generally reversible under the influence of increased temperatures.

This is true, except if the entire surface of the catalyst would be blocked, or for some chemical reactions like total oxidation. Reaction areas will form at non-blocked locations and will grow as they " burn the surface free." The third mechanism, blockage of the catalyst due to the formation of products from reactions with the carrier material, will not occur because of the non-corrosive nature of the carrier materials (stainless steel or ceramics).

I In the following two subsections, we discuss potential deactivation by inhibitors and poisons, respectively.

3.2 Deactivation by Inhibitors The three known mechanisms involving potential inhibitors of catalytic action in l

PARS are fouling during operation, wetting, and fouling during an accident.

l 3.2.1 Fouline Durine Ooeration. It is conceivable that contaminants like dust, dirt, paint spray, or deposited lubricant vapors could build up after very long periods under operating conditions and inhibit catalysis by direct mechanical blockage of the 7

I I

active catalyst surface. For example, the cause for poor performance in one of the l

many full-scale PAR tests in the Battelle model containment (Ref.14) was traced by post-test examination to be due to the depositing of greases on the surface of the catalysts. In nuclear plants, the usual precautions of covering the devices during nearby maintenance activities should and will be followed. Nevertheless, a I

preventive maintenance program similar to the one described in the following paragraphs is proposed. This surveillance will assure that the capacity of PARS is not degraded by long-term crud buildup, nor by other aging mechanisms.

l The traditional process of environmental qualification addresses the potential for aging degradation of material properties due to exposure to operating levels of temperature and radiation. For example, aging can significantly affect the properties of polymeric materials such as 0-rings in mechanical components.

Thermal and radiation aging effects are addressed mainly by the formal testing and/or analysis procedures established in industry standards for qualifying safety-related equipment.

Some PARS are constructed entirely of metal and ceramics. The physical properties of such materials do not change significantly under long term exposure to containment operating environments such as temperature and radiation.

Therefore, such PARS have no known significant aging mechanisms other than the physical / chemical aging mechanisms of inhibitors / poisons being addressed here.

This means that the potential effects of deactivators aside, a PAR constructed entirely of metal and ceramics is expected to have a qualified service life equal to the design life of the plant - 60 years for an ALWR.

For PARS with hydrophobic coating on the catalyst pellets, the non-metallic polymeric coating could be degraded after long-time thermal and radiation aging under operating conditions such that the wetproofness or recombination efficiency of the catalyst is degraded. One or both of two approaches can be used to address these aging mechanisms. The first is to include 60-year-equivalent accelerated thermal and radiation aging as part of qualification testing. The second is to perform periodic surveillance testing of PARS to ensure that all actual plant aging effects are addressed. Surveillance testing, a form of on-going qualification allowed by industry standards, has the advantage of addressing at the same time not only the thermal and radiation aging addressed by traditional qualification practices, but also the aging degradation mechanism of physical / chemical fouling of the catalyst due to settling or plateout of contaminants that might be present in the atmosphere of the containment during its operating life. There is no acceptable way to simulate or accelerate this aging mechanism as a part of an up front artificial qualification aging program. Therefore, periodic surveillance testing is needed for PARS both with and without a hydrophobic coating, even if accelerated thermal and radiation aging is included in qualification tests.

It is important to note that physical / chemical fouling is not expected to have a significant degrading effect on PAR catalysts. First of all, the fouling will be 8

minimal because of the normal precautions taken to keep the containment environment clean. For example, a PAR unit would be covered with plastic sheets to protect it from inadvertent coating from maintenance activities like nearby painting or welding.

i Secondly, even if a PAR were to be subjected to an atmosphere highly contaminated with particulates (such as might be produced by a fire in the containment), testing has shown that the recombination capacity of a PAR is not significantly diminished.

As described later in this document, in three separate test programs, PAR models were exposed to the vapors and soot produced by burning of cables and oils directly below the intake region. The amounts of burn products deposited were much i

greater than could be expected to reach a PAR in an actual fire. After the heavy deposition of burn products, the models functioned during subsequent recombination tests with little degradation from pre-exposure to a fire.

i Nevertheless, to address the small possibility of buildup of foreign materials enough to reduce the depletion rate of a PAR, a preventive maintenance program should be carried out. The program would consist of periodic visual inspection of all catalyst elements, supported by sampling surveillance tests (benchtop performance tests of catalyst specimens removed from selected PAR devices). This surveillance would be applied periodically during normal operational periods of the plant and should be performed after completion of any outage activities that could be a source of contamination. If some abnormal event such as a fire would occur, any PARS exposed to the burn products would be subject to an even more rigorous examination and performance check before being returned to service.

Periodic surveillance tests should be made on specimens removed from selected PAR devices. Each benchtop performance test would use one catalyst cartridge or plate from a PAR device. The specimens would be placed in a standard laboratory performance test apparatus. The specimen container in the test apparatus would include a gas flow channel on one or both sides of the cartridge specimen. A controlled flow of air containing a known quantity of hydrogen would flow through the specimen container. A measured recombination response parameter after a specified time from start of gas flow would indicate whether any degradation of catalytic reaction (in comparison with baseline tests of new specimens) has taken place. The parameter could be the temperature increase of gas within the specimen, or the temperature or hydrogen concentration of the gas exiting the test specimen.

At first the periodic tests would be performed on sample catalytic elements removed from PARS at every refueling outage. If, as expected, no significant degradation is observed, the test intervals could be increased.

Acceptance criteria for the surveillance tests will be specified in the environmental qualification report for the PAR.

9

r l

3.2.2 Wetting. PARS would most likely be wet when called upon to function during a postulated accident that releases combustible gases to the containment volume.

Because AP600's do not have emergency containment cooling sprays, the wetting would come only from condensation of moisture or steam in the atmosphere. For PAR applications in plants with sprays, despite spray covers provided with the PARS, some additional water could reach the catalyst elements. Therefore, water must be viewed as a potential inhibitor of recombination by direct mechanical blockage of the active catalyst surface. Although hydrogen or oxygen molecules do diffuse through water and can reach a wetted catalyst site to be recombined, the diffusion rate is so much less in water than in gases that recombination is virtually eliminated on a fully wetted catalytic surface.

Testing (Refs.15 and 16) has shown that once a PAR device starts up, its efficiency is essentially the same whether or not it was wet prior to startup. However, testing has also shown that startup of the PAR is delayed as expected by the presence of water on the catalytic elements. Full efficiency of the PAR is reached only after complete evaporation or boiloff of wetness. Evidently, once even a small area of catalyst sheds water or dries off, the heat of recombination from the local area is sufficient to lead to eventual dryout of all catalyst surfaces and to startup of the PAR.

The delay time for startup increases with increasing amount of water, decreases with increasing concentrations of combustible gas in the atmosphere, and is different for diffeGg fAR catalyst systems.2 Therefore, as part of a demonstration of Snctionability of PARS for a particular plant application, the effect of wetness on startup must be addressed. For use in a DBA, for which combustible gas buildup from radiolysis of water occurs very slowly (several weeks to build up even uncontrolled gases to a combustible level of about 5 vol %), delay times may be as long as many hours or even several days without compromising safety.

For PAR catalyst elements that include a hydrophobic coating, surveillance testing would be relied upon to ensure that aging due to operating temperature, radiation, or chemical contamination does not degrade the wetproofing function of the coating to an unacceptable extent. For such PAR specimens, after a recombination 2 Each PAR design differs with regard to werproofness. For example, to prevent water from collecting in the pores of the catalyst pellets and muumize water buildup between pellets, pellets in the NIS PAR design are coated with a thin layer of hydrophobic polymeric material. Tests have shown (Refs.15 and 16) that this hydrophobic coating suffices to keep startup delays acceptably short and that there is no effect on NIS PAR recombination efficiency with or without a hydrophobic coating on the pellets.

However, qualification of a PAR incorporating a hydrophobic coating must demonstrate that the wetproofing function of the coating can not be unacceptably degraded by damage from recombination l

heating or by radiation. On the other hand, the basic design of the Siemens design does not include any hydrophobic coating, depending instead on the inherent water shedding capability of the vertically oriented stainless steel plates to lead to an acceptably short delay time when wetted. Startup capability of Siemens PARS has been enhanced by adding a narrow strip of palladium along the bottom edge of each catalyst plate. Testing has confirmed (Ref.16) the adequacy of wet startup delay for Siemens PARS under a wide range of containment accident conditions. If desired, a hydrophobic coating can also be added to the Siemens catalytic plates.

I 10 1

i.

surveillance test is conducted on a dry specimen as described above, the specimen would be dipped in water and weighed to check whether the coating is maintaining its waterproofing function. If the weight of water retained is greater than it would be in the new condition, a recombination test of a wetted specimen would be run to confirm that the change in waterproofing ability does not have an unacceptable effect on startup time for the PAR specimen.

Because of their inherent ability to start up in the wet condition as demonstrated in l

generic performance testing, PAR catalyst elements designed to start up without a 4

hydrophobic coating would require a surveillance test only in the dry condition.

In summary, once a PAR starts up, initial wetness does not have a significant effect i

on recombination capacity. However, because initial wetness inhibits initial recombination and delays full functioning of PARS, this mechanism must be addressed in the design and qualification of the PAR combustible gas control system for a particular application. Results for wet startup from existing test programs (such as Refs.15 and 16) can be cited for addressing the effects of wetness on startup and recombination, or wet startup testing can be included in plant-specific qualification programs. The effects of wetness on PAR performance will not be

-addressed further in this report.

3.2.3 Fouling During an Accident. The periodic surveillance testing described above ensures that, in the event of an accident, a PAR's ability to perform its safety related function during or after an accident has not been compromised by thermal, radiation, or chemical aging mechanisms. We now address the possibility that substances that can reach and pass through a PAR during an accident may deactivate the catalyst. As indicated in Section 3.1, this deactivation can occur via mechanical blockage of catalyst sites by inhibitors or via chemical reactions of poisons with the catalyst. The following paragraphs address the possibility of mechanical blockage during an accident. The next subsection addresses the possibility of chemical poisoning.

It is conceivable that liquid or solid aerosols that become suspended in the containment environment during an accident can plate out on the catalyst elements and block active catalyst sites. Recombination in the PAR itself sets up forced convection currents that circulate a substantial fraction of the containment atmosphere along with suspended particles through the PAR. Hydrogen reaches catalyst sites by diffusion or turbulent motion transverse to the gas flow direction.

The heavy solid (and liquid) aerosols do not move to the sides of the flow channel nearly as much as the reactants. With the relatively wide open channel gas flow pattern used for the PAR (diffusion rather than fixed-bed ftiter), aerosols are not led directly over the catalyst surface and, in the pellet cartridge design, there is no pressure drop that would induce aerosols to enter the slots in the cartridge. Indeed, the exiting from the slots of steam produced by recombination further impedes the ability of aerosols to reach the pellets. The result of all these mechanisms is little or no effect.on catalyst efficiency by blockage.

11

In terms of their ability to block catalyst sites, liquid aerosols have no worse a potential for blocking than water. In this regard, liquid aerosols are addressed along with wetness as discussed above. The potential chemical poisoning effects of liquid aerosols are treated in the following subsection.

There are three sources of information that can be used to address the ability of solid aerosols to block catalyst sites.

One is the same evidence discussed above with regard to PARS having little reduction in recombination efficiency after exposure to a lot of smoke and soot from cable and oil fires - it is reasonable to assume that the solid aerosols from a cable and oil fire directly below the PAR exceed any core / fission-product solid aerosols dispersed in a containment, even for a severely damaged core.

The second is that blockage effects from solid aerosols are present whenever a test of potential chemical poisoning by solid aerosols is performed. Therefore, the results of chemical poisoning experiments on catalysts discussed later in this report inherently cover blockage effects of solid aerosols as well.

