ML20137Y562
| ML20137Y562 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 10/01/1985 |
| From: | Williams J TOLEDO EDISON CO. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-TM 1191, 44572, TAC-44572, NUDOCS 8510080035 | |
| Download: ML20137Y562 (2) | |
Text
TOLEDO
% EDISON Docket No. 50-346 JOE WwAMS, JR.
s.,-vc.% **- w License No. NPF-3 l$lEU$SS Serial No. 1191 October 1, 1985 Director of Nuclear Reactor Regulation
. Attention:
Mr. John F. Stolz Operatir.g Reactor Branch No. 4 Division of Licensing United States Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Stolz:
This is in response to your letter of June 7, 1985 (Log No. 1764) concern--
ing NUREG-0737 Item II.B.1, Request for Additional Information. By our letter dated July 19, 1985 (Serial No. 1171) we provided a partial response to the requested information. This letter will provide Toledo Edison's response to Question 2.
The remaining responses will be provided by December 2, 1985 for the Davis-Besse Nuclear Power Station Unit No. 1.
Very truly yours, j' ::?
- GAB:lah ttachment cc: DB-1 NRC Resident Inspector gh 1
8510000035 851001 PDR ADOCK 05000346 P
PDR THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO. OHIO 43652
Dockst No. 50-346 o"
Liccine No. NPF-3 Serial No. 1191 Attachment Question 2 Results from the EPRI tests on the Crosby 3K6 and 6M6 safety valves indicated that test blowdowns exceeded the 5% value given in the valve specifications.
If the plant-specific expected blowdowns also exceed 5%,
the pressure might be sufficiently decreased such that adequate core cooling might not be achieved for decay. heat removal. Expected blow-downs for the Davis-Besse plant at their current ring settings were not provided. Discuss the consequences of potentially higher blowdowns.
Discuss the adequacy of decay heat core cooling at the expected reduced
. pressures.
Response
The safety function of the Crosby Code Safety Valves located on the pressurizer is to prevent over pressurization of the RCS due to transient events. Following a lifting of the code safety valves, the valves remain open until RCS pressure decreases to the reseating pressure for the valves. The reseating pressure is expressed as a percent blowdown. The
' Davis-Besse safety valves.are set to reseat at 2 - 4% blowdown.
Failure of the safety valves to reseat at the specified pressure does not affect the ability to provide adequate core cooling for removal of decay heat. The steam generators and the AFW system are the primary mechanisms for removing decay heat from the RCS. The ability of the steam 1
generators to remove decay heat is unaffected by the reseat pressure of the code safety valves.
The major impact of extended blowdown of the code safety valves is to decrease the sub-cooling margin in the RCS. Loss of sub-cooling margin will result in an operator's action to trip the reactor coolant pumps; however, Davis-Besse is capable of establishing natural circulation in the RCS by use of the auxiliary feedwater system and the steam generator.
Natural circulation cooling of the RCS is sufficient to remove decay heat.
y Consequently, the actual percent blowdown of the RCS Crosby safety valves would not have an adverse effect upon core cooling. Extended blowdown may trip reactor coolant pumps due to loss of sub-cooled margin; however, natural circulation in the RCS would still provide adequate core cooling.
I