ML20100J931
| ML20100J931 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 12/07/1984 |
| From: | Wetterhahn M CONNER & WETTERHAHN, PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | Atomic Safety and Licensing Board Panel |
| References | |
| CON-#484-524 OL, NUDOCS 8412100502 | |
| Download: ML20100J931 (20) | |
Text
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'84 [E 1021 :27 UNITED STATES OF AMERICA'
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NUCLEAR REGULATORY COMMI NOF SECRETARf M ING & SERVIII.
Before the Atomic Safety and Licensi AM6hltrd In the Matter of )
)
Philadelphia Electric Company ) Docket Nos. 50-352 OL
)
. _ , . ' ~ '
50-353 O (__,
(Limerick Generating Station, )
Units 1 and 2 )
TRANSMITTAL OF REFERENCE 9 TO APPLICANT'S TESTIMONY RELATING TO CITY-18 AND CITY-19 On November 1, 1984, Applicant transmitted to the Atomic Safety and Licensing Board and involved parties its testimony relating to Contentions City-18 and City-19 and references to that testimony. Applicant is hereby transmit-ting to the Board and involved parties copies of " Fission Product Behavior During the First Two PBF Severe' Fuel Damage Tests" by D.J. Osetek, R.R. Hobbins, A.W. Cronenberg and K.Vinjamuri, which is Reference 9 to the testimony which had not been previously available.
Respectfully submitted, CONNER & WETTERHAHN, P.C.
A no
.Mlab Mark J. Wetterhahn Counsel for the Applicant December 7, 1984 8412100502 841207 PDR ADOCK 05000352 g PDR Dso3 - . .
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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of )
)
Philadelphia Electric Company ) Docket Nos. 50-352
) 50-353 (Limerick Generating Station, )
i Units 1 and 2) )
CERTIFICATE OF SERVICE I hereby certify that copies of " Transmittal of Reference 9 to Applicant's Testimony Relating to City-18 and City-19," dated December 7, 1984 in the captioned matter have been served upon the following by deposit in the United States mail this 7th day of Dacember 1984:
- Helen F. Hoyt, Esq.
- Atomic Safety and Licensing Chairperson Appeal Panel Atomic Safety and U.S. Nuclear Regulatory Licensing Board Commission U.S. Nuclear Regulatory Washington, D.C. 20555 Commission Washington, D.C. 20555
- Docketing and Service Section
- Dr. Richard F. Cole U.S. Nuclear Regulatory Atomic Safety and Commission Licensing Board Washington, D.C. 20555 U.S. Nuclear Regulatory Commission
- Ann P. Hodgdon, Esq.
Washington, D.C. 20555 Counsel for NRC Staff Office of the Executive
- Dr. Jerry Harbour Legal Director Atomic Safety and U.S. Nuclear Regulatory Licensing Board Commission U.S. Nuclear Regulatory Washington, D.C. 20555 j Commission Washington, D.C. 20555 1
- With enclosure
73 1 t ; ..
[*j ., 2-1 T/ ,
i 5e : Atomic; Safety and Licensing ' Angus Love, Esq.
107: East Main Street Board Panel-
-U.S. Nuclear Regulatory Norristown, PA 19401
. Commission.
Washington, D.C. 20555 Robert.J. Sugarman, Esq.
Sugarman,'Denworth &
- Philadelphia Electric Company .Hellegers ATTN: Edward G. Bauer, Jr. 16th Floor, Center Plaza Vice President's 101 North Broad Street General Counsel Philadelphia, PA- 19107 2301 Market Street Philadelphia,-PA 19101 Director, Pennsylvania Emergency Management Mr. Frank R. Romano Agency 61 Forest Avenue Basement, Transportation Ambler, Pennsylvania 19002: and Safety Building-Harrisburg, PA 17120 Mr. Robert L.-Anthony Friends of the Earth in
- Martha W. Bush, Esq.
the Delaware Valley. Kathryn S. Lewis, Esq.
106 Vernon Lane, Box 186 City of Philadelphia Moylan, PA 19065 Municipal Services Bldg.
15th and JFK Blvd.
Charles W. Elliott, Esq. Philadelphia, PA 19107 325 N. 10th Street ;
Easton, PA 18064
- Spence W. Perry, Esq.
Associate General Counsel ,
Miss Phyllis Zitzer Federal Emergency Limerick Ecology Action Management Agency P.O. Box 761- 500 C Street, S.W.
