ML19327B588
| ML19327B588 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 05/11/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19327A642 | List:
|
| References | |
| TAC-55417, TAC-55418, TAC-73427, NUDOCS 8911020127 | |
| Download: ML19327B588 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PLANT SYSTEMS BRANCH 0FFSITE RADIOLOGICAL' CONSEQUENCE OF LOCA DURING
,?
CONTAINMENT PURGE L
ZION NUCLEAR POWER STATION, UNITS 1 AND 2 DOCKET WOS. 50-295 and 50-304-L
1.0 INTRODUCTION
ZionUnits1and2(Ceco)hasrespondedtoanNRCrequesttoproposeTSto andexhaus,constrainoperationofthelarge(42")containmentpurgesupply primarily t valves on these units.
The former Plant Systems Branch, Section A, of the Division of PWR Licensing A, requested Section B of the same branch to review the offsite radiologica f
consequences of this proposal.
2.0 EVALUATION Background review shows that the facility was evaluated on the basis of r
normally closed purge valves so that these consequences were never included in the Zion SER.: Further, that a letter from Westinghouse fW) to Cosmonwealth LOCAandContainmentPurge"(Ref.1976onthesubjectof"0f*siteDos Edison Compa y dated October 22 2)hasneverbeenevaluatedbytheNRC.
Subsequent to the TMI-2 event, the operability and automatic control of these valves was evaluated leading to the request for the required TS, but the Radiological Assessment was left as a "long(er) tem issue" (Ref. 3) which was intended to be resolved in a subsequent probabilistic risk assessment which definitively excluded it from consideration without a v justification (Ref. 4).
uses an RCS The W analyses undertaken under Cossenwealth Edison instruction,f the accident operational inventory of 60 uc/gm equivalent I 131 at the time o with a resulting site boundan thyroid dose due to iodine (durfng closure of the valves), of 52 rom, and witch added to the containment leakage dose of 123 rem gives a total 175 rem which is within the 10 CFR 100 limit of 300 rem.
The total iodine inventory of the RCS is assumed to be released into containment on initiation of the LOCA; a 505 plate out is assused leaving the resNual 505 as part of containment inventory for discharge out through both fully open containmentpurgelinesforatotalofseven(7 seconds).
However, whed reviewed against the BTP CSB 6-4, Item B.S.a requires that:
"The source term used in the radiological calculations should be based on a calculation under the terms of Appendix K to deterintne the extent of fuel failure and the conconnitment release of fission products, and the fission product activity in the primary coolant."
DR ADOCK 0500 5[
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. Further: SRP 4.2 identifies fuel failure with infringement of DNBR crJteria, f
gr with the related requirement that gap activity be considered as part of the source term, and Regulatory Guide 1.77 recommends that under similar Fuel
' circumstances, gap activity should be assumed at 105 of core activity.
damage criteria also includes the occurrence of center line melting with measures of additional activity release also guided by Regulatory Guide 1.77, but the Zion SAR shows this does not occur.
Revising the source term to Appendix K calculations [in which all fuel goes to DNBR in i second) with related release of all gap activity into containment, with limited blowdown to offsite during the related 7 seconds closure time and absent a 505 plate out of iodine as can be interpreted from the above referenced item 8.5.a. increases offsite dose due to ::entainment purge above rem and would thereby be completely unacceptable.
by a factor of 3400 to 176 000 Limiting the purge line valves to an opening of 50' could reduce offsite dose l
l to 64,000 rem and represents the least value which may be proposed within the L
licensing basis.
The BTp C$8 6-4 proposing that valve closure within 5 seconds will Note:
ensure purge valves are closed before the onset of fuel failures has since
- Further, been extended by the staff on a plant-specific basis to 15 seconds.
the writer cannot find any safety evaluation report supporting these positions.
These positions cannot be sustained for Zion since a) DNBR infringement (from Appendix K calculations) and hence fuel failure and gap activity release [Ref.
SRP 4.2) of 105 of core inventory (Ref. Regulatory Guide 1.77) occur within i second of the initiation of the LOCA, b) related maximum clad temperatures of c) RCS pressure in the 1750'F occur issnediately and never reduce below 1400'F region of the core rapidly reduces from 2250 psia to g60 psia in 7 seconds activity to the RCS inventory, d)p across the cladding for release increasing potential pressure dro the massive bulk boiling and blowdown surrounding the failed fuel ultimately discharges 270,000 lbs of RCS inventory into the containment at 7 seconds into the event increasing containment pressure from 0.3 psig to 23.8 psig (in these 7 seconds), and e) causes 15,000 lbs of the resulting containment inventory to be discharged to the environment through 2x42" fully open lines, or 5400 lbs for the same lines with valve closed to 50'.
3.0 CONCLUSION
The42"valvesatZionshouldremainclosedinModes1,2,3}and4becauseduring a LOCA the consequences of the offsite dose to thyroid (from iodine The least value is unacceptably high; whole body dose has not bean evaluated.
for offsite dose to the thyroid which may be proposed within the existing licensing basis is 64,000 res.
The conventio" pal treatment of BTP CS8 6-4 which assumes that fuel failure does not occur over the first 5-15 seconds after a LOCA and thereby that only RCS operating inventory of fission products is released to the containment, and then to the environment, cannot in general be sustained against thermal hydraulic analyses for containment response, and licensing basis requirements (including
)
criteria) for the calculation for, and the occurrence of, fuel damage and the quantification and treatment of the resulting source tems.
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References o
!a, 2.
Letter from P. C. Blond (CECO) to H. P. Denton (#RC):
Subject:
Zion, Units 1 and 2, Proposed Amendment to Facility Operating License i
Nos. DPR.39 and DPR-48 dated February !!,1986.
j W toc. Reed (Ceco);
Subject:
Offsite i
Letter from R. L. Kelley <'Nn) ment Furge, dated October 22,1986.
2.
Dese During LOCA and Contl t
3.
Letter to L. P. De1 George (CECO) from $.A. Varga (NRC):
Subject:
Generic Concerns of Purging and Venting Containments, dated September 9, 1981.
l
" Evaluation of the Risk at Zion ' dated August 14,198I.
Subject:
Memo for F. H. Robinson from R. W. Houston 4
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Units 1 and 2 i
Zion Nuclear Generating Stations,Opnetion Plant Name:
Containment Purge and Vent Yelve
$ER
Subject:
TAC Nos.:
65417/8 i
Susunary of Review /insoection Activities
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The licensee provided an evaluation of offsite doses undertaken in 1976. This was undertaken with a methodology and source tem chosen by the licensee. The licensee did not present results from alternetin more detailed methodologies l
which could be considered enforceable under existing regulatory positions and i
I the related circumstances.
Narrative Discussion of Licensee Performance - Functional Area l
The single only methodolog used by the licensee is not an acceptable approach for estimating doses under the proposed circumstances and especially since I
alternate detailed evaluations required by the $RP give greatly increased l
l values beyond 10 CFR Part 100 limits. A prudent approach would have recognized the tieficiencies and risks in the single methodology adopted with i
j resulting substantively different recesmendations to ensure public asalth and l
safety.
t l-Author: Robert B. A. Licciardo j
h
.Date:
May 11, 1989 1
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