ML19220B836
| ML19220B836 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/18/1979 |
| From: | Fraley R Advisory Committee on Reactor Safeguards |
| To: | Gilinsky V, Hendrie J, Kennedy R NRC COMMISSION (OCM) |
| References | |
| ACRS-R-0826, ACRS-R-826, NUDOCS 7904270445 | |
| Download: ML19220B836 (3) | |
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April 18, 1979 MEMORA'OUM FOR: Chairman Hendrie Cornissioner Gilin"ky Commissioner Kennedy Cornissioner Bradford Comn41ssioner Ahearne FROM:
R. F. Fraley, Executive Directcr Advisory Coccittee on Reactor Safeguards Attached for your information and use is a copy of the recommenda-tions of the Advisor, Corcittee on Reactor Safegaards which were orally presented to and discussed with you on April 17, 1979 re-garding the recent accident at the Three Mile Island Nuclear Sta-tion Unit 2.
s V
R. F. Fraley Executive Director
Attachment:
Recommendations of the NRC Advisory Committee on Reactor Safeguards Re. the 3/28/79 Accident at 'Ihe Three Mile Island Nuclear Station Unit 2 790427046 83 1'Z9
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April 17, 1979 RECOMMENDATIONS OF WE NUCLEAR RmUIATORY COMMISSION ADVISCRY COMMITTEE CN REAC'IOR SAFEGUARDS REGARDING THE MARCH 28, 1979 ACCIDENT AT WE THREE MILE ISLAND N'JCLEAR STATION UNIT 2 Presented orally to, and discussed with, the NEC Commissioners during the ACRS-Commissioners Meeting on April 17, 1979 - Washington, D. C.
Natural circulation is an important mode of reactor cooling, both as a planned process ard as a process that may be used under abnormal circumstances.
The Committee believes that greater understarding of this mode of cooling is required and that detailed ulalyses should be develeped by licensees or their suppliers.
The analyses should be supported, as necessary, by experiment.
Procedures should be de-veloped for initiating natural circulation in a safe manner and for providing the operator with assurance that circulation has, in fact, been established. This may require installation of instrumentation to measure or indicate flow at low water velocity.
The use of natural circulation for decay heat removal following a loss of offsite pwer sources requires the maintenance of a suitable over-pressure on the reactor coolant system.
This overpressure may be assured by placing the pressurizer heaters on a qualified onsite power source with a suitable arrangement of heaters and power distri-bution to provide redundant capability.
Presently operating PWR plants should be surveyed expeditiously to determine whether such arrangements can be provided to assure this aspect of natural circula-tion capability.
The plant operator should be adequately informed at all times con-cerning the conditions of reactor coolant system operation which might affect the capability to place the system in the natural circu-lation mode of operation or to sustain such a mode.
Of particular importance is that information which might indicate that the reactor coolant system is approaching the saturation pressure corresponding to the core exit temperature.
This impending loss of system over-pressure will signal to the operator a possible loss of natural circulation capability.
Such a warning may be derived from pressur-1:er pressure instruments and hot leg temperatures in conjunction with conventional steam tables.
A suitable display of this information should be provided to the plant operator at all times.
In addition, consideration should be given to the use of the flow exit tempera-tures from the fuel subassemblies, where available, as an additional indication of natural circulation.
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. The exit temperature of coolant from the core is currently measured by thermocouples in many PWRs to determine core performance.
We Committee recommends that these temperature measurements, as currently available, be used to guide the operator concerning core status. We range of the information displayed and recorded should include the full capability of the thermocouples.
It is also recommended that other existing instrumentation be examined for its possible use in assisting operating action during a transient.
he ACRS recommends that operating power reactors be given priority with regard to the definition and implementation of instrumentation which provides additional information to help diagnose and follow the course of a serious accident.
This should include improved sampling procedures under accident conditions and techniques to help provide improved guidance to offsite authorities, should this be needed. The Committee recommends that a phased implementation approach be em-ployed so that techniques can be adopted shortly after they are judged to be appropriate.
he ACRS recommends that a high priority be placed on the developnent and implenentation of safety research or the behavior of light water reactors during anomalous transients. The NRC may find it appropriate to develop a capability to simulate a wide range of postulated tran-sient and accident conditions in order to gain increased insight into measures which can be taken to improve reactor safety.
The ACRS wishes to reiterate its previous recommendations that a high priority be given to research to improve reactor safety.
Consideration should be given to the desirability of additional equipnent status monitoring on various engineered safeguards features and their supporting services to help assure their availability at all times.
The ACRS is continuing its review of the implications of this accident and hope to provide further advice as it is developed.
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