ML19221A399
| ML19221A399 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/11/1979 |
| From: | Cunningham M NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| References | |
| NUDOCS 7905220442 | |
| Download: ML19221A399 (3) | |
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Dra?i-see sk"P on
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+o Tm l m.n u A brief examination of the Reactor Safety Studyf has been conducted i
to determine what the study said about the contribution of the TMI-2 event to the overall risks resulting from the operation of nuclear power plants.
It,should be recognized that the use of the Reactor Safety _ tudy i/
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I[r'esul ts'in con af ty desigh
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L operation nd rev/iue of the TMI-2 event,ha 3
zards.
These hazar der firstly from t act that the RSS was an overall f
assessme g the r k expected to'be undertaken by the-public due e lance _.cn-a pat basis _on_t ucl ea r-power.
The overall model used in the RSS was directed only toward risk assessment and consequently many elements were developed and le' implemented only towed that purpose; thus they are not directly applicable for other purposes such as optimization of safety designs or the determination of effects of reactor accidents at individual mo9d s forjuch sites.
The/'RSS acknowledged'that the usdeve o f ti.s purposes would req /
uire, further/
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analyses other than 'overall pi,te risk ass s/
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-Hazarddn tbrusn f the RSS to-de,termine-effects-of-specific ace pyD s
c.idents--e+so-der-ive--frem_dhedact thatdhe PWR analyzedhthe-RSS-h a a. m
-Fa reactor design, With_-Some design di f ferences from 7905220 m
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TMI-2 which could cause a di fferent response to the TMI-2 sequence of events.
The~ RSS ecognized^that the d fference in design
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between ario pla designs uggested t e furthe conside tion l
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of the' aiplicabilitj of the results/obtai led for t Surrey}Iand t edeaci Bottom-2 got to nuble/ar powerh1 ants i
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It is considered for purposes of comparison to the RSS nomenclature that the TMI-2 event included a transient (the loss of main feedwater),
the failure of the auxiliary feedwater syttem and the failure of the primary power operate 6 relief valve to reclose.
A failure of
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the ECCS was not considebedfitnc d he ECCS responded as designed upon
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u& rsJ w-damand A failure of the containment was not considered since the g
containmentrespondedasdesignedandinanyeventcontainedvirtually{
all of the radioactvity released from the primary sytem.
In the sense of the definitions of the RSS,a core melt was considered to have occurred since it is known that significant fractions of the core's radioactive constituents were released from the core. Alhgh the RSy@ fines a re,mell;as h release Qe en fthe cercp dioa::t ve co stituen The probability contributions that dominate the spectrum of PWR releases were found to be shared largely by three accident even,ts:
the small A e m Os-.
LOCA, the transient involving loss of offsite^pcwer and the low pressure injection system check valve failure.
Further, a transient in conjunction 161 314
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feilure of a primary power operated relief valve to reclose combined g g rt-m s j with a failure of containment function wou+d not make a significant c wt.E niih, U
c contribution to tiie tr-ansient probab444 ties.
Therefore it is concluded that the RSS did not identify a,W sequence tLJ.
4 of events such as the TMI-2 events be4ng dominating or contributin,,g;.
significantly to the nublic health and safety risks compared either to the risk contributed by other transient sequences or other acci-ksc( *+TL,.an Nd (fNW
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c dent sequences. Numerous-caveats ast-he observedL1rpmak-ing-this-(.omparim nr -
1 The RSS does not account for operator action in restoring systems that were initially failed or in deactivating needed systems that initially responded to a demand for them.
Thus in this comparison of the TMI-2 event with the RSS results auxiliary feedwater was ass:cied lost and the power operated primary relief valve was assumed stuck open.
Both of these situations were corrected by the operator later on.
Ontheotherjhand,theECCSwasinitially available and was intermittently stopped and started through-out the evers by the operator, b'K (49 b" u@p - Un., 3 4.Ma -ta-u+du C
b~^^ b""t' 2.
The differences in the designs of the Surrey-1 plant an2 M og the TMI-2 plant could lead to different assessments of the F4W.
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reliability of for the relevant TMI-2 systems such as main feedwater, auxiliary feedwater, relief valves and ECC systems.
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