ML19260C097
| ML19260C097 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 12/13/1979 |
| From: | Liebler G C-E OPERATING PLANTS OWNERS GROUP |
| To: | Ross D NRC - TMI-2 BULLETINS & ORDERS TASK FORCE |
| References | |
| NUDOCS 7912180550 | |
| Download: ML19260C097 (3) | |
Text
f 30-3O f December 1J,1979 Dr. Denwood F. Ross, Jr.
Director Bulletins and Orders Task Force Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission
Subject:
Additional Post-LOCA Guidance for Plants with High Pressure Safety Injection Pumps with a 2400 psi Shut-off Head
Reference:
NRC letter from Dr. D. F. Ross, Jr. to Mr. G. E. Liebler, dated November 14, 1979
Dear Dr. Ross:
Your referenced letter forwarded the NRC evaluation of the LOCA guideline for CE designed plants.
That evaluation concluded that the guidelines are acceptable for CE operating plants aaving high pressure safety injection pumps with shut-off heads less than 1600 psi. However, the NRC has not yet determined that the guidelines are acceptable for a plant (Maine Yankee) having high pressure safety injection pumps with shutoff heads of 2400 psi.
The NRC is concerned with potential events in which water could be discharged through the safety valves while the operator is attempting to achieve a RCS fluid condition of at least 500 below saturation.
The question is whether or not 500 of subcooling can be achieved, at which point the operator is allowed to stop high pressure flow to the RCS, before the pressure in the RCS reaches the setpoint of the safety valves and water is discharged through these valves.
The shutoff head of the Maine Yankee pump (2425 psi). is beluw the setpoint of the safety valves (2500 psi) but is above the setpoint of the PORV (2400 psi) and this needs to be addressed.
To evaluate the NRC concern, representative non LOCA events which depressurize the RCS were studied. The events chosen were a failure of the reactor coolant pressure regulating system and a steam line break.
Non-LOCA events result in the highest RCS repressurization due to high pressure pump action. These events esseritially represent a "zero break" LOCA case.
In this study it was assumed that all four RCP's were tripped following SIS actuation and that the resulting flow coastdown causes loss of pressurizer sprays.
The study confirmed that 500 of subcooling is achieved prior to reaching the setpoint of the PORV.
If no operator action is taken the high pressure pumps could cause the PORV's to lift.
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There is approximately 5 minutes between the point in time that 500 sub-cooling is reached and the setpoint of the PORV is reached. Additionally, when the PORV setpoint (2400 psi) is reached, the pressurizer is not water solid.
The study also indicates that there is an additional 5 minutes be-fore the pressurizer is filled solid assuming two HPSI pumps are operating.
This is judged to be sufficient time frame for the operator to take action.
The action the operator takes in this situation is as follows:
Preferred Action - Terminate high pressure pump flow to the reactor coolant system.
Alternative Action - Prevent operation of the PORV's by:
(a) shutting down stream block valves.
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(b) position PORV's control switch to prevent automatic opening.
As a result of the above evaluation it has been concluded that an additional precaution should be added to the CE Post LOCA Guidelines in order to incor-porate applicability to the Maine Yankee Plant.
That precaution forms the attachment to this letter. The addition of this precaution should result in a determination that the LOCA guidelines are acceptable for developing oper-ating procedures for Maine Yankee.
If you should have any questions regarding this guidance, please feel free to contact me or Mr. R. T. Harris of our Technical Advisary Committee at (203) 666-6911, extension 5519.
Very truly yours, C-E OWNERS GROUP George E. Liebler Chairman 1609 228
ADDITIONAL GUIDANCE FOR PLANTS WITH HIGH PRESSURE SAFETY INJECTION PUMPS WITH A 2400 PSI SHUT-0FF HEAD Add the additional precaution to the Post LOCA Guidelines as follows:
- 12. An SIAS can be generated by events other than a LOCA, such as a failure of the reactor coolant pressure regulating system. Con-tinued operation of high head-high pressure injection pumps can cause the RCS to repressurize to the setpoint of the PORV's.
Opening of the PORV's should be prevented by:
(a) operating the SIS to maintain RCS pressure below the PORV setpoint (2400 psi) while maintaining at least 500F subcooling.
E (b) position the PORV control switch to prevent automatic opening of the PORV's.
E (c) shut the PORV block valves to negate consequences of PORV's opening.
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