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Summary of 790622 Meeting W/Representatives of Mark I Owners Group Re Uncertainties Associated W/Definition of Pool Swell Pressure Loads & Relative Significance of Uncertainties to Design of Structure
	ML19242C942
Person / Time
Issue date:	07/10/1979
From:	Charemagne Grimes; Office of Nuclear Reactor Regulation
To:	Eisenhut D; Office of Nuclear Reactor Regulation
References
	REF-GTECI-A-07, REF-GTECI-CO, TASK-A-07, TASK-A-7, TASK-OR NUDOCS 7908140216
	Download: ML19242C942 (5)
	v • d • e

04 Ar o s-UNITED STATES

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C WASHING TON, D. C. 20555 S 'k f.....j-JUI.10 779 Generic Task A-7 MEMORANDUM FOR:

D. Eisenhut, Acting Director, Division of Operating Reactors THRU:

G. Lainas, Chief, Plant Systems Branch, Division of Operating Reactors V. Noonan, Chief, Engineering Branch, Division of Operating Reactors FRCM:

C. Grimes, A-7 Task Manager

SUBJECT:

PROPOSED POSITION FOR POOL SWELL LOAD DEFINITION AND LOAD COMBINATICNS FOR THE MARK I CONTAINMEdT LONG TERM PROGRAM On June 22, 1979, we met with representatives of the Mark I Owners Group to discuss the uncertainties associated with the definition of pool swell pressure loads and the relative significance of these uncertainties to the design of the structure. The Mark I Caners expressed the concern that, while individual margins in the loading functions appear inconsequential, the cumulative effect could result in substantial modifications.

Tnis point was evidenced by Sclosure 1, in which they quantified the cumulative effect of the pool swell upward lead ccmbinations.

The staff noted that the local safety-relief valve (SRV) negative pressure peak is a more substantial contributor to 'ile upward load ccmbination than the margin for unc~tainties being suggested by the staff. We concluded that it wculd be more sensible, technically, to recensider the DBA (i.e., pcol swell) + SRV event cccbination, than to deliberate about the uncertain-ties in the. individual (e.g., upward pressure) loading centributors.

In the Short Tem Program, the DBA + SRV event combinaticn was excluded en the basis that the ccmbination did not reflect a "most prcbable" load conditicn and would be reassessed in the Lcng Term Program (LTP).

The rationale for this ccnclusion is discussed in Section III.D.9 of the Short Term Program Safety Evaluation Report, NUREG 0408.

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7908140916

JUL 10 D73 The LTP reassessment of this event combination considered (1) the potential for a mechanistic actuaticn c' the valves; and (2) the potential' for spurious actuation of an SRV. GE has advised us that primary system analyses have been performed which demonstrate that SRV cannot mechanistically (i.e., pressure) actuate under CBA conditions; hcwever, these analyses have not been submitted for staff eview.

In considering the potential for spurious actuation, we concluded that, although the probability of the event combination is icw, the capability of the structure to withstand the event combination, without loss of function, should be demonstrated.

These concerns were previcusly discussed with the Mark I Owners in September 1977 and a staff position, similar to the cne presented here, was presented to them at that time.

This approach is also consistent with our requirements for long-term application of drywell to wetwell differential pressure centrol (aP) as a load mitigating feature, which were presented to the Mark I Owners in October 1977.

The aP positicn similarly, requires that the capability of the structure to withstand the loading conditions without differential pressure control and without loss of function be demonstrated, even though the loss of differential pressure control is an unlikely event.

We recognize that our proposed position for the definition of pool swell upward loads (i.e., mean load + 15i, + 2c) provides a conservative load 7d we agree that unnecessarily compounded conservatisms should be avoided.

In this particular case, the bulk of the conservatism arises from ne postulated SRV discharge event; however, it cannot be comp 1 tely neglected.

Therefore, we propose that this problem be addre-sed by modifying the structural acceptance criteria for this par-ticui r event ccmbination in recognition of the improbability of the superposition of the peak loads.

This approach would require that GE submit the primary system analyses, supporting the non-mechanistic event coupiing, for DSS to review as part of the Task A-39 generic SRV loading issue.

The modified structural acceptance criteria can be summarized as follcas :

LOCA = Servi:e Level A LOCA + SRY = Service Leval C The " ark I Cwners expressed an interest in pursuing this position.

However, the representativs of the Owners Grcup indicated that their ccnc!usions are presently based en generic structural studies, while tN udividual plant-unique analyses m.y identify other prcblems, d.*[ J

JUL 10193 We believe that the proposed position will permit a reasonably conser-vative load definition without resulting in unnecessarily compounded conservatisms.

Therefore, with your concurrence and that of the cognizant D0R Branch Chiefs, the A-39 Task Manager, and the Director of the Unresolved Safety Issues Program, we discussed this apprcach with representatives of the Owners Group in a meeting held on June 29, 1979.

The structural acceptance criteria proposed by the Owners Group and agreed to by the staff are presented in Enclosure 2.

Similar acceptance criteria will be developed for the attached piping and concrete containment design (i.e., Brunswick).

C.Cymx

~

C, Grimes Plant Systems Branch Division of Operating Reactors

Enclosures:

As stated cc:

S. Hanauer

8. Grimes G. Lainas Y. Noonan M. Aycock R. Tedesco J. Knight W. Butler J. Kudrick C. Anderson N. Su R. Bosnak F. Schauer K. Wichman J. Fai r E. Adensam C. Grimes

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EllCLOSURE 1 POOL SWELL UPWARD LOAD COMBIt1ATI0ft LOAD CASE LOADif4G COMBIf1ATIDN TEf4SI0ri STRESS (kips)

( A) fl0MItlAL PS + EQ - DL 75 (B) RAtlDOM MARGIfl (PS + 20) + EQ - DL 90 (C) "15%" MARGIf4 (1.15 PS + 2a) + EQ - DL 125 (D) SRV - TEST LOAD (1.15 PS + 20) + EQ + SRV

- DL 185 test (E) SRV - LDR (1.15 PS + 2a) + EQ + SRV

- DL 235 LDR (F) HEALER IMPACT - SRSS (1.15PS+20)+EQ+(SRVfDR+HDR)g 2

- DL 242 (G) HEADER IMPACT - ABS (1.15 PS + 2a) + EQ + SRVLDR + HDR - m.

275 PS = Pool Swell Pressure Load EQ = Earthquake 1.oad I,

DL = Deadweight Load

.? I SRV = Safety-helief Valve Discharge Load '

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HDR = Header Inipact Reaction Load C

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ML19242C942

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SUBJECT:

Enclosures:

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