The third body of evidence that solid aerosols do not dramatically inhibit recombination in a PAR is the study of aerosol deposition performed as a part of the PAR qualification study reported in Appendix E of Ref. 2. A theoretical study of aerosol deposition was performed to address the concern that deposition of aerosols during a severe accident might act as inhibitors, blocking access of combustible gas molecules to the catalytic surfaces. The study examined the extent to which typical accident acrosols based on current accident source terms, including those from core / concrete interaction, are deposited as a film on flat plates with the same dimensions as the catalyst cartridges in an NIS PAR. Since the plates served as simplified representations of the screened-in catalyst cartridges, the analysis applies also to the plate element of a Siemens PAR. Conservative assumptions were employed in selecting various parameters for the analysis, which had at its center an expression for the turbulent deposition of aerosols involving the Reynolds number, Stokes friction coefficient, and Schmidt number of the flow through the free channel between the catalyst cartridges. For example, the film is assumed to be as thin as possible (the thickness of one aerosol particle diameter), so that the film coverage is a maximum. Also, no credit was taken for the resistance to deposition that occurs as the heated product of recombination (steam vapor) expands away from the plate surface. Even with such conservative assumptions, the analysis estimated that the maximum coverage of the plates would be less than 0.2% during the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of an accident. The first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> should be the focus of concern because after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> the suspended aerosol concentration is very small and high hydrogen generation is most unlikely. Such a small coverage implies that the aerosol effect on the efficiency of the recombiner would be very small.

12

8 4

On the basis of the three factors described above, we conclude that mechanical blockage of catalyst sites by solid and liquid aerosols is not a significant degradation mechanism for PARS.

3.3 Deactivation by Poisons In simplest terms, poisoning can occur when contaminating chemicals react with atoms of the metallic catalyst, so these atoms are no longer available for adsorption followed by recombination of hydrogen and oxygen molecules. For a region of a catalyst system reached by a potential poison, the degree of poisoning (reduction in recombination rate) is proportional to the fraction of catalyst atoms deactivated.

Depending on how stable the product of the contaminant / catalyst reaction is, the poisoning can be relatively permanent (irreversible) or temporary (reversible, for j

example, by dissociation of the poison products by heating or upon removal of the poison from the feedstream under actual reaction conditions, Ref.17).

The science of catalysis is mature (it dates back to the discovery of the hydrogen catalyst properties of platinum in Germany by J. W. Doebereiner in the early part of the nineteenth century) and has become a standard process application in the chemical and automotive industries. Therefore, the literature is rich on the subject of catalytic poisoning, but needs to be consulted anew for each evolutionary application such as for PARS in nuclear plants.

To examine the potential effects of poisons on PAR performance, we first consulted the literature to identify known poison substances for noble metal catalysts. The results of this search are presented in the following paragraphs. The next question addressed is which of the known or potential poisons are expected to be present in the containment after the initiation of a postulated nuclear plant accident. This is

)

covered in the next section of this report.

According to Maxted (Ref.18), " poisons are usually strongly adsorbed species which, even if they are present in traces only, tend by virtue of their strong bonding to a catalyst... to accumulate in the adsorbed phase in the course of the adsorption-desorption equilibrium at the catalyst surface, which, by reason of this obstructive occupation by the poison, is rendered no longer free for its normal participation in the adsorption and catalysis of less strongly held potential reaction species."

Further, "The common catalyst poisons fall into the following main classes:

13

l-(a) Molecules containing elements of the periodic groups Vb and VIb, namely:

l l

Group Vb Group VIb l

N O

l P

S l

As Se Sb Te l

including (except in the case of nitrogen) the free elements.

l l

(b) Compounds of a large number of catalytically toxic metals [especially lead]

(c) Molecules containing multiple bonds, such as carbon monoxide, cyanogen l

compounds and even, to some degree, strongly adsorbed molecules such as i

benzene."

In general, physical and chemical forms are important to the, degree of poisoning.

Solid or liquid aerosols containing a potentially poisonous element are much less effective as a poison than the elemental form (the aerosol form is not as reactive and cannot diffuse to the catalyst as readily as the vapor elemental form). In general, gaseous forms of an element are more effective poisons than solids or liquids. With gases, the more reduced chemical compounds are more effective as poisons because they are more efficient at chemisorption on the catalyst. For example, H S 2

(hydrogen sulfide) would be more effective than 50 (sulfur dioxide). Organic gases 2

such as methyl iodide are more reactive than elemental iodine vapor.

A well known poison group is the halogens - iodine, bcomine, and chlorine (Refs.

19 and 20). For these elements, poisoning is temporary and reversible (results of i

testing in Ref.19 are summarized in Section 6.1.1).

I Ref.15 states " Catalyzer poisons for the catalyzers of the H oxidation on metals of i

2 the platinum group that are covered here are compounds with S, Se, Te, P, As and halogens as well as CO in higher concentrations which cause a deactivation through j

solid chemisorption."

i Still another form of poisoning is known as " coking," in which coke (elemental carbon) in carbon bearing gases is deposited on the surface of a catalyst, blocking the reaction of the recombinants. Coking is a complex process - an entire chapter of Ref. 21 is devoted to its description. The only known source of carbon-bearing gases in a reactor containment accident without core / concrete interaction is a fire. In this report, the potential effects of coking are addressed by citing the results of tests in which PARS were exposed to the smoke and soot from electrical cable fires prior to recombination performance tests.

_ In summary, the extensive body of literature on noble metal catalysts and their susceptibility to chemical poisoning that has been consulted in this study leads to i

l l

14 1

l

i

,\\

y e

l the conclusions that (a) catalyst poisoning mechanisms are understood (the elements most effective as poisons have been identified and gaseous forms of those t

elements are known to be much more effective as poisons than solid and liquid forms) and (b) there is no known." terminator" poisonous substance that can completely incapacitate substantial amounts of noble metal catalysts'"in a single bound" (the ability of any chemical substance to significantly poison noble metal catalysts depends on the substance's ability to be transported to widely distributed catalyst sites, to be reactive enough to deactivate catalyst sites, and to be plentiful enough to react with all or mostly all the catalyst atoms).

3.4 How Deactivators Reach PAR Catalyst To act as an inhibitor or poison, a substance must reach the surface of the catalytic element in a PAR. Mechanisms for substances reaching the catalyst are different when the PAR is inactive and when it is functioning.

3.4.1 Inactive FAR. During normal plant operation, there is essentially no hydrogen or other recombinable gases in the containment atmosphere, so the PAR is in a standby mode. With the PAR inactive, no gases are flowing through the open channels between the PAR elements (plates or pellet cartridges). Since the plates are oriented vertically, gravity does not act to foul the surface with dust or other aerosols that might be put in the atmosphere during maintenance activities.

The surfaces of the pellet cartridges are also vertical, limiting buildup of particulates by gravity. To an extent, the pellet surfaces are protected against particulate buildup i

by the sheet metal in the vertical slotted cartridge cover and by adjacent pellets.

Thus, during normal plant operation, contaminants reach the catalyst surfaces of a-PAR only by diffusion in the quiescent atmosphere surrounding the catalyst-elements.

3.4.2 Functioning PAR. When the PAR is functioning during an accident that releases hydrogen into the containment atmosphere, contaminants, including potential inhibitors and poisons, are drawn into and circulated through the PARS.

Hydrogen ~ molecules, which are the lightest, diffuse to the catalyst surfaces most readily. While oxygen is much heavier, some ten times the amount needed is in the air already present at the catalyst sites. Other potentially poisonous gases, like iodine and carbon monoxide, diffuse to the catalyst surfaces at a lower rate than hydrogen. Because any liquid or solid aerosols that may be entrained in the atmosphere at the location of the PAR have orders of magnitude less diffusivity than gases and because turbulence is limited, essentially all of them are carried.

through the flow channels without affecting the PAR catalyst. The ability of poisons to be transported to PARS and to deposit on PAR catalyst surfaces is discussed further in Section 5.6.

15

Section 4 COMBUSTIBLE GAS RELEASES AND REGULATORY LIMITS For any type of postulated accident in a nuclear power plant, hydrogen is generated by the following three mechanisms: (1) metal-water reaction involving the fuel cladding and the reactor coolant, (2) radiolytic decomposition of the reactor coolant, and (3) corrosion of metals. The mechanism of hydrogen generation that dominates I

depends on the level of core damage. For a relatively undamaged core as in a design basis accident, radiolysis and corrosion are the dominant contributors. For a highly damaged core as in a severe accident, metal-water reaction is the dominant contributor.

The Code of Federal Regulations (Refs. 22 and 23) specifies the generated and released quantities of hydrogen in PWRs required to be considered. Regulations (Ref. 22) require combustible gas control (CGC) systems to prevent volume average concentrations in a DBA from reaching combustible levels of 5 vol % for hydrogen in a non-inerted containment (in order to account for uncertainties in measurement capability, the actual limit is set at 4 vol %). For PWRs, post-TMI regulations (Ref. 23) require that hydrogen burns or detonations during a severe accident not compromise containment integrity, nor the ability of the plant to be brought to a safe shutdown condition. Detonation is prevented by the requirement that the average hydrogen concentration be less than 10 vol % (dry).

PARS alone can be deployed to control DBA hydrogen in PWRs (typically two full-size PAR units are sufficient to do the job with a large margin). For control of severe accident hydrogen in PWRs both PARS alone (Ref. 25) and PARS supplemented with igniters (Ref.1) have been proposed. The CGC system of the current AP600 design includes two PARS for control of DBA hydrogen and many distributed igniters for control of severe accident hydrogen.

The following subsections address the amounts of combustible gases released for different accidents.

4.1 Design Basis Accidents s

During and following a design basis loss of coolant accident, relatively small amounts of hydrogen and oxygen can be released to the containment of a nuclear power plant. Since a design basis accident involves a cooled core and mostly undamaged fuel cladding, regulations (Ref. 22) mandate the conservative assumption of a hydrogen generation from reaction of up to 5% of the active fuel clad material with the coolant water. The release to the containment is assumed to be virtually instantaneous.

I i

16

For a 600-MWe AP600, this regulatory assumption corresponds to a re kg of hydrogen into a 45,900 m' containment volume, which leads to a hydrogen concentration of 0.74 vol %. Additional hydrogen is produ k /hr (average for radiolysis of water in the coolant and sump at the rate i l bout j

/

0.01 %/hr (Ref. 2).

For DBAs in PWRs, PARS can keep hydrogen levels below the regu i

bove vol % by having a combined recombination rate that exceeds the rates g ve for radiolytic generation and release of hydrogen.

4.2 Severe Accidents For severe accidents in PWRs for which an active CGC system is neede has to control not only radiolytic hydrogen, but also the much greater amo produced by metal-water reaction of 100% of the active fuel clad m degraded core (Ref. 23).

For an AP600, this regulatory assumption corresponds to a release of 6 hydrogen into a 45,900 m' containment volume, which leads to a

(

R average hydrogen concentration of about 13 vol %. Thus, the DBA PA s a i

f supplemented with igniters to meet the volume average regulatory lim 10 vol % hydrogen in all compartments.

17

l For a 600-MWe AP600, this regulatory assumption corresponds to a release of 31.75 8

kg of hydrogen into a 45,900 m containment volume, which leads to an average hydrogen concentration of 0.74 vol %. Additional hydrogen is produced by radiolysis of water in the coolant and sump at the rate of about 0.4 kg/hr (average for j

first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> after shutdown). Thus, the rate of increase of hydrogen is slow, about 0.01 %/hr (Ref. 2).

I For DBAs in PWRs, PARS can keep hydrogen levels below the regulatory limit of 4 vol % by having a combined recombination rate that exceeds the rates given above j

for radiolytic generation and release of hydrogen.

j 4.2 Severe Accidents For severe accidents in PWRs for which an active CGC system is needed, the system has to control not only radiolytic hydrogen, but also the much greater amounts produced by metal-water reaction of 100% of the active fuel clad material in a degraded core (Ref. 23).

For an AP600, this regulatory assumption corresponds to a release of 635 kg of hydrogen into a 45,900 m' containment volume, which leads to an undepleted average hydrogen concentration of about 13 vol %. Thus, the DBA PARS are supplemented with igniters to meet the volume average regulatory limit of 10 vol % hydrogen in all compartments, i

17

Section 5

]

i POTENTIAL PAR POISONS IN NUCLEAR PLANT ACCIDENTS This section identifies the chemical constituents, amounts, and physical forms of potential PAR poisons that may exist after an accident in PWR containments.

5.1 Fission Product Releases A major source of chemical contaminants / poisons in the containment atmosphere during an accident is fission products released from overheating of and damage to the clad and fuel. As is the case for hydrogen generation in an accident discussed in the i

previous section, the amount of fission product releases depends strongly on the assumed level of core damage.8 Fission products comprise the " accident source term" for light water reactors. The source term being used for design of ALWRs is the revised source term described in NUREG-1465 (Ref. 24). NUREG-1465 is being used as the main basis for specifying the chemicals, amounts, and physical forms of fission products that should be addressed as possible poisons to the PAR catalyst (Ref. 26).

