,· UNITED STATES

NUCLEAR REGULATORY COMMISSION WASH1NOTON, 0 . C. 20S~S

April 16, 1993

Docket No . 50-285

Mr. Terry L. Patterson Division Manager - Nuclear Operations Omaha Public Power District 444 South 16th Street Mall Mail Stop 8E/EP4 Omaha, Nebraska 68102-2247

SUBJECT: SAFETY EVALUATION OF ALTERNATE SEISMIC CRITERIA AND METHODOLOGIES - FORT CALHOUN STATION (TAC NO. M71408) ·

By letter dated December 2, 1988, Omaha Public Power District (OPPD) submitted for tlRC review and approval, a proposed document regarding alternate seismic criteria and methodologies (ASCM) for the Fort Calhoun Station. These alternate criteria were proposed by OPPD as an alternative to the existing updated safety analysis report (USAR) criteria and methodologies. The document was intended to provide an alternate basis for future new designs, modifications, as well as reanalyses of piping and pipe supports, electrical raceways, heating, ventilation, and air conditioning (HVAC), and anchor bolts.

The staff review of the above document was assisted by Brookhaven National labortory (BNL), the staff's consultant. Its review found that while the above ASCM consisted of the use of more recent Codes and Standards, it also proposed several exceptions to the American Society of Mechanical Engineers Boiler and Pressure Vessel (ASHE) Code requirements. Although some of the exceptions proposed have been allowed by the NRC on a case-specific basis at certain plants, they have not been endorsed for general use . An extensive list of questions was generated by BNl which resulted in a request for additional Information (RAJ), that was sent to OPPD on December 6, 1989.

In responding to the above RAl, OPPD reevaluated the proposed alternate criteria and decided to respond only to questions they felt were of primary importance; those which were most needed or offered the mJst significant benefit. Consistent with that approach, the scope of the ASCM document was reduced significantly. BNl reviewed the responses and generated a second series of questions, which resulted in another RAJ to OPPD on June 3, 1991. OPPD and its consultants subsequently met with staff and BNL at NRC headquarters on September 5, 1991, and on April 23 , 1992, to clarify the issues and discuss approaches for final resolution of the remaining open items.

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Hr . Terry L. Patterson -2-

OPPD subsequently submitted a revised ASCH document, along with responses to the remaining questions on July 31, 1992. The revised document provided alternate seismic analysis methods for piping and HVAC systems as well as alternate seismic criteria for HVAC systems . Based Qn the final evaluation by the staff and BNL, it is concluded that the proposed seismic analysis methods for piping and HVAC are acceptable. The proposed HVAC qualification criteria based on analysis or testing are also acceptable, with the exception of damping values for non-rectangular cold-formed duct structures, which would need further staff review. The ASCH also proposed HVAC qualification by experience data, but was unable to provide the source of the data. The staff concludes that the use of this approach is not acceptable at this time . However, OPPD agreed that if this approach was to be pursued, supporting experience data and the methodology would be submitted for NRC review and final approval prior to Its application .

The staff has completed its review of the additional material submitted by OPPD in compliance with commitments made during the April 23, 1992, meeting held at the NRC headquarters. The commitments relevant to this portion of the review of the ASCH were:

1. OPPD agreed to generate floor response spectra using ground motion time histories whose spectra envel ope the corresponding 0. 17g Housner spectra published in the Fort Calhoun USAR and which have acceptable power spectral densities.

2. OPPD agreed to extend its soil-structure interaction analysis (SSI) to include two additional cases of soil p~operties, namely, the "lower bound' (LB) soil property equal to 70% of the 'best estimate• (BE) soi l property (0 .7BE), and the •upper bound' (UB) soil property equal to 130% of the BE soil property (1 .3BE) . The ASCH floor response spectra (FRS) will be obtained from the envelope of the UB FRS, the LB FRS, and the BE FRS broadened by +15% and -15% obtained earlier by the licensee .

3. OPPO agreed to provide addit ional information regarding the issues of a) overturning and sliding, and b) accidental torsion brought up in the course of the review.

4. OPPD also agreed to provide additional information on soil compaction and liquefaction.

Based on a review of the additional information provided, the staff finds that OPPD has satisfactorily answered the questions raised by the staff in the structural engineering and geosciences areas . Therefore, the staff considers that the remaining open items related to the structural and geosciences areas of the Alternate Seismic Criteria & Methodologies are closed . However, the staff would like to audit the licensee ' s calculations in the structural and geosciences areas at a mutually convenient time.