762 Queen Street Room 840 Pottstown, PA 19464 Washington, DC 20472
- Zori G. Ferkin, Esq.
- Thonia= Gerunky, Director Assistant Counsel Bureau of Radiation Commonwealth of Pennsylvania Protection Governor's Energy Council Department of Environmental I 1625 N. Front Street Resources-Harrisburg, PA 17102 Sth Floor . .
Fulton Bank Bldg.
Jay M. Gutierrez, Esq. Third and Locust Streets U.S. Nuclear Regulatory Harrisburg, PA 17120 Commission 631 Park Avenue King of Prussia, PA 19406 I
- - With enclosure i
3-
.N.
James'Wiggins Senior Resident Inspector U.S. Nuclear' Regulatory Commission.
P.O. Box 47 Sanatoga, PA 19464 Timothy R.S. Campbell Director Department of Emergency Services 14 Sast Biddle Street West Chester, PA '19380 Mr. Ralph Hippert Pennsylvania Emergency Management Agency B151 - Transportation and Safety Building Harrisburg, PA 17120 1
j d.///,(/ a4 /
'A Mark J. Wetterhahn I
l With enclosure 4
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ECC- M-l l 2P,4 PREPRINT Fission Product Behavior during the First Two PBF Severe Fuel Damage Tests D.J. Osetek R.R. Hobbins A.W. Cronenberg K. Vinjamuri July 15-19,1984 ANS Topical Meeting on Fission Product Behavior and Source Term Research This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without permission of the author.
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FISSION PRODUCT BEHAVIOR DURING THE FIRST TWO PBF SEVERE FUEL 6AMAGE TESTS
- D. J. Osetek,** A. W. Cronenberg,I R. R. Hobbins** and K. Vinjamuri**
ABSTRACT The results of the first two severe fuel damage tests performed in the Power Burst Facility are assessed in terms of fission product release and chemical behavior.
On-line gamma spectroscopy and grab sample data indicate limited release during solid-phase fuel heatup. Analysis indicates that the fuel morphology conditions for the trace-irradiated fuel employed in these two tests limit initial release. Only upon high temperature fuel restructuring and liquefaction is significant release indicated. Chemical equilibrium predictions, ba' sed on steam oxidation or reduction cunditions, indicate I to be the primary iodine s,pecies during transport in the steam environment of the first test and Csl to be the primary species during trans-port in the hydrogen environment of the second test. However, the higher steam flow rate conditions of tne first test transported the releas'ed iodine through the sample system; whereas, low-hydrogen flow rate of the second test apparently allowed the vast majority of iodine-bearing compounds to plateout during transport.
INTRODUCTION ,
As a result of the accident in the Three Mile Island Unit-2 pressurized water reac-tor (PWR) on March 28, 1979, the U.S. Nuclear Regulatory Commission has initiated an international Severe Fuel Damage Research Program.## The principal in-pile testing portion of this program is being conducted at the Idaho National Engineering Laboratory in the Power Burst Facility (PBF), where a bundle of 32, 0.9-m-long, PWR-type fuel rods is brought to coolant boiloff conditions, severe cladding 1
E
- Work supported by the U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, under DOE Contract No. DE-AC07-76!D01570
- Engineering Science and Analysis, 836 Claire View, Idaho Falls, 10
- Sponsors of the program include Belgium, Canada Federal Republic of Germany, Italy, Japan, Netherlands, United Kingdom, and United States.
l ,
oxidation, molten alpha-zircaloy dissolution of UO 2 , release of fission products, Four bundle experiments are presently planned in the I and ultimate rod destruction.
PBF Severe Fuel Damage (SFO) program.
This paper summarizes results with respect l
to the fission product behavior observed during the first two experiments LSFD Scoping Test (5FD-ST) and SFD 1-1]. Details of the test program are described in Reference Q).
FISSION PRODUCT DETECTION SYSTEM The on-line fission product sampling and monitoring system is shown schematically in Figure 1. The test effluent, consisting of steam, hydrogen, and fission prod-ucts, is drawn from the fuel bundle and routed to the monitoring system through a Six effluent steam samples are 1.3-cm (1/2-in.) diameter stainless steel pipe.
remotely opened at various times during the test to provide samples containing con-The remaining densed steam, fission products, and hydrogen for*posttest analysis.
