ML20059G641
| ML20059G641 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 11/01/1993 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20059G624 | List: |
| References | |
| TAC-M87247, NUDOCS 9311080279 | |
| Download: ML20059G641 (4) | |
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UNITED STATES f[hW j
NUCLEAR REGULATORY COMMISSION j
WASHINGTON, D.C. 2055641001 gv f
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.169 l
TO FACILITY OPERATING LICENSE NO. DPR-61 l
CONNECTICUT YANKEE ATOMIC POWER COMPANY l
HADDAM NECK PLANT DOCKET NO. 50-213 l
1.0 INTRODUCTION
By letter dated August 18, 1993, the Connecticut Yankee Atomic Power Company (CYAPC0/the licensee) submitted a request for changes to the Haddam Neck Plant Technical Specifications (TS). The amendment changes the TS by incorporating a new TS Section 3/4.8.3.1.2, "0NSITE POWER DISTRIBUTION." The new TS will incorporate an additional limiting condition for operation (LCO) into the TS which will require that the 480 VAC motor control center (MCC) 5 and its automatic bus transfer (ABT) scheme be operable during Modes 1, 2, 3, and 4.
In addition the LC0 currently numbered 3.8.3.1 and the surveillance requirement currently numbered 4.8.3.1 will be renumbered 3.8.3.1.1 and l
4.8.3.1.1, respectively, to support the incorporation of the additional LCO.
2.0 EVALUATION MCC-5 is the sole source of electrical power for some of the important emergency core cooling system (ECCS) motor operated valves and its loss would result in the total loss of ECCS. This single failure vulnerability was discussed in the Atomic Energy Commission's Safety Evaluation dated July 1, 1971.
Because of this vulnerability, MCC-5 is equipped with an ABT scheme, which is designed to align MCC-5 to either a preselected electrical train or switches to the other train if the preferred train is not energized. On June 27, 1993, during the performance of Surveillance Procedure 5.1-19, " Test of Train 'B' SIAS With Partial Loss of AC," the ABT scheme associated with MCC-5 failed to re-transfer and re-energize MCC-5 after the Train 'B' emergency diesel generator restored power to the load centers. This failure resulted in MCC-5 being de-energized. The Haddam Neck Plant was in Mode 5 at the time and the operators were able to re-energize the MCC-5 in a very short period.
This event has been the subject of extensive review and evaluation by CYAPC0 and an NRC Staff Augmented Inspection Team (AIT). As a result of these reviews and inspections, CYAPC0 took several compensatory actions and committed to perform a number of additional actions. The compensatory actions taken and commitments made were docketed in a submittal dated July 15, 1993.
In this letter, CYAPC0 committed to conduct on-line testing of the ABT scheme 9311080279 931101 PDR ADOCK 05000213 P
. associated with MCC-5 during Cycle 18. This testing is not authorized by the current Haddam Neck Plant TS and, therefore, a TS amendment is necessary to allow this testing.
Through this TS amendment, CYAPC0 has fulfilled their commitment to provide on-line testing of the ABT scheme.
CYAPC0 has incorporated an additional LC0 into Section 3/4.8.3 of the Haddam Neck TS. The new LC0 will require MCC-5 and its associated ABT scheme to be operable during Modes 1, 2, 3, and 4.
The new LC0 will state that MCC-5 shall be energized and capable of automatically obtaining power from 480 VAC Buses 5 and 6.
With the ABT scheme associated with MCC-5 inoperable and MCC-5 i
energized via an onsite electrical distribution system that includes an operable diesel, the ABT scheme will have to be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, or the unit will have to be in at least hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. A footnote has been added stating that the ABT scheme will be tested per CYAPC0's commitments in their July 15, 1993, letter.
In addition, the footnote states that the ABT scheme associated with MCC-5 may be inoperable for up to 30 minutes during performance of the Cycle 18 relay testing. To support the incorporation of the additional LCO, the LCO numbered 3.8.3.1 and surveillance requirement currently numbered 4.8.3.1 will be renumbered 3.8.3.1.1 and 4.8.3.1.1, respectively.
