ML20125C640
| ML20125C640 | |
| Person / Time | |
|---|---|
| Issue date: | 01/10/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| REF-GTECI-A-44, REF-GTECI-EL, TASK-A-44, TASK-OR NUDOCS 8001110058 | |
| Download: ML20125C640 (8) | |
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Description of Problem
,,4 j Electric power for safety systems at nuclear power plants is w nw j
supplied by two redundant and independent divisions.
Each of these J
3 electrical divisions includes an offsite alternating current (A.C.)
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source, an onsite A.C. source (usually diesel-generators), and a
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The safety systems are designed to 3
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i The unlikely, but possible, loss of all A.C. power (that is, the 5
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loss of A.C. power from the of ite source and Aneur the onsite source) for an extended period of time, would place reliance for continued hhw
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o emme cooling on systems that do not A.C. electrical power.
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Although all plants have some core cooling capability that does not 3.k rely on A.C. electric power; additional equipment failures, incorrect
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~ a or Wylay3 op,erator action, or other unexpected events could poten-d v
tially result in an inability to shutdown and cool the core.
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AL, O iv a - C JL4 [ pokd d The purpose of this task is to. evaluate the capability of 3
nuclear power plants to maintain core cooling in the event of the W&
WO 11 A.C. power,seemeos and determine w at additional require-loss of 3
-c ments, if'an, may'be needed to provide reasonable assurance that t
the public health and safety is adequately protected.
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Initiating events Identify and estimate the frequency of
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7 all events that might result in the loss of A.C. power.
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Event Sequences Determine the event sequences that could
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result from the initiating events, determine branches
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) ConsequeAc Evaluate th consequence of ch b ';I 3-
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) System Identification Identify the instruments, controls, equipment, systeins (including support systems) and operator
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J ([) ' System Reliabiiity ' Estimate the reliability of the systems.
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Identify and obtain failure rate and reliability data.
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() Safety Assessment Define the consequences to be used in assessing safety e.g. process parameters, fuel limits g,-)j
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Estimate the probability of
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Perform uncertainty analyses E: 3 lu and estimate possible error of estimates due to uncer-y
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initial conditions, process variables, system availabilities j/,/,', y I.u bt
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o n addition hated to the highest priority as Generic Task wparated sumps, two A4, under &c mon perd We of Tontain-
)dlied. A loo approach ment Emergency Sum; Ecliability." Because this 7 the sump is required to action has only recently been taken, a Task Ac-
! out before reaching the taon Plan and schedule for this task have not yet h required that the sump been developed.
jng that one-half of the r
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'0 o YVa ned, ne NRC stau Station Blackout ks in accordance with
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l 5tably resolve this SRC staff is continuing Electrical power for safety systems at nuclear l insulation under pipe power plants is supplied by two redundant and 4
la better understanding independent divisions. The systems used to remove decay beat to cool the reactor core beans of losing the abili-following a reactor shutdown are included he emergency sump among the safety systems that must meet these ytions in the sump or at requirements. Each electrical division for safety someno as air entrain-systems includes an offsite alternating current pve pressure drops.
(a. c.) power connection, a standby emergency pult in pump cavita-diesel generator a. c. power supply, and direct pssible dernage to the current (d. c.) sources.
l The issue of station blackout was originally psitions regarding included as Generic Task B-57 in the NRC Pro-ad in Regulatory Guide gram for Resolution of Generic Issues. The task festing of Emergency involves a study of whether or not nuclear pr Pressurized Water power plants should be designed to accom-pes the testing of the modate a complete loss of all a. c. power, i.e., a pth in-plant and scale loss of offsite a. c. sources and both onsite
- formed to demonstrats emergency diesel generator sources. Loss of all
$he sump can be reliably
- a. c. for an extended period of time in pressuriz-
> 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 staff through a contrac.
pump that is not dependent on a. c. power for further guidance for'the actuation or operation), could result in an in.
tergency sumps to assure ability to cool the reactor core, with potentially
$n can be developed, serious consequences. If the auxiliary feedwater
)y planned to study the pumps are dependent on a. c. power to func-
)ergency cump blockage tion, then a loss of all a. c. power for an extend-bf Generic Task C 3, ed period could of itself result in an inability to in Containment." in ad-cool the reactor core. Although this is a low t to study the vortex for-probability event sequence, it could be a signifi-Generic Task B 18, cant contributor to risk.
!quirements for Con-Current NRC safety requirements require as a ontainment emergency minimum that diverse power drives be provided
}amental to the suc-for the redundant auxiliary feedwater pumps. As h the emergency core noted above, this is normally accomplished by to cool the core) and the utilizing an a. c. powered electric motor driven l
E (nceded to assure con-pump and a redundant steani turbine driven swing a loss-of. coolant pump. One concern is the design adequacy of 3, these portions of plants licensed prior to adoption of the current e been combined and r'
requirements.
%023540' A-19
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An initial survey of operating plants has been completed which indicates that all operating pressurized 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 i
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.
j This safety issue was previously included in the NRC Program for the Resolution of Generic issues as Generic Task B 57, but has recently been 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.
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90023341 A-20
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