ML20137K509

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Summary Rept Poge Tnp SFP Project
ML20137K509
Person / Time
Site: Trojan File:Portland General Electric icon.png
Issue date: 06/28/1996
From:
Battelle Memorial Institute, PACIFIC NORTHWEST NATION
To:
Shared Package
ML20137K508 List:
References
PNWD-2350, NUDOCS 9704070044
Download: ML20137K509 (24)
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Abstract Under contract with Portland General Electric, Battelle provides technicalsupport to the Trojan Nuclear Plant, Spent Fuel Pool Project. This limited-scopeproject isfocused on evaluating two technologies proposedfor the processing ofspentfuel and associated debris. This report summarizes those evaluations.

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iii Abstract; 1.0 I n trod uction...............................................................

I 2.0 ! Criticality Evaluation........................................................

I 3.0 Hydrogen Generation Evaluation ~.............................................

2 i

3.1. Evaluation of GEND-041 Report.............. _.............................

2 l

3.2 ' Calcula;.'on of Hydrogen Limit.............................................

3.

4.0 Process Evaluation..........................................................

4 l

= 4.1 Steam Reforming Process Assersment......................................

5 l

4.1.1 Volatilization of Cesium...........................................

5 l

= 4.1.2 Volatilization of Other Radionuclides.................................

8 i

4.1.3 Use of CO Monitoring to Verify Copletion of Organic i

Destruction / Conversion............................................

9.

J 4,1.4 Other Comments / Questions on Stream Reforming..................,....

9 4.2. Flotation Separation Process Assessment....................................

11 5.0 Filter Analytical Results.....................................................

14 -

6.0 Conc l us ions.............s..................................................

16 6.1 Criticality Evaluation....................................................

16.

6.2 G END-041 Evaluation..................................................

16:

6.3 Hydrogen Limit Evaluation...............................................

16 i

. 6.4 Process Evaluation Steam Reforming.................................,.....

16

' 6.5 Process Evaluation Column Flotation.......................................

17 7.0 E Re ference s...............................................................

17 A.1 Appendix A Tables

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4.1 -' Vapor Pressure of Cesium Species as a Function of Temperature.....................

6-i 5.1 ' Sam ple Desci iption _.... _......................................................

15 5.2. Total Organic Carbon Analysis Results.........................................

15 0

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l 1.0 Introduction This report summarizes evaluations conducted by Battelle in support of the Partland General Electric (PGE) Trojan Nuclear Plant (TNP) Spent Fuel Project. The following evaluations are addressed:

1) criticality issues related to the treatment and storage of spent fuel at the TNP,2) the GEND-041 hydrogen generation calculation and proposed limit for hydrogen in the proposed storage container,
3) two proposed treatment technologies, and 4) the composition of the filter media used to store the spent fuel pellets. This report has been divided into the following 6 sections:

1.0 Introduction 2.0 Criticality Evaluation 3.0 Hydrogen Generation Evaluation 4.0 Process Evaluation 5.0 Filter Analytical Results 6 0 Conclusions Sections 2 through 4 describe Battelle's evaluations in each technical area: criticality, hydrogen generation, and process technology. The criticality evaluation provides a review of criticality informa-tion provided in the process technology proposals and a general assessment of criticality issues related to processed fuel storage at the TNP. The hydrogen generation evaluation reviews the GEND-041 calcula-tion and assesses a calculated limit for hydrogen in the storage capsule. The process technology evaluation provides a complete review of both technical proposals followed by an assessment of the filter media currently used to store the spent fuel.

2.0 Criticality Evaluation i

The proposals prepared by Framatome Technologies IN. (Framatome) and Scientific Ecology Group Inc. (SEG) for the PGE/ Trojan Spent Fuel Pool Debris Project have been reviewed for criticality safety concerns. Both proposals briefly discussed criticality safety; neither discussion is a sufficient analysis to proceed with the debris removal operation. The SEG proposal indicated that criticality is not possible.

Battelle agrees with the SEG proposal; however, che discussion is not sufficient to proceed with the analysis. The Framatome proposal provides an outline as to how they phn to prepare a criticality analy-i sis. In addition, Framatome indicates that the ar.alysis will be oflicensing quality and available for NRC review. Battelle agrees that the method proposed by Framatome will produce an adequate analysis for the p'rocessing equipment. Neither proposal indicated that any analysis would occur tojustify storing the I

r, '

~

2;& rake recovered debris in the process cans back in the spent fuel pool or other storage location at Trojan; this will need to be addressed before debris removal operations start.

As part of the review, a few hand calculations were perforTned, attached in Appendix A, tojudge whether a criticality problem exists. Based on these calculations, a formal criticality analysis will demonstrate that the expected number ofloose pellets at Trojan will not have criticality problems in the design of the equipment. The hand calculations are based on no geometry constraint, no moderator con-straint, less than 5% enriched fuel, and less tn n 0.4-inch-diameter pellets. Also, based on a recent Battelle analysis

  • on similar PWR fuel assemblies, the storage of process cans in the spent fuel pool will not present criticality problems. This reference considers a single spent fuel assembly in a cask; the assembly with 179 rods had a K of 0.93155, the one with 176 cods had a K of 0.93146, and the one with 173 rods had a K of 0.93134. This suggests that the existing Trojan spent fuel assemblies will not increase in reactivity by removing fuel pins or pellets. Also, storing the pellets in a fuel-assembly-sized i

can in the spent fuel basin will not increase the reactivity of the basin. Based on my preliminary review, a formal criticality analysis will not require any redesign of process equipment or limit the storage of fuel-assembly-sized process cans at Trojan.

3.0 Hydrogen Generation Evaluation His section summarizes Battelle's evaluation of the methodology for calculating hydrogen genera-tion described in the GEND-041 Report (Flaherty et al.1986), and evaluates the appropriateness of the hydrogen limit, proposed by SEG, of 0.592 moles per capsule. The GEND report treats the subject of I

radiolysis fairly thoroughly. However, use of this methodology would require more detailed character-ization of the waste and more involved calculations than are necessary. A simpler method for calculating hydrogen generation is discussed Section 3.1.