Mr. Terry L. Patterson -3-

Th is completes the NRC s l ~ff review of ASCM and closes TAC No. M71408. If you have any questions regarding this issue, please contact me at (301) 504 - 1313 .

Enclosure : Safety Evaluation

cc wtenclosure : See next pag~

DISTRIBUTION: Docket File PD4 - l r/f PNoonan MVirgilio ACRS (10) ABeach, RIV GGiesv -Koch GBagch i

NRC & LPDRs SBloom JRoe GHubbard OGC (IS- B- IB) Alee RPichumani JNorberg

• ee prev1ous concurrence

OFC LA/ PD4- I ,) i PM/Fl:J4-l ·" sBtromTv NAME PNoonan

DATE ./ I I ·/93 H J1 (,t93

Sincerely,

ORIGINAL SIGNED BY :

Steven Bloom, Project Manager Project Directorate IV-I Division of Reactor Projects - 111/IV/V Office of Nuclear Reactor Regulation

ECGD• EMEB* D/PD4- tJft GBagchi JNorberg GHubbard

4/12/93 4/13/93 t ) t)t/!93

OFFICIAL RECORD COPY Document Name: FC71408 . SER

Hr . Terry L. Patterson -3-

This completes the NRC staff review of ASCH and closes TAC No. H7!408. If you have any questions regarding this is sue, please contact me at (301) 504-1313 .

Enclosure: Safety Evaluation

cc w1enclosur2 : See next page

OISTRIBUTIOtl: Docket File PD4-1 r/f PNoonan ~Virgilio ACRS (10) ABeach , RIV GGiese-Koch GBagchi

NRC & LPDRs SBloom JRoe GHubbard OGC (15-B-18) Alee RPichumani Jtlorberg

*See previous concurrence

OFC LI\/P04-Di PH/I\J4-1

tlAME /!.-

Ptloonan '• ssffomrv

DATE . / //} /93 ~ !fv/93

Sincerely,

ORIGINAL SIGNED BY:

Steven aloom, Project Manager Project Directorate IV- I Civision of Reactor Projects - 111/IV/V Office of Nuclear Reactor Regulation

ECGD* EHEB* D/PD4-~ GBaQchi Jtlorberg GHubbard

4/12193 4113/g3 IJ ,)~193

OFFICIAL RECORD COPY Document Name: FC7!408.SER

Hr. Terry l. Patterson -3-

This con,pletes the NRC staff review of ASCH and closes lAC No. H71408 . If you have any questions regarding this Issue, please contact me at (301) 504-1313.

Enclosure : Safety Evaluation

cc wtenclosure: See next page

Sincerely,

Steven Bloom, Project Manager Project Directorate IV-I Division of Reactor Projects - Ill/IV/V Office of Nuclear Reactor Regulation

Hr. Terry L. Patterson Omaha Public Power District

cc:

Harry H. Voigt, Esg . LeBoeuf, lamb , Leiby & MacRae 1875 Connecticut Avenue, ~~ Washington, D.C. 20009-5728

Hr . Jack Jensen, Chairman Washington County Board

of Superv i•~ ·· Blair, Nebra ~~ij 6BOOB

Hr . Raymond P. Mullikin, Resident Inspector U.S. Nuclear Regulatory Commiss i on Post Office Box 309 Fort Calhoun, Nebraska 6B023

Hr . Charles B. Brinkman, Manager Wash ington Nuc l ear Operat ions Combustion Eng ineering, Inc . 12300 Twinbrook Parkway, Suite 330 Rockv i lle, MD 20BS2

Regional Admin i ~trator, Region IV U.S . Nuclear Regulatory Commission 611 Ryan Plaza Drive , Sui te 1000 Arlington, Texas 76011

Harold Borchert, Director Division of Radiological Health Nebraska Departme nt of Health 301 Centenn i al Hall, South Post Office Box 95007 lincoln, Nebraska 68509

Hr. James W. Chase, Manager Fort Calhoun Stat ion Post Office Box 399 Fort Calhoun, Nebraska 68023

Fort Calhoun Station, Unit No. 1