ML20032B076
| ML20032B076 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 10/26/1981 |
| From: | Pilant J NEBRASKA PUBLIC POWER DISTRICT |
| To: | Ippolito T Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0661, RTR-NUREG-661 LQA8100261, TAC-07934, TAC-7934, NUDOCS 8111040357 | |
| Download: ML20032B076 (3) | |
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M__ Nebraska Public Power Distn. t GENERAL OFFICE P. O. box 499, COLUMBUS, NEBRASKA 68601 c
mErno~E son sensei LQA8100261 M
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October 26, 1981 9
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Director, Nuclear Reactor Regulation Atta:
Mr. Thomas A. Ippolito, Chief g
Operating Reactors Branch No. 2 Division of Operating Reactors Oz U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Summary of Technical Decisions Mark I Containment Modification and Analysis Approach Cooper Nuclear Station NRC Docket No. 50-298, DPR-46
Reference:
1)
U.S. NRC, " Summary of Meeting held on May 22, 1981, with Mark I Owner's Group," issued June 1, 1981 by B
L. Siegel, Program Manager, Mark I LTP Implementation.
- 2) GE Letter (S. Stark) NEW 223-18 to U.S. NRC (T. Ippolito) dated June 29, 1981.
Subject:
Containment Modification Status Summary.
Dear Mr. Ipollito:
In January of this year, the NRC issued an Order for Modification of License and Grant of Extension of Exemption to NPPD as holder of Facility Operating License DPR-46 for Cooper Nuclear Station (CNS).
This Order requires completion by September 30, 1982 of all CNS plant modifications necessary to assure conformance with the acceptance criteria contained 4. Appendix A of NUREG-0661.
At a subsequent NRC meeting with Generam Electric and the Mark I Owner's Group, the staff requesten that Licensees notify the NRC of any alternate analytical P
approaches or interpretations of the criteria to be used in program implementation (reference 1).
This letter is written in response to that request.
It has been NPPD's belief that the best manner of addressing this generic issue involves installing required hardware modifications to the plant in the most timely fashion, while minimizing the hardship caused by extended outages.
This approach is substantiated by our containment modification program, which the District feels has been quite responsive.
\\OS{D 8111040357 811026 PDR ADOCK 05000298 P
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.e Mr. Thomas A. Ippolito October-26, 1981 Page 2 Of major note is the fact tha~ the Mark I containment evaluation for CNS has resulted in.the following:
- Significant upgrading of the torus support system including installation of saddle supports at all miter locations, column reinforcement, anchorage of column supports, and reinforcement of the ring girder and column-to-shell connections.
- Installation of deflectors below the vent header, reinforcement of the vent header at the downcomer intersections, and instal-lation of new downcomer restraints.
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- Relocation and/or reinforcement of nearly all submerged structures and piping in the torus.
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- Major modifications to all eight S/RV discharge ~ lines,' including addition of reinforcement of 89 drywell supports, installation of 16 new vacuum breaker valves, reroute and resupport of the wetwell portion of the lines, and replacement of all ramshead discharge. devices with T-quenchers.
- Identification of necessary additions or modi.Tications to supports on all torus attached piping systems to enable completion of these modifications by the Order deadline.
l-The status of the containment system modifications for CNS was~re.:ntly forwarded to the NRC by GE on behalf of the Mark I Owner's Group (reference 2).
i To evaluate the need for these modifications, it has been necessary to perform very complicated and costly analyses. These analyses have required a significant number of timely decisions to insure meeting our difficult program schedule commitment. We believe it appropriate at this time to summarize key decisions which are at variance with NRC acceptance criteria.
1.
In the analyses of structures for condensation oscillation (CO) loads, the 50 individual load harmonics will be combined using a realistic phasing technique. This phasing procedure has already been justified through both analytical and empirical studies, and in combination with
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other conservatisms in the CO analysis procedure produces a conservative design basis for evaluating containment components.
lu. : 'o.
P Mr. Thomas A. Ippolito October-26,1 198L Page 3 2.
In the calculation'ofLtorus shell pressure loads due'to multiple S/RV actcations, a modified SRSS technique using
'a-1.2 multiplier has been used instead of'the absolute sum combination method. Plant-unique statistical. studies show that the' modified SRSS method bounds peak pressures with an appropriate confidence level.
3.
For piping analysis, dynamic responses due.to S/RV discharge and LOCA loads are being combined by a modified SRSS method with a multiplier of 1.1 on the SRSS of the. response of the e
two loads.
This approach is an extension of the CDF procedure allowed by the structural acceptance criteria and will be supported by further plant-unique statistical studies.
4.
ASME code allowables for shell buckling will not be used' I
in the evaluation of the torus shell. Generic analyses performed in the Mark I program have demonstrated that torus buckling will not. occur as a result of LOCA and S/RV discharge dynamic loads.
Since the CNS torus shell geometry has a lower diameter / thickness ratio than the torus shell considered in the generic study, the results of this study can be conservatively applied to the CNS configuration.
We feel that this approach is in accordance with the intention of the ASME code.
5.
Fatigue. evaluations of all Class 2/3 piping systems, including S/RV discharge lines 'and torus attached piping, 'will be performed in accordance with standard ASME code procedures.
Further upgrade of fatigue requirements is not required due to conservatisms inherent in the existing methods.
Detailed evaluations of representative and critical piping systems-will be used to-demonstrate these conservatisms and verify-the adequacy of all Class 2/3 lines for fatigue considerations.
Should modifications associated with fatigue be required, these will be considered separate from the existing Order deadlines.
Although a great deal of progress has been made, we have not completed all analysis and design work and other issues may require resolution.
We will notify the Staff if other decisions are required, but will continue to move expeditiously toward completion of the containment modification program.
Sincerely yours, g
Jay M. Pilant Division Manager of Licensing and Quality Assurance
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