The hydrogen limit proposed by SEO has been determined to be over estimated. It does not take into recount the fact that the presence of process cans and debris reduces free volume in the capsule. A more conservative methodology, outlined in Section 3.2, yields a new limit of 0.050 moles of elemental hydro-gen per process can (0.250 moles of elemental hydrogen per outer capsule).

3.1 Evaluation of GEND-041 Report r

The GEND report was evaluated as to its applicability to the wastes generated and the containers proposed for use. The GEND report is a thorough and well documented treatment of gas generation in a number of waste matrices in different containers. However, the GEND report does not consider waste matrices and containers of the types under consideration for use by PGE, The GEND report is based on the assumption that most or all of the energy of radioactive decay will be deposited in the hydrogenous (a)

Memo SL Larson to M Dec; NCS Basis Memo 95-6 Rev.1; Limits for PWR and BWR Fuel Assembly Loading, Unloading, Storage, and Transportation in the NAC-1 Cask; to be issued.

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waste matrix. The geometries of the containers proposed for use by PGE are such that leakage rates will be relatively high. He GEND report does not characterize the effects of alpha radiation, which is a signiHeant source of radiolysis in the radioactive debris. Unfortunately, it is not possible to make accurate predictions of gas generation rates from alpha radiation based on rates for beta / gamma radiation.N Characterizing the rate of radiolysis accurately, using the GEND Calculation, requires a detailed analysis of the waste material and storage matrix. A simplified and equally valid approach assumes that all hydrogen present in the can will be converted to hydrogen gas. The total permissible hydrogen loading (including all hydrogen present in any chemical form) for the capsule may then be calculated as the maximum amount of hydrogen gas that could be present without exceeding the flammability limit.

The activity of the radioactive debris then need not be limited when using this simplified approach.

3.2 Calculation of Hydrogen Limit A limit on the allowable amount of hydrogen in a container must be based on the calculated volume '

of free space in the container. Since for a fixed amount of hydrogen, a higher free volume corresponds to a lower hydrogen concentration, calculations will be made conservative by assumptions that minimize the free volume.

The radioactive debris will be stored in metal process cans, which in turn will be stored in metal outer capsules. The current plan is to store five process cans in each capsule. The process cans are not scaled. Filters in the lids prevent debris from escaping, but permit gases, such as hydrogen, to escape.

l Re outer capsules will be sealed.

According to IE Information Notice No. 84-72 (NRC 1984), the hydrogen generated must be less than 5% by voNme of the secondary-container gas void at standard temperature and pressure (70* Fahr-enheit and one atmosphere). The notice does not state whether this limit refers to diatomic (H ) or 2

elemental hydrogen, but comparison with accepted values for flammability limits of hydrogen strongly suggests that this value is for diatomic hydrogen. Because the process cans will not be scaled, the capsules in which they are stored must be considered as the primary containers. Limiting the hydrogen to 5% of the capsule volume would then be conservative for any secondary container.

The Sierra Nuclear Company (SNC) fuel debris canister is 8525 cubic inches in volume. He SEG process can capsule has an outer diameter of 8.0 inches, a wall thickness of 0.135 inches, a usable length of 146.0 inches, and a cavity volume of 7339 cubic inches. As of this date, it has not been decided which design will be used for the outer capsule. Because the SEG process can capsule has a smaller cavity volume, it will be used in the following analysis to ensure conservatism.

j (a)

Gas Generation in TRU Wastes (Draft) by JO Henrie, GS Barney, NN Brown, DJ Flesher, and MM Warrant, Westinghouse Hanford Company, Richland, Washington (1988).

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A final design for the process can has not yet been completed. However, based on preliminary design work, it appears that the can will be 29 inches long, have an outside dianieter of 7.25 inches, and l

have a wall thickness of 0.125 inches. The lid will be 1.19 inches thick, and the base will be 1 inch thick.

For a conservative (minimum) estimate of the free space in the can, it is assumed that the inside length of the can will be 26 inches, and that the inside diameter will be 6.75 inches, yielding a cavity volume of 930.4 cubic inches when empty. The outer dimensions of the process can describe a total volume of -

1197 cubic inches. It is assumed that the process can will not be more than half-full after steam reforming, a thermal process that would drive off all water and decompose all hydrogen-bearing plastic materials at elevated temperatures?)

With five process cans loaded into the capsule, the remaining free volume of the capsule will be i

1353 cubic inches. Because the process can lids provide no impediment to the flow of hydrogen gas, the empty space in each process can is free, if each process can is half-full, each can will have 465.2 cubic inches of free space. Therefore, the total free volume in the capsule will be 3679 cubic inches. Five

. c.

i percent of the total free space in a fully loaded capsule would be 183.9 cubic inches, or 3.014 liters. In accordance with the ideal gas law, PV = nRT, where P = 1 atmosphere V = 3.014 liters R = 0.08206 liter-atmosphere / mole-K T = 70 degrees F = 294.25 K l

the permissible amount of hydrogen, n, is 0.125 moles of diatomic hydrogen, or Q.250 moles of j

elemental hydrogen, per SEG process can capsule, or 0.050 moles of elemental hydrogen per process Can.

4.0 Process Evaluation PGE issued a request for proposals for the processing of underwater vacuum and waste filter media stored in the TNP spent fuel pool. This project would include the segregation, inventory, and transfer'of debris currently stored either in debris containers or directly in spent-fuel-pool storage-rack cells. The debris consists mainly of the filter media (mostly polypropylene filter cloth and flanges) and particulate matter filtered from the water, including dross from electron-discharge machining (EDM) during plant modifications, fuel pellets, and fuel-pellet fragments. This material must be characterized and separated into low-level radioactive waste (LLW), nonfuel bearing components (NFBC), and " greater than-Class-C"(GTCC) waste.

The LLW is to be packaged and sent to Hanford for burial. Low-level waste must not contain more than 100 nCi per gram of uranium and other transuranic (TRU) radionuclides. The NFBC and GTCC wastes are to be packaged, sealed, and stored in dry fuel storage canisters with TNP's spent nuclear fuel.

