ML20137D423

Forwards Assessment of Consequences of Seismic Event at Big Rock Point Plant, Updating 830601 Weak Link Analysis,Per NRC Request Re SEP Topic III-6 on Seismic Design Considerations

ML20137D423
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	11/21/1985
From:	Frisch R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Office of Nuclear Reactor Regulation
Shared Package
ML20137D426	List: ML20137D423 ML20137D429
References
TASK-03-06, TASK-3-6, TASK-RR NUDOCS 8511270070
Download: ML20137D423 (5)

Text

o e Consumers Power Company oeneral offices: 1946 West Parnell Road, Jack on, MI 492e1 * (S17170s 0660 November 21, 1985 Director, Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLAhT -

INTEGRATED PLAN ISSUE 014 (SEP TOPIC 111-6) SEISMIC WEAK-LINK ANALYSIS UPDATE In our letter dated June 14, 1985, Consumers Power Company committed to provide an updat A report on resolution of Seismic Design Considerations.

Integrated Plan Issue 014 (SEP Topic III-6) by mid-October 1985. This commit-ment was also reflected in our Integrated Plan Semiannual Update 3 submitted on August 28, 1985. Verbal discussion between respective members of our staffs extended the report submittal to December 1, 1985. This submittal fulfills these previous commitments.

The initial seismic criteria as applied to big Rock Point were based on static requirements of the 1958 edition of the Uniform Building Code. The contain-ment design was based on a 0.05g horizontal static coefficient. The turbine building, concrete stack, intake structure, control room and rad waste storage buildings were designed based on a 0.025g horizontal static coefficient.

Piping design for seismic resistance was limited to the reactor vessel sup-ports and NSSS major piping. These components incorporated a 0.05g and a 0.025g horizontal static coefficient in the respective designs. The RDS was designed in 1974 in accordance with seismic design requirements as they existed at that time. These compare with more recent requirements which assume a 0.12g (Reg Guide 1.60) safe shutdown earthquake. The most signifi-cant activity with regard to establishing the seismic design of Big Rock Point has occurred in the last five years.

A complete review of the seismic design adequacy of the Big Rock Point Plant was initiated by the NRC staff early in 1979 as a part of Systematic Evalua-tion Program Topic 111-6. Plans were developed by Consumers Power Company and submitted April 25, 1979 with respect to important structures which were to be analyzed. The staff requested that major portions of the primary coolant loop 0011270070 051121 l'Dit ADOCK 05000155 l' PDH h

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Director, Nuclear Reactor Regulation 2 Big Rock Point Plant Integrated Plan Issue 014 November 21, 1985 be included in this initial structural analysis in July 1979. Initial struc-tural analyses employed Reg Guide 1.60 Spectra (anchored at .12g) while awaiting staff approval of a site specific seismic response spectra.

Preliminary results from analysis of 15 major site structures plus the primary coolant loop were submitted January 9, 1981 with the final report (by D'Appolonia) published August 26, 1981.

In July 1979 (IEB 79-14), the staff required all licensees to verify that the

' configuration of safety-related piping systems corresponded to that assumed in the plants existing design analysis. This activity resulted in an inspection of approximately 6000 feet of safety-related piping at Big Rock Point including examination of pipe geometry, support design, embedments, attachments and valve location and orientation. Results associated with this activity were published in October 1979, and were to be used eventually as input to the piping design review associated with SEP Topic III-6.

In January 1980, the staff published a formal request for the immediate identification and evaluation of important electrical equipment and its anchorage. As a part of the request, auxiliary failures which could result in the disabling or failure of safety related equipment (such as gas bottler, dollies, etc) were to be identified and evaluated as well. This Systematic l Evaluation Program work resulted in the identification, analysis, and

! anchorage of over 50 equipment itema. Among the major equipment important to safety were motor control centers, d!stribution panels, batteries and transformern. As requested, auxiliary equipment was also evaluated and included tanks, containers, cabinets and lighting located in the vicinity of

important safety equipment. The majority of the electrical equipment anchor-age work was completed by March, 1981.

In April, 1981 the staff requJeted a firm schedule for Completion of nelsmic design review activities. Included in their requent were not only the primary coolant loop but verification of fluid and electrical distribution system integrity and analyse 6 of the integrity and functionability of important mechanical and electrical equipment. Also requested was justification for continued operacion while the additional work was in progress. At this time the cost of evaluating this single SEP topic was well in excess of one million dollars and had at Icast as much evaluation and analysis awaiting completion as had been accomplished to date. In addition, work was ongoing in the development of renolutions to NRC questions raised with respect to work submitted to date. As a part of its justification submitted Jur.e 19, 1981 Consumers Power Company questioned the benefits of such an extensive, deter-ministic based reevaluation of the Big Rock Point ntructural design. Refer-enced were the results of the Big Rock Point risk assessment published in l

March, 1981 which suggested that neismic concerns represented only a small l contribution to the total risk of operation. Consumers Power Company proposed the detailed analyses completed to date used in conjunction with augmentation i of the PRA arguments would demonntrate a basis for concluding that meismic l risk at Big Rock Point was small compared to other contributors, and that l further determinintic analysen were not necessary.

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e O Director, Nuclear Aeactor Regulation 3 Big Rock Point Pli.nt Integrated Plan Issue 014 l

November 21, 198',

In a site visit. on June 30, 1981, the staff insisted that the deterministic approach was recessary and that the proposal to upt risk assessment as a basis for continued operation had little promise of working. Consumers Power l

Company submftted a plan for future evaluations with respect to SEP Topic III-6 an July 27, 1981 and on September 29, 1981, the staff concluded that our plan and justification for operation in the interim were acceptable.

