ML19260A025
| ML19260A025 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/11/1976 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Arnold R METROPOLITAN EDISON CO. |
| References | |
| NUDOCS 7910290661 | |
| Download: ML19260A025 (5) | |
Text
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GL II TS DISTRIBUTION:
NRC PDR TBAbernathy L PDR JRBuchanan Docket No.: 50-289 Docket Fil ACRS (16)
ORB #4 Rdg Dross VStello KRfoller TJCarter
!btropolitan Edison Company ATTH: fir. R. C. Arnol d OELD Yice President - GeneratioQI&E (5)
P. O. Box 542 RReid Reading, Pennsylvania 19603 Ghetzig GZech Gentlemen:
RIngram DEisenhut RE: THREE MILE ISLAND UNIT H0.1 A number of reported instances of reactor vessel overpressurization in Pressurized Water Reactor (PWR) facilities have occurred in which the Technical Specifications implementing 10 CFR Part 50 App?ndix G limitations have been exceeded. The majority of cases have occurred during cold shutdown in which the p.=inary system has been in water solid conditions. These overpressuritation events hav. been initiated by a variety of ccuses, including the following:
(1) Isolation of RHR system / letdown system while charging to a water sclid primary system, (2) Thernal expansion following the starting of a primary coolant pump due to stored themal energy in steam generators, (3) Inadvertent actuation of safety injection accumulators, and (4) Initiation of operation of a reactor coolant pump or a high pressure safety injection pump.
In essentially all of the events reported, a single personnel error, cauf pment nalfunction or procedural deficiency has been sufficient to cause the event.
We believe that appropriate steps should be taken promptly by all PWR licensees to minimize the likelihood of additional occurrences of reactor vessel overpressurization. To that end we recently completed a series of meetings with several PWR licensees and MSSS suppliers in Ccn we dis-cussed the reported overpressurization events and assessed the measures that are currently being employed to either avoid or reduce the probability of similar occurrences; or to control the pressure transient to less than Appendix G limits.
Exanples of those measures identified by the various licensees are as follows:
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Coaplete avoidance of water solid conditions by ei.,er maintaining a pressurizer steam bubble or by providing a inw pressure nitrogen blanket in the pressurizer when a steam bubble cannot be maintained, (2) Disabling liigh Pressure Injection and Safety Injection pumps by disconnecting electrical power supplies when at low primary system tempera tures, (3) Installation of dual setpoint pressurizer power relief valve (s) to provide protection against exceeding Appendix G limits while at low primary system temperatures, (4) Minimization of time at water.:01id conditions and upgrading plant procedures to include appropriate warnings and cautions when such operations are necessary, and (5) Installation of relief valves in charging pumo discharge lines with a setpoint to provide protection against exceeding Appendix G limits.
It was noted in our discussions with the P;n licensees that, for the majority of those plants involved, not all potential overpressurization events would be prevented by the neasures they had identified and that some of the remaining measures may have undesirable effects on reactor sa fe ty.
Based on the infomation gathered to date, we have concluded that all PWR licensees should evaluate their systen designs to detemine the susceptibility to overpressurization events. Specifically, you should provide the following:
(1) An analysis of the Reactor Coolant System (RCS) response to pressure transients that can occur during startup and shutdown.
Any design modifications determined to be necessary to preclude exceeding Appendix G limits are to be f acorporated in this analysis.
The artlysis should include a plot of pressure as a function of time until termination of the event. The analysis should assume the most limiting initial conditions (e.g., one WIR train ccerating or available for letdown, other coeponents in nomal operation when the system is water solid such as Dressurizer heaters and chargina pumps, and one or more reactor coolant punos in operation) with the worst single failure or operator error as the initiating event.
Justification should he provided for the choice of liniting con-ditions and Wrst single failure or coerator error assu~ed in the
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i "etropolitan Edison Company (2) A description of those design modifications determined to be necessary, including equipme't perfomance specifications and systen cocrational sequences. The oesign basis used in the choice of equipment should be incluced, and (3) A schedule for the prompt implementation of the crocosed design nodifications.
