ML19291C265
| ML19291C265 | |
| Person / Time | |
|---|---|
| Site: | West Valley Demonstration Project |
| Issue date: | 12/20/1979 |
| From: | NRC COMMISSION (OCM) |
| To: | |
| Shared Package | |
| ML19291C263 | List: |
| References | |
| NUDOCS 8001230247 | |
| Download: ML19291C265 (7) | |
Text
e STAFF COMMENT AND CONSEQUENCE ANALYSIS ON THE EARTHOUAKN FICM THE ACID LIOUID WASTE TANKS AT THE WETITRN NEW (CRK NUCLEAR SERVICICTTlTR~
WESi" VALLEY, NEW YORK
~
DOCKET M0. 50-201 As stated in our Interim Safety Evaluation I issued in August 1977, (Ref.1),
the Nuclear Regulatory Commission (NRC) staff has been investigating the potential risk resulting from the effects of a severe aarthquake on the acid liquid waste tanks and vault at the Nuclear Fuel Services, Inc.
(NFS) reprocessing plant in West Valley, New York. The staff has contracted with the Lawrence Livermore Laboratory (LLL) to conduct the seismic-structural analyses of the waste tanks and vault. LLL has reported the results of their analyses in " Seismic Analysis of the Acid Liquid Waste Tanks at the Western New York Nuclear Service Center, West Valley, New York," (UCRL-52500).
We have also asked Dr. William J. Hall of the Nathan M. Newmark Consulting Engineering Services to review and comment on these analyses.
Dr. Hall has extensive experience in seismic analytical methods and in the actual effects of earthquake on structures. His comments are presented in his letter report to the NRC staff dated May 25,1979 (Ref. 2).
Based on staff review of information submitted by Nuclear Fuel Services, Inc. and its cwn independent sources of information. the staff concluded that a site seismic design acceleration of 0.2g was appropriate for new additions and modifications. The tanks and vault were built to Uniform Building Code Zone III specifications during the period 1964-1965.
Zone III indicates an active earthquake zone.
In our investigations, we have assessed the capability of the tanks and vault against the design value of 0.2g.
As discussed in our Interim Safety Evaluation, the staff has also developed information on seismic recurrence intervals for the site. These estimates are equivalent to predicting the probability of the occurrence of a single earthquake as a function of its magnitude. This relationship is shown in Figure 1.
The curve of Figure 1 represents a fit to Central Stable Region earthquake histories from modified Mercalli intensities IV, VII, and VIII.
Acid Waste Storace System Descriotion The acid high level liquid waste storage system at West Valley consists of two separate 15,000 gallon stainless steel tanks, both contained within a single reinforced concrete vault. One of these tanks contains approximately 12,000 gallons of acid wastes, while the other tank serves as a spare. The tanks and vaults are completely buried within the silty clay soil and have a minimum of six feet of soil overburden covering the vault roof. Several surface systems provide services to the underground tanks. The tank ventila-tion system takes a suction on the tank vapor space, condenses and collects 1792 228 i
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- entrained water vapor, scrubs entrained acidic vapors, and filters airborne particulate matter before discharge to the reprocessing plant ventilation system. The ability of the surface tank support systems to withstand the effects of earthquake has not been analyzed; and in our analysis, these systems are assumed to be damaged.
Seismic-Structural Analysis The results of the LLL analyses indicate that the stainless steel tanks and vault are adequate as designed for ground accelerations up to and including 0.2g.
The analyses of the tanks further indicate that the only component of the tanks that could exceed yield strength is the base plate of the tank support legs. Although some yielding of tha base plate could occur, the supporting function of the legs would not be impaired. The vault is expected to experience some cracking near the roof to wall junction at peak horizontal ground accelerations between 0.18 and 0.2. This cracking is limited so that 9
the vault would remain standing after the earthquake.
