ML19291C061
| ML19291C061 | |
| Person / Time | |
|---|---|
| Issue date: | 12/31/1979 |
| From: | Baranowsky P NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Hanauer S Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19291C036 | List: |
| References | |
| REF-GTECI-A-44, REF-GTECI-EL, TASK-A-44, TASK-OR NUDOCS 8001110303 | |
| Download: ML19291C061 (2) | |
Text
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DEC 311979 MEMORANDUM FOR: Stephen H. Hanauer, Asst. Director for Plant Systems Division of Systems Safety Office of Nuclear Reactor Regulation THRU:
Frank H. Rowsome, Deputy Director Probabilistic Analysis Staff Office of Nuclear Regulatory Research FROM:
Patrick W. Baranowsky Probabilistic Analysis Staff Office of Nuclear Regulatory Research
SUBJECT:
TASK ACTION PLAN FOR UNRESOLVED SAFETY ISSUE A-44,
" STATION BLACK 0UT" This memorandum provides a description of the approach or plan of action that PAS is and will be taking to resolve the issue of Station Blackout. We have essentially completed a short term screening analysis to identify those operating plants most likely to suffer core damage due to a station blackout and plan to release our findings and recommendations to 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 contractors. During the approximately 3 years that will be required to complete IREP, we will provide assistance to NRR in implementing the intent of our shorter term recommendations to those operating plants having peculiar designs.
Outlined below is additional detail on the tasks which will comprise the PAS efforts on station blackout.
1.
Short Term Screening Analysis and Recommendations 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 1734 245 800111030 3
. Stephen H. Hanauer to identify operating plants most likely to suffer core damage due to a station blackout. As a result of the study, interim recommendations will be provided to limit the probability of a station blackout accident.
Schedule: Survey Analysis - Janaury 15, 1980 Recommendations - January 15, 1980 2.
Station Blackout Assessment in IREP A more detailed investigation of the probability of station blackout accidents will be evaluated in IREP. Event and fault tree analyses will be performed 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 station blackout scenarios which will be analyzed. As this phase of the program evolves, additional recommendations may be provided for operating plaats.
Schedule: CR-3 Pilot Plant Study - March 1980 IREP Six Plant Study - September 1980 Subsequent Studies - Annual Intervals 3.
AC Power Systems Reliability 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 analyses of IRIP. This work will include generic considerations on AC power systems reliability to identify the important failure modes (offsite and onsite systems), establish appropriate probabi-listic modeling (particularly with regard to common 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 In addition to the above tasks, the Division of Water Reactor Safety Research is performing reactor coolant system response analyses for station blackout scenarios. Over the next year 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.
sfUf&r'
atrick W. Baranowsky Probabilistic Analysis taff Office of Nuclear Regulatory Research 1734 2'46
sulation). The elevated to the highest priority as Generic Task d that,6 addition arated sumps, two A-43, under the more general title of "Contain-ment Emergency Sump Reliability." Because this ed. A low approach action has only recently been taken, a Task Ac-the sump is required to out before reaching the tion Plan and schedule for this task have not yet required that the sump been developed, ng that one-half of the ked. m NRC staff Station Blackout s m accordance with tably resolve this RC staff is continuing Electrical power for safety systems at nuclear sulation under pipe power plants is supplied by two redundant and better understanding independent divisions. The systems used to remove decay beat to cool the reactor core cans of losing the abili-following a reactor shutdown are included emergency sump among the safety systems that must meet these tions in the sump or at requirements. Each electrical division for safety omena as air entrain-systems includes an offsite alternating current ve pressure drops.
(a. c.) power connection, a standby emergency sult in pump cavita-diesel generator a. c. power supply, and direct ssible damage to the current (d. c.) sources.
The issue of station blackout was originally sitions regarding included as Generic Task B-57 in the NRC Pro-in Regulatory Guide gram for Resolution of Generic Issues. The task esting of Emergency involves a study of whether or not nuclear Pressurized Water power plants should be designed to accom-es the testing of the modate a complete loss of all a. c. power, i.e., a th in. plant and scale loss of offsite a. c. sources and both onsite formed to demonstrate emergency diesel generator sources. Loss of all n
he sump can be reliably
- a. c. for an extended period of time in pressuriz-e staff believes that ed water reactors, accompanied by loss of the ce with this Regulatory auxiliary feedwater pumps (usually one of two this issue. As sup-redundant pumps is a steam turbine driven taff, through a contrac-pump that is not dependent on a. c. power for r
further guidance for the actuation or operation), could result in an in-rgency sumps to assure ability to cool the reactor core, with potentially n can be developed, serious consequences. If the auxiliary feedwater g
planned to study the pumps are dependent on a. c. power to func-f 1
rgency sump blockage tion, then a loss of all a. c. power for an extend-f Generic Task C-3, ed period could of itself result in an inability to n Containment." In ad-cool the reactor core. Although this is a low to study the vortex for-probability event sequence, it could be a signifi-eneric Task B-18, cant contributor to risk.
quirements for Con-Current NRC safety requirements require as a ntainment emergency minimum that diverse power drives be provided amental to the suc-for the redundant auxiliary feedwater pumps. As the emergency core noted above, this is normally accomplished by o cool the core) and the utilizing an a. c. powered electric motor driven (needed to assure con-pump and a redundant steam' turbine driven wing a loss-of-coolant pump. One concern is the design adequacy of
, these portions of plants licensed prior to adoption of the current been combined and requirements.
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D A-19
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b, An initial survey of operating plants has been D
completed which indicates that all operating pressurir.ed water reactors have either steam tur-bine driven or diesel driven auxiliary feedwater pumps (neither of which are dependent on a. c.
power). This assures at least that some capability exists for accommodating an extended loss of all
- a. c. power. Further review of older plants in this regard will be conducted as part of the NRC's Systematic Evaluation Program (see earlier discussion in this chapter). Further study will include determining if any requirements beyond providing diverse power drives for the auxiliary feedwater pumps are needed-such as specific time requirements for the period during which the plant must be capable of accom-modating a station blackout.
This safety issue was previously included in l
the NRC Program for the Resolution of Generic Issues as Generic Task B-57, but has recently ben elevated to the highest priority as Generic Task A-44. Because this action has only recently been taken, a Task Action Plan and schedule for this task have not yet been developed.
1734 248 e
A-20 Ak