ML19224C450
| ML19224C450 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 05/16/1979 |
| From: | Carbon M Advisory Committee on Reactor Safeguards |
| To: | Hendrie J NRC COMMISSION (OCM) |
| Shared Package | |
| ML19224C451 | List: |
| References | |
| NUDOCS 7907020394 | |
| Download: ML19224C450 (5) | |
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r ADVISORY COMMITTIE CN REACTOR SAFEGUARDS
.k WAsmNG ton. o. C. 20555 Pay 16,1979 pr Hon ble Joseph M. Hendrie l
U. S. Nuclear Regulatory Cor. mission ' y b
Washington, CC 20555
Subject:
Ih7ERIM PIPCRT NO. 2 CN WRIE MILE ISLA.ND NTLEA.R STnTICN UNIT 2 Cear Dr. Hendrie:
During its 229th meeting Pay 10-12, 1979, the Advisory Committee on Re-actor Safeguards continued its review of the circu-stances relatirg to the recent accident 3: Three Mile Island Nuclear Station Unit 2 (TMI-2).
Tne recommendations presented orally to the Commissioners on April 17, 1979 were reviewed by the full Committee and are repeated in screwhat amplified form herein. Amplification of these iters is responsive to the recuest of Acting NRC Chairman Victor Gilinsky dated gril 18, 1979.
Natural Circulation - Procedures It is evident from the experience at TMI-2 that there was failure to es-tablish n-tural circulation of water in the primary system and failure to recognize in a timely canner that ratural circulation had cet been achieved. The need for natural circulation under certain circ = stances is common to all Pas.
The Cor.cittee recommends that procedures be developed by ill_ operators
. of Pas for initiating natural circulatien in a safe manner and for pro-vidlog the op3rator with assurance that circulatien has in fact beon es-
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tablished. 'Ihese procedures should take into account the behavior of the systers under a variety of abnormal conditions.
As a first step, the N3C Staff should initiate irrediately a survey of op? rating procedures for achievirq natural circulation, including the case when offsite pcwer is lost. At the same time, the operators of all PG plants should be recuested to develop detailed aralyses of the be-hav. lor of their plants folicwing anticipated transients ard small breaks in the prirary system, with appropriate censideration of potential ab-normal condiH.ons, op?ratcr errors and failures of ecuic a.t, p:wer sources, or e.strumentatien. Tnese analyses ar.3 nacessarf for the t#m d
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Honorable Joseph H. Handrie fay 16,1979 developent of suitable operatirq procedures. Tae review and evaluation of these analyses by the NRC Staff should receive a priority consistent with the priority being given to changes in operating procedures.
Natural Circulation - Pressurizer Heaters The use of natural circulation for deca / heat renoval.following an accident in a PG normally requires the maintenance of a suitable over-pressure on the reactor coolant system in c eder to prevent the v a-ra-tien of steam which can impede circulation. For many transients, main-tenance of this overpressure is best accomplished by use of the pres-surizer heaters.
Although the pressurizer heaters at MI-2 continued to receive power from offsite sources curing the entire accident, the availability of offsite power cannot be assured for all transients or accidents during which, or following which, natural circulation mast be established. The Comittee recommends that the NRC Staff initiate imrediately a survey of
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all FAs licensed for operation to determine whether the cressurizer
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heaters are new or can be supplied with power from gaalified ensite sources with suitable redundancy.
Natural Circulation - Saturation Conditions The plant operators should be informed adequately at all tices of those conditions in the reactor coolant system that might adect their capa-I bility to place the system in the retural circulation mode or to sustaia it in such a mode. Infomation indicating that coolant pressme is ap-proaching the saturation pressure corresponding to the core exit temper-
.ature would be especially useful, since an impending loss of' overpressure would signal to the cperator a patential loss of natural circulation.
Tnis information can be derived from available pressurizer pressure and he t leg temperature measurements, in conjuction with conventional steam tables.