The basic criteria to be applied in determining the adequacy of over-pressurization protection are that no single equipment failure or single operator error will result in Appendix G limitations being exceeded.
For those situations in @ich the necessary design channes identified cannot be inclemented within the next few nonths, you should identify short-tern measures to reduce the likelihoca that overpressurization events will occur in the interin neriod until the semanent desion changes can be made. Short torn measures shoula De identified separately for innadiate inplementation within the terns and conditions of your license. Snort tem neasures night incluce some.ce:Dination of, out would not be limited to, the folicwing suggestions:
(1) Procedural changes to nini '.:e the tine in wnich the primary systen is in a wat:r solid condition, (2) Upgrading existing plant procedures and adninistrative controls to assure that appropriate warninos and cautions are included to alert the operator whenever the potentia.
for primary systen overpressurization exists, (3) Provide al3rns and/or indications to alert the operator wtienever primary systen pressure increases toward Appendix G limits, M) Introducinq temporary plant uodifications for nresture relief, and (6) Assien,r at of additional personnel to monitor plant enerations dea va ar solid.
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t "etropoli tan Edison Comnany 4-llodifications to nreclude or.nininize the probacility of reactor vessel overpressur17ation events are plant dependent and the examples given may or may not be adaptable to your specific system design. Consideration riust also be given to the potential effects of both the short term and lonn tern nessures you consider to assure tnat other aspects of nuclear safety are not compromised.
To verify compliance with Appendix G pressure-temperature limits during startup and shutdown, you should assure that the appropriate instrumen-tation is installed to provide a continuous pennanent r srd over the full range of both pressure and tencerature. This instrunentation should be in service during long periods of cold shutdown as well as durinc startup and snutdown operations. Reliance upon the plant computer to reconstruct a pressure transient is not cons dered sufficient because of the likelihood of computer downtime especially during plant shutdown conditions.
We request that you notify us within 20 days af ter receipt of this letter that you will provide all the information reouested within 60 days or explain why you cannot meet this schedule and provide the schedule t;1at you will meet.
This request for generic infomation was approved by GA0 under a blanket clears ~ number B-180225 (R0072); this clearance exciros July 31, 1977.
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Robert W. Reid, Chief Oneratina Reactors ilranch.d4 Division of Operating Reacto s cc: See next page 1478 352 DOR : 0R.B,_.4 00R:0RB-DOR:0RB-4 o,,,C.,
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8//[G6 Tonn Af.C.313 (Rev. 9-S *,)
AECM 0240 W u. s. oovsRNMENT PRINTING QPPICEI 9 9 74 526-18e
w Metropolitan Edison Company cc:
G. F. Trowbridge, Es.
Shaw, Pi ttnan, Potts, & Trowbri.Je 1500 M Street, N. W.
Wa shington, 9. C.
20036 GPU Service Corporation Richard W. Howard, Project IMnaner Tnomas I1. Crimmins, Jr., Safety and Licensing Manager 260 Cherry Hill Road i
Parsippany, New Jersey 07054 Pennsylvania Electric Company Mr. R. W. Conrad Vice President, Generation 1001 Broad Street Johnstown, Pennsylvania 15907 Mr. Weldon B. Arehart, Chairman Board of Supervisors of Londonberry Township 2148 Foxiana Road Middletowm, Pennsylvania 17057 Miss Itary V. Southard, Chairnan Citizens for a Safe Environnent P. O. Box 405 Harrisburg, Pennsylvania 17108 Government Publications Section State Library of Pennsylvania i
Box 1601 (Education Building)
Harrisburg, Pennsylvania 17126 1478 353 i
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Form AIC 318 (Rev. 9 53) AECM 0240 W u. s. oovannessar ensNTiNo orricas to74 sas.ies
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