Table 1.1 of NUREG-1465 identifies the following five release phases for a severe accident: coolant activity release, gap activity release, early in-vessel release, ex-vessel release, and late in-vessel release. The fractions of core inventory of each of several radionuclide groups released into PWR containments are listed in Table 3.13 of NUREG-1465, which is reproduced in Table 1 (the gap release column includes coolant activity release).

As discussed in the previous section, the regulations on combustible gas control in 10CFR50.44 (Ref. 22) require the assumption of metal-water reaction generation of hydrogen corresponding to a core with slight fuel damage; i.e. decomposition of less than 5% of the fuel cladding. This assumption is consistent with the first two phases of release of fission products in Table 1.1 of NUREG-1465, viz., coolant activity release and gap activity release associated with fuel cladding failure, but no fuel melting. This leads to the releases into containment given by the gap release column in Table 3.13 of NUREG-1465 (see Table 1). This source of fission product release will be termed the " intact core release" in the remainder of this report.

3 Another possible source of contaminants released into the containment may be the result of decomposition of non-metallies by radiation effects; e.g., chlorine and sulfur compounds or acids from cable jacket and insulation decomposition. As discussed in Section 3.2.3, this possible source is addressed by the testing of PARS exposed to the almost complete decomposition of cable materials burned directly below PAR models prior to recombination testing in Germany and France. Still another source (for an ex-vessel severe accident only) is the carbon monoxide from core / concrete interaction.

Since this report focuses on PARS in a DBA, test results for PARS subject to carbon monoxide are not included.

18 s

- = _.

Table 1. PWR Releases Into Containment (taken from Tables 3.13 and 3.8 of NUREG-1465, Ref. 24 - values shown are fractions of core inventory)

Radionuclide Elements Gap Early Late Group in Group Release In-Vessel Ex-Vessel In-Vessel Noble Gases Xe,Kr 0.05 0.95 0

0 Halogens I,Br 0.05 0.35 0.25 0.1 Alkali Metals Cs,Rb 0.05 0.25 0.35 0.1 Tellurium group Te,Sb,Se 0

0.05 0.25 0.005 Barium,.

Ba,Sr 0

0.02 0.1 0

Strontium Noble Metals Ru,Rh, 0

0.0025 0.0025 0

Pd, Mo, Tc, Co Cerium group Ce, Pu, Np 0

0.0005 0.005 0

Lanthanides La, Zr, Nd, 0

0.0002 0.005 0

Eu,Nb, Pm, Pr, Sm,Y, Cm,Am According to NUREG-1465, the releases in the "early in-vessel" column of Table 1 are based on " severe core damage accidents involving major fuel damage but without reactor vessel failure or core-concrete interactions". A'ssumption of this release for the qualification of PARS for DBAs would conflict with the guidance in Regulatory Guide 1.89 (Ref. 27) that safety related equipment be qualified to demonstrate "that it can perform its safety function under environmental service conditions in which it will be required to function" - the function of PARS is to control hydrogen from an intact core release. If hydrogen consistent with the early in-vessel column of Table 1 were present, the amount of hydrogen produced in a severe accident, not a DBA, would need to be controlled (in the AP600 design, severe accident hydrogen is controlled by igniters). The sum of releases in the gap release and early in-vessel columns of Table I will be termed the " damaged core release" in the remainder of this report. Although the report evaluates the effects on PAR performance of fission products from both an intact core release and a damaged core release, it is important to recognize that the latter release is inconsistent with the l

amount of hydrogen that the PARS are required to control in a DBA.

j 5.2 Chemical Form of Fissien Product Releases l

All fission product elements in Table 1 are released as vapors from a damaged core

[

during an accident. Most of these vapors will react resulting in a number of l

different chemical forms. For example, according to an ORNL paper on tellurium 19

i behavior in containment under LWR conditions (Ref. 28), most of the tellurium in the core will be held up by oxidation with the Zircaloy cladding. After Zircaloy oxidation, the tellurium would be released as the solid tin telluride (SnTe). Tin telluride oxidation could lead to the formation of SnO and TeO, with both being 2

2 more thermodyn'amically stable than tin telluride.

L Table 2 lists the chemical forms expected under the low oxygen potential accident 1

conditions in a PWR (Refs. 29-32). Low oxygen potential conditions are consistent with the damaged core accident terminated in-vessel noted above. Not all the listed l

species will necessarily be present, and many, even if present, would exist in very small quantities. Also shown in Table 2 is the physical form (gas or particulate) of each species as it is transported into containment.

l-It is noteworthy that the only materials in the table that are gaseous are the noble l

gases and iodine compounds (HI,1, and CH I). The remaining materials are solid 2

3 i

aerosols at typical containment temperatures. This is important because as discussed previously the ability of aerosols to be transported to the catalyst, and thus l

act as poisons, is limited and any solid aerosols that do reach the catalyst are much less chemically reactive than gases.

Table 2. PWR Fission-Product Chemical Species Element Chemical Form Physical Form Comments l_

Noble Gases Xe Xe Gaseous Kr Kr Gaseous Halogens I

Csl Particulate Similar compounds for Br I

HI Gaseous I

I Gaseous 2

I CHI Gaseous 3

I

Fel, Particulate Also, Nil and Crl, 2

Alkali Metals Cs CsOH Particulate Gimilar compounds for Rb Cs Csl Particulate

]

Cs CsBO Particulate i

3 Cs Cs2UO.

Particulate Cs Cs2 moo, Particulate Cs Cs ZrO Particulate 2

3 l

Cs Cs2CrO Particulate 3

i

?

i

)

20 l

Table 2. PWR Fission-Product Chemical Species (continued)

Element -

Chemical Form Physical Form Comments Tellurium Group Te SnTe Particulate Similar compounds for Sb and Se Te TeO Particulate 2

Te CdTe Particulate Te ZrTe2 Particulate Te Sb Te3 Particulate

]

2 Te Fete 2 Particulate Te Nite Particulate 2

Te Cs Te Particulate 2

Te Cs2TeO Particulate 3

1 Barium, strontium Ba Ba0 Particulate j

Ba BaZrO Particulate 3

Ba BaUO Particulate 3

Sr Sr0 Particulate j

Sr SrZrO Particulate 3

Sr SrUO Particulate I

3 Noble Metals l

Mo Mo Particulate Mo moo Particulate i

2 l

Mo Ca moo, Particulate 2

j j

Ru Ru Particulate Liquid solution with Rh, Pd, Te, and Ni l

Cerium Group

]

Ce

' Ce O Particulate 2 3

}

Pu PuO Particulate 2

l Np

NpO, Particulate

)

Lanthanides La La O Particulate Similar oxides for Y, Nb, j

2 3 Pr, Nd, Pm, Sm, Eu, Am, Cm, and Nb

.i 21

W' I

i 5.3 Non-Fission Product Materials Releases

!ij' '

As well as fission products, non-fission-product materials are released as vapors from a damaged core during an accident (Ref. 24). These materials, made up of fuel, clad, control rod, burnable poison, and structural materials, will react in the vapor

]

phase resulting in a number of different chemical forms such as those listed in Table 3. The released mass of non-fission-product material can be somewhat higher i

than the released mass of fission product material, and the mass ratio is of the order of 1.5:1 (Ref. 31).

i Table 3. PWR Non-Fission-Product Chemical Species

[

Element Chemical Form Physical Form Comments Zr Zr Particulate Zr ZrO Particulate 2

j:.

U UO2 Particulate 4

j!

Fe Fe Particulate i

Fe

Fe30, Particulate Ni Ni Particulate.

f Ni NiO Particulate Requires somewhat high Cr Cr 0 Particulate 2 3 I

Mn MnO Particulate j.

Ag Ag Particulate 3

In In Particulate In In 0 Particulate Depends on oxygen potential 2 3 Cd Cd Particulate Cd Cd 0 Particulate Depends on oxygen potential 2

j B

H BO Particulate 3

3 I

B B,C Particulate Liquid solution with Fe, Ni, Cr Al Al O Particulate Al-Zr-O metallic alloy, liquid

)

2 3 above 1625 K, Al O -ZrO 2 3 2

{

eutectic, liquid above 2125*K j

Gd Gd 0 Particulate 2 3 i

i 22

1 5.4 Fission Product and Non-Fission Product Materials that are Potential Poisons To identify the subset of fission product elements that, according to chemical principles, are suspect poisons, we compare the list of fission product elements from NUREG-1465 with the elements identified by the literature search in Section 2 as l

being potential poisons to noble metal catalysts. This comparison gives only the halogens (I, Br) and the tellurium group (Te, Sb, Se) as the NUREG-1465 elements that are suspect poisons. However, of the fission product chemical species formed in the containment and listed in Table 2, only iodine, hydrogen iodide, bromine, and methyl iodide (or bromide) are in the gaseous form and hence are suspect poisons.

None of the non-fission-product chemical species identified in Table 3 match the suspect poisons identified in Section 2, and besides, all are in particulate form.

Therefore, non-fission products produced in an accident are eliminated as potential poisons to PAR performance.

Sulfur, produced by decomposition of certain cable materials, is also identified as a potential poison.

5.5 Amounts of Potential Poison Fission Products Released Design releases into the AP600 containment for the halogens and tellurium group are given in Table 4.

Table 4. Mass of Halogens Released to AP600 Containment Intact Core (DBA)

Damaged Core Core Gap Total Mass Gap + Early Total Mass Inventory Release Released In-vessel Released (kg)

Fraction (kg)

Release Fraction (kg) 18.37 0.05 0.933 0.40 7.47 5.5.1 Desien Basis Accident. From Table 4 the assumed halogen release for a DBA is 933 g (91% iodine and 9% bromine). For simplicity, we will assume that the poisoning effect of all fission product halogens can be represented by assuming an equal amount of iodine. According to NUREG-1465 (Ref. 24), of the total assumed 933 g of iodine, five percent will be released into the containment as gaseous forms of iodine, and a small amount (0.15 %) as organic iodides, such as methyl iodide, CH 1. The bulk of iodine released is in the form of particulate, mainly CsI.

3 However, in the aqueous environment of the containment, much of the Csl is expected to dissolve in water or plate out on wet surfaces as ionic iodine. Some of this dissolved or plated iodine may re-evolve as elemental gaseous iodine, but only 23

]

1 if pH control of the water is not maintained at a value of 7 or higher. Assuming pH control, the amount of gaseous inorganic iodine released into containment is 0.05 x 933 = 46.7g and the amount of organic (methyl) iodide released is 0.0015 x 933 = 1.4 g.

5.5.2 Damaged Core. From Table 3 the assumed halogen mass released for a damaged core is 7470g (91% iodine and 9% bromine). For simplicity, we again assume that the poisoning effect of all fission product halogens can be represented by assuming an equal amount of iodine. Of the total assumed 7,470 g of iodine, the gaseous forms are taken as comprising no more than 5% and iodine in organic form no greater than 0.15%. Therefore the quantities released into containment are 0.05 x 7470 = 373 g of gaseous inorganic iodine and 0.0015 x 7470 = 11.2 g of organic (methyl) iodide.

5.6 Transport and Deposition of Aerosols to PARS LWRs are designed to remove the accident fission products from the containment atmosphere relatively quickly in order to limit the amoant which could leak from containment. The fission product removal system varies depending upon the plant type. Typical operating PWRs, for example, use containment spray systems for fission product removal. AP600, on the other hand, relies on natural aerosol removal processes which are enhanced in passive plant designs by the convection heat transfer which occurs in containment. The following discussion treats the AP600 design, for which natural removal is somewhat slower than spray removal.

As noted above, most of the fission product and non-fission product materials are in solid aerosol form. There are several mitigating factors for suspect poisons which are aerosol. First, the residence time for aerosol in the containment atmosphere is limited. For AP600, the suspended mass of aerosol peaks at about 3 g/m' at about 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after the initiating event, and drops by over an order of magnitude by 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> (Ref. 33) due to plateout and sedimentation. Second, based on the low gas velocity through the PAR, laminar flow conditions exist (the flow rate of gas through a typical PAR with a 1-4 vol % hydrogen concentration is expected to be in the range i

of 20 to 50 cm/s with a PAR channel width of about I cm, leading to a Reynolds Number of ~500). Of the particulates that manage to reach the PAR, the large majority are expected to pass through the flow channels without reaching the catalyst sites on the PAR elements because of the low diffusivity of the particulates in the laminar flow. This together with the fact that the PAR is hotter than the flowing gas (and thus heat transfer is from the PAR wall to the gas) suggests that little if any aerosolis expected to deposit in the PAR. Even under turbulent conditions, an analysis indicates that less than 0.2% of the PAR wall surface would be covered by aerosol (see Section 3.2.3). Finally, even aerosol which does deposit on a surface will not readily react with the surface due to limited contact area and relative chemical stability of solids.

