ML20086D155

Deficiency Rept Re Reinforced Concrete Compartment Walls of Intake Structure.Design of Auxiliary Salt Water Pump Compartments Reviewed for Tsunami Loading.Design Satisfactory

ML20086D155
Person / Time
Site:	Diablo Canyon
Issue date:	11/20/1972
From:	Searls F PACIFIC GAS & ELECTRIC CO.
To:	Kreusi F US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086D152	List: ML20086D155
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8311300223
Download: ML20086D155 (2)

Text

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O O PACIFIC OAS AND E LE C T RIC C O M PANY  !

M O tDi b l 77 BE ALE S TREE T . S A N F R ANCISCO, C ALIFO R NI A 94106 . (415) 781 4211 P R E D E R I C K T. S E A R L S US "),'U. . .

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Mr. Frank E. Kreusi ";;/L*;=:

Director Directorate of Regulatory Operations United States Atomic Energy Commission Washington, D.-C. 20545 i

Re: Dockets 50-275\ 50-323

Dear'Mr. Kreusi:

On October 19, 1972 we notified the office of the Directo-rate'of Regulatory Operations, Region V, that an incident reportable under paragraph (e) (1) (ii) of 10- CFR 50.55 appeared to have occurred in the design of the reinforced concrete compartments housing the auxiliary salt water pumps located within the'Diablo Canyon intake structure. This letter includes the written report summarizing our investigation of the past 30 days. '

The auxiliary salt water pumps provide sea water to the component cooling-system heat exchangers, which in turn remove heat from vital services within-the plant. There are two full-rized  ;

auxiliary aalt water pumps for each unit, each in a separate water-tight compartment within the main pump room'of the intake structure.

The auxiliary salt water pumps are Class I equipment and:are to be protected ' from a tsunami runup to elevation +30 feet MLIN (+27.4 feet MSL) .

A recent comprehensive design' review of the auxiliary salt water system revealed _ that the side walls 'of the compartments -had

. been designed for a hydrostatic head: of sea water to elevation +17.'5:

MSL on the judgment of the design engineers that flooding of the main -

pump _ room would be' limited'by the short duration'of the tsunami and the restricted inlets for water flow. This judgment was not supported by any. calculations.or'other verification at_the= time. The~recent de-

' sign' review :has shown:that calculations will not support the thesis that the - openings -in the structure would substantially ' limit the flood-ing'_of the main pump. room. Thus,-it appeared that~with the original wall design and with a design condition of hydrostatic ~ head to; elevation -

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4 Mr. Frank E. Kreusi 2 Novcmber 20, 1972

+27.4 MSL the calculated wall stresses exceeded the working stress i values established by ACI 318 of the American concrete Institute.

Therefore, it was not possible to demonstrate that these walls could

. safely withstand this condition.

The original design had been approved and issued to the field for construction, but the construction. work had not progressed to the stage of placing the walls when the deficiency was noticed.

The design has now been revised to accommodate the full hydrostatic forces, and the field construction crews have been issued revised drawings for the stronger walls.

The design of the auxiliary salt water pump compartments

, has now been reviewed in detail for the tsunami loading and appears to be fully. satisfactory. Additionally, the project design groups have been informed of the circumstances and have been alerted to design -situations where judgments are made whic.h cannot be supported by calculation.or other verification. The value of the comprehensive design reviews for finding such problem areas has been emphasized within the Company.

Very truly yours, 1,

CC: Mr. R. W. Smith

, Director, Region V 7

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