ML19289G219
| ML19289G219 | |
| Person / Time | |
|---|---|
| Site: | West Valley Demonstration Project |
| Issue date: | 06/20/1979 |
| From: | NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | |
| Shared Package | |
| ML19289G213 | List: |
| References | |
| NUDOCS 7908030534 | |
| Download: ML19289G219 (6) | |
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STAFF COMMENT AND CONSEQUENCE ANALYSIS ON THE EARTHQUAKE RISX FROM THE hEUTRALIZED LIQUID WASTE TANKS AT THE WESTERN NEW YORK NUCLEAR SERVICE CENTER WEST VALLEY, N.Y.
DOCKET NO. 50-201 As stated in our Interim Safety Evaluation 4 of August 1977,1 theNuclear Regulatory Commission (NRC) staff has been investfoeting the\\ potential risk l
resulting from the effects of a severe earthquake w the neutralized liquid waste tanks and vaults at the Nuclear Fuel Service (, Inc. (NFS) reprocessing plant in West Valley, New York. The staff has con;racted with the Lawrence Livemore Laboratory (LLL) to conduct the seismic-structural analyses of the waste tanks and vaults. LLL has reported the resulis'o# their analyses in
" Seismic Analysis of High. Level Neutralized Liquid Waste Tanks at the Western New York State Nuclear Service Center, West Valley, New York,"
(bCRL-52485).
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We have also asked Dr. William J. Hall of the Nathan M. Newmark Consultirg Engineering Services to review and comment on ~cosse a1alyses.
Dr. Haii'nas extensive experience in seismic analytical nNthods add in the actual.
effects of earthquake on structures. His ccaments are oresented 3n his letter report to the NRC staff dated March 2, 19'./
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Based on staff review of information submitted by NucIear Feel Services, Jnc.
and its own, independent sources of information, the staf'f concluded thatia site seismic design acceleration of 0.2g was appropriate for new additions and modifications. The tanks and vaults were built to Unifom Building Code Zone III specifications during the period 1964-1965. Zone.III indicates an active earthquake zone.
In our investigations, we have a:sesud the capability of the tanks and vaults against the design value of 0.2g. As discussed in our s
Interim Safety Evaluation the staff has also developed informatiart an seismic recurrence intervals for the site. These esticates are equivalent to predict-ing the probability of the occurrence of a slaqla, earthquakir asia function of its magnitude. This relationship is shown b: figure 1.
The kurve of Figure 1 represents a fit to Centeral Stable Ragito earthquak( histories frem.
modified Mercalli intensities IV, VII and VIII.
3 Neutralized Waste Storage System Description The neutralized high level liquid waste storage system at West Valley consistr of two separate 750,000 gallon carbon steel tanks each containec withis; its 4 own reinforced concrete vault. One of these tanks contains approximately 585,000 gallons of neutralized wastes, while the other tank serw s as a spare.
1 Nuclear Regulatory Commissicn 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.
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,s The tanks and vaults are completely buried within the silty clay soil and have a minimum af eight feet of soil overburden covering the vault roof.
Several surface systems provide services to the underground tanks. The tank ventilation system takes a suction on the tank vapor space, condenses and collects entrained water vapor 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' rot been analyzed and therefore in our analysis these systems are assumed to be damaged.
Seismic-Structural Analysis The results of the LLL aralyses indicate that the carbon steel tanks are adequate as designed for ground accelerations up to and including 0.29 The analyses further indicate that the coefficient of friction between the carbon steel tank and the perlite blocks is sufficiently high to preclude sliding of tank on the blocks and striking the vault. The analyses indicate that significant cracking along the bottom circumference. of the vault wall will occur at peak horizontal ground accelerations bstween 0.13 and 0.16.
9 The amount of cracking can be expected to increase for accelerations between 0.16 and 0.2g; but no excessive compressive stresses, causing crushing of concrete or gross collapse of the vault, would occur up to 0.2g.
Some spalling concrete from the inside of the vault roof could fall on the tank during such a severe earthquake. There is a negligible likelihood that the tank could be damaged by this falling concrete. As Dr. Hall states, "It is extremely unlikely... that these [ concrete pieces] would puncture or penetrate the roof of the steel tank in view of the linited distance separating the vault roof and the tank roof, and in view of the tank roof thickness and the strength and ductility properties of the roof material."
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 carbon steel high level liquid waste tanks will remain intact following a severe earthquake. Some cracking of the vaults can occur, but the vaults will remain standing. Finally, there is a negligible possibility that damage to the vaults could result in breaching of the tanks.
Quantity of Radioactivity at Risk The radioactive waste in the on-service tank (8D-2) exists in two phases -
a relatively dense layer of sludge at the tank bottom composed of precipitated solids from the neutralization reaction and a liquid supernatant phase above the sludge. The sludge is mostly composed of the hydroxides of process chemicals and fission products which are insoluble in the strong basic pH 2082 252 4
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-3 of the solution. The supernatant is cheifly sodium nitrate solution with ions of the few fission products (e.g. Cesium) which remain soluble in the strongly basic solution.
The concentrations of Cesium 134 and Cesium 137 in the supernatant are measured quarterly by NFS and reported to the NRC.
