ML20235H498
| ML20235H498 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 09/23/1987 |
| From: | Stolz J Office of Nuclear Reactor Regulation |
| To: | Mroczka E NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| TAC-66050, NUDOCS 8710010076 | |
| Download: ML20235H498 (3) | |
Text
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l September 23, 1987 Docket No.:
50-423
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1' Mr. Edward J. Mroczka
{
Senior Vice President i
Nuclear Engineering and Operations j
Northeast Nuclear Energy Company l
l Post Office Box 270 l
l Hartford, CT. 06141-0270
Dear Mr. Mroczka:
SUGJECT: CLASS lE CONTAINMENT ELECTRICAL PENETRATIONS (TAC 66050)
By letter dated August 28, 1987, the Northeast Nuclear Energy Company (NNECo) informed the staff that contrary to its commitment by letter dated June 12, 1984, backup overcurrent protection devices will not be installed on 23 contain-ment penetrations for which the circuitry within the containment is environmentally qualified. The letter provides analysis per 10 CFR 50.59 to justify the change in commitment; and, although the proposed change is not a backfit per 10 CFR 50.109, an analysis was provided on that basis as well to further support the change.
Your previous commitment was to have such backup overcurrent protective devices installed by the startup following the Cycle 2 refueling that is now scheduled for December 1987.
The staff reviewed a previous submittal of yours on this subject dated May 20, 1987.
By letter dated July 6,1987, we stated that the staff did not concur l
with your conclusion in that letter that your commitment to install certain backup protective devices for containment electrical penetrations should not I
be implemented. However, the staff has reviewed your most recent analysis.
l Our conclusions are as follows:
l.
Changes can be made under 10 CFR 50.59 without prior Commission approval only if the change does not involve an unreviewed safety question. A i
change is deemed to involve an unreviewed safety question if the malfunc-tion of equipment important to safety previously evaluated in the safety analysis report may be increased. To justify not installing a backup protective device for the 23 Class IE penetration circuits in question, you calculated the probability of occurrence of a Class 1E' circuit fault in conjunction with the primary circuit breaker failure. You stated that the probability of this occurrence would be negligible and concluded that failure modes associated with the change would not result in a credible increase in the probability of malfunction of equipment necessary to mitigate a design basis event, i.e., containment penetration integrity.
However, the staff believes that for a LOCA environment, the failure rate you have used for a Class 1E circuit fault is optimistic. The failure rate used was for an electrical conductor under normal environmental conditions. The staff believes that the circuit failure rate under the 1
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J E. Mroczka stress of the LOCA harsh environment would.likely be higher than that which was used. We cannot conclude that the environmental' qualification of Class IE circuitry results in a sufficiently low probability of circuit failure 'for a LOCA environment that would compensate for the elimination of backup circuit breaker protection.
2.
Your analysis does not consider the potential for an uncleared fault to-cause catastrophic failure of the penetration or to cause secondary faults involving other circuits in the penetration.
3.
The impact of such failures on the response of the remaining systems, operator actions, the containment response, and the recovery actions have not been evaluated.
4.
Regulatory Guide 1.63, Revision 2 stipulates that the electrical penetration assembly should be designed to withstand, without loss of mechanical-inte-grity, the maximum short-circuit current vs. time conditions that could occur given single random failures of circuit overload protection devices.
It also stipulates that the circuit overload protection system should conform to the criteria of IEEE Standard 279-1971. This requires that the I
circuit overload protection system itself be able to' withstand a single failure (regardless of whether the penetration circuit is Class 1E or non-Class IE) if the penetration can be damaged by the available. fault currents.
Redundant overcurrent protective devices are therefore required to meet these criteria.
Based on the above, we deem the' change to your previous design ~ commitment to be an unreviewed safety question and do not concur with your bases for the proposed change in the design commitment.
Please let us know within 30 days the action yo.: plan to take to resolve this.
issue.
Sincerely,
/s/
John F. Stolz, Director Project Directorate I-4 Division of Reactor Projects I/II
- See previous white for concurrences PDI-4I, PDI-4*
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- F0rr;eh JStolz FRosa AThadant 9 / 3/87 9/23/87 9/23/87 9/23/87 l
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NRC & Local PDRs PDI-4 Reading S. Varga B. Boger.
S. Norris R. Ferguson OGC-Rathesda
- c. Jordan ACRS (10) dfodioJ l
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