ML19291C052
| ML19291C052 | |
| Person / Time | |
|---|---|
| Issue date: | 08/10/1979 |
| From: | Meyer R Office of Nuclear Reactor Regulation |
| To: | Hanauer S Office of Nuclear Reactor Regulation |
| References | |
| REF-GTECI-B-06, REF-GTECI-PI, REF-GTECI-RV, TASK-B-06, TASK-B-6, TASK-OR NUDOCS 8001110191 | |
| Download: ML19291C052 (3) | |
Text
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- MEMORANDUM FOR:
S. H. Hanauer, Assistant Director for Plant Systems, DSS FROM:
R. O. Meyer, Leader, Reactor Fuels Section, Core Performance Branch, DSS
SUBJECT:
UtiRESOLVED SAFETY ISSUE B-6 A month ago I promised you some words that would clarify the background and goals of B-6.
I found that difficult so I went on vacation, flow that I'm back, things seem clearer and my summary is enclosed. My con-clusion is that combination of loads is not an unresolved issue, and I believe TAP B-6 could be closed out.
s
" *A Ralph 0. Meyer, Leader Reactor Fuels Section Core Performance Branch Division of Systems Safety
Enclosure:
As Stated,-
cc:
M. Aycock R. Mattu 1734 199 8001110
Enclosure Comments on Unresolved Safety Issue B-6 General Design Criterion 2 is not clear about whether to combine major accident loads with major (but unlikely) natural loads or whether to combine them with minor (but likely) natural loads. A clear inter-pretation of GDC-2 has never been made by NRC; that is, whether to combine (major) loads has not been decided definitively.
One line of thought is that a seismically caused LOCA should be analyzed
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as a design-basis accident (DBAl becauce major natural phenomena (earth-quakes) might increase the probability of a major accident (.a LOCA).
This is an illogical position because the piping is designed to with-stand earthquakes without damage (loss of integrity).
Another line of thought is that loads should be combined on components whose failure could lead to a LOCA to increase the protective margin aginst a LOCA because earthquakes might increase the probability of a LOCA.
This is an illogical position because the LOCA load is entirely irrelevant if the LOCA is to be prevented. To accomplish this goal, one should just increase the seismic margin for those componets.
Notwithstande the lack of logic in these arguments, seismic and LOCA loads have been traditionally combined for some components.
Since we are a regulatory agency with statutory responsibilities, precedents are important and we must take overt action to change procedures that we are currently following. We could now do any of the following:
(a) Declare that there is no need to combine loads, for reasons sug-gested in the above paragraphs, and admit that we had previously failed to reach an obvious conclusion.
(b) Continue an illogical review as we have been doing (i.e., follow precedent) since no present information clarifies the need to combine loads.
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(c) For only those components for which we currently combine loads, make the conservative assumption that a seismically caused LOCA is a DBA and justify SRSS; this is a variation of (b).
(d)
Investigate the seismic margin on components whose failure could lead to a LOCA; this is confirmatory research, which is being per-formed.
(e)
If (d) shows inadequate margin, increase the seismic margin.
(f)
If (d) shows inadequate margin and if (e) is not achievable, declare that a seismically caused LOCA is a DBA.
(g) Declare as a matter of licensing philosophy (defense in depth) that a seismically caused LOCA is a DBA.
Of all of these options, only (f) and (g) constitute an unresolved safety issue. The research that would lead to (.f) will not be finished for several years, and I have seen no interest in (g).
For all other options we know exactly what to do legally and technically so that TAP B-6 could be closed out immediately.
1734 20i
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