ML20235H134

Forwards Response to 890208 Request for Addl Info on Proposed Increase in Control Bldg Wall Shear Forces.No Alterations of Major Structural Members of Complex Required to Accommodate Mods Already Installed

ML20235H134
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	02/15/1989
From:	Cockfield D PORTLAND GENERAL ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 8902230492
Download: ML20235H134 (7)

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Pbetlard General ElectricCervisy l~~ .

David W. Cockfield Vice President, Nuclear February 15, 1989 Trojan Nuclear Plant Docket 50-344 License NPF-1 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk ll Washington DC 20555

Dear Sirs:

Response to Request for Additional Information on Proposed Increase in Control Building Wall Shear Forces During a conference call with your staff on February 8, 1989, three questions previously provided by you on the proposed increase in Control Building shear ws11 forces were discussed. Attached is Portland General Electric (PCE) Company's response to these questions.

In addition, two new questions raised during this conference call concern-ing Technical Specification provisions allowing a 10 percent increase in control Building equipment weight, and the basis for increasing the control Building wall shear force limit to 3 percent, are also addressed. I sincerely,

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1 Attachmeet c: Mr. John B. Martin Regional Administrator, Region V U.S. Nuclear Regulatory Commission  !

Mr. William T. Dixon State of Oregon Department of Energy Mr. R. C. Barr '

NRC Resident Inspector Trojan Nuclear Plant i0 8902230492 990215 Ns PDR ADOCK 05000344 P PDC 121 S W SaWon Street, Portand Oregon 97204

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. Trojen Nucicer Plant Document Control Drak

- Docket 50-344 February 15, 1989 License NPF-1 Attachment Page 1 of 6 i

RESPONSE TO NUCLEAR REGULATORY COMMISSION (NRC)

REQUEST FOR ADDITIONAL INFORMATION ON PROPOSED INCREASE IN CONTROL BUILDING SHEAR WALL FORCES NRC Question Discuss the effect on the peak response frequency due to the use of.the 3 percent increase in weight, which appears to be larger than the actual reported increase in Table 1-1 of your submittal.

PGE Response The effect on the peak response frequency due to 3 percent increase in weight is discussed in Item 2, Shear Wall Reevaluation, Attachment A of PGE letter to the NRC, dated September 2, 1988, and is summarized below. ,

A 3 percent increase in the weight would result in a 1.5 percent increase in the period of the structure. For the Control-Auxiliary-Fuel Building (Complex), th6 "lcst and second modes of vibration dominate the overall structural responses in the north-south and east-west direc-tions, respectively. Higher modes of vibration, although having much less influence in the overall response of the structure, are also simi-larly affected. Therefore, the periods of the first and second modes can be used to illustrate the effects on spectral accelerations corres-ponding to a 1.5 percent increase in the period. The dominant period of the Complex in the north-south and east-west directions, based on the original STARDYNE analyses, are compared with the periods corresponding to the 3 percent weight increase as follows:

Frequency

• Increased (Cycles per Period Period Direction second) (Sec) (Sec) j North-South 7.62 0.131 0.133 East-West 9.89 0.101 0.103

• Table 3.3-1 of PGE-1020, " Report on Design Modifications for the Trojan Control Building" As can be seen from the Operating Basis Earthquake (OBE) Ground Response Spectra [ Final Safety Analysis Report (FSAR) Figure 3.7-1] attached, the change in the spectral acceleration at 2 percent damping is so slight that a difference in spectral acceleration cannot bt determined from the curve.

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. Trojan Nucicer Plcnt Docum nt Control Dsak Docket 50-344 February 15, 1989 Licence NPF-1 Attachment Page 2 of 6 NRC Ouestion Identify if the proposed Control Building modification will require altera-tion of structural components (i.e. , walls, floors, columns, beams etc.) in the Control Building or other Category I Structures at the Trojan site.

Provide detailed discussions of their impact on the FSAR commitments, if the above stated modifications are to take place.

pCE Response No alterations of major structural members of the Complex have been required to accommodate modifications already installed, and none are expected to be required to accommodate modifications planned for the 1989 refueling outage. Some attachments to structural members associ-ated with such modifications have been necessary in the past and will be in the future (attachments for new equipment support framing, anchor bolts, etc.). Modifications and attachments affecting structural components are performed in accordance with the structural design criteria described in Trojan FSAR Section 3.8, " Design of Seismic Category I Structures".

The total weight increase at the roof level of the Complex due to the modifications planned for the 1989 refueling outage, when combined with weight additions from previously installed modifications, will have the effect of increasing the lateral shear force on the upper story of the Complex up to the present Technical Specification 5.7.2.2(a), " Seismic Classification", limit of 1 percent. There will be essentially no margin available for weight additions for field change conditions which are likely to occur.

As stated above, all modifications to the Complex or other safety-related structures, have been and will continue to be in accordance with Trojan FSAR commitments. The only Trojan Plant License Change Applica-tion (LCA) with regard to our September 2, 1988 submittal, is associated with proposing that the present 1 percent increase limit in lateral shear forces on any story of the Complex per Technical Specification Section 5.7.2.2(a) be increased to 3 percent (see LCA 174, February 10, 1989).

