ML19208B536
| ML19208B536 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 08/15/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19208B534 | List: |
| References | |
| NUDOCS 7909200519 | |
| Download: ML19208B536 (4) | |
Text
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ep ELECTRICAL, INSTRUMENTATION AND CONTROL.
ASPECTS OF THE POINT BEACH UNITS 1 AND 2 LOW TEMPERATURE OVERPRESSURE SYSTEM PREPARED BY: Plant Systems Branch Division of Operating Reactors 790920051
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1.0 INTRODUCTION
By letter to the Wisconsin Electric Power Company (WEPCO) dated August 11, 1976, we requested an evaluation of system designs to determine susceptibility to overpressurization events and an analysis of these possible events, and proposed interim and permanent modifi 3 cations to,the systems and procedures to reduce the likelihood and consequences of such events. By letter dated September 3,1976 and subsequent letters (refer to references), the the Wisconsin Electric Power Company submitted the additional information requested by us, including the administrative operating procedures and the proposed low temperature overpressure mitigating system. The system hardware includes sensors, actuating mechanisms, alams, and valves to prevent a reactor coolant system transient from exceeding the pressure and temperature limits of the Technical Specifications for Point Beach Units 1 and 2, 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 technical assistance program.
3.0 DESCRIPTION
OF OVERPRESSURE MITIGATING SYSTEM The WEPC0 Overpressure Mitigating System (0!% design infomation detailed in this section was derived from References 1 and 5.
The WEPC0 design for the Point Beach OMS consists of two methods of relieving pressure during periods of water-solid operation and when the reactor coolant system (RCS) temperature is below the value permitted to perform the primary system leak test. The primary methoa of pressure relief utilizes the pressurizer PORV's, and the diverse method utilizes the relief valves on the residual heat removal (RHR) system.
The PORV's are made operational for low-pressure reliMby utilizing a dual setpoint where the low-pressure circuit is energized and de-energized, depending on plant conditions, by the operator with a key-lock switch. The logic required for the low-pressure setpoint is in addition to the existing PORV actua+.icn logic and will not interfere with existing automatic or manual actuation of the PORV's.
The relief valves on the RHR system are available for pressure relief whenever the RHR system is connected to the RCS. The RHR system is normally connected to the RCS during plant conditions when overpressuri-zation events have been most prevalent, i.e., during low-temperature and low-pressure conditions.
The RHR-system relief valves can be con-sidered a diverse relief system at Point Beach because the RHR system isolation valves do not automatically isolate the RHR system during a pressure transient, therc!, making the relief valves available tnrough-out the transient.
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_2 During plant cooldown and prior to the collapse of the steam bubble in the pressurc:er, the operator acting under administrative procedure places the keylock switch in the " low pressure" position ,
and connects the RHR system to the RCS.
An alarm will alert the oper-ator when the pressure is sufficiently low so thatactivation of the low pressure setpoint circuit will not inadvertently open a PORV.
Placing the keylock switch in the " low pressure" position blocks the alarm indicating low pressure ar.d enables the low-temperature high-pressure alarm.
During plant heatup, the operating procedure will identify the plant conditions for which low-pressure protection is no longer needed.
The operator places the keylock switch in the " normal" position, thereby returning control of the PORV's to the operating high-pressure condition and avoiding inadvertent opening of the PORV's.
Placing the keylock switch in the " normal" position removes or blocks the low-temperature high-pressure alarms and enables the low-pressure operation alert alarm.
We find the above design features acceptable.
4.0 CONCLUSION
S Based on our review of the enclosed consultant's Technical Evaluation Report, we agree with their findings that the administrative controls and hardware changes proposed by the licensee provide adequate protection for Point Beach Units 1 and 2, from overpressure transients at low RCS temperatures by reducing the probability of initiation of a transient and by limiting the pressure of such a transient to below the limits set by Appendix G of the Technical Specification. We, therefore, conclude that the EI&C aspects of the overpressure pro-tection system mee+ qur criteria, and as such, are acceptable as a long term solutica to the problem of overpressure transients.
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REFERENCES 1.
WEPC0 letter (Burstein) to NRC (Case) dated July 23, 1977.
2.
WEPC0 letter (Burstein) to NRC (Case) dated October 28, 1977.
3.
WEPC0 letter (Burstein) to NRC (Rusche) September 3,1976.
4.
WEPCO letter (Burstein) to NRC (Rusche) dated October 14, 1976.
5.
WEPC0 letter (Burstein) to NRC (Rusche) dated March 2,1977.
6.
WEPC0 letter (Burstein) to h2C (Rusche) dated April 18, 1977.
7.
" Staff Discussion of Fifteen Technical Issues Listed in Attactment G, 3 November 1976 Memorandum fr om Di rector NRR to NRR Staff",
NUR EG-0138, Novemoer 1976.
8.
NRC letter (Lear) to WEPC0 (Burstein) dated August 11, 1976.
9.
" Pressure Mitigating System Transient Analysis Results" prepared by Westinghouse for the Westinghouse User's Group on Reactor Cool ant System Overpressurization, July 1977.
10.
" Supplement to the July 1977 Re po rt, Pressure Mitigating Systems Transient Anal ysi s Results," prepared by We sti ng house for the Westinghcuse User's Group on Reactor Coolant System Overpressuriza-tion, September 1977.
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