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One criterion for dry storage of this material is the removal of potential sources of hydrogen gas that may be produced by radiolysis from the spent fuel. Water and the plastic-Giter debris are examples of such hydrogenous materials.

Technologies proposed to process this filter debris must efficiently separate both hydrogenous materials from the dry storage container wastes and TRU radionuclides from the LLWs. The limit for TRU materials is well established in regulations as 100 nCi/g. The limit for hydrogenous materials in the dry storage container wastes is less defined and is reviewed in Section 3.0.

PGE is considering two proposals for treating the filter debris, each describing a different approach to this challenge. PGE requested that Battelle perform a technical assessment of the two proposals:

1) SEG proposed steam reforming and 2) Framatome Technologies, Inc. (Framatome) proposed a physical separation of the hydrogen-bearing plastics from the GTCC waste, first by sorting out the larger chunks and then by separating the remaining materials with a combination of density separation and froth flotation. The " plastic-free" GTCC waste would then be dried to remove water from the remaining debris and process cans.

Assessing the SEG and Framatome proposals brings up several considerations. Regarding the SEG proposal, Battelle was requested to evaluate 1) the capability of the process to minimize the loss of radionuclides (e.g., cesium volatilization) from the process cans during the thennal treatment,2) the likelihood for and potential risks associated with generating hydrogen or other flammable gases during processing, and 3) the proposed use of a carbon monoxide monitor to indicate the completion of each processing cycle.

For the Framatome proposal, Battelle is to assess the capability of the proposed column flotation process to achieve the required degree of separation of 1) TRU from the " floated" low-!evel waste fraction containing mostly plastic debris, and 2) hydrogenous plastic debris from the remaining GTCC waste fraction.

i Our evaluation method includes a direct evaluation of both the SEG and Framatome proposals, with analogous comparison of each proposed technology with existing data from similar industrial and research applications.

4,1 Steam Reforming Process Assessment (SEG) 4.1.1 Volatilization of Cesium PGE is concerned that the SEG steam reforming system has the potential to volatilize cesium and separate it from the degraded fuel pellets. Such a separation could be construed as fuel reprocessing, which is not permitted under their NRC license. A discussion of relevant data from similar processes relating to cesium separation is followed by conclusions regarding the application of SEG's process at the Trojan Spent Fuel Pool.

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. Under SEG's proposed operating conditions, gas enters the feed can evaporator at 1100*F (593*C).

Volatilized organics are processed in the reformer reactor at 2200* F (1204*C). ' An offgas purge stream is taken off, and the remaining gases are recycled through the evaporator. Resi6nce time is estimated at 8 to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Offgases are processed through a high ef6ciency particulate air (RIPA) filter and then to the building's heating, ventilation, and air conditioning (HVAC) system. Most ex wrts contacted believe that the fuel pellets have been significantly degraded and soluble fission products have leached from the sludge into the pool. No data are available to verify whether this is the case.

On June 27 through 29,1994, a selection panel was convened in Salt Lake City to select a baseline technology for organic / ferrocyanide destruction in Hanford Tank Waste. Five technologies were evaluated: 1) low-temperature hydrothermal / wet-air oxidation ;>rocessing,2) electrocherr.ical treatment,

3) high-temperature hydrothermal processing,4) calcination / dissolution, and 5) steam reforming. The team representing steam reforming consisted of staff from Sandia National Laboratory, Lawrence Livermore National Laboratory, and Synthetica Technologies, Inc.

The validity of cesium was discussed in a presentation on the application of steam reforming for treatment of organics and ferrocyanide in the Hanford Tank Wa:tes. Steam drives cesium to hydroxides:

2Cs + 2H O(g)----> 2CsOH + H (g), K=1.4x10'2 at 550*C 2

2 Furthermore, CO converts hydroxides to nonvolatile carbonates:

2 2CsOH + CO ----> Cs CO + H O(g), K = 1.1x10' at 550'C 1

2 2

2 N

Table 4.1. Vapor Pressure of Cesium Species as a Function ofTemperature Vapor Pressure at Vapor Pressure at Vapor Pressure at f

Species 500'C (1 Atm) 600*C (1 Atm) 700*C (1 Atm) l Cs 0.12 0.44 1.1 Cs:O 0.0002 0.007 0.1 CsOH 0.0006 0.005 0.03 j

(CsOH),

0.0003 0.002 0.02 Although the claim was made during the presentation that cesium volatility could be minimized, no j

data were presented from the actual demonstration testing performed with Hanford tank waste simulant.

A recent (4/25/96) contact with the principal presenter from Sandia National Laboratory confirmed that no actual e.xperimental data on cesium volatility were taken during the testing of steam reforming for this 1

6

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.em application. Results from the steam reforming demonstration presented in Salt Lake City during June 1994(*) showed that more than 95% of the organics were gasified and 99.99% were destroyed.

A calcination technology was also evaluated for treatment of organics, nitrates and ferrocyanide in the Hanford tank waste." In this process, liquid tank waste was subjected to plasma torch incineration, and the calcined material was held at 650*C to 800'C for approximately 20 to 40 minutes. Under steady-state operating conditions,46% of the cesium was retained with the calcined materia; the rest was volatilized or entrained in the process offgas.

A similar technology selection meeting in May 1993 evaluated calcination and steam reforming.N The calcination team presented information regarding cesium volatility. In a calcination demonstration test,290 gallons of tank waste simulant were treated, and 60% of the cesium was volatilized or removed by entrainment. The material was maintained at approximately 900*C for 4 to 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

Two samples of actual Hanford tank waste (110-U and 101-SY) were calcined for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> at 1100C.N Less than 1% of the cesium volatilized from the sample from Tank 110-U, but 99.98% of the cesium volatilized from the sample from Tank 101-SY. These differences were not adequately explained. However, they vividly illustrate the variability and difficulty of accurately predicting cesium losses at high temperatures. It can be postulated that the variability of cesium volatility observed is due to the differences in amount of offgas volume produced and the form in which cesium is present. More cesium was volatilized from 101-SY because a greater amount was present in the complexed form.with

)

organics. As the organic thermally degraded, the unbound cesium volatilized. The high level of degrading organics in tum produced a greater volume of offgas, which acted as a carrier for the volatilized cesium.

