ML20034A531
| ML20034A531 | |
| Person / Time | |
|---|---|
| Issue date: | 04/16/1990 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Sterzinger G VERMONT, STATE OF |
| Shared Package | |
| ML20033D916 | List: |
| References | |
| NUDOCS 9004230418 | |
| Download: ML20034A531 (6) | |
Text
{{#Wiki_filter:g Mr. George J. Sterzinger, Chairman Yemont State Nuclear Advisory Panel Department of Public Service 120 State Street State Office Building Montpelier, Vermont 05602
Dear Mr. Sterzinger:
i Your letter of February 22, 1990, requested additional information from the Nuclear Regulatory Comission (NRC) concerning containment. venting for severe accidents. It contains five additional follow-up questions associated with-your request of October 23, 1989, to which the NRC responded in a' letter dated [ November 22, 1989. To better understand the background for these questions, sqy staff also met with Mr. Sheman of_your panel on March 27, 1990. Our response to these additional questions is provided in Enclosure 1. We have also enclosed a copy of the--referenced materials.in response to Question 4. ~. '. U I hope this infortnation is useful. Sincerely, grigtsalSigned Byi Thomas E. Murley, Director Office of Nuclear Reactor Regulation
Enclosures:
DISTRIBUTION w/ Enclosure 1 See next page TMurley/FMiraglia Secy 'JKudrick TMartin, R:1 RArchitzel .JTaylor' AThadant HThompson WRussell JSniezek CL1 JBlaha ^ JRidgely EBeckjord,RES LSoffer WBeckner, RES Yellow Ticket File HDenton, GPA-DMossburg #0909033 JPartlow JWemiel DCruthfield. JMonninger .FG111espie DISTRIBUTION w/all Enclosures 'ContrebF11e- [(o$ NRC PDR %}p .)g)[ l SPLB File- )g RES:SAIB Tech. Edit. NkR:ADT WBeckner* JMain* WRussell* urley
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JMonninger* JKudrick* CMcCracken* AThadan1* RWessman* 4/05/90 4/05/90 4/05/90 4/05/90 4/11/90 4/11/90 l W"iM ME NRC RLE CENTER COPY I
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l George J. Sterzinger
Enclosures:
1. Response to VSNAP letter, February 22, 1990 il 2. "Sumary Paper on Filtered Vented Containment Effectivenass," International Technology ] Corporation August 7, 1987 i 3. Sumary of the Shoreham Supplemental Containment ,l System 4. NUREG/CR-3317, " Technical Bases and User's Manual for the Prototype of a Suppression Pool Aerosol Removal Code (SPARC)," May, 1985 5. BNL A-3788, " Effectiveness of BWR Pressure Suppression Pools in Retaining Fission Products," August, 1986 6. Nati Merilo, " Scrubbing of Aerosols by Water Pools ~ ' ' Under Severe Accident Conditions," EPRI presentation, April 9, 1986 7. "Filtra-MVSS Multi-Venturi Scrubber System," ABB Presentation to the USNRC staff on.the Swedish Containment Venting Implementation Program, April 25, 1989 8. NUREG-0800. Standard Review Plan, Section 6.5.5, " Pressure Suppression Pool as a Fission Product Clean-up System" 9. NUREG/CR-4C24, Vol. 1, "Radionuclide Release Calculations for Selected Severe Accident Scenarios." July 1986, pages 6-7 through 6-21 l t l f l 1
. ~. Response to VSNAp letter dated February 22, 1990 na
Background:
NUREG-1150identifiedStationBlackout(SBO)andAnticipatedTransientWithout Scram (ATWS) as the dominant severe accident sequences for the Peach Bottom Atomic Power Station in terms of risk and of the probability of-core damage. This finding was made as a result of having given credit for venting at Peach Bottom for the loss of decay heat removal (TW) accident-sequence. Other probabilistic risk assessments (PRAs) indicate that if no operator actions receive I credit in the PRA and if the frequencies identified in WASH-1400 are used, then the TW sequence is the dominant accident sequence, both for core ~ damage frequency.and risk, w Ouestion 1: "Can you provide us with documentation of your generic-plant l analysis of external filters? 'Did.you consider types other i than large containment-like structures? What were their costs?" [ l
Response
No generic-plant analysis of external filters exists. The use l3 of external filters was eliminated by inspection because of the j-low potential benefit (see response.to Question 2)'and the high i installation costs. Two types of external filters were-considered, the FILTRA system and the Multi-Venturi Scrubbing System (MVSS). The original response relating to the costs was not clear. The MVSS was estimated to cost approximately $5 million. The FILTRA t was estimated to cost approximately $30 million. No other external filter designs were considered. A summary paper on filtered vented containment effectiveness is attached as Enclosure 2. Question 2: "You have identified costs of one method of filtration. Can you-provide an indication of benefits of this, and other types of filters, as they relate to their costs (see the Discussion sectionabove)?"
