ML19343D361

LER 81-031/01T-0:on 810415,notified by Scsi That Wall C130-39 in Plant Control Bldg Had Local Stress Exceeding Design Allowables.Caused by More Conservative Stress Criteria in Ieb 80-11 than in Original Design

ML19343D361
Person / Time
Site:	Hatch
Issue date:	04/28/1981
From:	Coggin C GEORGIA POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19343D359	List: ML19343D358 ML19343D361
References
IEB-80-11, LER-81-031-01T, LER-81-31-1T, NUDOCS 8105040341
Download: ML19343D361 (3)

Text

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EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h l0 l 2 l lon 4-15-81, with Unit 1 in the refueling mode and the Unit 2 reactor in l i o i3, inormal power operation at 740 MWe, the plant was notified by SCSI that I o 4 l wall C130-39 in the Plant Hatch Control Building has a local stress l lOlsiIwhich exceeds design allowables during a postulated OBE and/or DBE. Thisl 10 Ic I loverstress con'dition was determined in the process of responding to l l 0 l 7 l lIEB 80-11. This is a repetitive occurrence - see LER 50-321/1980-115. I iogi;There were no effects on public health or safety due to this event. I E CODE SUSC E COMPONENT CODE SUBC dE SU E loial 'l xl xl@ [xj@ [x 9 10 12 _

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS 27 i,,og;The acceptance criteria for allowable stresses during a postulated i i,,,,jearthquake utilized in the response to IEB 80-11 are more conservative i

, , ;than the criteria utilized in the original design of the wall. The wall i

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.g LER #:. 50-321/1981-031

< Licensee: Georgia Power Company T

' Facility-Name: Edwin'I.' Hatch

.Q m - Docket #:- 50-321 -

. Narrative Report' '

for LER- 50-321/1981-031 .

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On 4-15-81, with Unit 1 in'. the refueling --mode; and Unit .2 -in normal steady state- operation at 740 MWe, .the ' plant- was ' ~.

notified by SCSI that wall C130-39 in the Plant ^ Hatch Control Building requires a minor modification - to lower the calculated stresscs et one localized section of the wall to within design allowables during a postulated DBE and/or OBE. SCSI had performed a reanalysis of wall- C130-39 in response to- a

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Bechtel letter indicating that additional evaluation should be performed on certain. concrete- masonry walls which were ',

analyzed in the 180-day response . to IEB 80-11.- This is a .

repetitive occurrence - see LER 50-321/1980-115.- .There were no effects on public health or safety due to this event.

The acceptance criteria for design allowable stresses during a postulated earthquake used in the 180-day response to IEB 80-11 are more conservative than the design criteria : utilized -

pd in the original design of concrete masonry - walls. The new-acceptance criteria caused wall C130-39 to have a calculated stress which slightly exc'eeded design allowables.- Wall' C130-39 will be modified to relieve the overstress condition when materials are available.

The concrete masonry walls at Plant Hatch are reinforced vertically and horizontally. Horizontal extra-heavy Durowall reinforcing is provided in the ' mortar' joint at every block course. Vertical reinforcing is provided at l'4" or. 2'3" centers (maximum spacing) for solidly filled and partially filled walls, respectively. The walls are tied mechanically to the supporting columns 'or walls, and to the floor supporting the walls by dovetail stone anchors, expansion .

anchors, and reinforcing dowels. .

The reinforcing will serve to distribute wall loads and " hold" the wall together in the event an carthquake should occur.

This would tend to ensure that blocks will not be indiscrimin,ately tossed about, even though local cracking -

might occur.

The floor response spectrum for the floor located above the wall was used in the analysis as a conservatism.

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Although v211 'C130-39 in the Plant. Hatch Control Building

(), shows local stress above the code allowables during an OBE and/or Dub, it is unlikely that the wall will totally coJ1 apse and render safety related equipment or systems ' inoperable.

The following considerations were used to substantiate this conclusion:

1.- The overstress condition identified is a localized condition only.

2. The overstress condition is based on code allowables not-material yield' stresses or ultimate stresses.

3. As local yiciding takes place the wall will -lose _ some . of -

its ability to carry load at the point of local yielding,_

and the stresses will be distributed to adjacent elements via the reinforcing and ma:.onry thus spreading- out' the loads. -

4. If local cracking develops in the masonry ~during an earthquake the wall loses its ability to transmit - -

stresses across the ' discontinuity at the crack; therefore, damping is. increased and earthquake forces are not as readily transmitted throughout the wall.

5. Maximum wall displacements identified from our seismic analyses are less than .02" for the wall. This small displacement should not degrade ' the integrity of safety related equipment in the event of an earthquake.

Local points of attachment to the wall were checked to verify-that no local failures would occur during an earthquake. 4 O'- modes no of failure at local attachments were investigated, and overstresses were identified when compared with code allowables. .

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