ML19259D284
| ML19259D284 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 09/11/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19259D281 | List: |
| References | |
| NUDOCS 7910170563 | |
| Download: ML19259D284 (3) | |
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Attachment SAFETY EVALUATION REPORT ELECTRICAL. INSTRUMENTATICN AND CONTROL DESIGN ASPECTS OF THE LOW TEMPERATURE OVERPRESSURE MITIGATING SYSTEM FOR THE MAINE YANKEE NUCLEAR POWER PLANT 1163 003 7 910170 b b
1.0 INTRODUCTION
By letter to the Maine Yankee Atomic Power Company (MYAPCO) dated August 11, 1976, the U.S. Nuclear Regulatory Commission (NRC) reque,sted an evaluation of system designs to determine susceptibility to overpressurization events and an analysis of these possible events, and proposed interim and perma-nent modifications to the systems and procedures to reduce the likelihood and consequences of such events. By letter dated December 2,1976 and subsequent letters (refer to the Appendix), the Maine Yankee Atomic Power Company submitted the additional infomation requested by the NRC staff, including the administrative operating procedures and the proposed low temperature overpressure mitigating system. The systen hardware includes sensors, actuating mechanisms, alanns, and valves to prevent a reactor coolant system transient from exceeding the pressure and temperature limits of the Technical Specifications for Maine Yankee as required by the Code of Federal Regulations, Title 10, Part 50 (10 CFR 50), Appendix G.
2.0 EVALUATION The enclosed Technical Evaluation Report was prepared for us by the Lawrence Livermore Laboratory, as part of our DOR technical assistance program.
3.0 SYSTEM DESCRIPTION The MYAPCO design for the Maine Yankee CMS is based on the use of two pressurizer solenoid-operated relief valves (SCRV's) along with two passive spring-loaded safety valves (SV's) which are located on the suction line of the RHR system piping. These valves, in conjunction with specific procedural controls, fann the bases for the following conditions:
(1) Each pressurizer SORV will provide sufficient and redundant relief capacity to ensure that the reactor coolant system (RCS) pressure remains belcw 589 psig when the RCS tempera-ture is below 2200F. The pressurizer SCRV low pressure setpoint is 500 psig.
(2) The two RHR SV's together will provide sufficient and redundant relief capacity to ensure that the RCS pressure remains below 589 psig when the RCS temperature is cetow 2200F. The RHR SV low pressure setpoint is 400 psig.
(3) A 2250F temperature switch will be provided to ensure that the RHR SV isolation valves and the pressurizer-50RV isolation 0
valves are open at temperatures below 225 F.
Valves that are not open will be annunciated on the main control board.
(4) Additional assurance of preventing inadvertent blowdown at 0
RCS temceratures above 300 F is provided by the inclusion of 3 3000F temoerature switch. This switch will ensure that the RHR SV isolaticn valves are closed and that the pressurizer SCRV's have been reset to the high set::oints required for normal plant operstion. Failure of the RHR SV isolation valves to close or failure of the pressurizer 50RV's to be reset to the nigh setcoint will be annunciated on the main control board.
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2-The two pressurizer SORV's are equipped with a low pressure setpoint feature. This feature, when enabled by the operator by means of a key lock switch, causes each pressurizer 50RV to open when the pressurizer pressure reaches a setpoint of 500 psig.
In accordance with plant cooldown procedures, the pressurizer 50P.V's are set to the low pressure setpoint when the system pressure is less than 450 psig. This low pressure setpoint is to be established prior to decreasing the RCS temperature below 2200F. Plant operating proce-dures provide that normally the RHR system suction isolation valves are open below 2200F thereby making available the relief capacities of these two safety valves as reactor vessel overpressure protection devices. We find these desis' features acceptable.
4.0 CONCLUSION
S The design of the Maine Yankee low te.'cerature overpressure mitigating system in the areas of electrical, insirumentation and control (EI&C) is in accordance with those design criceria originally prescribed by us and later expanded during subsegur_nt discussions with the licensee.
We find the EI&C aspects of the modifications acceptable on the basis that: (1) the system is redundant and satisfies the single failure criterion; (2) the system is testable on a per Mic basis, and (3) the recommended technical specifications redus_
probability of overpressurizaticn events to an acceptable level.
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