ML19289F811
| ML19289F811 | |
| 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 | |
| ML19289F809 | List: |
| References | |
| NUDOCS 7906200029 | |
| Download: ML19289F811 (4) | |
Text
4 g** "4g f,
fg UNITED STATES y
T e.
i g NUCLEAR REGULATORY COMMISSION t5:
j ADVISORY COMMITTEE ON REACTOR SAFEGUARDS g
g wAsma roN, D. C. 20555 K3y 16, 1979 Honorable Joseph M. Hendrie Chairmn U. S. Nuclear Regulatory Ccenission Washirston, DC 20555
Subject:
Ih"ERIM REPORT NO. 2 ON 'HGEE MILE ISLAND hV' LEAR STATION LNIT 2
Dear Dr. Eendrie:
During its 229th meeting May 10-12, 1979, the Advisory Comittee on Re-actor Safeguards continued its review of the circumstances relatirg to the recent accident at Wree Mile Island Nuclear Station Unit 2 ('lMI-2).
The recorrend:tions presented orally to the Cecmissioners on April 17, 1979 were reviewed by the full Comittee and are repeated in somewhat amplified forn herein. Amplification of these items is responsive to the request of Acting NRC Chairman Victor Gilinsky dated April 18, 1979.
Natural Circulation - Procedures It is evident from the experience at 'MI-2 that there was failure to es-tablish natural circulation of in the primary system and failure to recognize in a timely ranne. cnat ratural circulation had rot been a chieved. De need for rutural circulation under certain circu:nstances is ccxmen to all PWRs.
The Cemittee reconcends that procedures be developed by all operators of PdRs for initiatirq retural circulation in a safe manner and for pro-viding the operator with assurance that circulation has in fact been es-tablished, nese procedures should take into account the rehavior of the systers under a variety of abnorral corditions.
As a first step, the hRC Staff should initiate immediately a survey of operating procedures for achievirs natural circulation, including the case when of fsite pawer is lo::t. At the same time, the operators of all FWR plants should be request.d to devrlop detailed analyses of the be-havior of their plants follt. wing anticipated transients and strall breaks in the prirary system, with appre
' ate consideration of potential ab-norral conditions, operatcr erro and failures of equipnent, power sources, or instruacntation. mese aralyses are necessary for the 7 9 0 6 '2 0 0 0 2"t 233 005
6 Honorable Jose;t M. Hendrie Msy 16, 1979 develo; rent of suitable operatire procedures. he review and evaluation of these a:ulyses by the h3C Staff should receive a priot.ty consistent with the priority being given to changes in operatire procedures.
71 Circulation - Pressurizer Heaters
~
se of retural circulation for decay heat receval followirq an accident in a F%R normlly requires the mintenance of a suitable over-pressure cn the reactor coolant system in order to prevent the genera-tion of steam which can impede circulation. For many transients, min-temnce of this overpressure is best accomplished by use of the pres-surizer heaters.
Althatgh the pressurizer heaters at MI-2 continued to receive power f roa offsite sources during the entire accident, the availability of offsite Fower cannot be assured for all transients or accidents during which, or followirg which, natural circulation must be established. he Comittee reconnends that the h2C Staff initiate imediately a survey of all F%Rs licensed for operation to determine whether the pressurizer heaters are now or can be supplied with power frce qualified msite sources with suitable redundancy.
Natural Circulation - Saturation Conditions ne plant operators should be informed adequately at all times of those conditions in the reactor coolant system that might affect their capa-bility to place the system in the mtural circulation code or to sustain it in sud a code.
Information indicatirg that coolant pressure is ap-proachirig the saturation pressure correspondirg to the core exit temper-ature would be especially useful, since an impendirg loss of overpressure would sigral to the operator a patential loss of natural circulation.
This information can be derived from available pressurizer pressure and hot leg temperature measurements, in conjtetion with conventional steam tables.