24

4 t

5.7 Summary In summary, the literature was searched first to identify the known mechanisms for i

physical inhibition or chemical poisoning of noble metal catalysts. These were matched with potentialinhibitors and poisons that could reasonably be expected to j '

be present during accident conditions in a nuclear plant. This matching process

' identified only halogens, sulfur, and the tellurium group (plus carbon monoxide for a failed vessel severe accident) as potential PAR poisons. Although elements in the tellurium group could be poisons, these elements appear only in chemical compounds that are particulates, which are ineffective as deactivators for several reasons explained in this section. It is important to note that in all of the sources of information on catalyst poisons found in the literature, there were no data or

{

information to point to a particular substance or mechanism in the amounts expected in a nuclear plant accident as having the ability to completely or almost completely compromise the recombination capacity of a PAR. ~

The following section examines available data from catalyst poisoning tests performed specifically for application to hydrogen control in nuclear plant accidents.

The above estimates of the amounts of halogens released to the atmosphere in DBA and damaged core scenarios will be used to relate results of the tests to AP600 accident conditions.

25

)

t Section 6

SUMMARY

OF TEST DATA ON THE EFFECTS OF POTENTIAL DEACTIVATORS ON NOBLE METAL CATALYSTS l'

i

\\

In this section we summarize the pertinent results on the effects of potential chemical deactivators for palladium and platinum catalysts from the several test programs listed in Table 5. As discussed in Section 3, although water is a

' deactivator / inhibitor for initial startup, it does not significantly affect recombination capacity, and hence will not be discussed in this section. Also, although the effects of L

the carbon monoxide that may be produced by concrete / core interaction in a severe i

l

' accident have been examined in more than one test program, those results are not L

covered here because carbon monoxide is not released during a DBA (or even during early in-vessel release).

i Three of the four test programs in Table 5 were conducted on either NIS or Siemens PARS or PAR models. The fourth examined the effects of many chemicals on u

palladium and platinum catalysts in a. fixed bed pellet configuration, which, as discussed below, is more susceptible to poisoning than the diffusion filter configuration of PARS. '

l l

g Table 5. Test Programs Addressing the Effects of Poisons on PARS and Catalysts L

L L

Test Programs References Potential Deactivators RWE NIS PAR Model Tests Battelle Tests (Ref.15)

I, coke EPRI/EdF NIS/Siemens-CEA KALI Tests (Ref.

S, coke I

PAR Model Tests 16) g Siemens PAR Aerosol Tests IPSN H2 PAR Tests Many fission product (Ref. 34) materials, including I, Te, Sb, t

L and Se i

Southern Nuclear SNE Report (Ref. 35, Many industrial and fission Engineering Laboratory Tests see Appendix) product materials, including on Fixed Bed Pellet Catalysts I, S, Cl, Te, and Se i.

After summarizing the results of the test programs in Table 5, this section discusses another source of information about the effects of chemicals as poisons to catalysts.

The information consists of the concentrations of various applied chemicals for which the manufacturer of the pelletized catalyst used in the NIS PAR guarantees

[

the rated performance of the catalyst over a stated lifetime.

n s

L l

26

y -

6.1 NIS PAR Model Tests s

The PAR developer, RWE, and supplier, NIS Ingenieurgesellschaft, conducted some performance tests themselves and had other tests conducted by Battelle Frankfurt.

Results from this program pertinent to chemical inhibitors and poisons are summarized in the following paragraphs.

6.1.1 Battelle Iodine Results In the Battelle tests (Ref.15), three grams of solid crystalline iodine were heated in a plate five centimeters below an NIS PAR one-l tenth-size segment model in a test compartment volume of 10 m. If the sublimed 8

i elemental iodine vapor were allowed to diffuse into the open volume (and not 8

i plated onto the PAR) the concentration would have been 0.3 g/m. The equivalent 8

8 8

value for an AP600 DBA is 933 g/45,900 -m = 0.02 g/m or 7470 g/45,900 m = 0.16 8

g/m for a damaged core. Therefore, the Battelle test is a conservative representation of an AP600 condition (especially since the vapor plume was directed

[

immediately into the PAR model).

1-j

. The hydrogen concentration depletion history measured in the Battelle test vessel showed about a 15 percent reduction in PAR recombination efficiency (see Fig. 3 --

the solid curve is the empirical fit through data at reference conditions and the data i

[

points show the effect of exposure to the iodine). Note that from 1.1 hrs to 2.35 hrs, the unpoisoned PAR reduced the concentration from 3.6 vol % to 1.4 vol % (a i

' change of 2.2 vol %), while the PAR model exposed to iodine reduced the hydrogen concentration from 3.6 vol % to 1.9 vol % (a change of 1.7 vol %). The percentage difference in hydrogen removed with and without iodine was (1.7 - 1.4)/2.2 = 0.14 or i

about 15 %.

i The literature also contains experiments investigating the influence of iodine on the efficiency of precious metal catalyst materials. These experiments have been performed by leading the gas stream directly through a bed of catalyst particles (Ref.19). The experiments examined the effects of iodine concentration and temperature on the recombination effectiveness of palladium-coated aluminum F

oxide pellets. The pellets were packed in a 2-liter volume container heated from the outside. A hydrogen-air-steam mixture was led via a gas heater into the container.

Iodine was vaporized in an electric furnace and added with nitrogen via heated t

j pipes to the gas stream, which flowed continuously through the test device. The concentrations of hydrogen and iodine were measured in front of and behind the i

catalyst. Figure 4 shows the reduction in recombination efficiency as a function of the inlet temperature of the gas mixture with two amounts of iodine added to the l

gas stream (although the two iodine loadings were not quantified in the reference, j

they were sufficient to reduce total recombination efficiency at 100*C between 50 l

and 70%). It is seen that the poisoning effect of iodine disappears when temperature is increased to about 200*C. Since the temperature of the gas in the flow channels of l

r a PAR has been observed to increase about 80 C for each I vol % H recombined, the 2

effect of iodine as a poison would disappear (i.e. the iodine would burn off) when H2

[

concentration in a containment reached somewhere between 2 and 3 vol % (the 1

27-1-

i f

r 12 be i

10 0>

i

~

c On e

t v.

e bu f

M e

u e

c O

u ce tn 4

o i

b

't3 A

2 g

l f

i 0

O 2

4 6

8 10 Time [hj Measurement Data Approximation (with Chimney) x i

Figure 3. Hydrogen Depletion Curves for NIS PAR Model Without (Solid Curve) and With (Data Points) Iodine (Ref.15) w c

w

,,-m.

i s

10 0 -

g I

(T Conversion %

/

8 h U mb 6 O C Oo h W 4 p O) O L U>. 3-2 j o 0 2 4 6 8 10 Time [hr] x t1easured data Approximation (with chimney) Figure 5. Hydrogen Depletion Curves for NIS PAR Model Without (Solid Curve) and With (Data Points) Exposure to Cable Fire (Ref.15). 4 - -. = .. _. - -, - -. ~,, 1 i l as in the previous tests by developers, these tests addressed the possibility of coking from pure carbon soot deposited onto the catalyst surfaces. Indeed, a greater poisoning effect was measured from exposure to burning a cable containing sulfur than was observed in the previous developer tests on burn products from cable not containing sulfur. For a test with PWR conditions (oxygen rich), the exposure to fire reduced PAR recombination rate by about 10 percent. l 6.3 IPSN H2 PAR Siemens PAR AerosolTests Because EdF is exploring the feasibility of using PARS for hydrogen control in beyond design basis accidents in French PWRs (Ref. 36), test programs in France are being conducted to demonstrate the performance of PARS under accident environments. Two programs are examining the effects of potential deactivators on PAR performance. l One, performed in the same KALI test facility used for the EPRI/EdF PAR model tests discussed above, has shown that Siemens PARS function adequately in the presence of containment sprays containing soda and boric acid (Ref. 36). Another test program is being conducted in the "H2 PAR" facility at the Cadarache research center by the French nuclear regulatory agency IPSN (Ref. 34). These tests subject a PAR to a hydrogen / air atmosphere simulating a severe accident. Simulated 2 fission product aerosols are released into the test facility (7.6 m plastic tent) by an induction furnace heated to 2900'C for 15 minutes. Within the furnace,24 chemical elements are being used to simulate a reactor core inventory. Among these elements are all of the elements in Groups 2,3, and 4 of the radionuclide groups in NUREG-1465, l including many of the elements that are candidate poisons: iodine, tellurium, L selenium, and antimony (Group 1, the stable noble gases xenon and krypton, is not l included because these gases are not suspect poisons). Hydrogen is released into the tent l as soon as the aerosols have been injected. An initial series of recombination tests using Siemens PARS has been completed. Preliminary information obtained informally indicates that the capacity of the Siemens PAR in the tests was not significantly affected by the French PWR simulated aerosols. Final results to be reported this year are expected to confirm the conservativeness of the conclusions about PAR poisoning reached in this report. l 6.4 Laboratory Tests on Fixed Bed Pellet Catalysts About 25 years ago, an extensive series of benchtop laboratory testing was conducted l to examine the effects of potential chemical poisons on the recombination efficiencies of pelletized platinum and palladium catalysts. Conducted by Southern Nuclear Engineering (SNE), the tests (Ref. 35) were part of a feasibility study of forced flow through fixed-bed catalytic devices located inside a containment as a means of controlling hydrogen produced in postulated accidents in PWRs and BWRs. Although the envisioned internal catalytic recombiners were never developed, the test data was cited in 1978 in the licensing application for use of an l external. catalytic recombiner manufactured by Air Products for combustible gas 32 j. l control in a BWR (Ref. 37). This resulted in NRC approval of the only catalytic l recombiner used for accident combustible gas controlin the US. The Air Products recombiner is installed at the WNP-2 plant of the Washington Public Power Supply System. l Two of the several types of catalysts investigated by SNE were of a pellet type similar to the catalysts in the NIS PAR, except that the pellets were cylindrical, not spherical. l One type had a ceramic substrate coated with palladium and the other had an alumina substrate coated with platinum. Both substrates had norous surfaces similar to that of the NIS catalyst. Both catalyst types were subjected in the SNE tests to a large array of substances that could be airborne in the catalyst's environment both during various plant operating modes (power operation, refueling, etc.) and under accident conditions. The substances included the following, identified above as being suspect poisons l cxpected to be released to the containment atmosphere during an accident: halogens (elemental, methyl iodide, hydrogen iodide, and bromine), tellurium oxide, selenium oxide, sulfur (elemental and sulfur dioxide), and carbon monoxide. Also examined were compounds of chlorine, lead, rubidium, and cesium. The tests were conducted by passing a gas stream containing a measured quantity of hydrogen at a pre-set temperature through 7/8-inch-diameter catalyst pellet beds. The bed thicknesses tested were 1 inch and 2.25 inches. The effect of various poisons injected into the gas stream was measured by the hydrogen removal efficiency (ratio of hydrogen concentration change in one pass through the catalyst bed to that in the entrance stream). The most pertinent SNE test data for the two catalysts have been compiled and are presented in the appendix. The data showed that the halogen gases were by far the most deleterious to palladium and platinum performance, with methyl iodide being the most deleterious per unit mass of the halogen forms examined. Comparison of the results with fission product mass loadings in the AP600 shows that reductions from both methyl iodide and the much greater amounts of gaseous iodine present in an AP600 containment are less than ten percent even for the conservative assumption of a damaged core. Thus the SNE results for gaseous iodine are consistent with the Battelle iodine results in Section 6.1.1. SNE tests with a wide variety of gaseous and aerosol non-halogen chemicals selected on the basis that they could be present in a containment during operation or during an accident showed reductions of 20 percent or less in fixed-bed catalyst efficiencies from each chemical.' These effects are expected to be much less for a PAR, for which

• An exception was elemental sulfur, for which a loading of 700 g/ft' reduced the efficiency of platinum by 80%, with a barely measurable reduction on palladium efficiency. However, the large poisoning effect of sulfur on platinum is not applicable to PARS because the only source of sulfur in a contamment is decomposition of sulfur-containing cable insulation material and this potential source was address directly by the exposure of PARS to cable burn in the EPRI/EdF tests (see Section 6.2).

