ML20215H400
| ML20215H400 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 10/15/1986 |
| From: | Hukill H GENERAL PUBLIC UTILITIES CORP. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| 5211-86-2180, NUDOCS 8610230164 | |
| Download: ML20215H400 (3) | |
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GPU Nuclear Corporation g
gf Post Office Box 480 Route 441 South Middletown, Pennsylvania 17057-0191 717 944 7621 TELEX 84 2386 Writer's Direct Dial Nurnber:
October 15, 1986 5211-86-2180 Office of Nuclear Reactor Regulation Attn:
J. F. Stolz, Director PWR Projects Directorate No. 6 U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Mr. Stolz:
Three Mile Island Nuclear Station Unit I (TMI-1)
Operating License No. DPR-50 Docket No. 50-289 EFW System Reliability Comparison As a result of two (2) telephone conversations with Mr. J. Thoma of your staff, it was requested that we submit a letter documenting the results of a reliability comparison for two (2) different Emergency Feedwater (EFW) System configurations. Specifically, the comparison was to be made between an EFW System with flow control valves (EF-V-30 A/B/C/D) that fail closed and an EFW System in which those same valves fail open.
This letter will serve to document the results of the reliability comparison and to discuss the logic for the configuration we have chosen to implement.
The current GPUN Pian for TMI-l EFW ccnfiguration is to have manual block valves (EF-V-52, 53, 54 and 55) and to have flow control valves which fail closed. These plans have been transmitted to the NRC previously.
Based on requests from the NRC, GPUN contracted Pickard, Lowe, & Garrick Inc., to develop a reliability comparison between a f ail open and a fail closed design for the EFW control valves.
The results of the reliability study appear below:
8610230164 861015 PDR ADOCK 05000289 p
PDR GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation t\\D
5211-86-2180 October 15, 1986 TMI-l EFW RELIABILITY CRITERIA INSUFFICIENT EFW*
EXCESSIVE EFW**
FPEQUENCY OF FREQUENCY OF FAILURE TO FAILURE TO PREVENT PROVIDE SUFFICIENT EXCESSIVE COOLING CASE CASE CODE FEEDWATER ON DEMAND CASE CODE ON DEMAND CASE 1:
- All support systems EFC 4.8x10-5 EFA 3.9x10-5 available
- Manual block valves
- Flow control valves fail closed CASE 2:
- All support systems EFCl 4.8x10-5 EFA1 2.7x10-4 available
- Manual block valves
- Flow control valves fail open It is assumed that main feedwater is lost.
It can readily be seen from the above table that the excessive EFW case in which the EFW flow control valves fail open (case code EFA1) increases the frequency of failure of the EFW system to prevent excessive cooling on demand compared to the case in which the EFW flow control valves fail closed (case code EFA).
There is no significant difference between the fail open and fail closed cases for the frequency of failure of the EFW system to provide sufficient feedwater on demand.
GPUN has chosen the manual block valves for TMI-l because it is consistent with our corporate design philosophy to simplify design as long as it does not degrade the inherent safety function of the system. We believe that the manual block valves and fail closed flow control valves enhance the safety function of the TMI-l EFW system for the following reasons:
Babcock and Wilcox (B&W) plant overcooling conditions (e.g., due to excessive EFW) are reached sooner than insufficient Reactor Coolant System heat removal conditions.
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5211-86-2180 October 15, 1986 TMI-1 Abnormal Transient Procedures are prioritized to respond to an overcooling event first and then to respond to a loss of heat sink event second.
There are four (4) EFW flow control valves, any one (1) of which will provide sufficient cooling capability to prevent the uncovering of the core during any design basis event.
Having a control valve fail closed, sufficient cooling without operator action is retained through.the redundant flow control valve, whereas operator action would be required to prevent overcooling if the valves were designed to fail open.
In the long term, during an event in which all EFW flow control valves fail closed, we still have ample time to take manual actions to establish cooling for the plant.
Sincerely, f
H. D. Hu i 1 Vice President & Director, TMI-l HDH:JA:jh:4025f cc:
J. Thoma R. Conte.
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