Battelle has performed many vitrification tests (liquid-fed ceramic metters) with simulated high level tank waste. The resulting projected design basis melter decontamination factor (DF)(for the Hanford i

Waste Vitrification Plant [HWVP]) for cesium is 14; that is, approximately 7.2% of the cesium leaves the melter by volatilization and aerosol suspension (Goles and Schmidt 1992; Goles et al.1990). During Run PSCM 23 (Goles et al.1990), the plenum (melter headspace) temperature was maintained at approximately 530'C, and the bulk glass temperature was approximately ll50*C. The average resi-dence time of glass in the melter was approximately 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />. During the course of the run, cesium i

melter DFs ranged from 54 to 240 (i.e.,0.42% to 1.9% of the cesium in the feed left the melter and was captured in the offgas treatment system. Additionally, approximately 76% of the cesium aerosol leaving the melter was less than 1 pm in size. The small size of cesium aerosol indicates that gross entrainment did not play a dominant role in establishing the cesium aerosol emission source tenn; rather, volatiliza-tion most likely was the dominant route for cesium escaping the metter.

(a)

Second IPM Technology Selection Meeting. June 27 29,1994, Doubletree Hotel, Salt Lake City, Utah, Final Report, July 21,1994.

(b)

IPM Technology Selection Meeting. May 24-27,1993, Doubletree Hotel, Salt Lake City, Utah, Final Report, June 15,1993.

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I Significant variability in existing data makes precise predictions impossible. Ho that percent levels of the cesium in the spent fuel sludge will volatilize from the' SEO fe evaporator, which operates at 1100* F (593 *C).

De potential exists that a signi6 cant fraction (> 50%) of the cesium will leave the feed rator by entrainment. However, SEG indicates that the syngas will Cow through the evap cbout I ft/sec. Maintaining such a low velocity during processing would minimize entrain c:sium and other radionuclides. If gross entrainment is significant, it will likely be uns is unlikely to affect a clean separation between cesium and TRU. Furthermore, SEG p

1. m sintered metal filter between the evaporator can and the steam refonner furnace collect entrained cesium.

Thermodynamics predict that steam reforming will yield cesium species with low test data from a pilot scale plasma are calcination system showed that approximately l

was vaporired or entrained in the offgas stream. After inject, ion through the plasma arc maintained at approximately 900'C for 4 to 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. In the vitrification process, severa cesium in the feed left the melter. Temperatures were higher and glass residence time those projected for the SEG feed can evaporator.

4.1.2 Volatilization of Other Radionuclides Ruthenium-96. Oak Ridge National Laboratory conducted an investigation (Rimshawf en the volatility of ruthenium-106, technetium-99, and iodine-129 during the calcina radioactive nitric acid w.hte. The volatility of RuO. in a stainless steel spray calciner w ih j

tures of 400,500, and 725'C was very low (less than 1% in all cases). The RuO appears to i

ill the heated stainless stee' walls to form RuO, which is relatively nonvolatile. A similar situa 2

likely exist in the SEG feed can evaporator, in which the sludge is expected to conf amount of stainless steel dross, The design basis melter DF for rathenium isotopes was 42 (2.4% of the ruthenium p volatilize)(Goles and Schmidt 1992).-

Technetium-99. The volatility of technetium varied from 0.2% to 1.4% over the temperature rang of 250 to 600'C (Rimshaw et al.1980). The design-basis HWVP melter DF for technetium is 11 (approximately 9% of the technetium predicted to volatilize)(Goles and Schmidt 19 lodine-129. A high fraction ofiodine components are decomposed or volatilized under conditions (Rimshaw et al.1980). At 550*C, about 57% of the iodine volatilized, and at 6 97% volatilized. The design basis HWVP melter DF for iodine-129 was 1 (i.e.,100% of melter predicted to volatilize)(Goles and Schmidt 1992).

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4.1.3 Use of CO Monitoring to Verify Completion of Organic Destruction / Conversion i

To verify that all of the organics have been destroyed or gasified, SEG plans to monitor the system vent gas downstream of the HEPA filter for CO. SEG asserts that when no CO remains in the vent gas,

)

the reactions will be complete.

l In general, Battelle concurs with this approach. In effect, SEG will be monitoring flow from evapo-rator and steam reformer. As the solid organics are gasified and steam reformed, a gas stream of H, CO, 2

H 0, CO, CH, (and trace amounts of other organics) will be generated. At the proposed reactor condi-2 2

tion, approximately 25% of the generated offgas will be CO. Therefore, when all of the organics have j

reacted, gas generation and production of CO will cease, and it will no longer be measured in a CO monitor.

Because of the large quantity ofdilution air added (approximately 2000 cfm) to cool the vent gas (and dilute H ), measuring the drop offin the flow rate from the actual process (0 to 5 scfm) would be i

2 extremely difficult. Therefore, using CO as an indicator of the process gas generation is reasonable, especially considering that CO monitoring equipment is relatively inexpensive.

Several issues should be considered when using CO as specified above. The actual process gas will be significantly diluted (by a factor of several hundred to several thousand) before it reaches the CO monitor. At an instrument detection level of I ppm, it would translate into 2000 ppm CO in the undi-luted process stream, assuming a vent gas flow rate of I cfm. Consequently, the instrument must have

,I sufficient sensitivity to compensate for the expected dilution.

J Monitoring background CO in the dilution air (atmospheric air does contain a trace of CO) would

)

help avoid running the batches for longer than necessary.

j 4.1.4 Other Comments / Questions on Stream Reforming Offgas Treatment. SEG claims that the process offgases are CO and water vapor and that 2

radionuclide carryover and filter plugging have not been observed in their other operating steam reforming units.