r 33 j little of the aerosols and gases heavier than hydrogen traveling up through the open channels would reach the catalyst surfaces and for which testing has shown a backup reserve of catalyst (most of the heatup and recombination occurs in the lower third of the catalyst elements). 6.5 Warranty Level of Halogens for Poison Resistance of Catalyst Pellets A useful source of information on the effects of chemical poisons on catalysts is the product guarantee provided by the fabricator, Degussa, of the catalyst pellets used in the NIS PAR (Ref. 38). The warranty states the levels of various contaminants in an atmosphere for which a catalyst is guaranteed to operate at rated capacity for a lifetime of 3 years. Of special interest for the current study is the level cited for gaseous halogens (including fluorine, chlorine, bromine, and iodine). The warranty states that the halogens may not exceed 500 ppm. The level of halogens calculated for an AP600 containment atmosphere of air, hydrogen, and steam with a volume of 45,900 m at a temperature of 424*K and a pressure of 2.2 bars is 0.6 ppm for a DBA and 5 ppm for a damaged core - much less than the level for manufacturer guaranteed functioning at rated capacity. 6.6 ' Conclusion Review of all test data available to EPRI on the effects of potential poisons on PAR performance indicates that for the conditions expected to be present in an AP600 under DBA conditions, a minimal reduction in PAR recombination capacity would be expected. Therefore, an assumption of a 10 percent reduction factor (based on results of a test in which sulfur-bearing cable insulation was burned immediately ' below a PAR) is sufficent to cover both DBA fission products and a cable fire. Even if the accident were to progress beyond a design basis accident to substantialin-vessel damage, PAR recombination capacity would be reduced by no more than 25%, which is sufficent to address both the 15 % reduction in efficiency observed for an NIS PAR model exposed to a conservatively large mass of elemental iodine vapor i and, separately, the 10 percent reduction observed for PARS in cable fire tests. t 34 Section 7 REFERENCES 1. . Advanced Light. Water Reactor Utility Requirements Document," Volume III i Utility Requirements for Passive Plants, EPRI Report NP 6780-L, Rev. 7, December 1995, Chapter 5, Section 6.5. L l

2. ;" Qualification of PARS for Combustible Gas Control in ALWR Containments,"

j EPRI ALWR Program Report, April 8,1993. i 3. U. Wolff and G. Sliter, " Passive Autocatalytic Recombiners for Combustible Gas ~ Control in Advanced Light Water Reactors," Fourth Intemational Topical y Meeting on Nuclear Thermal Hydraulics, Operation, and Safety, Taipei, Taiwan, j April 1994.'

4. ~ G. Sliter, U. Wolff, H. Zimmer, D. Gluntz, and J. Thompson, " Passive

[ Autocatalytic Recombiners for Combustible Gas _ Control in SBWR Advanced Light Water Reactors, ANS ARS.'94, International Topical Meeting on Advanced Reactor Safety, Pittsburgh, Pennsylvania, April 1994. ~ 5. "NIS Catalyst Module for Hydrogen Removal in Containment . Atmosphere," NIS Ingenieurgesellschaft MBH, August 1992. 6. R.' Heck, W. Heinrich, and V. Scholten, " Igniters and Recombiners for Hydrogen Reduction Following Severe Accidents," Siemens Service Report No.14, September 1991. 7. W. Dewit et al., " Hydrogen Recombiner Development at AECL," OECD Workshop on the Implementation of Hydrogen Mitigation Techniques, Winnipeg, Manitoba, Canada, May 13-15,1996. 8. F. Ferroni and A. Chakraborty,." Design Comparison of Devices for the' Catalytic . Removal of Hydrogen," Int. Conf. on Nuclear Containment, University of . Cambridge, UK, September 1996. . 9. Thomas, C. L., Catalytic Processes and Proven Catalysts. Academic Press, 1970.-

10. Kohl, A. L. and F. C. Riesenfeld, Gas Purification; Fourth Edition, Gulf Publishing Company,1985.

11. Muller, H., et al., " Catalytic Purification of Off-flow Gases Containing.

CKW using Precious Metal Catalysts," paper by DeGussa AG and Hoechst AG at Achema Conference,1991.' 35 ^^ l i

12. Engelhard Industries, Inc, Chemical Division. Bulletin El-4419A.9.

l

13. C.A. Negin, L.O. Kenworthy, and G. Worku, "BWR Off-Gas Systems -

l Operating Experience and Planning Study," Final Report l NP-1839, May 1981.

14. Behrens, U., "Experimentelle Untersuchungen zum Verhalten des vom i

l NIS entwickelten Katalysator-Moduls im 1:1-Massstab bei verschiedenen Systemzustanden im Modell-Containment (Experimental Investigations of the Behavior of the NIS-Developed Catalyst Module in Full Scale under Various System Conditions in the Model-Containment)," Batelle Institute Report, June 1991 (PROPRIETARY).

15. Behrens, U. et al., "Experimentelle Untersuchungen zum Verhalten des von NIS entwickelten Katalysator-Modell-moduls bei verschiedenen Systemzustanden und Anordnungen (Experimental Investigations of the Behavior of the NIS-Developed Catalyst Model Module under Various System Conditions and Arrangements)," Batelle Institute, Volume I (Report) and Volume II (Test Data), March 1991 (PROPRIETARY).

16. " Generic Model Tests of Passive Autocatalytic Recombiners (PARS) for Combustible Gas Control in Nuclear Power Plants," Vols.1,2, and 3, l

EPRI/EdF/CEA Final Report TR-107517, June 1997.

17. L. L. Hegedus and R. W. McCabe, Catalyst Poisoning. Marcel Dekker, Include., New York and Basel.

18. E. B. Maxted, "The Poisoning of Metallic Catalysts," in Advances in Catalysis and Related Subjects. Volume III, edited by W. G. Frankenburg, V. I Komarewsky, and E. K. Rideal, Academic Press Inc., New York, N.Y.,1951.

19. Berndt, M., D. Ksinsik, and D. Durrwachter, "Einfluss verschiedener Verunreinigungen auf die Wirksamkeit von Edelmetallkatalysatoren" (Influence of Different Poisons on the Effectiveness of Precious Metal Catalysts)," Chemie-Technik,9(1980) 63.

20. A. K. Chakraborty, " Poisoning of Catalytic Recombiners Due to Radioactive Release of Sulphur and Halides During Core-Melt Accidents," and "The Influence of Catalyst Poisons and the Measures to Maintain the Functionability l

of Catalysts for the Removal of Hydrogen During a Core-Meltdown Accident," l GRS Final Report, GRS-A-2235, December 1994.

21. D. L. Trimm, " Poisoning of Metallic Catalysts," Chapter 4 of Deactivation and Poisoning of Catalysts., edited by J. Oudar and H. Wise, Marcel Dekker, Include.,

New York and Basel,1985. 36 c

22. U.S. Code of Federal Regulations,10CFR50.44, " Standards for Combustible Gas Control System in Light-Water Power Reactors."

23. U.S. Code of Federal Regulations,10CFR50.34(f), " Additional TMI-Related Requirements".

24. NUREG-1465, " Accident Source Terms for Light-Water Nuclear Power Plants," US NRC Final Report, February 1995.

25. J. Snoeck, C. Solaro, and PAR. Moeyaert, "First Experience with Installation of Passive Autocatalytic Recombiners," OECD Workshop on the Implementation of Hydrogen Mitigation Techniques, Winnipeg, Manitoba, Canada, May 13-15, 1996.

26. Letter from T. T. Martin, NRC, to N. J. Liparulo, Westinghouse, "AP600 Use of Passive Autocatalytic Recombiners (PARS) for Design Basis Hydrogen Control," April 1,1997.

27. Regulatory Guide 1.89, Rev.1, " Environmental Qualification of Certain Electric Equipment Important to Safety for Nuclear Power Plants," US NRC, June 1984.

28. E. C. Beahm, " Tellurium Behavior in Containment under Light Water Reactor Accident Conditions," Oak Ridge National Laboratory Report, NUREG/CR-4338, February 1986.

29. R. R. Hobbins, D. A. Petti, and D. L. Hagrman, " Fission Product Release from Fuel Under Severe Accident Conditions," Nuclear Tecnology, Vol.

101,p.270,1993.

30. R. R. Hobbins, D. A. Petti, D. J. Osetek, and D. L. Hagrman, " Review of Experimental Results on Light Water Reactor Core Melt Progression,"

Nuclear Technology, Vol. 95, p. 287,1991.

31. D. A. Petti, R. R. Hobbins, and D. L. Hagrman, "The Composition of Aerosols Generated During A Severe Reactor Accident: Experimental Results from the Power Burst Facility Severe Fuel Damage Test 1-4,"

Nuclear Technology, Vol.105, p. 334,1994.

32. Handbook of Chemistry and Physics,45th Edition, Chemical Rubber Company,1964.

33. "AP600 Containment Aerosol Calculation Results," Polestar Applied Technology, Inc., Calculation PSAT0902H.03, April 10,1997.

l 37 ~. _. _.

34. E. Studer and P. Rongier, 'The H2 PAR Facility for Hydrogen Research,"

OECD Workshop on the Implementation of Hydrogen Mitigation i Techniques, Winnipeg, Manitoba, Canada, May 13-15, 1996.

35. ' G. M. Brown, et al., " Catalytic hydrogen Recombiner Development Program, Post-LOCA Conditions Investigation," SNE-100NP, Southern 2

Nuclear Engineering Inc., December 1971. l - 36. S. Guieu, "EDF Analysis of Hydrogen Problem on Present NPPs," OECD Workshop on the Implementation of Hydrogen Mitigation Techniques, Winnipeg, Manitoba, Canada, May 13-15, 1996. i

37. " Air Products Post LOCA Recombiner Test Summary," prepared by Air Products for Washington Public Power Supply System, Report No. APCI-i 78-8, July 1978.

L

38. " Guaranteed Conditions for Catalytic Recombination by Degussa Catalysts," product warranty of Degussa (fabricator of NIS PAR catalyst) l t

i I I L l L 4 j i l 1 38 k l -e 'o i 1 APPENDIX A LABORATORY TESTS ON POISONING OF FIXED BED CATALYSTS i L I A.1 Background and Objectives j i During the first decade of commercial nuclear power in the US, catalytic s recombination was investigated as a means of controlling hydrogen produced in postulated accidents in PWRs. A feasibility study used benchtop laboratory tests to examine the effects of potential poisons and gamma irradiation on the } recombination efficiencies of platinum and palladium catalysts. Early testing had l been conducted by Combustion Engineering (Ref. A-1). A subsequent two-year l laboratory study conducted by Southern Nuclear Engineering (SNE) for several _ utilities including Consolidated Edison was summarized in Ref. A-2, but detailed l results in the files of SNE were not publisbed in the open literature. EPRI l recognized the value of these results for assessing the effects of chemical poisons on l PARS and executed a consulting agreement with Gilbert M. Brown, who managed L the CE tests and directed the SNE test program, to describe the SNE testing and l provide EPRI with selected test data relevant to the effects of potential poisons on catalyst systems similar to those in PARS. These test data and conclusions based on

them are presented in this appendix.5 1

Since the test data were intended to be used to assist in the' design of combustible gas - control devices in nuclear plants, the testing was performed with quality assurance practices appropriate for applications in nuclear plants in the late 1960's. For use today, d.ne results can be viewed as having at least research quality and as providing an understanding of PAR catalyst vulnerability to a wide range of potentially - poisonous chemical substances. SNE first' performed preliminary scoping tests on approximately a dozen types of commercial catalyst types with different catalyst materials and physical forms. The objective was to identify catalyst types whose performance and cost were suitable for

use in' nuclear plant applications. Two of the types selected for further testing were pelletized ' catalysts consisting of cylindrical pellets. The catalyst pellets designated as j