Tne Comittee recommends that infomation for detecting an approach to saturation pressure be displayed to the o;arator in a suitable fom at all times. Since there may be several equally acceptable means of providing this infomation, there is no need for the NRC Staff to as-sign a high priority to the development of pres:riptive requirements for such displays. Mcwever, a raasonably early regaest that licensees and vendors censider and cement on the nead for such a disclay would be apprcprinte.
C F00R ORTRAL
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4 Honorable J:se:h M. Hendrie May 16, 1979 Core Exit Therrecouples The MC Staff should request licensees and vendors to consider whether the core exit temperature measurements might be utilized, where avail-able, to provide additional indication regardirg natural circulation or the status of the core. For the latter purpose, it is rec:c. ended that the full te perature range of the core exit thermocouples be utilized.
4 At 'N-2, the temperatures displayed and recorded did rot in:1Me the full range of the thermocouples.
The Co=.ittee believes it.wuld be appro,:riate for the GC Staff to re-cuest licensees and vendors to consider and cer.ent on this reco=.enda-tion.
'Ihi.e regaest should be made as soon as convenient and the time allowed for responses should be such as not to degrade responses on higher priority matters.
Plant changes that might result eventtully from consideration of this recommendation w:uld not at this time seem to regaire a high priority.
Instrumentation to Follow the Course of an A,:cident The ability to follow and predie the course of an accident is essential for its mitigation and for the provision of credible arx! reliable pre-dictions of potential offsite consequences.
Instre.entation to follow the course of an eccident in power reactors of all types has long been a concem of the ACRS, is the subject of regulatory Guide 1.97 (which has not yet been implemented en an operatire plant), and is t.1e subject of an NRC Staff Task Action Plan for the resolution of generic issues.
The Committee believes that the Ecsitions of Regulatory Guide 1.97 should be reviewed, and redefined as necessary, and t. hat the' Task Action Plan should be reexamincd, as scon as manpower is available. We les-sons learned from MI-2 should be the bases for these reviews.
For ex-ample, improved samplirs procedures under accident conditions should be considered.
Although review and reexamination of existing criteria may take some tirc.e, the studies completed tc date, together with the understandirs gained from the accident at m1-2, should provide suf ficient basis for planned and appropriately pnased actions.
The Ccemittee believes that the installation of improved instrumentation on cperatire reactors of all types should be under,eay within one year.
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r H:norable Joseph M. Hendrie Pay 16,1979 Reactor Safety Research The ACES recom. ends that safety research en the behavior of light ater reactors during anomalous transients be initiated as seen as possible and be assigncd a high priority. We ACRS would exact to see plans and proposals within about three months, prelimirarf results within an additienal six manths, and core comprehensiv'e results within a year.
Of particular interest would be the development of the capability to simulate a wide range of pestulated transient er accident c:nditiens, including various abner.a1 er Icw probability rechanical failures, ele:-
trical failures, or hte.an errors, in order to gain increased insight into measures that can be,taken to improve safety.
The new pregram of research to improve reactor safety lus been initiated caly recently, and then only on a relatively small scale.
'Be Cortaittee reiterates its previous recommendations that this program be pursued and its expansion sought by the Commission with a greater sense of urgency.
Status Moniterine Although the closed auxiliary feedwater system valves may not have cen-tributed directly or significantly to the core da. age or environmental releases at 'nc-2, the pot:ntially euch rore severe consequences of un-availability of engineered safety features in plants of any typ.e is of concem and deserving of attention.
Status monitorir,; not dependent chiefly on administrative control, and thus pessibly less subject to hu-man error, might help assure the availability of essential feature 3.
A reg;est should be made within the next few m:nt% r.nat licensees cen-sider additieral status monitoring of varicus engineered safety features and their supporting services. te NRC Staff should begin studies on the advantages a.~! disadvantages of such ronitoring on about the sa: e time scale. Responses from licensees should be expected in about one year, at which time the NRC Staff should be in a position to review and evalu-ate them.
The. Comittee recognizes that some of the reccxc ded actions in this report have already been taken by the EC Staff.
S'ncerely, M-
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