The proposed change to permit on-line testing of the ABT scheme associated with MCC-5 during Cycle 18 does affect the reliability and availability of MCC-5. Analysis compiled in support of the Haddam Neck Plant Probabilistic Risk Assessment indicates an overall failure probability of the ABT scheme of about 5 percent for the condition posing the greatest challenge to the ABT scheme. Major contributors to this failure probability are the infrequent testing of certain relays, time-related failure mechanisms, and demand-related 1
failure mechanisms. The contributions made to the failure rate by the infrequent testing of certain relays and time-related failure mechanisms will be reduced by incorporation of the proposed on-line testing. More frequent testing will identify the component (s) being in a failed state, and reduce the overall failure probability at the time of an accident from 5 percent to about 1 - 2.5 percent. The contribution to the failure rate by demand-related mechanisms will not be reduced by the more frequent testing of the ABT scheme.
Testing of the MCC-5 ABT scheme as proposed will render the ABT scheme inoperable; thus, increasing the unavailability of the ABT scheme. An upper bound unavailability for the ABT scheme would be 3.0E-3 assuming weekly testing for the maximum allowed 30 minutes.
In practice, the testing of the ABT scheme is expected to require approximately 5 minutes or an unavailability of 5.0E-4.
The long term unavailability of the MCC-5 ABT scheme due to testing will be insignificant, as the test frequency of the ABT scheme will increase during Cycle 18. The testing is scheduled to be conducted once a week for the first 4 weeks after the receipt of the amendment, then once per month for the following 4 months and finally once per quarter for the remainder of Cycle 18. The staff agrees with the licensee's conclusion that the improvement in the reliability of MCC-5 (between 2.5E-2 and 4.0E-2 decrease in failure probability) more than compensates for the increase in
1 i I unavailability due to testing of the ABT scheme associated with MCC-5 (5.0E-4 to 3.0E-3 increase for weekly testing).
In addition, the licensee has estimated the increase in core melt frequency (CMF) based on the unavailability of the ABT during testing. The frequency of a major loss-of-I coolant accident (LOCA) (1.0E-3) combined with the conditional probability of a coincident loss of offsite power (less than 1.0E-2), combined with the MCC-5 ABT unavailability due to testing (maximum 3.0E-3), and additional failures j
(0.1 order of magnitude) estimates a CMF of 3.0E-9/ year or less. This j
potential increase in CMF due to system unavailability is more than offset by i
the potential decrease in CMF due to improved reliability gained by on-line-testing. The surveillance testing required for this new TS has only been defined for Cycle 18. The licensee is investigating potential modifications to improve the ABT reliability. The licensee will re-evaluate the surveillance requirements for this TS after the permanent modifications have been determined. The modifications and new surveillance requirements will be implemented during Cycle 19. Based on the above, the staff concludes that j
this change constitutes an additional limitation, restriction, or control not presently included in the TS for which the staff has determined is beneficial to the safety of the plant.
In addition, the staff has determined that the wording of the TS and the allowed outage times in the Action statement are consistent with other TS of similar importance. Based on the above, the staff concludes the TS revisions are acceptable.
The licensee has also proposed to renumber LCO 3.8.3.1 and surveillance requiremae 4.8.3.1 to LC0 3.8.3.1.1 and surveillance requirement 4.8.3.1.1, respectively. The staff has concluded that this is a purely administrative change to the TS and is acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Connecticut State official was notified of the proposed issuance of the amendment. The State official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. The NRC staff has determined i
that the amendment involves no significant increase in the amounts, and no l
significant change in the types, of any effluents that may be released I
offsite, and that there is no significant increase in individual or cumulative 1
occupational radiation exposure. The Commission has previously issued a i
proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (58 FR 48380). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR i
51.22(b) no environmental impact statement or environmental assessment need be l
prepared in connection with the issuance of the amendment.
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5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, r
that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the propened manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
l Principal Contributor:
A. Wang Date: Noveraber 1,1993 I
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