The panel representing technologies at the Technology Selection Meeting in 1994N rated steam reforming below the other four technologies. Most of their concerns with the technology were associated with a moving bed evaporator, which will not be required for the PGE project. Additionally, the panel noted that further treatment of the oligas from the high temperature re,etor would be required, presum-ably to eliminate hydrogen, methane, and carbon monoxide.

(a)

Second IPM Technology Selection Meeting. June 27-29,1994, Doubletree Hotel, Salt Lake City, Utah, Final Report, July 21,1994.

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Consultations with individuals having experience in steam reforming (including a technology developer at Sandia National Laboratory) and a review of text books (Rostrup-Nielsen, Jr.1984a 1984b) indicate that the process offgas will contain some hydrogen, methane, and carbon monoxide Funher, the supplemental material on steam reforming provided in the SEG proposal includes informa-tion that vent gas from demonstration testing contained high levels of hydrogen and carbon monox In the paper, " Steam Reforming Test of Sandia National Laboratory Surrogate Mixed Waste," the ve gas contained 20% H, and 10% CO (organic destruction was nearly complete). In the paper,"O Bio hazardous Waste Destruction with the Synthetica Steam Detoxifier-Test Organism Kill and Chlorocarbon Destruction," the vent gas contained 49% H, and 21.5% CO (organic destruction was nearly complete).

Additionally, offgas purge in the proposed system will be continuously withdrawn (to maintain th pressure balance). Early in the processing cycle, the offgas in this purge stream may conta pletely destroyed hydrocarbons. Air pollution regulators may be concerned about potential hy methane, carbon monoxide, and partially decomposed polymers. Additionally, ar: hough the syste designed to exclude air (and oxygen), the possibility exists that the vent system will conta gas.

Entrainment of TRU and Other Radionuclides. Depending on the velocity of the syngas through the evaporating can, it is probable that TRU and radionuclides will be entrained in the gas stre captured on the cold filter and/or the HEPA filter.

1-pm Cold Filter. SEG proposes a 1-pm filter between the evaporator can and the steam furnace. He can will operated at about il00*F and the furnace at approximately 2200*F. The cold filter will be maintained at approximately 300*F. It is intended to capture entrained radionuclides culate and condense and capture volatilized cesium. The operating experience of SEG and Synthe suggests that entrainment should be minimal at the low projected flow rates through the evaporato and that at 600*C, volatilization of cesium should be minimal. Battelle has some concerns that at 3 some of the organics gasified at 1100*F will condense and plug this filter, especially during start-up (while the evaporator is heating from ambient to 1100'F. Although there are provisions for back-flushing, condensed organic polymer may not be easily removable and could adhere to filter. In the cold filter may create a more significant problem than it solves.

It was stated earlier in this discussion that 76% of volatilized cesium was less than I pm in size. The conclusion drawn from this information is that the cesium is in vapor form rather than an entrained p culate. His conclusion seems to make sense until reviewing previous literature. At 600*C, there is sig-nificant potential for volatilization considering the boiling point of cesium is 671 *C. Earlier studies support the idea that volatilization occurs. However,it was observed that the cesium actually co and forms sub-micron f.esium particulate, which traveled through micron filters at ambient temperature using inert gas / steam as a carrier. (Woodley 1986; Woodley 1987). Ultimately, the cesium pan aerosols were trapped by using a particulate filter followed by a copper oxide trap heated to 400*C (Baldwin 1978).

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Control During Startup. Initiating the evaporation / steam reforming process with each can is anticipated to be the most difficult stage. During this time, chances appear greatest for " burps" in the wet wastes to cause rapid evolution of gases from the evaporator can. These excursions, if they occur, could result in problems with pressure and flow control throughout the system.

Maturity of SEG System Design. It appears that the proposed design of SEG's steam reforming system to be used for PGE's spent fuel pool is not final. For example, the stated process offgas composi-tion has changed, the type and operating temperature of the cold filter has not been established, and the steam injection rate during processing seams to be undecided. These uncertainties suggest that for this application, the process is still under development. If this is the case, unexpected processing problems may be encountered, and difficulty in maintaining schedule and cost may be anticipated.

4.2 Flotation Separation Process Assessment (Framatome)

Although Framatome describes their proposed process as a column flotation process, it is in fact a combination of two common separation techniques (dense medium separation and froth flotation). Both processes are used extensively in the mining / minerals processing industry and have lesser applications in other processing industries.

Dense-medium separation, as the name implies, involves the use of a dense medium to separate rela-tively heavier and lighter particles. Typically the fluid has a density between the densities of the mater-ials to be separated. Dense medium separation is not highly efTective for separating fine particles. In the mining industry, use of the process is generally restricted to concentrating ores when the valuable minerals can be liberated from the gangue minerals at a relatively large size. Coal cleaning is one ofits major applications (Kelly and Spottiswood 1982).

In the proposed Framatome approach, water would be used as the separating medium. The various plastic filter materials in general are significantly less dense than the remaining debris (e.g., spent fuel residues, stainless steel EDM dross). However, because the plastics densities are similar to water, the plastics will not readily separate from the rest of the debris simply by density difference. The capacity of this process to incorporate the benefits of dense medium separation would be enhanced by increasing the density of water, such as by salt addition, to a point between the densities of the plastics and the other debris. However, that is neither proposed nor feasible for this particular application.

The other part of the Framatome proposal involves the use of froth flotation to separate plastics from the remaining debris. As noted, froth flotation is used extensively in the mining industry to separate valuable minerals from the worthless bulk of mined ore, usually after fine grinding. Ores are typically ground to about 208 pm (65 mesh), not only to liberate the valuable minerals but also to reduce them to particle sizes that may be easily levitated by froth flotation.