SN-15 in the original program had a ceramic substrate coated with palladium and had diameters of approximately 1/8 inch and lengths between 1/8 and 3/16 inch. ] The other pellets, designated as SN-18, had an alumina substrate coated with ^ (: s The SNE program also exammed the effects of gamma radiation on recombination. Comparison of temperature rises in beds of palladium-and platinum-coated ceramic pellets with a continuous stream q of a 3.0 vol% hydrogen-air mixture at temperatures between 120 and 160*F showed that irradiation of the catalysts with over 100 Megarads of gamma irradiation from a Cobalt-60 source had no effect on i hydrogen removal efficiency. This was expected because of the high radiation damage resistance of metals and ceramics to gamma irradiation.- l 39 platinum and had diameters of approximately 1/8 inch and lengths ranging from 1/8 to 1/4 inch. Although both pellet types were commercial catalysts with exact composition proprietary to the manufacturers, both substrates had porous surfaces with pores providing very large surface areas per unit weight. Test data for these two catalysts, referred to henceforth as palladium (SN-15) or platinum (SN-18) were j compiled and are presented in this appendix. 1 Both catalyst types were subjected to an array of substances that could be airborne in the catalyst's environment both during various plant operating modes ( power operation, refueling, etc.) and under LOCA conditions. The objectives of this appendix is to assess whether (and to what degree) the recombination performance of the two catalyst types were degraded by these substances and draw conclusions to I the extent possible regarding these substances' poisoning effects on catalytic elements in PARS. We next discuss how potentially poisonous substances were selected, we then describe the tests, and finally we give the results and conclusions. A.2 Potential Poisons Selected for Testing The chemical substances examined in the tests were selected from both industrial substances and known post-LOCA fission products. All the substances except halogens that were examined in one stage of the SNE test program are listed in Table A-1. All substances known from practical experience to be present in significant amounts in a reactor containment were included as a potential poison, even if there was no reason to suspect that it could affect catalyst activity. The industrial substances included common plant chemicals used for example in sprays for iodine trapping, in painting, as cleaning solvents, for filter testing, from welding fumes, and found in plant laboratories. The fission products were selected based on regulatory guidance in TID-14844 (Ref. A-3) and other then-current information (Ref. A-4), which identified the many substances that could be released in significant quantities from a reactor core during a LOCA or a severe accident, and hence could threaten the activity of a catalyst being used for combustible gas control. Halogens were examined in a second stage of the SNE test program because (1) they were already expected to be poisonous and (2) there was some concern that they would permanently contaminate the test equipment (this did not happen). The halogens tested were elemental iodine, hydrogen iodide, methyl iodide, and bromine. In the past 30 years, substantial information has been developed updating our knowledge about LWR accidents and the released fission products. Partly motivated by the ALWR program, a revised source term has been developed based on current understanding of light water reactor accidents and fission product behavior. A review of the revised radionuclides in Table 3.8 of NUREG-1465 (Ref. A-5) shows that, although a few elements have been added to the list in TID-14844, none of the 40 added elements appear in significant enough quantities or can be expected to poison ) noble metal catalysts. The conclusion is that the fission product substances 1 identified for inclusion in the SNE test program (see Table A-1 and the list of l halogens above) are, to our best knowledge today, representative of potential catalyst poisons released in a typical operating plant or advanced plant LOCA or severe l accident. l l Table A-1. Miscellaneous potential poisons tested (exclusive of halogens) and their chemical form' l Gases High Solution poisons Low volatility volatilityliquids solids andliquids l Acetylene Acetone H O (14,000 gm/cu ft) S j 2 SO NH.OH Pb(NO )2 Te (as TeO ) 2 3 2 l CO

CCl, Alcohol (8,000 gm/cu ft)

Mo (as moo ) 3 Freon-12 Hydrazine

CuSO, Cs (as Cs CO )