The Cccrnittee recccraends that information for dete ing an approach to saturation pressure be displayed to the operawc in a suitable form at all tires. Since there rey be several equally acceptable means of providing this inforration, there is no need for the h30 Staff to as-sign a high priority to the developt of prescriptive recuirements for such displays. Fowever, a reasorably early request that licensees and vendors consider and concent on the need for such a display would be appropriate.
233 Obb
Honorable Joseph M. Hendrie P.y 16, 1979 Core Exit herroccuoles The NRC Staff should request licensees and vendors to consider whether the core exit tergerature measurements might be utilized, where avail-able, to provide additional indication regardirg ratural circulation or the status of the core. For the latter purpose, it is reccaneMed that the full temperature Jmge of the core exit therroccuples be utilized.
At 'IMI-2, the te:Teratures displayed and recorded did rot include t%
full rarse of the thermocouples.
ne Ccrrtittee believes it would be appropriate for the NRC Staff to re-quest licensees and vendors to consider and corment cri this recomerda-tion. his request should be made as soon as emvenient ard the tim allr wed for responses should be such as rot to degrade responses on higher priority ratters. Plant changes that might result eventtally from consideration of this recorrmendation would rot at this time sean to require a high priority.
Instru entation to Follow the Course of an Accident The ability to follow and predict the course of an accident is essential for its mitigation and for the provision of credible and reliable pre-dictions of potential offsite consegaences.
Instrumentation to follow the course of an accident in Iower reactors of all types has long been a concern of the ACRS, is the subject of Regulatory udide 1.97 (which has not yet been implenented cn an operating plant), and is the subject of an HEC Staff Task Action Plan for the resolution of generic issues.
ne Comittee believes that the pasitions of Regulatory Guide 1.97 should be reviewed, ard radefined as necessary, and that the Task Action Plan shoulc be reexa:nined, as soon as ranpower is available. %e les-sons learned frcan DiI-2 sbculd M the bases for these reviews. For ex-ample, improved samplirg procedures uMer accident conditicms should be considered.
Althotyh review ard reexamination of existing criteria ray take come time, the studies ecx pleted to date, together with the understandirg gained frce the accident at 'IMI-2, should provide sufficient basis for planned and appropriately phased actions. We Ccanittee believes that the installation of ir: proved instrunentation on operatirg reactors of all types should be urderway witnin one year.
233 007
s s
I Eonorable Joseph M. Hendrie May 16, 1979 Reactor Safety Research The ACRS recccmends that safety research on the behavior of light-water reactors during anocalous transients be initiated as soon as possible and be assigned a high priority. Be ACRS would expect to see plans and proposals within about three renths, preliminary results within an additicnal six conths, arx! unre comprehensive results within a year.
Of particular interest would be the developnent of the capability to simalste a wide range of postulated transient or accident conditions, includire various abnormal or low probability mechanical failures, elec-trical failures, or hunan errors, in order to gain increased insight
.nto measures that can be taken to improve safety.
he new program of research to improve reactor safety has been initiated
_ only recently, and then only on a relatively small scale-he Committee reiterates its previous reconmendations that this program be pJrsued and its expansion sought by the Cmmission with a greater sense of urgency.
Status Monitorirn Although the closed auxiliary feeowater system valves may not have con-triNted directly or significantly to the core damage or environnental releases at 'mI-2, the patentially much nore severe consequences of un-availability of ergineered safety features in plants of any type is of concern and deserving of attention. Status monitorirg not dependent chiefly on administrative control, and thus possibly less subject to hu-man error, might help assure the availability of essential features.
A request should be made within the next few conths that : ?.censees con-sider additional status monitoring of varbus engineered safety features and their sup;crti~; services. De NRO Staff should begin sttx31es on the advantages and disadvantages of such nonitorirg cn about the same 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 arx3 evalu-ate them.
The Conraittee recognizes that some of the reconnended actions in this report have already been taken by the NRC Staff.
- cerely, Pax W. Carbon Q> airman 233 000