Nost minerals are naturally hydrophillic, meaning they are readily wetted by water. For the flotation process to work, air bubbles must attach only to the desired particles. One or more of a variety of flota-tion reagents is added to the water slurry to regulate the surface chemistry of the particles, making the 1i

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surface of the desired particles more hydrophobic than the other solids. Den the particles with a specific affinity for air bubbles rise to the surface of the froth and are thus separated from the more hydro' particles. Froth Dotation does not rely on density differences to aid panicle separation. For exam dense mineral like galena (lead sulfide) can be easily separated from its much lighter gangue minerals b flotation when the galena attaches to air bubbles and Hoats away from the rest of the material.

l Framatome correctly states that the plastics are naturally hydrophobic relative to the rest of the debris. Therefore, air bubbles will selectively adhere to and float the plastics. The maximum size of a plastic particle that can be readily floated is not known; it depends on the shape as well as mass j particle. The maximum panicle size oflower density plarties will be larger than for most minerals, b will likely be signi0cantly smaller than can be visually dist nguished and then hand soned from the i

)

debris.

Flotation separation of minerals works well when the particles are freshly broken discrete panicles -

not aggregates or agglomerates of fine particles. An uncertainty in this application would be the amount of nonplastic debris that might be clinging to or embedded within the plastic fibers of the filter media Contamination of the plastic with other residues could mask the hydrophobic surface of the plastic from

)

the air bubbles, preventing flotation, or if the plastic should float, significantly add to the amount of TR in the plastic fraction, depending on the nature of the contaminating residue. Initial estimates indicate that a significant mass of TRU waste could be included in the plastics fraction before exceeding the 100 nCi/g limit. It seems likely that an acceptable separation could be achieved and that the plastics fraction could be collected and disposed of without the need for much secondary processing after the flotation step.

Framatome mentions the possibility of using an " attrition scrubber" to process the residues before flotation. Such a scrubber would probably aid in separating loosely bound plastic and nonplastic parti-cles; it seems less likely that the action of the mixer would do much to reduce the size of the plastic par cles that are too large to Coat.

When the particles and attached bubbles rise to the surface, the bubbles would break and the floated particles would again sink into the slurry without the aid of other reagents known as "frothers." The frother stabilizes the foam layer on the surface long enough for entrained undesirable particles to separate back into the liquid, yet permit the removal of the desired particle-laden bubbles from the surface. Frothers are usually oily organic additives. The use of such a material would seem highly undesirable for this application, in which the water circulates to the Cask Load Pit (CLP). The use of a frother may not be necessary to achieve some degree of separation, but it may not be possible to achieve the high degree of separation required to remove plastic from the GTCC waste fraction without the us a frother and perhaps other flotation reagents.

Framatome proposes the use of" column" flotation for this application. Column flotation refers to a type of" cell" or enclosure within which bubble attachment and flotation occur. Column Dotation cells are one of tnany types ofcells that have been developed. However, it is only more recently that column Dotation has seen significant production-scale application. Regardless of the type or size of cell, or the 12

.?

-,qs%M.

nature of particles being Doated, the successful operation of a flotation circuit often requires lengthy fine tuning to achieve the desired separation. Without prior experience with this specific application, the risk ofinadequate system performance appears to be significant, necessitating further treatment of both the i

plastic concentrate fraction and the residual GTCC waste fraction.

The Framatome proposal states that alternating cycles of flotation and attrition scrubbing would be repeated "... until only acceptable levels of radiation are present in the upper Repository / Filter Canister (RFC) and only acceptable quantities of polypropylene remain among the fuel and corrosion products in the lower RFC." Analysis of the radiation from the plastics fraction seems reasonably straightforward, but methods for routine sampling and analysis of the GTCC fraction for " hydrogenous" materials may not be routine at all and should be better described in this proposal. On page 3-11 of their proposal, Framatome states that "When it becomes impossible to identify pieces, the remainder will be identified as mixed non-hydrogenous waste that can be sampled as required by Trojan." Because of the extremely j

low concentration of allowable residual plastic in the GTCC waste, Battelle believes that the chances are slight that the waste will in fact be non-hydrogenous when pieces can no longer be visually identified.

The proposal describes a video ofinitial bench scale testing by Framatome in which polypropylene

" powder"(the particle size distribution was not given) was floated in borated water. They reported j

apparent success at floating the powder using "... very fine application of a standard commercial frother."

)

If addition of frother reagents to the water in the CLP is acceptable, this would almost certainly improve system performance. However, a more convincing demonstration would have included dirty degraded plastics and residue resembling the dirt and EDM dross at TNP rather than a finely divided plastic powder. In a simple bench-scale test performed at Battelle, chopped poylpropylene fibers (~1/4 inch long or less) were mixed with dirt and metal particles collected under a bench grinder. The solids were mixed with water in a column and allowed to settle. Air was bubbled up through de mbmerged solids through the glass fritted (~5-pm pores) bottom of the column. A significant portion of the plastic

]

particles did not float during this test.

Given that the column flotation process proposed by Framatome successfully separates plastic from the GTCC waste, the GTCC waste will still be wet and therefore will exceed the limits for hydrogen content. PGE told Battelle at the outset of this evaluation that Framatome recognized this issue and proposed to vacuum-dry the cans and their GTCC contents. The vacuum-drying portion of the Framatome process was not to be included in the scope of this evaluation.

In summary, froth flotation has been successfully used for decades to separate particles. This includes the flotation oflead sulphide, which has a much greater density (but also a higher affinity for air bubbles) than the gangue material from which it is separated. A well designed flotation circuit can be tuned to provide a high specificity for a particular type of particle and thereby recover very low concentrations of the desired particles from the initial mixture. This fine tuning usually requires much testing to determine the optimum operating parameters, such as degree of agitation, types and dosages of colleitors, frothers, and other reagents, conditioning time, air injection rate, or coh.mn height.

13

_T

. t.;,,,,,

p A

b Plastic is naturally hydrophobic and therefore should readily separate from the other residues in the t

filter-media wastes. However, many factors will influence the capability to float enough of the plastic toj qualify the remaining residue as a non-hydrogenous material suitable for sealed dry storage. Tho factors include 1) the likelihood of plastic particles too large to float (or ones coated with other residues that rnake them unfloatable), but smaller than can be identified and hand sorted, and 2) uncertainty about the acceptability of using flotation reagents to enhance the performance of the flotation cell.

f Preliminary estimates indicate that a reasonably large quantity of TRU (plutonium, uranium, and americium) might be carried over with the plastic concentrate without exceeding the 100 nCi/g limit.