Based on these measured values and calculations using reprocessed fuel burnup data and fuel dis-charge and decay data, the fission -product and actinide inventory for tank 80-2 have been computed. The most recent tabulation of this radionuclide inventory can be found in Tables 3.7 and 3.9 of the U.S. Department of Energy (Companion Report to their Western New York Nuclear Service CenterThis inv Study TID-28905-3).
has been used by the staff as the source term in its evaluation of the consequence of a severe earthquake on the neutralized high level waste tank storage system.
Potential Releases Following the Earthquaba The equipment servicing the neutralized waste tanks was not designed to current seismic design criteria, but rather was designed using the Uniform Building Code for Zone III. This surface equipment has not been analyzed for its capacity to withstand the effects of a severe earthquake. For the purposes of this analysis, the staff has assumed that, in the event of a severe earthquake,, the surface 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 this assumption, the radioactivity contained in the tank vapor is that amount of radioactivity from the supernatant that is carried over into the vapor during the prccess of evaporation. The decontamination factor (DF) for evaporating semi-volatile species from the NFS waste tanks has been measured ~by comparing the 137Cs concentration in the supernatant to the 137Cs concentration in the knockout drum.
For the present conditions in the tank, with waste temperature about 180 F, this DF ranges between 5x105 and 7x105 For the purposes of this analysis, the staff has used a DF of 5
5x10 The present rate of evaporation from the waste tank is approximately 65,000 gallons per year. Several years would be required to evaporate the 585,000 gallons waste to dryness. Thus, ample time is available for action to be taken to prevent complete evaporation of the wastes.
A potential consequence resulting from the effects of a severe earthquake on the high level waste storage system results from the inhalation of radio-nuclides that have evolved from tne 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 radio-nuclides at the site boundary were computed and compared with the maximum 2082 253
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$ j5sible concentrations (MPC's) for release of airborne radionuclides to untestr.icted areas during normal operation. Th MPC's are tabulated in 10,CFR 20, Appendix "B", Table II.
For shorter postulated exposure times (e.g.One poorest o}r least amount of dispersion that can be expected during a givenouf)",th day. The X/Q values for longer exposure times (e.g. several weeks) represent a weighted average of all meteorological dispersion conditions that can be expected within the particular time period.
The results of the comparison between calculated airborne radioactivity concentrations and the MPC's indicate that an individual at the closest site boundary exposed to the worst meteorological 'dfspei;slon that could be expected in any given hour would inhale airborne concentrations of radioactivity that are less than 25% of 10 CFR 20 limits.
If an individual were to be exposed to the airborne radioactivity at the site boundary for six weeks, experiencing the effects of average meteorological dispersion that can be expected during that time, the average airborne concentrations would be less than 0.5% of 10 CFR 20 limits. Frequently, when evaluating the consequences of extreme accidents such as a severe earthquake, comparisons are made with the much higher accident limitations contained in 10 CFR 100.
- In this case, the predicted radioactivity concentrations are less than that which is permitted for continuous, unrestricted release of radioactive effluents under normal operating conditions.
Following the postulated earthquake, action would be taken by operators to restore any damaged tank ventilation systems. The time required for operators to restore ventilation, condensation and filtration following an earthquake is unknown.
If damage to above ground equipment is extensive, several weeks may be required to complete repairs. Temporary systems could be installed in an emergency if necessary. A temporary tie-in to the main reprocessing plant ventilation system could also be accompiished in order to diminish the amount of activity released.
It is expected that personnel perfoming this work would require respiratory protection.
Radiolytic Decomposition of the Waste The radiation field in the high level liquid waste causes radiolytic decomposition of water into hydrogen and oxygen gas. This same radiation field is sufficient to heat the liquid waste and cause evaporation of the water. The S ama flux due to Cesium 137 is the most important source of the radiation field in the supernatant.
Based upon the amount of gamma flux present, the staff has estimated that the amount of hydrogen gas produced by radiolytic decomposition may be as high as 5.5 standard cubic feet per hour.
At the same time, the production rate of steam due to evaporation of water caused by the same radiation field is approximately 3300 standard cubic feet per hour, which is six hundred times the production rate of hydrogen.
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l 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 per cent. 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 inopera-tive. In order to conservatively determine potential radiological consequenccs, the staff has further assumed that severed piping from the tanks permits the ground level release of vapors.from the tank. Hydrogen gas would be released along with other components of the vapor. Regardless 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 condi~tions 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 neutralized high level liquid waste storage tanks at the reprocessing plant in West falley, New York. The carbon steel tanks as designed would withstand the effects of the earthquake, and the surrounding concrete vaults would remain standing.
In the absence of a formal seismic-structural analysis of the above ground structures and equipment that provide support services to the tanks, the staff has assumed that damage to this above ground equipment would permit the release of radioactivity from the tank vapor space.
The resulting airborne concentrations of radionuclides at the site boundary would be less than permitted for unrestricted release during normal operations.
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.010 Figure 1 Estimate of Probability of
. Earthquake at West Valley, N.Y.
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.05g.10g.159.20g.25g.30g Peak Horizontal Acceleration, fraction of gravity
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