ML20196F926
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R AUG 171977 MEMORANDUM FOR: Robert L. Baer, Chief, Reactor Safety Branch Walter P., Dutler, Chief, Plant Systems Branch Brian K. Grimes, Chief. Environmental Evaluation Branch '
Lawrence C. Shao, Chief, Engineering Branch 1 THRU: Darrell G. Eisenhut, Assistant Director for Operational Technology l
FROM: Dennis L. Ziemann, Group Leader, Systematic Evaluation Program l
SUBJECT:
SEP TOPIC CULLING - LACK OF SAFETY SIGNIFICANCE Enclosed for your cansideration are topic's that the SEP Group proposes to delete from the To;,1c List on +.he basis of lesser safety significance.
' The bases for our conclusions are provided in the enclosure for your review and coment by August 25, 1977. If no coments are received by August 26, 1977, your concurrence will be assuned and these topics will be deleted from the list. . . . . .
Oricinal s gno3 by:
Dennis L. Liecann
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' Dennis L. Zienann, Group Leader Systenatic Evaluation Program j
Division of Operating Reactors ,,
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Enclosure:
Topics of Lesser Safety Significance - - . _ . . _ _ . _... _. ,_
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8803040255 880229 PDR FOIA CONNOR87-854 PDR i
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C ENCLOSURE TOPICS OF LESSER SAFETY SIGNIFICANCE 11-3.0 Surface Water Pathways of Accidental Releases of Liquid Effluents II-3.E Ground Water Pathways of Accidental R,eleases of Liquid Effluents The review of these topics are needed only to estimate the consequences of radioactive liquid spills discussed in Topic XI-2.
Topic XI-2, "Control of Radioactive Wastes" has been removed from the Comprehensive List of SEP T'; pics on the basis of lesser safety, significance.
Similarly, these two topics have, therefore, also been culled from the list. ,
I III-10.A Passive Mechanical Valve Failures This topics is Issue 17 discussed in NUREG-0153. In that report the staff concluded that single passiva failure of valves need not be considered j as an initiating event of an anticipated operational occurence. It also concluded that the probability of a transient or an accident combined with a single passive mechanical valve failure is low enough that it does not warrant changes in present licensing practices or requirements.
VI-2.F Containment External Design Pressure with Respect to Containment Depressurization by Inadvertent Spray Operation The probability of inadvertent spray operation is judged to be of low magnitude - estimated to be of the order of not mqre than one in 200 :
reactor years of PWR experience or 1/200 (5 x 10-3).
The period of time the plant would be vulnerable (loss of containment integrity) would be litrited to the time required to safely bring the plant to cold shutdown, approximately 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />. l The probability of operation with loss of containment integrity with a l system vulnerable to a LOCA or potential release is then - 1 1
-6 l (5 x 10-3) ( 10 ) I 7 x 10 8460 If the grobability is's10-9 of having abecomes then the probability LOCA duriog thig)(10-4)
(7 x 10-0 period
= 7gfxvulnerability 10-10, This probability estimate is so low that the depressurization by spray operation'is unlikely and the problem is of lesser safety significance, i
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2-VI-4 Dual Containment Bypass Leakage .
Bypass leakage is only significant for those postulated accident scenarios which assume breaks of large reactor coolant system piping and i. very conservative estimate of the quantity of fission products released to the containment. The~ probability of a large reactor coolant system pipe break and such a conservative quantity of fission products being released to the containment is very Icw. Even if the fission products released to the containment bypassed the secondary containment filtration system they would in most cases have to pass through multiple barriers (e.g., pipes, valves, closed structures) before escaping to the atmosphere. These factors combined with the reasonable assurance of containment leak tightness which is periodically verified by testing results in a very low probability of significant offsite doses from containment bypass leakage.
Therefore it is concluded that this topic can be deleted from the SEP review on the basis of lesser safety significance.
VII-1.A Automatic Resetting of Reactor Trip System Trip Bistable Relay The concern for bistable relays that automatically reset when the offending channel exceeds its setpoint and then returns to normal is that the pro-tective action may not go to completion. The actual design requires a-pg scram to be initiated on the occurrence of two or more channel trips, and ,
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not a sir.gle channel, and since the system scram is sealed-in (action cannot be reversed) when two or more channels are tripped, lack of safety significance justifies deletion of the topic. (Basis from NUREG-013,8).
VII-1.0 Protection System Automatic Trip Point Changes for Operation with Reactor Coolant Pumps Out of Service This question was considered and deemed acceptable at the time each operating reactor was licensed. The t. rip setpoint changes are controlled administrative 1y by the plant technical specifications.
Secondary backup trips not requiring resetting would act to limit the consequences of transients and accidents if a setpoint was not changed, or incorrectly changed, during operation with reactor coolant pumps out of service. The probability of an operator error in changing a setpoint or forgetting to change it combined j with the probability of occurrence of a transient or accident not -
terminated by a secondary trip is exceedingly low. Therefore, {
we ha^ve concluded that the topic may be deleted as lesser safety significance and that our original position on the topic is still ,
valid, i
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XV-7A Analysis of Postulated Reactor Pump Seizure Incidents This incident assumes seizure of a reactor cbolant pump shaft with concomitant core flow reduction simultaneous with a loss of offsite l power. The probability of occurrence of the shaft break with simultaneous ;
loss of offsite power was judged by the staff to be too small to warrant t further consideration. (Basis from NUREG-0138).
XI-2 Control of Radioactive Wastes l This topic has been deleted from the Comprehensive Topic List on the basis of lesser safety significance. The expected failures of the gaseous, l liquid or solid radwaste systems will not exceed the 10 CFR Part 20 limits, l' based on past experience. Even if the worst possible failure of any of these systems is postulated to occur, it is calculated that the consequences will l,l not exceed the 10 CFR Part 100 guidelines.
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