2 3 N H ** H 0 (30% solution) CCl,(22,500 gm/cu ft) Rb (as Rb CO ) 3 2 2 2 3 Oil (450 gm/cu ft SeO (in NaOH solution) RuO. 2 l increments) H 0 (4,000 gm/cu ft) (517 gm/cu ft) 2 2 Cs CO, Hg (liquid) 2 RbCl H BO 3 3 Na S 0 22 3 l NaOH H B0 /NaOH/NA S O 3 3 22 3 Nacl l TeO2 FeCl3 ZnCl2 SnCl 2 NaVO3 'Unless otherwise shown, poison added in a quantity equivalent to about 700 gm/cu ft of catalyst pellet. Standard test conditions were: 1-in.-deep, 7/8-in.-diameter catalyst bed; 2% H -air mixture; 1.2 CFM and 170-180 F inlet temperature. 2 " Background only. e 41 A.3 Description of Tests A.3.1 Test Arrangement, The tests were conducted by passing a gas stream containing a measured quantity of hydrogen through a catalyst pellet bed (see schematic diagram of test apparatus and catalyst specimen in Figs. A-1 and A-2). The test specimen was a 7/8-inch-diameter bed of palladium-coated pellets (SN-15) or platinum-coated pellets (SN-18). The effect of various poisons injected into the gas stream was measured by the hydrogen removal efficiency (ratio of hydrogen concentration change in one pass through the catalyst bed to that in the entrance stream). 1 Initial testing was conducted to select the catalyst bed depth to be used in the program. Measured effluent concentrations for an inlet stream of 2 vol % hydrogen into unpoisoned platinum and palladium specimens of various depths are shown in Fig. A-3. On the basis of this data, a 2.25-in. bed depth was selected for most of the tests to ensure a baseline unpoisoned efficiency of essentially 100% for both catalyst materials. It is important to recognize that this depth is significantly less than that of the fixed-bed recombiners envisioned for plant use at the time of this study. The depth for the test had to be reduced to this small dimension so that the degree by which a potential poison reduces recombination efficiency could be measured. The measurement techniques used for these tests were most accurate for removal efficiencies in the range of 10 to 90%, so the pellet bed depth was chosen to give efficiencies in this range for the hydrogen concentrations and amounts of poisons used in the tests. If pellet bed depths representative of the envisioned fixed bed plant recombiners were used, scoping test results showed that the bed efficiency would be 100%, or close to 100%, for all test conditions. This means that any results or conclusions based on the efficiencies measured in 2.25-in.-deep beds are conservative (err on the safe side) with respect to efficiencies of the greater bed depths that were envisioned for use in a plant fixed bed filter configuration. (Results of some tests, conducted on 1-in.-deep beds, were even more conservative.) A similar consideration applies to PARS -- test measurements have shown that the vast majority of recombination takes place over the lower third of the height of a PAR element (cartridge or plate). Therefore, even if the entire element was poisoned to some degree, the portion of hydrogen not recombined as it passed along the lower third of the catalyst elements could be recombined as it reached the upper two-thirds of the catalyst elements, which will have a reserve of unpoisoned catalyst available. The quantity of substances applied to the specimen in each SNE test was established as follows. For the potential industrial poisons conservative estimates of the mass of each substance that could be present in a containment atmosphere were made. For the fission products it was assumed that a 3200 Mwt PWR core was operated to l fission product equilibrium, the fractions of core inventory of each product according to TID-14844 were released to the containment as an aerosol, and some l plateout limited the amount of aerosol that could reach the recombiner. The quantity.of substances applied in a test was arrived by using the same unit poison 42 l loading (ratio of total mass of expected poisons in the containment atmosphere to recombiner catalyst volume) in the tests as for the plant situation. It was assumed that four cubic feet of catalyst would be used in a typical containment. This I approach led to a range of nominal test quantities which, for most of the substances was bounded conservatively by a loading of 700 grams per cubic foot of catalyst. Therefore this amount was applied to the specimens in most of the tests (see Table A-1), allowing a direct comparison of the relative poisoning effect for a given loading. As indicated in the table, greater amounts were applied for a few substances. To pass a stream of well-characterized gas through the catalyst bed, air from a compressor was metered first into a 2-inch diameter pipe and mixed with a l separately metered stream of hydrogen. The air-hydrogen mixture was passed through a heated pipe and then through the upper portion of the test rig shown in Fig. A-1. The feed gas mixture temperature was set by adjusting power to an inline cartridge or pipe heater. The feed flow rate was set by using an ASME-specification orifice. As the air-hydrogen mixture flowed downward in the test rig, its path narrowed through a conical section of pipe and entered a 7/8-inch inside diameter stainless steel tube which held the catalyst bed test specimen (see Fig. A-2). Readouts from a series of sheathed thermocouples penetrating the wall of the catalyst holder provided local bed temperature data. (As indicated in Fig. A-2, seven thermocouples i were installed - only five of them are shown in Fig. A-1.) Thermocouple locations j were measured relative to a fixed screen, mounted on a lip rolled into the tube holder below the catalyst bed. Gas sampling lines in the exit stream below the catalyst bed and in the inlet stream above were connected to a Hays hydrogen analyzer by a valve arrangement that allowed the sampling location to be selected. Values of concentration measured by the analyzer were checked by calculated concentration based on measured temperatures of the inlet and outlet streams with the knowledge that a reaction of 1 vol. % of hydrogen in air causes the temperature to rise by about 150 F. A poison injection nozzle penetrated the flow-tube wall immediately above the conical section, approximately 14 inches above the catalyst support screen (see Figure A-2). A 3/8-inch-diameter orifice constriction located immediately below the point of poison injection was used to create a local region of high air velocity to assure thorough mixing of the inlet feed with the injected poison. A.3.2 Application of Gaseous Substances. Potentially poisonous substances normally in a gaseous state at room temperature were metered into the test rig from high-pressure tanks at known flow rates for a period of roughly 30 minutes. A.3.3 Application of Liauid Substances. Poisons that exist as liquids or solutions with relatively low boiling points were placed in a glass test tube connected to the test rig, with air or nitrogen passed over the material to sweep it, as vapor, into the 43 l test rig. In most cases, heat was applied (by such means as warming the test tubes) to speed up the poison vaporization. For most liquids about 700 grams per cubic foot of catalyst was added over a period of roughly 30 to 60 minutes. A.3.4 Application of Particulates. Potential poisons that would be carried into the catalyst either entrained as particles or as a solution in water droplets in the gas stream were also tested. For these tests, the poisons were injected by using an aspirator-type spray (fog) nozzle with nitrogen as a driver gas. A mist containing the poison was injected downward toward the catalyst. Except as noted below,5 cc of liquid containing 5 gm of poison per 100 cc of water was used. Hydrogen peroxide (30% solution), water, alcohol, and carbon tetrachloride were injected directly (not in solution) in quantities of 5 cc each. Since poisons were generally added sequentially, visible amounts of various materials accumulated on the catalyst surface. i Low volatility scFd poisons were vaporized from a zirconium " boat" that was electrically heated to 1400-1800 F. The boat was located about 12 inches above the catalyst support screen. The quantities of these poisons again corresponded to 700 gm per cubic foot of catalyst (it should be pointed out that any of the poisons that plated out on the inside walls of the test section did not reach the catalyst). To maximize the amount of potential poisons reaching the catalyst, no up-stream trapping devices, such as filters or adsorbers, were used. Feed temperatures were not affected by the addition of poisons, because their quantity and rate of additions vere small (this was confirmed by bed inlet temperature monitoring (see Fig. A-2). A.4 Applicability of Test Results to PARS We now address the question of how the results regarding the effects of poisons on the pelletized fixed bed filter catalyst systems modeled in the SNE program apply to catalyst pellets in the diffusion filter configuration in PARS. Note that, although the SNE test specimens included both palladium and platinum catalysts, they were both of the pelletized form, so that comparison of results with those for pelietized PARS (such as NIS PARS) are more directly applicable than for plate-type PARS (such as Siemens PARS). An important difference between the two configurations is that the poisons are more likely to have a greater dfect in the fixed bed configuration, in which the pellets are directly in the path of the poison-laden gases passing through the filter. This contrasts to the lesser effect to be expected for the PAR diffusion filter in which the light hydrogen atoms readily reach the catalyst surfaces due to their high diffusivity, while the poisons, which are heavier in both gaseous and liquid / solid forms, tend to flow by the catalyst with low (gaseous) or very low (liquid / solid) diffusivity. This difference applies to both the pellet-type and the plate-type PAR. On the basis of this difference, we conclude that, for gaseous poisons, the reduction in hydrogen rwval efficiencies observed in these tests with a pellet bed lead to reasonable, but uservative estimates of the reductions that a like amount of 44 I test rig. In most cases, heat was applied (by such means as warming the test tubes) to speed up the poison vaporization. For most liquids about 700 grams per cubic foot of catalyst was added over a period of roughly 30 to 60 minutes. A3.4 Application of Particulates. Potential poisons that would be carried into the catalyst either entrained as particles or as a solution in water droplets in the gas stream were also tested. For these tests, the poisons were injected by using an aspirator-type spray (fog) nozzle with nitrogen as a driver gas. A mist containing the poison was injected downward toward the catalyst. Except as noted below,5 cc of liquid containing 5 gm of poison per 100 cc of water was used. Hydrogen peroxide 4 (30% solution), water, alcohol, and carbon tetrachloride were injected directly (not in solution) in quantities of 5 cc each. Since poisons were generally added sequentially, visible amounts of various materials accumulated on the catalyst surface. 2 4 Low volatility solid poisons were vaporized from a zirconium " boat" that was electrically heated to 1400-1800*F. The boat was located about 12 inches above the catalyst support screen. The quantities of these poisons again corresponded to 700 gm per cubic foot of catalyst (it should be pointed out that any of the poisons that plated out on the inside walls of the test section did not reach the catalyst). To maximize the amount of potential poisons reaching the catalyst, no up-stream trapping devices, such as filters or adsorbers, were used. Feed temperatures were not { j affected by the addition of poisons, because their quantity and rate of additions were l small (this was confirmed by bed inlet temperature monitoring (see Fig. A-2). j i A.4 Applicability of Test Results to PARS i I We now address the question of how the results regarding the effects of poisons on the pelletized fixed bed filter catalyst systems modeled in the SNE program apply to catalyst pellets in the diffusion filter configuration in PARS. Note that, although the i SNE test specimens included both palladium and platinum catalysts, they were both of the pelletized form, so that comparison of results with those for pelletized PARS (such as NIS PARS) are more directly applicable than for plate-type PARS (such as Siemens PARS). An important difference between the two configurations is that the poisons are more likely to have a greater effect in the fixed bed configuration, in which the pellets are directly in the path of the poison-laden gases passing through the filter. This contrasts to the lesser effect to be expected for the PAR diffusion filter in which the light hydrogen atoms readily reach the catalyst surfaces due to their high diffusivity, while the poisons, which are heavier in both gaseous and liquid / solid forms, tend to flow by the catalyst with low (gaseous) or very low (liquid / solid) diffusivity. This difference applies to both the pellet-type and the plate-type PAR. On the basis of this difference, we conclude that, for gaseous poisons, the reduction in hydrogen removal efficiencies observed in these tests with a pellet bed lead to reasonable, but conservative estimates of the reductions that a like amount of 44 l I poison would have on pellet or plate catalyst elements in a PAR configuration. On the other hand, for aerosols, the vast majority of which flow through a PAR without reaching the catalyst surface, the pellet bed test results cannot be used to i estimate the levels to which PARS would be poisoned by equal amounts of poison - the effects of aerosol poisoning on pellet beds is expected to be dramatically less on PAR elements. For these reasons, we are able relate the SNE test results with PAR performance quantitatively for gaseous poisons, but for aerosols, only qualitative conclusions can be drawn. For gaseous poisons, we use the same definition of above (ratio of mass of poison to catalyst volume).' poison loading as descr It must be recognized however that using the same definition for poison loading for the fixed bed filter configuration as for the PAR diffusion filter configuration is an approximate but conservative assumption. The assumption would only be completely valid if all of l the gaseous flow through a PAR was able to reach all of the volume of the pellets as it does in the fixed-bed configuration. Since reaching the catalyst pellets in a PAR relies on diffusion, not as much of the heavier-gas poisons like iodine reaches the catalyst pellets as the hydrogen gas. Therefore, although mass per unit volume of catalyst is a reasonable definition of gaseous poison loading for both PARS and fixed beds, its use gives a somewhat conservative result for PARS. The PAR halogen poison loadings for an AP600 are given in Table A-2 (based on halogen release masses from Section 5.6 and volume of catalyst in the two AP600 l 8 PARS equal to 0.1584 m or 5.59 ft'. These are the AP600 halogen poison loading parameters equivalent to the SNE test halogen poison loading parameters. l Table A-2. AP600 PAR Halogen Poison Loading DBA Damaged Core Poison Mass Poison Loading Poison Mass Poison Loading (g) (g/ft3) (g) (g/ft3) Iodine (all 46.7 9.4 373 66.8 halogens) Methyl 1.4. 0.25 11.2 2.0 iodide I i i ' This measure of unit poison loading r.ssumes that the effective noble metal catalyst area or loading is similar in the benchtop test pellets as in the PAR pellets. This assumption is reasonable because both pellets are of a standard type typically used in industrial applications. 'lhe concentration measured by the analyzer is a more accurate value. 45 l l t l l [ ~ A.5 Test Results and Comparisons with AP600 Poison Loadings l As mentioned previously, the poisoning tests were performed in two stages. The first stage (" fixed quantity non-halogen tests") addressed many industrial substances and known post-LOCA fission products with a fixed quantity of each potential poison applied. The second stage of testing (" variable quantity halogen tests") l addressed halogens only, and measured poisoning effects for each halogen (iodine, bromine, and methyl iodide) as a function of poison loading and various gas l temperatures and flow conditions. First, the results of the second stage halogen 3 testing will be treated quantitatively with respect to the AP600, and then the results of the first stage non-halogen tests will be treated more qualitatively. 1 - A.51 Halogen Test Results. The halogens iodine and bromine, including the i organic form methyl iodide, were tested using the test rig and injection procedures } described above. In one series of tests, elemental iodine dissolved in ethyl or isopropyl alcohol was spray injected into a stream of 2% hydrogen in air at an inlet temperature of about 200*F. Each increment of concentrated solution added to the stream corresponded to about 10 gm per cubic foot of the 2.25-in.-deep catalyst bed. For this liquid aerosol application of iodine, substantial reductions in efficiency are observed for poison loadings of several hundred grams per cubic foot. In another series of tests, the gaseous form of elemental iodine was introduced with a sweep gas was passed over iodine crystals to transport iodine vapor into the test l bed. _ The rate of iodine addition was adjusted by varying the temperature of the iodine container and the sweep gas flow. Results of gaseous iodine tests are shown in Fig. A-5. ' Methyl iodide was also tested and found to be the most deleterious poison encountered in the program on an equal mass loading basis. Results for palladium and platinum are shown in Figures A-6 and A-7, respectively. Poisoning effects of hydrogen iodide were also tested. The hydrogen iodide was dissolved in water to form a 50% (by weight) solution, which was heated and the - vapors swept over a 1-in.-deep catalyst bed. At a cumulative loading of 710 gm per cubic foot, the hydrogen removal efficiency of palladium (SN-15) was reduced to j 39% and that of platinum (SN-18) was reduced to 21%. This is roughly the same l degree of poisoning as observed for elemental iodine. Therefore, comparisons with i L iodine from the AP600 will be made on the basis of elementaliodine. I L Finally, poisoning of a 2.25-in.-deep bed by bromine was tested. For these tests, the . high vapor pressure of bromine made it difficult to regulate the rate of addition, . which led to large scatter in the results (see Fig. A-8). With bromine, the efficiency t i b 1 l l -- 1 l - for palladium was reduced more than for platinum - the opposite result from i poison tests with iodine compounds. However, comparison with the results for elemental iodine in Fig.' A-4 show that the range of poisoned efficiencies observed j for bromine are roughly the same as for iodine. In any event, as noted above, we j will treat the smaller AP600 bromine releases as equivalent iodine poisoning, so 1 l Lthat these results for bromine will not be used. i i To determine how the measured SNE efficiency reduction curves discussed above j relate to AP600 conditions, we enter the curves with the poison mass loadings given in Table A-2. Results of this process for both gaseous iodine (actually all AP600 I halogen releases treated as iodine) and for methyl iodide are given in Table A-3. Table A-3. SNE Test Results applied to AP600 Poison Loading Poisoned Efficiency of a 2.25-in.-deep Bed (%)* Palladium Platinum Test Condition Figure DBA Damaged DBA Damaged Core Core l Iodine Spray A-4 92 90 88 72-Iodine Gas A-5 98 95 98-95 Methyl Iodide - A-6, A-7 99 98 99 93 ' Values correspond to the lower of measurements taken either by the hydrogen analyzer or by the change in inlet to outlet temperature. l To compare the results in this table with the results for an iodine poisoning test of a NIS PAR model (Section 6.1.1), we calculate the mass poison loading in the Battelle test to be 3 g/0.001 m' of catalyst or 3000 g/m' = 85 g/ft'. This value is about 20% i more than the iodine loading for the damaged core assumption in Table A-2. From the palladium curve in Figure A-5, we obtain a reduction in efficiency for iodine gas of 6 % for the Battelle iodine loading, in rough agreement with the 15 % reduction ) in efficiency measured in the Battelle test. A.5.2 Fixed Ouantity Non-Halogen Test Results. For this stage of testing, a certain j quantity of each chemical substance (see Table A-1) was added to the test stream one after another with the hydrogen gas mixture stream continually flowing through a 1-in.-deep catalyst bed. Once in a while, after several chemicals had be added sequentially, the flow would be stopped and testing in a given series would be resumed later (e.g. after lunch or the next day). When this occurred, " restart" would L consist simply of restarting the gas flow, measuring the removal efficiency with no poison in the gas stream, and then adding the next chemical. Prior to restart, the l inner surface of the holder tube would be cleaned of plated materials, but neither 7 47 the catalyst pellets, nor the lower screen supporting the pellets was cleaned (materials accumulated on the pellets would sometimes be visible). Results for the high volatility liquids and solution poisons in Table A-1 are given in Figures A-9, A-10, and A-11. As indicated by the " stair step" plots in these figures, the testing was performed in a number of series of sequential additions of chemicals. Each series started with an " initial" measurement of an unpoisoned pellet bed. The initial measurement of each series gave values of removal efficiency between 92 and 97%, which is an indication of the measurement scatter and accuracy observed for all the measurements. It can be seen that there is also a degree of scatter between a measurement made before and after " restart." Part of this is measurement scatter and part may be any changes induced in the highly contaminated ("gunked up") bed during shutdown and startup (this change was particularly large toward recovery in the restart measurement shown in Fig. A-11). The results in these 'igures show that, in general, each added chemical produced an increase of poisoning (reduction in removal efficiency) between 1 and 10 percentage points (on an absolute scale of 100% removal). Since a cumulative effect is being measured (except for the first chemical applied to a fresh catalyst), it is not possible to differentiate among permanent poisoning from previously applied chemicals, permanent or temporary poisoning caused by the chemical being added, or the ability of an added chemical to clean off accumulated chemicals that might be affecting recombination. Nevertheless, the increment from one application to another gives an indication of the poisoning capability of the newly applied chemical. Alcohol produced an increased efficiency of about 1% for palladium (Fig. A-10) and about 9% for platinum (Fig. A-11) - alcohol evidently reacts exothermically to increase the basic catalytic reaction or is effective in cleaning off the catalyst so that its efficiency is improved. As indicated in Fig. A-9, a few other gaseous or volatile substances also improve removal efficiency by a small amount. For palladium, none of the added chemicals caused a decrease in removal efficiency of more than 10 percentage points. For platinum, only two chemicals caused a greater decrease - a 15-point drop due to SeO (about a 20% decrease) and an 18-point 2 drop due to H O (about a 30% decrease). The latter result is not applicable to PARS 2 2 because hydrogen peroxide is not present in containments in significant amounts. Results for the seven low volatility solids in Table A-1 were not plotted as above for the other potential poisons in the table. Also, unlike the other substances, these seven were applied individually to a clean 1-in.-deep catalyst bed, all with 700 grams per cubic foot (excepting ruthenium oxide with 517 grams per cubic foot). The measured reduction in efficiency of the palladium catalyst (SN-15) was barely measurable (less than one percent) for all seven substances. For the platinum catalyst, only sulfur and tellurium oxide had significant effects - sulfur reduced the efficiency by as much as 80 percent and tellurium oxide by 13 percent. Before 48 -.. 7. 1 - discussing the results for tellurium further in the following paragraph, we note that the substantial poisoning of platinum observed for sulfur in these tests is not applicable to PARS because the only source of sulfur in a containment is L decomposition of sulfur-containing cable insulation material and this potential i - source was address directly by the exposure of both types of PARS to cable burn in the i l EPRI/EdF tests (see Section 6.2). The sulfur poison mass loading in the cable burn tests was at most 4 grams per cubic foot, much less than the 700 grams per cubic foot - loading in the SNE tests. i Of particular interest are the results of these tests regarding tellurium - a suspected poison that is released from a core in substantial amounts. In Section 3 we concluded that since all forms of tellurium are solid aerosols, they either are removed from the containment atmosphere before they have a chance to reach the PARS or they flow through the PAR flow channels without diffusing to the catalyst surfaces. Therefore, tellurium is not expected to be a significant poison, even for a degraded core assumption. The results in Figs. A-9, A-10, and A-11 and the result for vaporized tellurium oxide described in the previous paragraph confirm this conclusion in that 700 g/ft' of tellurium oxide produces no more than about a thirteen percent reduction in efficiency even though the aerosols were led directly onto the fixed-bed pellets. The tellurium group poison loading for an AP600 degraded core is 2050 g (84% tellurium,11% selenium, and 5% antimony) divided by 5.59 ft' or 366 g/ft' - about half the loading in the SNE tests. Thus, even for a shallow fixed-bed recombiner, the amount of tellurium in an AP600 containment with a damaged core (even if it could reach the recombiner) would have only a small (less than 10%) effect on efficiency. References A-1 G. M. Brown, et al., " Catalytic hydrogen Recombiner Development Program, Post-LOCA Conditions Investigation," SNE-100NP, Southern Nuclear Engineering Inc., December 1971. A-2 C. T. Sawyer and F. M. Stern, " Final Report: Investigation of Catalytic Recombination of Radiolytic Oxygen and Hydrogen," USAEC Report CEND- ' 529, Combustion Engineering, Inc., March 1,1965. l A-3 J. J. DiNunno, et al, " Calculation of Distance Factors for Power and Test Reactor Sites," TID-14844, Atorde Energy Commission, March 1962. A-4 ' H. N. Culver, " Maximum Credible Accident Exposures at Reactor Site Boundaries," Nuclear Safety. 2(1) pp 83-96, September 1960. A-5 NUREG-1465, " Accident Source Terms for Light-Water Nuclear Power Plants," US NRC Final Report, February 1995. i L - A-6 AP600 Safety Analysis Report-49 . -.. ~ _ H2 Inlet - V M M M WX W W I / e s Air Heoter Orifice ~ V I W W x A t \\ lh o DN 4-v /fiih a M W'] Test Cololyst Bed =>c e TN r3 g 3 h Monit e r g Cotolyst Bed ^I' 0"EPIY