Therefore, it is anticipated that a flotation column could be operated without exceeding unacceptable levels of entrained TRU residues in the floated plastic fractiors thereby preventing disposal of the plastics as low-level waste (or requiring additional processing of the wastes.

5.0 Filter Analytical Results Several filter types used by PGE may be present in the spent fuel pool sludge. PGE contacted the suppliers in an attempt to verify the chemical makeup of trie various filters. The s' appliers in turn contacted the manufacturer of the materials but had little success in this effort. To verify the composition of the filters provided, Battelle performed total organic carbon (TOC) analysis of the materials. Table 5.1 provides a description of each of the samples provided by PGE to Battelle.

The most common filters used ':sy PGE were samples 40 and 41, which use Dacron and polypropyl.'

ene as the filter media. liowever, sample 40 is perhaps as much neoprene by weight as dacron. No i

bonding agent is apparently used as it appeared that the filter media is set directly in the neoprene.

Sample 41 is a fabric filter, as are al! of the other samples, which includes a flange ring on the op I

of the filter. Sample 43 contained a metal flange ring, and this portion was not sampled. Subsamples were obtained by cutting portions of the filter, flange ring, and gasket if present. Table 5.2 provides the results of the TOC analysis, nese results indicate that almost all of the materials used in manufacture are as stated. Sample 40 Gasket and 41 ring may contain inert filler materials. Sample 45 is apparently not polypropylene.

The TOC results indicate sample 45 may be Nylon. In all cases, a calculation of hydrogen generation potential based on the materials originally specified would over predict the amount produced.

14

.i

.s Table 5.1. Sample Description Sample No.

Manufacturer Description 40 Ronningen-Petter Expanded area bag,10-20 micron, pleated dacron media with neoprene top and bottom.

41 Ronningen-Petter Woven polypropylene,5-10 micron item # 4200PYL00545 42 Ronningen-Petter Bonded nylon,5-10 micron, item # 4200NYL00545 43 Como Industries Felt lined filter bag 44 Filter Specialists, Woven polypropylene,10 micron, filter with polypropylene Inc. (FSI) flange, # BPONG 10 P2P l

45 FSI Woven polypropylene,25 micron, filter with polypropylene flange, # BPONG 25 P2P Table 5.2. Total Organic Carbon Anclysis Results (Merck Index 1989)

Molecular Anticipated Specific weight Melting TOC Expected TOC Measured Sample Material Gravity (monomer)

Point 'C

% Carbon

% Carbon

  1. 40, Filter Dacron 1.38 210.2 250 57.1 57.9 54.3 42.1
  1. 40, Gasket Neoprene 1.23-1.35 88.5
  1. 41, Filter Polypropylene 0.90-0.92 42.1 165 85.6 87.5
  1. 41, Ring Polypropylene 0.90-0.92 42.1 165 85.6 79.9 (note 1)
  1. 42, Filter Nylon (46) 1.20 216.3 283-319 55.5 58.6 (note 2)
  1. 42, Ring Polypropylene 0.90-0.92 42.1 165 85.6 79.9 j

(note 1)

  1. 43, Filter
Felt, 0.90-0.92 42.1 165 85.6 82.5 Polypropylene
  1. 44, Filter Polypropylene 0.90-0.92 42.1 165 85.6 83.0
  1. 44, Ring Polypropylene 0.90-0.92 42.1 165 85.6 87.2
  1. 45, Filter Polypropylene 0.90-0.92 42.1 165 85.6 84.6
  1. 45, Ring Polypropylene 0.90-0.92 42.1 165 85.6 59.8 Note 1: Actual material not specified. Material listed is based upon visual determination before TOC analysis.

Note 2: Material was specified generically as Nylon, calculation of molecular weight and percent carbon are based on Nylon 46.

15

.e 6.0 Conclusions 6.1 Criticality Evaluation r

Review of the Framatome and SEG proposals indicates that criticality will not be possiMe with either of these processes; however, the SEG proposal did not have adequate information to pennit a formal criticality analysir.

Review of the processed fuel storage configuration also reveals no criticality concerns. This analysis is based primarily on an analysis of a similar fuel storage configuration.

6.2 GEND-041 Calculation

)

The GEND-041 calculation is highly conservative for the PGE application.

l 6.3 Hydrogen Limit Evaluation Battelle's evaluation of the proposed hydrogen limit in each container did not validate the value proposed by SEG (0.592 moles). Our calculations indicate a lindt of 0.250 moles of elemental hydro per SEG Process Can Capsule.

6.4 Process Evaluation of Steam Reforming (SEG) a Battelle staff believe that essentially all the " hydrogenous" materials (plastics and water) should be I

removed from the% aste in the can feed evaporator over the course of a complete cycle of the steam reforming process as described in the proposet. It would seem that some measure of agitation withi the evaporator can would provide greater confidence that all of the organics and water will be removed. However, based on SEG's claimed success in steam reforming animal carcasses without agitation, it may not be essential to provide agitation for PGE's application.

. Flammable gases such as hydrogen will be produced during the steam reforming reactions. How-ever, concentrations of flammable gases in the process off gas should be negligible because of a planned 1000-fold dilution of process gases at the exit from the process equipment.

  • Available data suggest that a small fraction of cesium remaining in the filter media waste may leave the can feed evaporator by either volatilization or entrainment in the circulating gas. However, with the series of filters included in the process, this should not present significant operational difficulties.

This may require a series of filters / traps to be used that were not originally proposed by SEG.

= In general, the proposed use of a CO monitor in the system off gas appears to be a reasonable approach to monitoring the steam reforming process. Although the concentration of CO will likely 16

ocwmw remain high in the system, the amount of off gas generated will decrease to zero as destruction of the organics and removal of water is completed. Therefore, use of a CO monitor should be an effective and inexpensive way to monitor the system as compared to other considered approaches. However, the planned 1000-fold dilution of the off gas may affect the sensitivity of equipment that would use J

off gas composition to monitor the process, depending on type and location of such equipment.

l 6.5 Process Evaluation Column Flotation (FRAMATOME)

  • Plastic is naturally hydrophobic, and therefore small plastic particles should readily sept. rate from the other residues in the filter-media wastes if the plastics are not tightly bound to other residues.