The effluent then steam is condensed and cooled to a temperature below 340 K.
enters a separator vessel, where a continuous nitrogen gas purge sweeps hydrogen, fission gases, and other noncondensables from the separator, past a ganrna spectrom-The liquid from the separator eter and a hydrogen monitor, into a collection tank.
lon mom, l chamber \\\\
\ \ \ \
- Nal Q Condenser Effluent steam line Q Ge8 1 r J L
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v vvvv j- Carrier hauld Steam m in pite tube-samples 1 (6) "
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Nat Q _ [] eparator Fallback barrier Gas Ge @ -
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- q Continuous l H2 monitor NalCE-) CDGe Bundle flow @ lj"j'
- ; i
- ...... 4 tube Filter l
V l Gas sample tap Collection -
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-2 tank
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Liquid sample tap - Liquid samples (6) INEL 4 0399 Figure 1. SFD Fission Product and Hydrogen Monitoring System for Test 1-1.
me ,w s
vessel was monitored during the SFD-ST by two ganna spectrometers located upstream Downstream of the filter the ifquid effluent and downstream of a 5-micron filter.
passed through one of six remotely operated flow-through liquid grab samples into the collection tank. The gamma spectrometer located downstream of the filter was relocated to monitor the steam line upstream of the condenser during Test SFD 1-1.
TEST RESULTS Table i presents an overview of the test parameters and basic results for the SFO-ST and Test SFU 1-1.
Both tests employed fresh fuel, which was preconditioned prior to the transient to ensure the generation of both short- and long-lived fission products. At the end of preconditioning, the high temperature transient was ini-tlated at an' effective burnup of =0.008 to 0.009 at.%. The SFO-ST was conducted on Octuuer 29, 1982. The 32-rod bundle was subjected to a slow heating ramp of
=0.13 K/s to peak fuel temperatures in the range of 1700 K in an oxygen-rich environment, followed by oxidation-driven heatup at =10 K/s to 2400 K, and was terminated by a rapid quench and coolant reflood. Considerable cladding oxidation and melting, fuel liquefaction, and fuel fragmentation occurred.
Test SFD l-1 was conducted on September 8, 1983. This test was designed to simulate the fuel heatup during a small-break loss-of-coolant accident without emergency core cooling. The initial heating ramp was =0.45 K/s to cladding temperatures of
=1300 K, followed by an exothermic oxidation driven heatup rate of =1.3 K/s to The test 1700 K, with a subsequent runaway oxiaation ramp of =30 K/s to 2400 K.
was terminated by a gradual decrease in power and fuel cooldown. An , argon purge was used during part of the cooldown to sweep fission products from the bundle.
Figure 2 illustrates the noble gas and iodine behavior for both tests, as a function of peak fuel temperatures. A small burst of activity (fractional release rate
~I min ~I) is noted at fuel temperatures of =1100 K, which corresponds to
=10 the approximate time of rod failure and release of the fuel-cladding gap inventory of noble gases. Only a small amount of fission product release was detected in either test until the fuel temperatures reached 1700 K. Fractional release rates increased from 10-6 to 10-3 min-I as fuel temperature increased to 2400 K.
Fission product release rates increased sharply in the SFD-ST when the fuel bundle Helease was quenched frcm hign temperature by rapid injection of reflood water.
N
l Table 1 ]
SUMMARY
OF THE SFD-ST AND SFD 1-1 TEST CONDITIONS Nominal Fuel Coolant Burnup Flow Cooldown (g/s)_ Mode Coninents _
Test Heating Rate (at.% )_
16.0 Quench Oxygen rich U.13 K/s to 1700 K 0.0089 Highly oxidized bundle SFD-ST 10.0 K/s to 2400 K Fuel liquefaction 375 g H2 generated 0.67 Slow Steam starved 0.4S K/s to 1300 K 0.0079 Less oxidation 5FD l-1 1.3 K/s to 1700 K Fuel liquefaction 30 K/s to 2400 K 72 g H2 generated
, 'u'qMd MW ' SFD ''''!
