ML19207B459
| ML19207B459 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/14/1979 |
| From: | Carbon M Advisory Committee on Reactor Safeguards |
| To: | Hendrie J NRC COMMISSION (OCM) |
| References | |
| TASK-TF, TASK-TMR ACRS-R-0842, ACRS-R-842, NUDOCS 7908290496 | |
| Download: ML19207B459 (4) | |
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ADVISORY COMMITTEE ON REACTOR SAFEGUARDS o,
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WASHINGTON, o. C. 20555 s
August 14, 1979 Honorable Joseph M. Hendrie Chairman U. S. Nuclear Regulatory Commission Washington, D.C.
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Subject:
STUDIES 'IO IMPROVE REAC'KR SAFETY
Dear Dr. Hendrie:
he Advisory Committee on Reactor Safeguards has'several recommendations to make concerning studies to improve reactor safety.
1.
Accident Analysis The ACRS recommends that an analysis be undertaken of pstulated accidents involving a steam line rupture followed by a snall break in the primary system, arising from an open relief valve, a steam generator tube break or some other opening. te analysis should not only review the capability of engineered safety features to cope with such an event but also examine the symptoms available to the operator and determine the adequacy of existing operating procedures.
2.
Studies to Reduce the Probability of an Accident The ACRS recommends a systematic reevaluation of the com: Ton-mode failure potential of compressed air systems used for centrol or service in both safety and non-safety applications. Among the matters to be considered in such a review should be the effect of moisture and corrosion products, and a total loss of air supply. Also of concern is any interconnection of compressed air supplies to both safety and non-safety devices and to other fluid systems. Consideration should be given to the adequacy of separt ion rules for air systems.
3.
Studies to Reduce the Probability of an Accident he ACRS recommends that sttxlies be made of the interrelationship between the operation and interconnection of the auxiliary feedwater system, the main feedwater system, the atmospheric dump and the control system, in-board of the isolation valves on the main feedwater and main steam lines in order to ascertain whether there are significant undesirable interactions under various pstulated accident scenarios.
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Honorable Joseph M. Hendrie August 14, 1979 The ACRS also recommends exmination of feedwater flow during postulat:d ruptures of the main steam line in order to assure that adequate, but not excessive, heat removal capability is retained.
4.
Studies to Reduc'e the Probability of an Accident he ACRS reccxnmends that studies be made of possible significant effects adverse to safety arising from shared systems or locations in existing multiple-reactor stations, of the probability of str:h adverse effects, and of possible mitigating features. Dcamples of potentially adverse effects to be considered incitxle the passible loss of access to systems needed for one unit due to unexpected releases of radioactivity from a neighbor, and the potential overloading of emergency diesel capability arising from con-current IDCA signals (real or spurious) for a system using a shared diesel.
5.
Operating Procedures he ACRS reccxamends that a study be made on inw operating procedures should best be written. For exmple, should procedures be characterized in terms of events or in terms of symptoms, or both? Should the operator actions be keyed to changes in symptoms? Is the priority of operator action fixed so as to optimize public safety? How does one determine whether a given pro-cedure is understood by the operator, and that the operator will carry it out properly?
Se ACRS also reccamends that a systematic exmination be made of steps that the operator rhould be advised not to take, when and why. One exmple of such a step could arise in connection with the operator's capability to iso-late certain IDCAs in BWRs and some RTrts. It is possible that such isolation following a relatively large loss of original primary system inventory could lead to reactor repressurization and an inability of the avai'.aD high pres-sure capacity to keep the core adequately covered for a perioi long enough to cause significant core damage before the situation was recognized and reedied.
6.
Environmental Qualification of Systems in Containment
%e ACRS recommends a review and reevaluation of the current basis for judging enviromental qualification requirements for equipnent in containment and in other buildings where a hostile envircrrnent might result. We same review should be made of the locations of vital sensors and other measurment devices.
We pros and cons of modified envirormental qualification and equignent loca-tion should be examined with due consideration given to the difficulties of modifyina existing equipnent.
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t Honorable Joseph M. Hendrie August 14, 1979 7.
Design, Construction, and Operation Review he ACRS reccamends.that consideration be given to the need for joint review by the nuclear stem system supplier, the architect-ergineer, and the operat-ing utility, prior to operation of a reactor, to coraider, amorg other things, the adequacy of interfaces and other features developed undar the aegis of multiple suppliers, the acceptability of technical specifications and other safety-related operational limits, and the adequacy of operational and acci-dent procedures.
8.
Decay Heat Removal Systems in ECCS The A~RS recommends a reevaluation of the design basis of the low pressure recirculation heat removal system of the ECCS, includirg system capability and long-term reliability when circulating highly radioactive fluid contain-ing particulates which might jeopardize certain ccrapnents.
9.
Direct Rather than Derived Safety Signals he ACRS reccramends that a review be made of the prsible improvment in actua-tion reliability that could be achieved by employing a safety signal directly related to the matter of concern; e.g., radiation level for containment iso-lation. Derived signals have merit but they may be tied to specific scenarios for a transient or accident and hence subject to failure if some unanticipated course of events were to transpire.
- 10. Systems Interactions Involving Air, Instrument, or Hydraulic Lines The ACRS recetrends that each licensee be requested to review and evaluate his as-built plant for possible significant systems interactions wherein rupture in a medium or high pressure line could cause loss of vitally important air, instrument, 6ad hydraulic lines and electrical circuits and equipnent. For boiling water reactors, attention should be given particularly to the lines related to actuation of the scrm system.
- 11. Accident and Transient Analyses We ACRS recommends that further analyses be made of the course, consequence, and probability of transients which would lead to gross overfilling of the secondary side of the stem generator in IHRs and the equivalent event in BWRs in order to ascertain whether any additional measures are appropriate to provide additional protection of the public health and safety.
- 12. Studies to Imorove Safety he ACRS has previously reccrmnended on several occasions that the NRC Staff utilize the methodology of probabilistic analysis to exmine the reliability 853 305
Honorable Joseph M. Hendrie August 14, 1979 of the design of systems important to safety, both for existing reactors and as it might apply to reactors to be constructed. Ebr example, on July 11, 1978 the ACRS, in a letter from R. F. Fraley to L. V. Gossick, recmmended that the NRC Staff provide an evaluation of the reliability of the auxiliary feedwater systems of current IWRs and BWRs in terms of various transients end incidents.
Recently, following the t ree Mile Island Accident, the NRC Staff performed a short-term, intensive review of the auxiliary feedwater system for Combustion Engineering and Westinglouse operating EWRs and found many items of interest, including some which stqgested a need for early regulatory action to remedy deficiencies. he ACRS recmmends that this same procedure be applied, as expeditiously as practical, to each of the otheresystems of impartance to safety in order to ascertain whether there are other features on operating reactors warranting early or near-term improvements.
Sincerely,
/
Max W. Carbon 01 airman h