However, if plastic particles are coated with hydrophillic debris or if heavy particles are trapped in the fibers, the plastic particles may not float. Also, plastic particles larger than about 1/4 inch may not readily float (although the tendency to float depends on particle shape as well as size).

  • Density differences between the plastics and the other residues will probably not significantly enhance their separation. This is a minor, and prcbably insignificant consideration, but Framatome had claimed this difference as part of their ability to make the separation.

Column flotation should provide an acceptable separation such that the TRU content of the floated plastics f ction shall be low enough (<100 nCi/g) to classify the waste as " low-level."

= lt is much less certain that the removal of plastic from the unfloated GTCC fraction will be effective enough to lower the " hydrogenous" material content to belo,w the limit of 0.250 moles of elemental hydrogen per container specified for dry storage.

7.0 References Baldwin, DL. I978. New InstrumentalMethodfor Determining Fission Gas Retainedin Irradiated Oxide fuels, HEDL-TME 78-2, Westinghouse Hanford Company, Richland, Washington.

Flaherty, JE, A Fujita, CP Deltete, and GJ Quinn.1986. A Calculational Technique to Predict Combustible Gas Generation in Sealed Radioactive Waste Containers, GEND-041, EG&G Idaho, Inc.,

Idaho Falls, Idaho.

i Goles, RW, RK Nakaoka, JM Perez, GJ Sevigny, SO Bates, MR Elmore, DE Larson, KD Wiemers, ME Peterson, CM Anderson, WC Buchmiller, and CM Ruecker.1990. Hanford Waste Vitrification Program Pilot Scale Ceramic Melter Test 23, PNL-7142, Pacific Northwest Laboratory, Richland, Washington.

i 17

i 3

~,.,

.. - - ~.. _.. - -.

., Ag,.

1 l

Goles, RW, and AJ Schmidt. June 1992. Evaluation ofLiquid-FedCeramic Melter Of-Gas System t

Technologiesfor the Hanford Waste Vitrification Plant, PNL-8109, Pacific Northwest Laboratory, j

Richland, Washington.

Kelly, EG, and DJ Spottiswood.1982. Introduction to MineralProcessing, John Wiley & Sons, Inc.,

New York.

Rimshaw, SJ, FN Case, and JA Tomkins.1980. Volatility ofRuthenium-106. Technetium-99, and lodine-129, and the Evolution ofNitrogen Oxide compounds During the Calcination ofHigh-Level, Radioactive Nitric Acid Waste, ORNL-5562, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

1 Rostrup-Nielsen, Jr.1984a. Catalytic Steam Reforming, Springer-Verlag Berlin.

Rostrup Nielsen, Jr.1984b. Steam Reforming Catalysts, Tekr.isk Forlag A/S (Danish Technical Pres Inc.) Copenhagen 1975.

The Merck Index,1Ith Edition.1989. Merck and Company,14.c., Rahway, New Jersey.

- )

United States Nuclear Regulatory Commission (NRC).1984 Clarification ofConditionsfor Faste Shipments Subject to Hydrogen Gas Generation, IE Information Notice No. 84-72, NRC, inspectio Enforcement, Washington, D.C.

WoodIey, RE. 1986. The Release ofFission Products From IrradiatedSavannah River Plant Fuels at' Elevated Temperatures, HEDL-7598 Westinghouse Hanford Company, Ri:hland, Washington.

Woodley, RE. 1987. The Release ofFission Products From IrradiatedSavannah River Plant Fuels at Elevated Temperatures, HEDL-7651, Westinghouse Hanford Company, Richland, Washington.

l l

l 18

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i f $gddI,f ju.,"pp% 4 9 4 %#h}[ *N$t*), - -', : (. +a y *, +,

4 se ep 'MA/- y e g.Qp4, ** *

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I 1

l Appendix A 1

6 I

I I

I l

l 4.y Appendix A Table A.I. Hand Calculations to Estimate a Safe Number The mass of a single pellet is 10.296 grams. The calculations assume 5% enriched UO.

2 Ave Pellet U-235 Migration Critical Reflector Sphere Sphere UO, Critical Size Density Area Buckling Savings Radius Volume Mass

  1. of (in)

(gm/L)

(cm^2)

(cm^-2)

K-inf (cm)

(cm)

(L)

(gm)

Pellets 0.4 190.13 31.71 0.01495 1.474 7.02 18.7 27.3 117947 11455 158.28 30.97 0.01638 1.507 6.77 17.8 23.5 84658 8222

~

135.57 30.34 0.01702 1.520 6.61 17.5 22.3 68823

'6684 1I8.56 30.28 0.01721 1.521 6.5 17.4 22.3 59969 5824 105.35 30.14 0.01710 1.515 6.41 17.6 22.9 54798 5322 94.78 30.06 0.01682 1.506 6.35 17.9 23.9 51533 5005 78.94 30.05 0.01593 1.479 6.26 I8.6 27.1 48631 4723 67.64 30.14 0.01481 1.446 6.2 19.6 31.6 48597 4720 59.17 30.29 0.01360 1.412 6.17 20.8 37.5 50493 4904 52.59' 30.48 0.01234 1.376 6.15 22.1 45.4 54292 5273 47.32 30.7 0.01106 1.340 6.15 23.7 55.9 60130 5840 43.01 30.93 0.00988 1.303 6.17 25.6 70.1 68478 6651 36.39 31.45 0.00733 1.231 6.2 30.5 118.8 98212 9539 31.53 32.02 0.00504 1.161 6.25 38.0 229.7 164621 15988 27.82 32.64 0.00299 1.098 6.3 51.1 559.7 353898 34371 24.89 33.25 0.00139 1.046 6.88 77.3 1937.

IE+06 106393 These data were take from Cntical andSafe Masses and Dimensions of Uand UO, Rods in Water, Hugh K Clark; DP 1014; February 1966.

4 A.1

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