ML14184A788
| ML14184A788 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 01/31/1991 |
| From: | Varga S Office of Nuclear Reactor Regulation |
| To: | Eury L Carolina Power & Light Co |
| References | |
| TAC-72969 NUDOCS 9102050131 | |
| Download: ML14184A788 (5) | |
Text
otxIR REG&~
UNITED STATES A
NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 January 31, 1991 Docket No. 50-261 Mr. Lynn W. Eury Executive Vice President Power Supply Carolina Power & Light Company Post Office Box 1551 Raleigh, North Carolina 27602
Dear Mr. Eury:
SUBJECT:
SINGLE FAILURE CRITERION, ELECTRICAL SYSTEMS - H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 (TAC NO. 72969)
On March 17, 1989, the NRC wrote you a letter requesting you to respond, under the provisions of 10 CFR 50.54(f), with an outline of those actions, taken or planned, regarding the single failure evaluation of the emergency core cooling system (ECCS) and other safety systems.
By letters dated April 19, May 19, and June 14, 1989, you responded to the staff's request. The staff has had a number of discussions with you on the method and scope of your evaluation. These discussions include two meetings on April 19, and November 20, 1990 (Ref: Meeting Summaries issued on May 14, 1990 and December 6, 1990, respectively) and your response on August 3, 1990. The purpose of this letter is to document our understanding of your actions and to determine their adequacy as a response to our request under 10 CFR 50.54(f).
You stated that H. B. Robinson Steam Electric Plant, Unit No. 2 (HBR2) was not designed, constructed and licensed to be in conformance with 10 CFR Part 50, Appendix A, General Design Criteria (GDC), as formulated in its final revision in 1971. Specifically, you state that certain provisions of GDC-17, such as two independent circuits from the transmission network to the onsite electrical distribution system and the current definition of an electrical system single failure, do not apply to HBR2. As to single failure assumptions, you stated that the emergency power design criterion (Section 3.1.2 of the Updated FSAR) commits for failure of a single active component without the consideration of passive components. Nevertheless, your response to the staff's 50.54(f) request commits, for the ECCS, to meet the single failure criterion under the requirement of 10 CFR 50.46. As to the single failure criterion as applied to other safety systems, you are performing an electrical distribution system design basis review program and a plant-based probabilistic risk assessment program. You stated that the overall objective of these programs is to assure that the plant meets the basic intent of the GDC which, in part, states that the onsite electrical power "shall have sufficient independence, redundancy...assuming a single failure."
9102050131 910i31 PDR ADOCK 05000261 V
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Mr. Lynn January 31, 1991 For the single failure evaluation of the ECCS, you have embarked on a failure modes and effects analysis (FMEA) program, which is performed in accordance with industry standard IEEE 352. The scope of the ECCS, as defined in Section 6.3 of the HBR2 Updated FSAR, includes the high-head and low-head safety injection pumps, the safety injection accumulators and the refueling water storage tank. You reported that approximately 3,500 potential failures and their effects have been analyzed and none of the effects was identified to be more damaging than those previously evaluated and submitted to the NRC to demonstrate compliance with the ECCS regulation. Therefore, you conclude that these results tend to confirm that the acceptance criteria of 10 CFR 50.46 are being met with the ECCS evaluation model, including consideration of electrical single failure of passive components as stipulated in Appendix K.
As to the issue of single failure vulnerability of the onsite electrical system components, other than those addressed in the FMEA evaluation related to the ECCS, you are performing a design basis electrical distribution system review.
This design basis review indicates that the on-site emergency power system was designed for two redundant electrical trains, each of which represents an independent power supply system with 100% emergency load capacity.
Your review also found that the two redundant power supplies were designed with separation attributes, such as functional and spatial separations. Although the licensing basis is for the availability of power to safety equipment assuming failure of a single active component, the design basis review, to date, concludes that passive electrical system single failure vulnerabilities, if they exist, are bounded by short circuits in cable routings (e.g., due to non-safety cables in cable trays of the two redundant safety trains). The electrical distribution system design basis review will also include a number of cable walkdowns to further identify and evaluate potential single failure vulnerability. Although the design basis of the H. B. Robinson electrical distribution system does not meet the GDC for single failure of passive electrical components, you contend that the design basis review along with the plant-based Probabilistic Risk Assessment to scope potential risk-significant failures would provide adequate assurance for meeting the intent of the GDC on single failures. As stated in your letter dated August 3, 1990, the results of the PRA are used to maintain the overall core damage frequency within the goals of the Severe Accident Policy/IPE generic letter by taking the necessary action for improvement, i.e.,
changes to design, procedures and/or training.
As a result of our review of your position, we agree your programs, when completed, would adequately demonstrate that: (1) the ECCS meets 10 CFR 50.46 requirements with the current single failure criteria for electrical components and (2) the redundancy and separation design features of the on-site electrical distribution system are such that the safety significance of any discrepancy on meeting current single failure criteria for electrical system components other than those related to the ECCS is low and bounded by the plant-based PRA.
Mr. Lynn W. Eury
-3 Therefore, pending your submittal of the results of these programs, the staff finds your action plan to be an adequate response to our requests made under 10 CFR 50.54(f).
Sincerely, Orgiwal signed bt Steven A. Varga, Director Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation cc:
See next page DISTRIBUTION See attached page
- SEE PREVIOUS CONCURRENCES OFC
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- 1/S(j91 OFFICIAL RECORD COPY Document Name:
LTR EURY 72969
Mr. L. W. Eury H. B. Robinson Steam Electric Carolina Power & Light Company Plant, Unit No. 2 cc:
Mr. R. E. Jones, General Counsel Mr. Dayne H. Brown, Director Carolina Power & Light Company Department of Environmental, P. 0. Box 1551 Health and Natural Resources Raleigh, North Carolina 27602 Division of Radiation Protection P. 0. Box 27687 Raleigh, North Carolina 27611-7687 Mr. H. A. Cole Special Deputy Attorney General Mr. Robert P. Gruber State of North Carolina Executive Director P. 0. Box 629 Public Staff'- NCUC Raleigh, North Carolina 27602 P. 0. Box 29520 Raleigh, North Carolina 27626-0520 U.S. Nuclear Regulatory Commission Mr. C. R. Dietz Resident Inspector's Office Manager, Robinson Nuclear Project H. B. Robinson Steam Electric Plant Department Route 5, Box 413 H. B. Robinson Steam Electric Plant Hartsville, South Carolina 29550 P. 0. Box 790 Hartsville, South Carolina 29550 Regional Administrator, Region II U.S. Nuclear Regulatory Commission Mr. Heyward G. Shealy, Chief 101 Marietta Street Bureau of Radiological Health Suite 2900 South Carolina Department of Health Atlanta, Georgia 30323 and'Environmental Control 2600 Bull Street Mr. R. Morgan Columbia, South Carolina 29201 General Manager H. B. Robinson Steam Electric Plant P. 0. Box 790 Hartsville, South Carolina 29550
DISTRIBUTION Docket File NRC PDR Local PDR S. Varga 14-E-4 G. Lainas 14-H-3 L. Reyes RH E. Adensam 14-B-20 F. Rosa A. Thadani J. Moore P. Anderson 14-8-20 R. Lo 14-B-20 OGC (For inform. Only) 15-B-18 E. Jordan MNBB-3302 ACRS (10)
P-315 Robinson File