Response
Neither the suppression pool nor an external filter will reduce the release of noble gas fission products. Filters are only effective for the removal of particulates. For plants with Mark I containments, any radioactive material to be filtered by an external filter would have passed through the suppression pool i first. The suppression pool has a realistic decontamination factor (DF) for particulate fission products of about 100 depending upon the accident sequence and the temperature of i the water. Thus, there would be little additional benefit from the use of an external filter, because virtually all the particulates would have already been removed by the suppression pool; and because the overwhelming majority of the remaining fission products, namely noble gases, would not be removed by the external filter. Title 10 CFR 50.109(a)(3) states that requiring a backfit must be based on finding that with the proposed backfit "there is a substantial increase in the
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., overall protection of the public health." - Because the l, 4 installation of the external filter is not considered to provide "a substantial increase in the overall protection of the public - health," the staff did not continue to consider the installation of an external filter. However, for completeness, Enclosure 2 includes a description-of the FILTRA system, the French filtered vent, and the German-filtered vent concept. In addition ' Enclosure 3 provides a sumary of the proposed Supplemental Containment System for [ Shoreham Nuclear Power Plant Station, Question 3: "Canyouprovidecore-melt-(SB0andATWS).sequencevent flow rates, pressures and durations representative of the-hardened vents identified in NRC_ Generic Letter 89-16? j -- .s (Section 4.1 of NUREG/CR-5225 identifies some vent sizes. but infomation on flow rates, pressures and durations could i not be found.)" No vent flow rates, pressures, or durations were de'termined for
Response
SBO, ATWS, or TW sequences. The information in-NUREG/CR-5225 was provided based on dry steam, a containment pressure of 60-psig, and a calculation of the choke flow. The actual effective-choke plane diameter will vary with pipe size, length of run, number and type of bends, and obstructions such as valves and strainers. Similarly, because-the pressure in the vent line and the duration of the venting operation will-be specific to each site and sequence, they were not calculated. Therefore, the staff specified a performance criterion (that is, the capability to remove one percent of the full power heat generation rate at the vent pressure) instead of a. system or l design criterion. Ouestion 4: "Can you provide us with studies and documents relating to wetwell scrubbing? Also, can you identify the Peach Bottom assumptions used in NUREG-1150 for wetwell scrubbing?" l
Response
Yes. Enclosed are copies of the following materials that j contain the information you requested about wetwell scrubbing: 1) NUREG/CR-3317 entitled " Technical Bases an'd User's Manual for the Prototype of a Suppression Pool Aerosol Removal Code (SPARC),"-dated May 1985;- q 2) Technical report entitled " Effectiveness of BWR Pressure Suppression Pools in Retaining Fission Products," dated August 1986; 3) Presentation by the Electric Power Research Institute (EPRI) to the NRC entitled " Scrubbing of Aerosols by Water Pools Under Severe Accident Conditions", dated April 9, 1986; j h-___