Throughout this evaluation, the attempt has been made to strip the analysis of much of the conservatism inherent in the method. This is not done because the staff does not want to be conservative in its approach to protection of the public; but rather, the removal of conservatism is necessary in order to realistically determine the risk to the public. The staff continues to require for any new construction the conservatism inherent in its guides and regulations and analyses. The staff concludes from these analyses that the stainless steel high level liquid waste tanks will remain intact following a severe earthquake. Some cracking of the vault can occur, but the vault will remain standing.
Cuantity of Radioactivity at Risk The radioactive waste in the on-service stainless steel tank (80-4) exists in a single liquid, acidic phase. The fission products and actinides remain soluble in the strongly acidic solution.
The radionuclide inventory in 80-4 has been previously reported by NFS and others (Refs. 3 and 4) on the basis of fuel burnup and decay data and Thorex reprocessing data. A small sample of acidic waste frcm 80-4 was analyzed by the Oak Ridge National Laboratory (CRNL) in 1978. The results of the ORNL anlyses were included in the DOE study report on the West Valley site (Ref. 4). This radionuclide inventory, adjusted for decay up through 1979, has been used by the staff as the source term in its evaluation of the consequence of a severe earthquake on the acidic high level waste tank storage system.
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- ' Potential Releases Following the Earthouake The equipment servicing the acid waste tanks was not designed to current seismic design criteria, but rather was designed using the Uniform Building Code for Zone III. This equipment has not been analyzed for its capacity to withstand the effect of a severe earthquake. For the purposes of this analysis, the staff has assumed that, in the event of a severe earthquake, the equipment could be damaged such that normal condensation and filtration of the waste tank vapors would no longer occur. Furthermore, the staff has assumed that the waste tank vapors would then be directly released at ground level rather than condensed, filtered and then released via the plant stack.
Under the assumption, the radioactivity contained in the ta'nk vapor is that amount of radioactivity from the liquid that is carried over into the vapor duri ng5the process of evaporation. The decontamination factor (DF) of 5 x 10 previously used by the staff in its analysis of the effects of earthquake on the neutralized high level waste storage system (Ref. 5) is again used by the staff in this analysis.
The rate of evaporation from 80-4 has not been measured, but is presently quite low due to the low temperature of the waste (110* F to 120" F).
In event of a severe earthquake, with the tank cooling system possibly disabled, the waste temperature and evaporation rates could be expected to rise.
In the absence of measured evaporation rate data for tank 80-4, the staff has calculated an evaporation rate based on the conservative assumption that the entire waste heat generation is removed by evaporation, with no waste heat removed by the mechanisms of convection, conduction or radiation.
This conservatively calculated evaporation rate is 4.9 gallons per hour.
A potential consequence resulting from the effects of a severe earthquake on the high level waste storage system results from the inhalation of radionuclides that have evolved from the tank vapor space and have been dispersed to the surrounding atmosphere. Meteorological dispersion factors were developed by the staff for various possible exposure times to individuals at the site boundary. The airborne concentrations of the released radionuclides at the site boundary were computed along with the maximum inhalation doses to hypothetical individuals positioned at the site boundary. The doses were computed using the REDIQ computer code (Ref. 6) which uses the Task Group Lung Model for computing inhalation doses.
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- ' The results of dose calculations indicate that an individual at the closest site boundary exposed to the worst meteorological dispersion that could be expected in any given hour would receive a lifetime (50 year) dose commitaent of approximately 0.7 millirem to the lungs, 3 millirem to the liver, 7.4 millirem to the bone, and 1 millirem to the whole body. The predominant isotopes contributing to the dose are strontium 90 and plutonium 238.
If an individual were to be exposed to the airborne radioactivity at the site boundary for six weeks, experiencir.9 the effects of average meteorological dispersion that can be expected during that time, that individual would receive a lifetime (50 year) dose commitment of approximately 9 millirem to the lungs, 40 millirem to the liver,100 millirem to the bone, and 13 millirem to the whole body. Again, the principal contributors to the dose are strontium 90 and plutonium 238.
Following the postulated earthquake, action would be taken by operators to restore any damaged tank ventilation systens. The time required for operators to restore ventilation, condensation and filtration following an earthquake is unknown.