10 7iiiiii 1 1-1 Noble Gay 16' i. - . ; '
5 10 r NUREG-0772, '
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' .,, SFD 1-1 lodine 5 g <*
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5= 10', n, r v fi /
SFD-ST Noble gas)'
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ti 10'1 i k >',---sFD-srWodine r-
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-s 7, ,,, u,0, , t , , ,- / , , , , , yopyo,Wny,l ,
1700 1000 1000 T100 2400 es oso-se4 os Fuel Temperature (K)
Figure 2. Comparison of the Noble Gas and Iodine Behavior During the SFD-ST and Test 5FD l-1
~
min" momentarily during rate constants for noble gas and iodine reached 10 the quench, Grain botndary shattering that occurs as a result of such quenching is believed to be the reason for the enhanced release rates. ~ ~I min Fractional release rates of noble gas during Test SFU 1-1 peaked at 3 x 10 This is several orders of magnitude higher than the during the cooldown period.
j release rates during heatup at the same temperature. This lack of a direct depend-ence on fuel temperature of fission product release is indicative of the importance of fuel behavior to release modeling. Although the bulk temperature in the Test SFD l-1 fuel bundle was decreasing, the probable formation of a low melting point (1400 K) metallic U. Zr-phase at grain boundaries and pellet surfaces, as noted in Reference (2_), could account for the continued release of fission products until temperatures dropped below sl400 K.
Iodine was measured during heatup in the SFD-ST and found to agree with the noble gas release data, but iodine was not measured in Test SFD l-1 until after slow cooldown was initiated. This difference may be due to iodine transport effects, since the effluent flow rate was higher ( 16 g/s) in the SFD-ST and was predomi-nately steam; whereas, the flow rate from the SFD l-1 bundle was slower (=0.08 g/s) and principally hydrogen. Iodine transport in an oxidizing steam environment is predicted ,to be in the atomic iodine form, which undergoes little reversible (con-densation) plateout. This is consistent with th'e measured iodine release for the SFU-ST. However, for a highly reducing environment, Cs!, HI, and I species are predicted, where Csl undergoes rapid plateout such that. little iodine would be detected, as indicated by the SFO l-1 data. The influence of oxidizing versus reducing environments on steam-iodine chemistry is discussed later in this paper.
Fission product washout occurred in both tests during reflood; iodine and cesium release rates from the bundle peaked during reflood at s3 x 10-2 min-I .
The measured fission product fractional release rates are compared in Figure 2 with the correlations for noble gas release presented in NUREG-0772 (3). During the fuel heatup phase of the SFD tests, the release data were found to be generally lower 3
than the out-of-pile data by a f actor of =10 . Only when temperatures in the bundle were held above the U0 -Zr liquefaction temperature (=2170 K), did the 2
release rates increase and eventually exceed those predicted in NUREG-0772. Release rates measured during quench and reflood phases were also consistently larger than those predicted from NUREG-0772 based on temperature alone. Details of fission proouct release from fuel and transport behavior in either the steam (during bundle boiloff) or water (upon bundle requench) carrier, are presented in the following section.
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FISSION PRODUCT RELEASE BEHAVIOR l To interpret the noble gas release behavior for the SFD-ST and Test SFD l-1, analy-sis was performed with the FASTGRASS code (4), which is a mechanistic model for fuels dur-predicting fission gas and volatile species (I and Cs) behavior in UO 2 ing steady state and transient conditions. A comparison of calculated (FASTGRASS and NUREG-0772) and SFD-ST measured noble gas release rates as a function of fuel temperature is shown in Figure 3(a). As indicated, the FASTGRASS-predicted 3 and ST measured release rates agree quite well, while a discrepancy of 10 is noted relative to the predicted rates based upon the temperature correlations in NUREG-0772.
Such a discrepancy is explainable based on the morphology character-istics of the trace-irradiated fuel employed in the SFD tests. The correlations in NUREG-0772 were developed primarily from release experience for medium-to-high burnup conditions, while the fuel tested in both SFD tests was essentially fresh, except for the develcoment of a small inventory o( fission products at an effective burnup level of =0.008 to 0.009 at.%.
FASTGRASS analysis indicates that for trace-irradiated fuel, most of the nuble gas and volatile I and Cs inventory is still retained within the interior of the fuel grains, primarily as individual atoms. Since fission products in atomic form are readily acconnodated within the solid fuel microstructure, they experience little release from fuel in the solid condition. Only at elevated temperatures is there a change in morphology characteristics from one of atoms in lattice solution to bubble precipitation at grain boundaries. This situation is illustrated in Figure 3(b), where at luw temperatures the vast majority of the noble gas inventory is predicted to be retained in lattice solution, while at temperatures above 1900 K 10 0
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iirgiiil 6,w i 10 - Total 0.8 Lattice atoms
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aastsaassp,.hrea j j o,4 _ /_
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bubble f-2 -8 1000
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0 !'