NRC Ouestion The evaluation presented in your submittal addresses the effects of the Operating Basis Earthquake (OBE) on the structural evaluation. Please state why you have not addresu:d the effects of the Safe Shutdown Earthquake (SSE). Provide the results of the evaluation of the applicable structural components utilizing the SSE loads.

Trojen Nucleer Plant Docum:nt Control D sk

- Docket 50-344 February 15, 1989 License NPF-1 Attachment Page 3 of 6 PGE Response As indicated in Trojan Technical Specifications 5.7.2.2, the lateral shear forces in the Complex cannot be increased by more than 1 percent without prior NRC approval. Our September 2, 1988 submittal was developed specifically to address this issue. In the complete evalua-tion of the Control Building for control room emergency ventilation system modifications, control room annunciator upgrades, etc. , both horizontal and vertical evaluations were performed. The response in the vertical direction was evaluated for both operating basis earthquake (OBE) and safe shutdown earthquake (SSE). In the horizontal direction, however, only the OBE needs to be evaluated because of the unique seismic design criteria for the Trojan Plant and modifications made to the complex in 1980. The detailed results of the modifications and the conditions leading to them are reported in PGE-1020 and were the subject of several public hearings. A summary of these events is provided below:

An evaluation of the shear walls of the Complex indicated the SSE load combinations could be satisfied, but not the OBE load combinations.

This was the subject of public hearin5s in December 1978. The conclu-sion of the hearings was that the safety issues were satisfied by virtue of satisfying the SSE conditions. Since the OBE conditions could not be satisfied, it was ruled that margin must be restored to the Complex.

The Trojan Plant was allowed to operate at this point, while most of the modifications were being made since the SSE conditions had been satisfied. After the modifications were installed, the OBE criteria could be satisfied. As a result of these modifications, the shear capacity of the Complex was increased substantially and therefore, satisfies tha SSE load combinations by a large margin. Since the margin for the SSE is larger than for the OBE across the board in the hori-zontal direction, the OBE criteria controlled all locations. For this reason, only the OBE evaluation was reported since the limit of a 1 percent increase in the lateral shear forces of the Complex involves only the horizontal response.

NRC Ouestion Describe how the provision in Technical Specification 5 7.2.2 which allows, without prior NRC approval, an increase in equipment weight not to exceed 10 percent on a per story, per building basis is related to the September 2, 1988 letter.

PCE Response The exclusion of 10 percent of equipment weight per story, per building l was reviewed for applicability in the development of the evaluation i presented in our September 2, 1988 submittal. This provision would not

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Trojin Nuclocr Plant Docum:nt Control Desk

. Docket 50-344 February 15, 1989 License NPF-1 Attachment Page 4 of 6 provide the needed weight addition allowance because 10 percent of the equipment weight tributary to the control Building roof is only a small percentage (about 3.8 percent) of the allowance provided by the existing 1 percent lateral shear force increase per Technical Specification Section 5.7.2.2(a).

In general, becauae the contribution of equipment weight to total weight (structure and equipment) is small throughout the Complex, this provi-sion would not provide en exclusion from the 1 percent limit in any of the buildings.

NRC Ouestion Describe the basis for choosing a 3 percent limit in increar' )d lateral shear forces on any story of the Complex.

PCE Response The celection of a 3 percent weight increase limit was based on the following two considerations:

1. The total weight increase at the roof of the Complex due to modifi-cations planned to be performed during the 1989 refueling outage when combined'with weight additions from previous modifications will

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have the effect of essentially reaching the present 1 percent limit.

Modifications presently planned for subsequent years, including additional modifications to the control room emergency ventilation system and other proposed modifications, are expected to result in exceeding the 1 percent weight increase limit. It is, then, desired to have some weirht increase margin available to provide for these and other future modifications that may be required without the need to request an additional change to Technical Specification Section 5.7.2.2.

Other floor elevations in the Complex are not as sensitive to the 1 percent weight increase limit as is the Control Building roof (Elevation 117 feet) although Elevation 105 feet is also somewhat sensitive because the tributary weight upon which the 1 percent limit is based is not large (the addition of only 22.72 kips can .

presently be allowed, and this could be approached in 1990). Future weight increases at Complex elevations other than 117 feet and 105 feet are expected, but would probably remain as small percent-ages of the total weights. However, in our view, a Technical Specification written with varying percentage limits (shear force l

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Tr:Jen Nucicer Pitnt Document Control Drak

. Docket 50-344 February 15, 1989 LLicense NPF-1 Attachment Page 5 of 6 increase, shear resistance decrease, relative displacement increase, etc.) would be quite difficult to generate and would be unner,es-sarily complicated.

2. The reevaluation of the Complex was performed for a hypothetical weight addition of 3 percent at all mass points in the STARDYNE model, not just at the control Building roof. For this small percentage of weight increase, it was found that the seismic res-ponse characteristics of the complex were essentially unchanged.

The story shears would be increased linearly by 3 percent and still remain acceptable with adequate overall margins. Floor response spectra would not be noticeably affected, and interstructure rela-tive displacements would remain small and within the present Technical Specification limits. This reevaluation concluded that the 3 percent uniform weight addition, bounding the weight addition due to presently planned and expected future modifications does not result in structural considerations for the Complex that are sig-nificantly different from those previously reviewed and accepted.

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