ML20197D424
| ML20197D424 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 03/26/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20197D405 | List: |
| References | |
| NUDOCS 8704080321 | |
| Download: ML20197D424 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAP. REACTOR REGULATION RELATING TO AMENDMENT NO. 9?_TO FACILITY OPERATING LICENSE NO. DPR-36 MAINE YANKEE ATOMIC POWER COMPANY MAINE YANKEE ATOMIC POWER STATION DOCKET NO. 50-309
1.0 INTRODUCTION
By letter dated October 7, 1982, the Maine Yankee Atomic Power Company (MYAPCo) requested a modification to the Technical Specifications (TS) for the Maine Yankee Atomic Power Station. These changes concern the reactor protection system (RPS) channels and the engineered safeguards features actuation system (ESFAS) sensor bypass. The proposed changes were submitted in response to a USNRC letter dated March 31, 1982 reouest-ing such TS's, and were modified subsequently by letters dated March 4, 1985, and April 26, 1985, following discussions with NRC staff. MYAPCo's currentTS'scontainlimitingconditionsforoperation(LC0's)whenRPS channels and ESFAS sensors are bypassed. The proposed change modifies and restructures these specifications in accordance with the USNRC ietter dated March 31, 1982.
It also proposes certain exceptions to thu e LCO's.
2.0 Discussion and Evaluation 2.1 Reactor Protection System The reactor protection system is designed to shut down the reactor rapidly and automatically in the event that selected nuclear steam supply system conditions deviate from predetemined ranges. The system acts to prevent violation of safety limits, and maintains operation within bounds assumed in safety analyses.
The system is designed for high reliability. The design incorporates sufficient redundancy to assure that surveillance testing, trouble-shooting, and maintenance activities can be accommodated.
Each automatic trip function usually operates in a two-out-of-four coincidence mode. One trip channel at a time within a functional unit can be bypassed, in which case a trip signal generated by that channel will not contribute to the coincidence necessary to produce a reactor trip.
In this case, a coincidence trip of two of the j
three remaining channels will produce a reactor trip. Bypass of a channel is limited to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> by this change except for periods when the channel is actually being worked on to restrict the time when the degree of redundancy is reduced to one.
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. An inoperable channel, i.e., one that cannot automatically develop a trip signal as required, may be placed in the trip mode. A channel placed in the trip mode is considered " operable."
In this case, only one additional trip of the three remaining channels in the functional unit is required to produce a reactor trip. This restores the degree of redundancy to two.
However, RPS :hannel surveillance requirements may be performed under bypass conditions. Also, when a channel becomes inoperable, the main-tenance, troubleshooting, and surveillance activities required to restore channel operability may be best perfumed under bypass ccnditions.
This avoids requiring a reactor shutdown or long periods of reactor operation with the inoperable channel in the trip mode. Thus, an exception has been requested that allows use of the channel bypass beyond the 72-nour limit during required surveillance, or maintenance, troubleshooti1g and surveillance activities being actively carried out to restore chennel operability.
The staff has evaluated this overall approach in comparison with Option 1 described in USNRC letter dated March 31, 1982, which allows an inoperable channel to be bypassed for up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. Beyond this time period, and aside from the exception, the inoperable channel must be placed in the tripped mode or reactor shutdown initiated.
The staff finds that, except as noted above, the LCOs proposed by MYAPCo for the RPS are consistent with the staff's recommended operability requirements, as stated in Standard Technical Specifications for Com-bustion Engineering facilities.
Furthermore, the exception proposed by MYAPCo to allow additional (beyond the staff-proposed time limit) use of the bypass condition is found to be only a minor deviation from the guidance of the USNRC letter dated March 31, 1982. Such testing and maintenance activities assure reliable RPS operation, and therefore, the staff finds the proposed exception to the LC0's to be acceptable.
2.2 Engineered Safeguards Features Actuation System Engineered Safeguards Features provide for continued cooling of the reactor core and reduction in containment internal pressure in the event of a reactor accident. Redundant sensors and logic are provided for the initiation of all engineered safeguards system.
In both the containment isolation and containment spray systems, two identical subsystems are used with their own sets of sensors. Each subsystem is capable of parforming the required safety function.
In the safety injection actuation system, two sets of sensors (i.e., four for high containment pressure and four for low pressurizer pressure) provide parallel signals used for the initiation of two identical sub-systems. The containment isolation and containment spray systems each operate with two subsystems utilizing two-out-of-three logic (three channel functions) whereas the safet out-of-four (four channel functions)y injection system utilizes two-actuation circuitry. MYAPCo has proposed to bypass inoperable channels associated with these functions for a period of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. MYAPCo has also proposed an exception which
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' allows channel surveillance or maintenance activities to be performed under bypass conditions (beyond the 72-hour limit) to restore inoperable channels to operable status.
This exception allows a malfunctioning channel to be repaired and restored to service without necessitating a. shutdown and to avoid long periods of operation with an inoperable channel in the trip mode. The 72-hour period allowed for channel bypass is consistent with other MYAPCo TS (e.g., 3.6) which permit one train of other redundant safety systems to be taken out of service for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The staff has evaluated this approach in comparison with Option-1 described in USNRC letter dated March 31, 1982. This option allows bypass of one inoperable channel for up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. Beyond that time i
period, and aside from the exception, the inoperable channel must be placed in the tripped mode or reactor shutdown initiated.
The staff finds that, except as noted above, the LCO's proposed by 4
j MYAPCo for the ESFAS are consistent with similar existing MYAPCo TS's and with recommended operability requirements, as stated in Standard i
Technical Specifications for Combustion Engineering facilities.
Furthermore, the staff finds the exception proposed by MYAPCo allowing one sensor to be placed in bypass beyond the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limit to be only a minor deviation from the guidance of the USNRC letter dated f' arch 31, 1982. Such surveillance or maintenance activities assure reliable ESFAS operation, and, therefore, the proposed exception to the LCO's is found
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to be acceptable.
3.0 Technical Specification Changes The MYAPCo TS's define the LCO's needed to assure safe system opera-tion. Section 3.9 of the TS contains the LCO's for the RPS and the ESFAS. MYAPCo has proposed a new version of this TS in response to USNPC letter dated March 31, 1982. The staff has reviewed this change 4
in the TS's in terms of the safety issues discussed in Section 2.0.
Based on this review and the modifications discussed in Section 2.0, these changes to the MYAPCo TS are found to be acceptable.
The staff has evaluated the proposed changes to the TS's and conclude that they do not involve any physical change to the plant's safety-j related structures, systems, or components.
Further, these changes do not increase the likelihood of a malfunction of safety-related l;
equipment, increase the consequences of an accident previously analyzed, i
or create the possibility of a malfunction different from those pre-viously evaluated. Therefore, as stcted above, the staff finds the licensee's requested changes to be acceptable.
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4.0 ENVIRONMENTAL CONSIDERATION
This amendment involves a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or a change in surveillance requirements. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Com-mission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, this amendment meets the.
eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuantto10CFR51.22(b),noenvironmentalimpact statement or environmental assessment need be prepared in connection with the issuance of this amendment.
5.0 CONCLUSION
The staff has concluded, based on the considerations discussed above, that (1) thera is reasonabla assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Date: March 26,1987 Principal Contributor:
David F. Limroth, Region I i
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