1800 2200 1400 600 1000 1400 1800 2200
- b Peak fuel temperature (K) Maximum temperature (K)
Figure 3. Comparison of the Measured Noble Gas Release Rates During the SFD-ST with FASTGRASS-Predicted Release Rates.
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~. - ._ . _ . - _ _ _ _ _ _ - _ - _ _ _ _ _ _ - _ _ _
e the noble gas and volatile fission products are swept to grain boundary edges and faces. Upon destruction of the fuel grain structure, either due to fuel liquefac- '
tion (as occurred in the SFD-ST and Test SFD l-1) or quench induced grain-boundary shattering (as occurred in the SFD-ST), the fission products pinned to grain boundaries are released (5,).
In Figure 3(a), it is noted that two calculational approaches were used in the FAST 6RASS analysis of the SFD-ST release data, one employing a nominal grain-growth model and the other for fuel-oxidation enhanced grain growth. Both models are of the functional form:
(1)
D = 0,2 + Aexp (Q/RT)t where A is a proportionality constant, Dt is the' grain size at time t, D o is the initial grain size, Q is the activation energy, R is the gas constant, T is temper-ature, and t is time. The parameters A and Q are dependent upon such fuel crystal The results properties as atomic packing, atomic mobilities, and oxidation state.
shown in Figure 3(a) indicate that the enhanced grain growth model more closely approximates the SFD-ST data.
Steam-induced fuel oxidation following cladding f ailure, can have a pronounced effect on atomic mobilities and, therefore,. fission product release characteristics.
133 Figure 4 presents a plot of the diffusivity of Xe in U02 +x as a function of Temperature (K) 1666 1250 1000 853
- 12 i i i 7 ,
133Xe g j o-13 - %8%:: .s
- 85Kr ~ & - 14
- i 6 + * *
- "' *% g a133Xe data 1250 K -
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- c o .
S si . UO2.67- -
g
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- " - 1000 K .
c
$. - 16 '\
j \.U0 .12 2
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5 - 17 -
g .\UO 2.02 %
-0 ~
UO.0 2 , E~$.8 2.0 2.02 2.04 2.06 2.08 2.102.12 6 7 8 9 10 11 12 13 Stoichiometric condition (x) of UOx 4 INEL 3 0908 (b) INEL 3 0909 la) 10 !T(K)
Figure 4. Illustration of the Effect of UO 2+x Stoichiometry on the Diffusivity of Hoble Gas.
l
,- l fuel stoichiometry (6) and shows that increased oxygen content in solution in 002 is observed to increase the diffusivity of I Xe. Enhanced atomic mobilities result in enhanced grain growth, which in turn causes a sweeping of once-entrapped fission products from the grain interior to grain boundaries. This situation is illustrated in Figure 5 and supported by posttest examination of the SFD-ST fuel.
Figure 6 is a photomicrograph of the SFD-ST fuel indicating a change in fuel stoichiometry from initially UO2.0 02 +x plus U4g0 precipitates, and an increase in grain size from an as-fabricated condition of 4 to 35 microns. Fur-ther discussion of the governing role that fission product morphology characteris-tics, grain growth, and the formation of low melting point eutectics exert on release behavior are presented in References (2_), (4), (5), (6_), and (7).
In summary, the sequence of events leading to fission product release for the trace-irradiated fuel employed in the SFD-ST and Test SFD l-1 appears to be as follows: .
e initial high-fission-product retention within individual grains as a result of entrapment of gaseous and volatile fission products as individual atoms or intragranular microbubbles, with nil gas release.
e In a steam-rich environment (i.e., SFD-ST), fuel-oxidation-enhanced grain growth can result in intragranular atomic and microbubble sweeping to grain boundaries and initiation of slow gas release. Under steam starvation conditions (i.e., SFD l-1) this effect is less pronounced.
e Destruction of the grain structure via fuel liquefaction or quench-induced grain boundary shattering, with rapid-enhanced intergranular gas release.
e Sustained gas release during cooldown as the liquefied U, Zr mixture remains molten to lower temperatures ($1400 K).
Analysis of the SFD data indicates that the release characteristics for the trace-irradiated fuel employed in the SFD-ST and Test SFD l-1 differ from the release characteristics predicted by NUREG-0772 which is attributed to large differences in fuel morphology for low versus medium-to-high burnup fuel. In addition to morphology, fission product behavior is also strongly influenced by steam chemistry once released from fuel, as discussed in the following section.