Justificatfon was based on analysis of plant structures and systems performed to date, apparent inherent seismic resistance of remaining systems and struc-tures, an1 the low seismic hazard associated with the Big Rock Point site.

In April, 1982, as a part of its review of Consumers Power Company seismic evaluations that had been completed, the staff raised questions with respect to ao11 properties assumed in these analyses. This placed into question the adequacy of the Reg Guide and site specific spectra used in the analyses. In August 1982, work explicitly aimed at analysis of piping and equipment was suspended (except for model development) while these uncertainties were resolved.

I On October 19, 1982, the staff issued a draft SER with respect to the status of the seismic reevaluation of Big Rock Point. This report identified several areas of concern that the staff had with respect to the appropriateness and completeness of analysea performed to date. As a result, the staff stated that thuy were unable to come to a conclusion with respect to the seismic capability of the Big Rock Point Plant. They did conclude, however, that there existed inherent seismic resistance in the design of the plant, that operation was justified in the interim while the Integrated Assessment was performed and that alternato approaches to resolving this topic should be Investigated. ,

A meeting was held with the staff in December, 1982 in which Consumers Power Company wan encouraged to respond to the staff comments presented in the October SER. The staff concluded that because of the significant cost of continuation of the seismic analysis program it was recommended that Consumers Power Company consider and propose alternate approaches. These approaches could include bounding analyses with selected plant upgrading assessments of the consequences of failures, comparison of probabilistic risk and repre-sentative cross-sections of current plants, or combinations thereof. The resulting approaches would be considered in the Big Rock Point Integrated Plant Safety Assessment.

In June, 1983, explicit response to the etcff's concerns in their draft SER were provided in addition to the alternatives Consumers Power Company was proposing for final resolution of this SEP topic. The alternatives included a comparison of the risks associated with Big Rock Point Pinnt consequences on the health and safety of the public in comparison with a newer typical facil-ity, as the staff suggented. Also an approach to identifying, evalunting and upgrading the seismic "wenk-links" at Big Rock Point was presented with  :

explicit results. Commitmonts were made to upgrade the report to more com-plately identify the perceived weaknesses associated with the pinnt design, if the staff approved of the approach.

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Director, Nuclear Reactor Regulation 4 Big Rock Point Plant Integrated Plan Issue 014 November 21, 1985 In September and November of 1983 the staff and Consumers Power Company presented joint testimony before the Advisory Committee on Reactor Safeguards in regard to the alternate " weak-link" approach. The ACRS was requested to comment on the appropriateness of the proposed approach. In their testimony the staff concluded that the " weak-link" approach was prudent and correct for Big Rock Pm*nt. They intended to monitor its implementation in the form of analyses and backfits before concluding as to the level of protection afforded by the plant design against seismic events. Preliminary conclusions by ACRS members indicated that it was not necessary to get Big Rock Point up to the level of a new plant and that the " weak-link" approach was appropriate.

In May 1984, the final Integrated Plant Safety Assessment was published by the staff. In that report, both the staff and the ACRS conclude that the proposed

" weak-link" approach is appropriate and that they will continue to monitor its implementation.

The attached report is the firat update of the seismic " weak-link" evaluation published in June 1983 for the staff's comments. Commitments were made in that submittal, which along with staff and ACRS comments, have been incor-porated in the revised report. These commitments included l 1. Examination of motor operated valves in the core spray, emergency conden-

! ser and main steam systems to ensure that the valve operators will not impact surrounding structures if motion occurs during an earthquake (This examination has been completed and it has been determined that the main steam isolation valve is sufficiently restricted that it will not impact surrounding structures. Examination of the emergency condenser outlet valves ar.d core spray valves reveals that they may have the potential for impacting utructures in the vicinity. Bumpers are to be installed which ,

will preclude the valve operator frcm coming in contact with these  !

ntructuren in the event motion occurs). .

2. Complete the cable tray evaluations using criteria developed by the ,

Seismic Qualification Utilities Group and determine whether auxiliary I seismic dependencies exist for power and control cabling important to equipment included in the analysis (Results of the Seismic Qualification Utilities Group work on cable trays has been incorporated into the report.

Walkdown of conduit and cable traya has been completed and important equipment in the vicinity which could result in failure of these cables have been incorporated into the logic models).

3. Prnvent the cleanup demineralizer hoist from being an auxiliary failure

! for enclosure spray equipment (The cicanup hoist has also been identified as a potentini auxiliary failurt for core spray valve circuitry. A mechanical block precluding motion of the hoist over this equipment has been proposed).

4. Identify " weak-links" associated with equipment important to failure to acram (This evaluation includes examination of equipment such as control j

rod drive piping, control rod drive acchanism housings and reactor inter-l l

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Director, Nuclear Reactor Regulation 5 l Big Rock Point Plant Integrated Plan Issue 014 November 21, 1985 nals. This evaluation is utill in progress at this time and will be submitted as an addendum to the attached report when it becomes available.

Preliminary results indicate that the weakest components important to the ability to scram do not fail at ground accelerations comparable to the

" weak-links" identified in the attached report).

5. Update the " weak-link" evaluation, identify additional cost-effective seismic upgrading (see the attached report).

The attached report updates the original June 1, 1983 " weak-link" analysis as requested by the staff. Explicit identification of the weakest links with respect to the seismic design of Big Rock Point are presented. Proposals for their resolution and identification of future " weak-link" evaluations are identified. These backfits and proposals for future evaluation have been presented and ranked by the Big Rock Point Technical Review Group. Results of this ranking and schedules for their implementation will be provided as a part of future updates to the Big Rock Point Integrated Living Schedule.

C.

Ralph R Frisch Senior Licensing Analyst CC Administrator, Region III, USNRC NRC Resident Inspector - Big Rock Point Plant Attachment OC1185-0002-NI.02