• Thermocouple in a 50l0"'d Catolyst Pelle t O

Figure A-1. SNE Fixed-Bed Hydrogen Recombiner Test Loop Air H h. Inlet 2 7 Thermoccuple Positicn I 15 /2" Above Catalyst ( y l Hydrogen analyzer i sampling tube - Poison l -Spray Nozzle _d\\ -Orifice Plate injection I h-. Poison Spray

• 7 " Pipe Union 2

r-- -7 \\ '/ 3 ,f \\ i / \\ f' - -Cotolyst Holder I I I Insulation a i l j 4 9" l L a Thermocouple Positions l 2" " 1/"h I b-3 l 2 e. I/2" Q " 4 - 9 Catalyst I)2 ' / / Support Screen t 7 "1.D. Tube /g / u r -Hydrogen Analyzer [ l. Sampling Tube h Outlet Air Figure A-2. Test Section of SNE Test Loop i 51 L. I 1 l 1 1 I I I I .:t 2.0 o i!: l.0 50 a. ~ i 1.0 CFM oir flow at o 7D'F and atm press 2 */. I n l e t H2 concentration and el86*F 0.5 75 7/8" Dio catalyst bed N a e .S E u E Platinum E S N - 18 eo" \\ S N - 15 l u Palladium x O.1 95 e E W 1 O.05 - i +

r o

y; O.01 8 l i l i 99.5 ; g:l I/4 1/2 3/4 I 18/4 l'/2 .:s .g ' Catalyst bed depth, inches .:1 Figure A-3. Measured recombination efficiency for increasing pellet bed depth (unpoisoned) g'i e 52 9 i i i i l l l l [ i i i l i 100 i l l

s. a%.._

nA.4 ~~~ a .'} g % 4, q- A. a 80

• 4. s 4

'r ~.&]~ SN-15 -A Palladium g E 60 s*A,k 1~k-A,4*w.q f o S N - 18 vi 1.0 CFM of 70*F and atm press

• Platinum W

o 40 o E 7/s" Dio., 2 /4" Deep catalyst bed 8 e 2% Hg -Air feed stream of M2OO'F ~ g inle t temp. o H2 Analyzer dato 20 A AT dato 12 added in increments of 3 10 grams /f t catalyst I l I' I I I o i I I o 10 0 200 300 400 500 3 grams 12 /f t catalyst Figure A-4. SNE Results for Iodine in Spray Form in a 2.25-in.-deep Bed (Palladium and Platinum) = o: .i 100 i i i i j i i i i l l i i 6 l i i i i l 4 i lodine Poisoning Tests 90

i. O CFM Air of 70*F and I otm 3.6 - 3.7 x i 0-e 9,, f e,s _ g 2 80 2.25" Deep catalyst bed.-

i Palladium inlet air of 2OO*F ond 2% H2 70 su-e s - e.as o..,t.e 4 - 0 60 N C C.50 Platinum w* SM -18 E.25" Deep bee g cn E 40 i...ee... i,. i. ma.it nr. 4 o E 2 t , - 30 Z ~ 20 b 10 l O e e r I i i i a a i l i i i i i O 500 1000 1500 2000 J added / f t3 catalyst gms 12 Figure A-5. SNE Results for Gaseous Iodine in a 2.25-in.-deep Bed (Palladium and l Platinum) t m .. _ ~.. _ _ _. _ __m.. b I 3 3- -3 8 4 6 I l l l-1 I l l 1 I I 10 0 ~ Test of 2 /15-17/71 N - Test of 2 /11-13/ 71 80 s'%s ~' N. N Palladium N A% f N SN -15 N y N qTest of 12/30/70 .* 60 Inlet temp 2OO'F g to I / I / 71 1.23 CFM oir @ 2% H2 N N = 7/e' ' di o b e d - gg

2. 2 5"' d e e p bed

' N. >o CHal inlet co n cen t ra tion N*s E 40 N O 3.6 xIO-'O gm/cm oir N 3 [ s 68 o 3.6 = 10-10 gm /cm 3 oir I a 3.9 = IO-10gm/cm3 cir i 20 I l I i i i i i i i i i i i i I O i i i O 10 20 30 40 gms CH 1/ f t3 3 catalyst Figure A-6. SNE Results for Methyl Iodide in a 2.25-in.-deep Bed (Palladium) i ... -.... ~, -. I 8-1 I l I I I i l 4 I i 1 -l 1 I I i Platinum S N - 18 inlet temp 2OO*F 80 1.23 CFM oir @ 2% H 2 N 7/g" dio bed 2.25" d e e p bed CH31 inte t concen f ration o s N a 3. 9 s lO-10 gm /cm3 cir 60 s wN 3.6 a 10-10 gm/cm3 cir [ s% N e s NC A 6.2 = 10'8 gm/cm3 cir = ~ en s s, s s e 40 x Test of 2 /13 -15 / 78 N E Test of 12 /22/70 g N %' -o N s 20 N' s., 'A s ~a l 1 I I I I 1 I I O I I I I I I I I O 10 20 30 40 gms CH 3 1/.f t3 co toly st Figure A-7. SNE Results for Methyl Iodide in a 2.25-in.-deep Bed (Platinum) 8 O l 1 1 I I I I I I l 1 i O I O j" s /: Ia 8 f 8 g I / a e e l 8 2 1 2 / 2 / e \\ 6-E I n / i / &l T / i d T/ 2 / 2 / O C 8 I El

• /

p/ O ~ ~ n g

• 3

/ / I / l / E$ / / /d f A ,f } / I / i I / / l ,i / I l/ / / I 8r 1 / / / / e 3 e // l o ak / / u // // / m m !I J, j 2 l / f // s a /! 8 / l/\\ / 8 /. /2 ~ ? e f c / l c d / / 6 = f If O / *$c ~ c n / F.s O p p / ET / O T C a / / / 145/ tu g 0 / / / -v y =. =g *O .e =2 g I / n m/ m e v / / / d. ~ .5 i ,/ / ll / ? 6 /l/ / c i. z e n / // / w m / / dA O w // / Y O / "EN N m / // / d' I )"E t/ // 3 o U f d / - n< w= 0D

• e

-4 /f / CD / 4N / l l 1 I l -l l I l O j O O O O O O 8 2 E I.

• /, ' Aouelol;;s inAowaJ Z H iC i-i 57 l.

!!i l ,l( L::l1; j : l 'I, ';li t,lli;l '!,lillllt ll\\l! ,lllll, -.e. F i - a*j

{:; #

E=

• !e

'f.!.a # g u 1 1 r 9 9 0 s 9 9 0 e 0 5 0 s 0 5 0 A. l l

f. -.:a 9

2:_ - m ' u. S P jSP cS ig cfl *" PS t. Na a N l l aN 4:_.: i t 4 oo 2 c. i. i 5a .r a - l 1 i I 1 l " 0 t E i I nR , 8n, d u 7 8' i u , Cm Zz og c u 0 C e 7 ms xioz 0 0 Am' c P i- . 0 p A u . r T .i. '8 T . g 8 A Cl i g i o A 0 L t as i / *. Y L g. o - t a:.a-i / .f . Y af t S o a yr f s. S 5 A. l 8 T

s. T s

d t sG 3 i.. e ~ t s a oU. U Ge se o z =*w5. u z ". c. m s ~ 5 a 8 n d z o. zuo* H i ig h 4 * ~2c. g.?'- V 1 o l a mo. 4u.? :. ti li ty oo Moa T e s s e ".: Uo t o I n .L P o= ge 2 _ s a l lad o= o~e iu m l o= o~o an d o~e o = 8I. s

• m.No

":c L '1 jjii{i14j ),Ii;li tll'1ll1 t !l,ll 'l1i1l\\l lll; t D r y. P 10 0 Paila.dium -30 7 SN-15 CATAt.YST . ve? oi.'...,

• o... s.t.

^g . teru r e n es ne.r..e a Ai.. . Air 'et 2% Mg S: too *F : '~' 80 1 ~. s . 70

• ~ 60 u

.c ..c

o

..~e r.5 0 .W. o-e ,..'O. ., s,s. *.. 'o

40 - :.

E E-'. . e.. s . g = o; O. o. = -30 r Incremental Poison Addition . of.700 gms/f t3Catolist Equivalent. o Es ce pt. ' os : Noted ' e 2d e n 10 O =- m .o z O 45 n; o .. en.- 8D

s'

_. le g, - '[ ' z,, E ' s. an s 1 E o. E O E o w. .o-o 2 8' -

• o g O

e .[. 'o o .w., .m. .n ~e,.

,.T

..o ..,g. :..:r.,,:: y=..m. o.. ' e.,.., :,, o... 4.-.

• N.

g- . _. 'g o -.s.n... : ~ L 1

• 3

• O.;. o.

  :.U..o.;;.m..;

...u u-

u.

..:..; 1. :<.:..u :::x. d ~.:*' O.

• U

6.,.:,. n 'i'.T:; O:!: O..

" J- ........-....:'.gn ..,u:.......,. x..

.x. x :y :u.::a.

u. u. m;.x.-

Figure A-10. SNE Results for Solution Poisons on a Palladium Catalyst j 59 ' .. ~ _. t 4 l i l i i l t r ,l l . 7 .t l . 10 0.. 1 g Platinum 2 ~ = S N -18 CAT A LY SY

r 90 o

7/e* Die. ster l* Does ted g 0 l CFM Feed fles et 70'F end l Alm 1 & 100

• F l-l Alt et 1% N2 N

x. l. = u go c E O o

• a=

"O l r-us. 70 o c E o o E 60 e e x Incremental ' Poison ' Addition ~ = . at 700'gms / f t Cat'alyst Equivalent O, 3 - 50 Except'. ~cs Noted O z 40 ce no ,~ : ~ m mx ~..q. -

.n ; ;. e _-:,

. s '.

n..'

... : o:

.e: 1 o.: 7.N : o . s 'co'=:

, G

.

a '.IE ;'; o ;- ^ 9, '. z

• '-:.o o.

• ?.

.o.e- ,m. o. j. g'f . ~.. -

8..

o '. f . ;.,Lz..

o.

• n

- =. .n-g_ e- . w u. ~ 5.~.:.E.E.': g;.1.#:;:~ .:= u..*~." a..Q 'o,. v '. ' E , y u u o.u u m ' _w o o. g u o' 1 o. a. u, ... e. ... u. z4 o' s z.2 2 3 z. u. >* O N 0; Q. u u m,1 c l e 1 i i Figure A-11. SNE Results for Solution Poisons on Platinum Catalyst t I 59 =. 4 .