FISSIUN PRUDUCT/TRAhSPURT CHEMISTRY Upon release from fuel, fission products such as Cs and I can mix and react with the steam and hydrogen produced by the steam-zircaloy reaction. The chemical
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l Grain boundary Edge bubbles Atoms in lattice solution Intragranular bubbless
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s g g O o 1
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- O t 0 o
- 5
- O e , Grain e # growth O As. Irradiated Condition Ultimate Grain-Growth Condition
- Small grains
- Enhanced sweeping of l
atoms to edge bubbles
- Majority of fission products retained within indis; dual
- Edge bubbles r ecipitate release viainterlinked porosity grains aslattice atoms (NEL 4 4234 Figure 5. Illustration of Retained Noble Gas / Volatile Distribution for Trace-Irradiated Fuel Subjected to Grain-Growth and Fission-Product Sweeping Phenomena p ,
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GRAIN GROWTH
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V0 ,; .; y .i . ., < ,g . N3 to 5 pm 4 9 as fabricated; precipitates ,.
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N35 km posttest
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J UO 2 Figure 6. Postirradiation Microstructure of the SFD-ST Fuel Remains, Indicating Grain Growth to 35 microns and U02 0xidation to U40 9-Inclusions.
1 composition of this vapor mixture depends on species concentration, temperature, pressure and oxidation / reduction conditions. From thermodynamics, the equilibrium composition, at a particular temperature and total pressure, can be found by noting that the total free energy of formation (AG*f) at chemical equilibrium approaches zero, that is: _ . . . _ _
(2)
[aGf(Products)-[aGf(Reactants)=0 For an ideal gas, AG) can be expressed as (3) aGy=RTin(pj) where pg is the partial pressure of a particular gaseous component of the react-ing mixture. Changes in the H-0 ratio will produce a change in the concentration levels of the other components, such that equilibrium is maintained. The results of Sallach's equilib'rium analysis (8_) for the Cs-I-0-H system, was used to assess the primary chemical forms for the SFD-ST and Test SFD l-1 conditions.
Table 2 sununarizes the fission product concentration and thermal-hydraulic cunal-tions at the time of enhanced fission product release for the SFD-ST and Test SFD l-1; that is, the time at which fuel temperatures exceed =2000 K. The Cs-!
atom ratio was estimated to be =10, based upon the ORIGEN-calculated fission product yields and associated radioactive decay chains at the initiation of the high temperature transient. The concentration and H-0 ratio were determined from '
the experimental steam and H2 -gas flow rates measured during each test.
Table 2 ,
SUMMARY
OF THERMODYNAMIC AND CONCENTRATION CONDITIONS FOR THE SF AhD TEST SFD l-1 AT THE TIME OF EkHANCED FISSION PRODUCT RELEASE SFO-ST SFD l-1 Parameter Steam temperature System pressure =1400
=7.0 MPa K (=ll30'C))
(=70 bar =1400
=6.6 NPa K (=ll30*C))
(=66 bar
=2.06 .45 H/0 mole ratio =10 cs/1 mole ratio =10
=10-9 =10-8 1/H2 O mole ratio =10-7 Cs/H2 O mole ratio =10-8 r
v ._
l l
l Figure 7 illustrates the approximate fractional iodine species concentrations as calculated by Sellach, in the steam / hydrogen environment for the SFD-ST and SFD l-1 test conditions. At lower temperatures, Csl is stable in a steam environment; however, at increased temperatures the Cs1 molecule undergoes dissociation via the reaction:
2 CsI(g) + 2 H2 0(g) 2 Cs0H(g) + 2 I(g) + H2 (g) 2 Cs0H(g) + 2 HI(g) (4) resulting in increased cesium-hydroxide (Cs0H) formation, where temperature, _
pressure, and oxidation / reduction conditions affect the distribution of iodine among I and HI species.