9 l 1 L., L ) 4)_ Presentation by Asea Brown Boveri (ABB) to the NRC: on the Swedish Containment Venting Program Implemen-tation,' dated April 25,1989; and ~ 5) NUREG-800.. Standard Review Plan, Section 6.5.5, " Pressure. d Suppression Pool as a Fission Product Clean-up' System." 6) NUREG/CR-4624. Vol. 1, "Radionuclide Release Calculations-for Selected Severe Accident Scenarios," July 1986,.pages-6-7.through 6-21. NUREG/CR-3317 is now considered to be outdated. Although new r work is in the process to update the SPARC ccde, there is' no documentation available on this: new work. The NUREG-1150 analysis of suppression pool scrubbing in boiling water reactors (BWRs), is described in detailed supporting documents to that report, including: A. C. Payne, Jr., et al., " Evaluation' of Severe Accident Risks: - [ Peach Bottom Unit 2." Sandia National Laboratories, NUREG/CR-4551, Vol. 4, Draft Revision 1. SAND 86-1309, to be published, and C. N. Amos et al., " Evaluation of Severe Accident Risks and the Potential for Risk Reduction: Grand Gulf Unit 1," Sandia. National Laboratories NUREG/CR-4551, Vol. 4. Draft Report for Coment April 1987. The technical basis for the analysis;was developed principally l from a series of sensitivity studies using-the SPARC computer code. The sensitivity studies considered the effect on pool' decontamination factors caused by variations in such physical-parameters as incoming bubble size, bubble aspect ratio, and the fraction of fission products entering the' suppression pool in coluble fom. These studies are documented in the following report: R. S. Denning et al., "Radionuclide Release Calculations for Selected Severe Accident Scenarios: BWR Mark I Design," [ Battelle Columbus Division,-NUREG/CR-4624 Vol. '1, July 1986. ~ Ouestion~5: "The letter concluded with the statement, 'In this event [1.e., substantial release on core-melt sequences], the addition of a filter or hold-up tank would not significantly affect risk consequences.' Concerning our comments in the Discussion section, could you provide additional explanation of this conclusion."
Response
During a core melt, venting through the suppression pool would release a portion of the noble gas inventory of the core. This release would occur after at least several hours and would be an elevated release through the plant stack, which would tend to dilute the release and significantly reduce-any doses. Based on a simplified analysis, we estimate that individual
m 9 -4. i doses resulting from such a release would compare to the maximum permissible value (25 rem whole body) given in the NRC's siting. criteria (10 CFR Part 100) for the individual. exposed to the jj highest _ dose at the site boundary. Because this dose results from the release of a portion of the noble gases, it is clear from the response to Question 2-p that an external filter would not reduce these consequences.. because it provides no filtration against noble gases. Although a holdup tank that retains the noble gases can reduce these low consequences, the following analysis shows that a holdup tank-is not considered to be cost-beneficial. The Strip report (NUREG/CR-2723, " Estimates of: the Financial Consequences of Nuclear Power Reactor Accidents" September 1982F '- E indicates that an SST2 release at the Vemont Yankee-Rowe Nuclear Power Station would result in $5 total-population dose (out to a distance of 350 miles) of 6x10-man-rem (Page A-139) (a release coming out of the_ suppression pool'looks similar.to SST2). The inclusion of the, cumulative dose out to this. distance of 350 miles-(typically 50 miles in cost-benefit' analysis)' adds conservatism in analyzing the: radiological: impact..Its use is motivated since it is the best information available. If the holdup tank retains all the noble gases coming out of the+5 suppression pool, then the benefit is a reduction of 6x10 man-rem. However, this figure-is used.only in the event of ~ a. core-melt accident ghat has an assumed probability of _ approximately 1x10' per reactor _ year. Therefore the expected: benef[t is about 6 man-rem per reactor year-(6x10+5 man-rem *- L 1x10. occurrences per reactor year = 6 man-rem per reactor year). Assuming 30 years of remaining plant. life, the benefit over the plant lifetime would be 180 man-rem (6 man-rem per reactor year
- 30reactoryears). At a cost of $1000 per man-rem, the holdup i
tank would be cost beneficial if the total cost was $180,000 or less. The cost of the holdup tank is expected to exceed $1,000,000. Therefore, the staff believes that the holdup tank would not be cost-beneficial. .i I Y i,. =. - -.-}}