ML19291C037
| ML19291C037 | |
| Person / Time | |
|---|---|
| Issue date: | 01/04/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19291C036 | List: |
| References | |
| REF-GTECI-A-44, REF-GTECI-EL, TASK-A-44, TASK-OR NUDOCS 8001110117 | |
| Download: ML19291C037 (6) | |
Text
Task A-44 Preliminary Draft January 1980 1.
DESCRIPTION OF PROBLEM Electric power for safety systems at nuclear power plants is supplied by two or more redundant and independent divisions.
Each of these electrical divisions includes an offsite alternating current (A.C.) source, an onsite A.C. source (usually diesel-generators), and a direct current (D.C.) source.
The safety systems are designated to function with either the offsite A.C.
power source or with the onsite A.C. power source.
The unlikely, but possible, loss of all A.C. power (that is, the loss of A.C. power concurrently from the offsite source and the onsite source) for an extended period of time, would place reliance for continued shutdown cooling on systems that do not require A.C. electrical power. Some plants have some core cooling capability that does not rely on A.C. electric power; even for these plants, additional equipment failures, incorrect or delayed operator action, or other unexpected events could result in an inability to shutdown and cool the core.
The purpose of this task is to evaluate the characteristics of events with a potential for inducing loss of all AC power and the capability of nuclear power plants to maintain core cooling in the event of the loss of all A.C. power, and from this infonnation to detennine what additional requirements, if any, may be needed to provide reasonable assurance that the public health and safety is adequately protected.
1734 239 8001110117
2-1 2.
PLAN FOR PROBLEM RESOLUTION A.
Approach The evaluation of this issue will involve a quantitative probabilistic assessment of the loss of all A.C. power, leading to re-evaluation of requirements related to onsite and offsite A.C. power systems and also to the capability for shutdown cooling without A.C. power. We have essentially completed a short term screening analysis to identify those operating plants most likely to suffer core damage due to a sta-tion blackout and plan to release our findings and recommendations to s
NRR by mid January 1980.
A probabilistic evaluation for station blackout considerations not included in the screening analysis will be provided through the Integrated Reliability Evaluation Program (IREP) and by smaller and more specific studies performed within PAS or by PAS con-tractors.
During the time that will be required to complete IREP, we will implement the intent of our shorte'.- term recom-mendations to those operating plants where it is appropriate.
B.
Management of Work By memo dated July 13, 1979, from the Director of NRR to the Director of RES, this issua was transferred to RES.
However, NRR must maintain cog-nizance and issue blackout-related licensing requirements as appropriate.
Accordingly, the lead for each task in subsection C below is assigned to RES or NRR as appropriate.
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2-2 C.
Task Descriptions 1.
Short Tenn Screening Analysis and Recomendations (RES lead)
All operating plants are being analyzed to make a rough, plant-specific estimate of the failure probability for all AC power.
The probability of a loss of decay heat removal capability given a blackout is also being evaluated for PWRs.
The analyses are intended to be a screening mechanism to identify operating plants most likely to suffer core damage due to a station blackout. As a result of the study, interim recomendations will be provided to limit the probability of a station blackout accident.
Schedule:
Survey Analysis - January 15, 1980 Recommendations - January 15, 1980 2.
Station Blackout Assessment in IREP (RES lead)
A more detailed investigation of the probability of station blackout accidents will be evaluated in IREP.
Event and fault tree analysis will be perfonned for all operating LWRs which will include transient accident sequences associated with a station blackout.
In addition to the station blackout sequences evaluated in the screening analysis (Task 1), the hazards posed by extended blackouts and reactor coolant system inventory considerations will be included in a complete set of stction blackout scenarios which will be ana?yzed. As this phase of the program evolves, additional recommendations may be provided for operating plants.
Schedule: CR-3 Pilot Plant Study - March 1980 IREP Six Plant Study - September 1980 Subsequent Studies - Annual Intervals 1734 241
2-3 3.
AC Power Systems Reliability (RES lead)
A reexamination of the frequency and duration relationships for station blackouts will be conducted by PAS and its contractors to support the detailed plant-specific ane'.yses of IREP. This work will include generic considerations on AC power systems reliability to identify the important failure modes (offsite and onsite systems),
establish appropriate probabilistic modeling (particularly with regard to coninon cause and interactive types of failure modes), and to identify and quantify, where possible, practical improvements to AC power systems reliability.
Schedule: Reexamination of AC Reliability - October 1980 4.
The Division of Water Reactor Safety Research is performing reactor coolant system response analyses for station blackout scenarios.
During CY 1980, at least one typical NSSS of each LWR vendor will be analyzed in detail to provide a better estimate of the core damage times and to determine the important operational characteristics which will be particularly useful for accident recovery.
5.
Short-term improvements in operating reactors (NRR lead)
The results of Task 1 and the initial parts of Task 2 will be used to identify potential short-term improvements in offsite electrical supply reliability, onsite power capability, and plant cooling capability.
Each operating reactor licensee will be required to review his plant in the light of this information, and to propose and implement appropriate improvements.
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2-4 6.
Interim licensing guidance (NRR lead)
The results of Task 1 and the initial parts of Task 2 will also be used to identify improvements to be made in near-term operating license reviews.
7.
Revised licensing requirements (NRR lead)
The results of Tasks 1-4 and other infonnation being developed under the TMI Action Plan will be used to develop, for public comment and promulgation, licensing requirements related to station blackout.
3.
BASIS FOR CONTINUED PLANT OPERATION AND LICENSING PENDING COMPLETION OF TASK A.
Low probability of blackout Redundant offsite sources Reliable grid Redundant onsite sources Single failure criterion B.
Ability of some plants to cool core even in blackout C.
Improvements in Aux Feedwater (TMI follow-on Bulletins & Orders)
D.
Interim Improvements as appropriate per Task 5 and 6 4.
NRR TECHNICAL ORGANIZATIONS INVOLVED (later) 5.
TECHNICAL ASSISTANCE (later) 6.
ASSISTANCE REQUIREMENTS FROM OTHER NRC 0FFICES - RES to fill in 7.
INTERACTIONS WITH OUTSIDE ORGANIZATIONS (later) 1734 243
2-5 8.
Potential Problems A.
Liaison needed NRR/RES B.
Translation of probabilistic results into licensing requirements C.
Ensuring that IREP starts out with blackout problem in its technical structure D.
Potential delays in resolving A-44 if IREP is delayed E.
Manpower limitations in RES and its contractors 1734 244