It should be noted that for trace-irraciated fuel, the release concentration of
-8 ~
iodine into steam is on the order of 10 to 10 , while the lowest concentra-tion levels presented by Sallach are on the order,of 10-I Since the effect of .
decreasing iodine concentration is toward a diminished abundance of CSI at thermo-chemical equilibrium, the results plotted in Figure 7 may overpredict somewhat the Csl mole fractions for the SFD test conditions. Neverth'eless, using Figure 7 as a guide, the following fractional partitioning of I and Cs species are estimated:
1.0 , ,; i , , , , ,
1.0 , , , , , , . m
\ Csl e HI _
0.9 0.9 -
\ I 0.8 -
l ,,, - -.-j/ -
0.8 -
Csl
/
/ \ -
0.7 - Csl \ l_
f 0.7 g, l
/ '
/ -
0.6 - \ f-E 0.6 -
5 o
\fL-e -
C 0.5 -
o 0.5 -
,o u
N 0.4 \
/ \-
G 0.4 -
= H I -
l) -
@ 0.3 g
/
I-g 0.3 g 3 -
0.2 - \, - - - ~ %HI - 0.2 -
0.1 -
\ si
' ' ' '~
N 0.1 0
' 'a
\ / I '
0 1475 1875 2275 2675 1075 1475 1875 2275 2675 1075 Temperature (K) Temperature (K)
~7 ; HlO = 2.0; Csll = 10. (b) llH O = 2 x 10~ 7; HIO = 30; Csil = 10.
(a) llH O 2 = 2 x 10 2 Pressure equals 1 bar -- Pressure equafs 150 bars tr4EL 4 C33 Figure 7. Relative Abundance of Iodine Species in the Cs-I-H-0 System for the Conditions Approximating the SFD-ST, (a), and Test SFO 1-1, (b).
A . .
f e SFD-ST SFD l-1 Tsteam = 1400 K Tsteam = 1400 K H/U = 2.06 H/0 = 45 Cs/I = 10 Cs/I = 10 Moles of I as Csl = 10% Moles of I as Csl = 48%
Moles of I as HI = 10% Males of I as HI = 48%
Moles of I as I = 80% Moles of I as I = 4%
Moles Cs as Cs0H = 99% Moles Cs as CsVH = 95.2%
Although Figure 7 presents only iodine partitioning information, the Cs0H mole fraction can be estimated, based on the fact that at temperatures below =2000 K little compound dissociation into atomic cesium occurs; thus, any cesium not bound to iodine is considered to be Cs0H. For a Cs/I' ratio of =10, a 10% mole fraction of I as Csl equates to 99% Cs as Cs0H, while 48% I as Csl is equivalent to 95.2% Cs as Cs0H. For the oxidizing environment of the SFD-ST, the vast majority of fodine in the high temperature bundle region is predicted to exist as low boiling point volatiles, namely 80% atomic iodine and 10% Hl. As indicated in Table 3, 12 and 5 HI have low vaporization temperatures and, thus, are subject to limited reversible plateout (condensation) during the short transport time (s3 s) through the test train pipe network to the monitoring system. Atomic iooine is assumed to behave similar to 1 . The high .ncle fractions of I and HI in an oxidizing environment, 2
therefore, explain the fact that similar iodine and noble gas release rates were measured for the SFD-ST.
! Table 3 VAPORIZATION TEMPERATURES OF I AND Cs SPECIES Species HI I2 Cs Cs0H Csl 238* 457 951 1263 1553 Tvap (K) at I atm 411 860 2275 2180 2745
.Tv ap (K) at 70 atm 1
- At 4 atm.
~
- , . , . - - - ---w,-,-,
.= ,
For the reducing environment of Test SFD l-1, however, approximately 48% of the iodine is predicted to be in the form of Csl and, thus, is subject to a condensa-tion made of plateout within the high temperature regions of the test bundle. The remaining iodine, as I and HI gases, would then be carried by steam and/or hydrogen from the bundle through the flow pipe to the fission product monitoring system.
Due to the relatively low flow rate (from =0.67 g/s H O 2 to 0.07 g/s hydrogen) and long transport time (s60 s), cooldown of the effluent in the piping is con-sidered to result in transformation of I and til to Csl at lower mixture temperature (s600 K), such that chemical equilibrium is maintained, as indicated by the arrow in Figure 7(b). This transformation to Csl results in additional iodine condensa-tion and plateout on the inside piping surface, and is considered the reason for the nil iodine release m'easured during the high temperature phase of Test SFU 1-1.
Only upon bundle reflood was significant fodine measured for Test SFD 1-1, indicative of washout of reversible Csl deposits.-
Such results indicate that the observed I and Cs behavior for the PBF-SFD tests can be explained in terms of thermochemical phenomena, and again illustrate the point that an in-depth evaluation of such data can be used to confirm physical, chemical, and mechanistics models of fission product behavior for severe accident conditiens.