If damage to above ground equiprent is extensive, several weeks may be required to complete repairs. Temporary systers could be installed in an emergency if necessary. A temporary tie-in to the main reprocessing plant ventilation system could also be accomplished in order to diminish the amount of activity released.
It is expected that personnel performing this work would require respiratory protection.
Radiolytic Decomcosition of the Waste The radiation field in the high level liquid waste causes radiolytic decomposition of water into hydrogen and oxygen gas. The same radiation field is sufficient to heat the liquid waste and cause evaporation of the water. The decay of cesium 137, strontium 90 and yttrium 90 produce the most important sources of the radiation field in the waste. Based upon the amount of radiation present, the staff has estimated that the amount of hydrogen gas produced by radiolytic decomposition may be as high as 2.2 standard cubic feet per hour. The production rate of steam due to evaporation of the water is many times larger than the production of hydrogen.
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6
, During normal operation, the hydrogen gas produced in the waste will collect in the tank vapor space and be removed by the ventilation system. The measured hydrogen concentration in the effluent vapor stream has been less than one percent. After discharge to the atmosphere, the hydrogen will rapidly diffuse and will also recombine with oxygen in the atmosphere.
Following a severe earthquake, the staff has assumed, in the absence of formal structural analysis, that the tank ventilation system is damaged and inoperative.
In order to conservatively detemine potential radiological consequences, the staff has further assumed that severed piping from the tanks pemits the ground level release of vapors from the tank. Hydrogen gas would be released along with other components of the vapor. Rega rdless of the condition of the tank support systems following a severe earthquake, the production rate of steam is so much larger than the production rate of hydrogen that conditions within the tank vapor space would be further driven from flammability limits.
Conclusion The staff and its consultants have examined the effects of a major earthquake on the acid high level liquid waste storage tanks at the reprocessing plant in West Valley, New York. The stainless steel tanks as designed would withstand the effects of an earthquake, and the surrounding concrete vault would remain standing.
In the absence of a formal seismic-structural analysis of the above ground structures and equipment that provide support servicas to the tanks, the staff has assumed that damage to this above groNd equipaent would permit the release of radioactivity from the tank vapor space. The resulting airborne concentrations of radionuclides at the site boundary would produce a dose to individuals at the site boundary that is only a fraction of the natural radiation background (about 100 millirem / year whole body). The dose would also be many times lower than doses specified under the accident design values of 10 CFR 100.
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- -.010 Figure 1 Estimate of Probability of Earthquake at West Valley, N.Y.
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.0001 L i
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1.6 x10'
.00001
.05g.109.159.20g.2Gg.30g Peak Horizontal Acceleration, fraction of gravity
References 1.
Nuclear Regulatory Commission Staff, Interim Safety Evaluation 1, August 1977, Docket No. 50-201, Nuclear Fuel Services, Inc. and New York State Energy Research and Development Authority, Western New York Nuclear Service Center, West Valley, N. Y.
2.
Letter from Dr. W. J. Hall, Nathan M. Newmark Consulting Engineering Services, to Dr. A. T. Clark, U.S. Nuclear Regulatory Commission dated May 25,1979.
3.
" Alternative Processes for Managing Existing Commercial High Level Radio-active Wastes," Batteile Pacific Northwest Laboratory, (NUREG-C043) dated April 1976.
4.
" Western New York Nuclear Service Center Study," Companion Report, U.S. Department of Energy (TID-28905-3).
5.
NRC Staff Comment and Consequence Analysis of the Earthquake Risk from the Neutralized Liquid Waste Tanks at the Western New York Nuclear Service Center, West Valley, N. Y., enclosure (3) to letter from L. C. Rouse, NRC, to R. W. Deuster, NFS, and J. Larocca, NYSERDA dated June 20, 1979.
6.
D. L. Strenge, E. C. Watson, W. E. Kennedy, "REDIQ - A Computer Program for Estimating Health Effects from Inhalation and Ingestion of Radionuclides,"
Battelle Pacific Northwest Laboratories (BNWL-2110), December 1976.
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