However, it should be noted that this analysis was limited to the I-Cs-H-0 system, and the presence of other fission products and bundle materials could influence the chemical forms produced in these tests.
t C0kCLUSIONS From the foregoing analysis, the following conclusions can be drawn relative to noble gas and volatile fission product release from fuel and transport behavior in the SFD test environments:
e Fission product release is strongly influenced by prior irradiation-induced fuel morphology characteristics. Analysis of the PBF SFD-ST and Test SFD 1-1 release data for such trace-irradiated fuel indicates limited release on heatup to temperatures up to 1900 K, since the majority of the noble gases and volatiles are retained within the grain interior as individual atoms.
e A comparison of fission product data, posttest fuel examination, and 4
analysis indicotes that in a steam-rich environment (i.e., SFD-ST),
oxidation-induced grain growth and sweeping of fission products to grain boundaries can result in enhanced noble gas and volatile release for trace-irradiated fuel in the solid state. Subsequent fuel liquefaction and quench-induced grain boundary shattering result in rapid fission product release, as indicated by the SFD-ST and Test SFD 1-1 data.
l e Iodine and cesium chemistry in a steam environment are strongly influenced The high steam flow by oxidation / reduction and concentration conditions.
rate and low concentration conditions of SFD-ST result in predominately free iodine and Cs0H transport in steam. However, for the low-flow rate reducing environment of Test SFD l-1, the predominant chemical forms are CsI, Cs0H, and Hl.
e The fact that free iodine is subject to limited reversible plateout, accounts for transport and measurement of iodine during the heatup phase of the SFD-ST. However, for the reducing atmosphere of Test SFD l-1, plateout of Cs! and cooldown-induced transformation of HI to Cs! account for the observation of limited iodine detection during the heatup phase of Test SFD 1-1. Only upon posttransient reflood of the Test SFD l-1 bundle was significant iodine release observed, which is considered to be washout of reversible Csl deposits.
ACKNOWLED6MENTS The authors gratefully acknowledge the FASTGRASS calculations performed by Dr. J.
Rest of Argonne National Laboratory, and the gamnia spectral data provided by J. K. Hartwell of EG&G Idaho, Inc.
NOTICE This paper was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or
- any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, apparatus, product or process disclosed in this paper, or '
represents that its use by such third party would not infringe privately owned rights. The views expressed in this paper are not necessarily those of the U.S.
Nuclear Regulatory Commission.
REFERENCES
- 1. P. E. MacDonald et al., "PBF Severe Fuel Damage Program: Results and Compari-son to Analysis," Proceedings of International Meeting on LWR Severe Accident Evaluation, Cambrioge, Massacnusetts, August 28-September 1,1963.
- 2. W. Dienst, P. Hufmann, D. Kerwin; Peck, " Chemical Interactions Between U02 and Zircaloy-4 from 1000 to 2000 C " Nuclear Technology, 55, 1984, pp. 109-124.
- 3. United States Nuclear Regulatory Commission, Technical Bases for Estimatino Fission Product Behavior During LWR Accidents, NUREG-0772, 1981.
1 e
~..
- 4. J. Rest, "The Mechanistic Prediction of Iodine and Cesium Release from LWR Fuel," Proceeding of Topical Meeting on Fission Product Behavior and Source Term Research, Snowbird, Utah, July 15-19, 1984.
J. A. W. Cronenberg et al., "An Assessment of Liquefaction-Induced I, Cs, and Te Release from Low and High Burnup Fuel," Proceedings of International Meeting on LWR Severe Accident Evaluation, Cambridge, Massachusetts, August 28-September I, 1983.
- 6. J. Belle, Uranium Dioxide: Properties and Nuclear Applications, USAEC, 1961, pp. 512-515.
- 7. A. D. Appelhans, A. W. Cronenberg, M. L. Carboneau, " Effects of Burnup on Fission Product Release and Implications for Severe Fuel Damage Events,"
Proceedings of Topical Meeting on Fission Product Behavior and Source Term Research, SnowDird, Utah, July 15-19, 1984.
- 8. R. A. Sallach, Chemistry of Fission Products Elements in High Temperature Steam: Thermodynamic calculations of Vapor Composition, 5AhD81-U534, 1984.
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