ML20056F385
| ML20056F385 | |
| Person / Time | |
|---|---|
| Issue date: | 07/23/1993 |
| From: | Chilk S NRC OFFICE OF THE SECRETARY (SECY) |
| To: | Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| References | |
| REF-10CFR9.7 NUDOCS 9308270094 | |
| Download: ML20056F385 (5) | |
Text
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July 23, 1993
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OFFICE OF THE l
SECRETARY l
MEMORANDUM TO:
James M. Taylor R
l Executive Director for OpdRations FROM:
Samuel J.
Chilk, Secretar
SUBJECT:
SECY-93-108 - REVISED GUI DELINES FOR PRIORITIZATIONOFGENERICSgFETYISSUES The Commission (with all Commissioners agreeing) has approved the revised guidelines for the prioritization of generic safety l
issues (GSIs) subject to the changes indicated below and in the i
attachment.
The Commission approved the conversion to an impact /value ratio from the former value/ impact ratio.
However, toe Commission expressed concern that the impact /value ratio has little or no l
meaning in the presence of large uncertainties if the ratio of means is used as opposed to mean ratios.
The staff should therefore, exercise care in using the ratio of means when an impact /value ratio is required for prioritizing an issue.
The staff should change the priority ranking grid and incorporate the changes as shown in the attachment.
(EDO)
(SECY Suspense:
9/17/93)
Attachment:
As stated i
l l
l l
l SECY NOTE:
THIS SRM, SECY-93-108, AND THE VOTE SHEETS OF ALL COMMISSIONERS WILL BE MADE PUBLICLY AVAILABLE 10 WORKING DAYS FROM THE DATE OF THIS SRM
[I 9308270094 930723 PDR 10CFR I
PT9.7 PDR
. cc:
The Chairman Commissioner Rogers Commissioner Remick Commissioner de Planque OGC OCA OIG Office Directors, Regions, ACRS, ACNW (via E-Mail)
ASLBP (via FAX)
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l Revision 4 v:10/impactyVilungatTd pricrity :: r is presented in Figure 1.
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might result in a low priority score. When a GSI is considered important from the safety viewpoint, the assignment of a HIGH priority to its resolution should not be deterred by the initial absence of an identified solution.that could be-implemented with a moderate cost.
At the other extreme, an issue's safety significance could be too minor to warrant diversion of attention from more im
. safety issues even if it-has a HiMagny~mmewatW @portant pri:rity :::r: because an inexpeiishv~e solutToT~ls~6ilieved to be available. Below a minimal safety significance threshold, the priority would always be DROP; where the potential risk
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5.
Other Considerations The formula-based rankings represent the primary concern of the NRC:
I public safety. The secondary concern is the impact on licensees, evaluated in terms of cost. However, the tentative priority rankings are j
subject to the limitations of an often incomplete and imprecise data base and to possible distortions due to the nature of the necessarily highly simplified quantitative formula underlying them.
(Thi: i: th: prin:ip:1 r n n f: ::teli:hing l= thrnh:Id v:hn fer th: LO" =d 0".^"
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Special situations with respect to some issues may cause added difficulty in priority assignment. While the formula-based tentative rankings must generally indicate that the safety significance is sufficient to justify NRC action, other considerations not adequately reflected, or not reflected at all, in the numerical formula are often needed to corroborate or adjust the results. Decision-making is helped by i
explicit identification of such other considerations and explanation of how they bear on the resulting final priority ranking, whether the effect is one of corroborating or of changing the estimates.
Listed below are some factors that may be important in arriving at a sound priority ranking and may lead to adjustment of a tentative, formula-derived ranking.
Possible effects of occupational doses,:vertM plantege :ecty, and uncertainty bounds ((a)(1), (a)(2), (:)(3)1 and (b)(1) below) require particularly careful consideration for all issues.
The factors listed are not considered all inclusive. Others thought significant are discussed OR2j@
24 NUREG-0933
l and, when practical, quantified appropriately in the overall rierity andithei 6 as s oc;uanti fi ed frisid si gni fi cinceinensiniiiahd EimpactfW
=:r: =d it: :
iated~6ncertainties~Sometimes7thireWe special~""~~~
binii' eMfions.that are quite specific to an issue or some aspect of it.
d The partial list of other factors is listed below.
IWsh661diliiihatid d&r*M thathin%essNissibihetheE~ihiissusiiEuldiFEsiffeTa?HIGH!PrioHtylonly thosslofsthe ifactorsithathel ateitotsafetyMe sisenicolsiderationf~
(a)
Special risk and cost aspects not included in or potentially masked by the numerical formulas:
The not change in occupational doses i:::plicit in ~.~Q)its; :Tjd (1) implementing the current versus the proposed requirense 1=,
n= r:dici:;i=1 =: ;:ti:::1 5:=rd; inh =:nt in, = cff::t:d by, th: pr:;=:d rn :1 ti:::.3 (2) Any significant non-radiation-related occupational risk sffEtedibfM_jsiii3BIiFiiis615tibhiR (3) "c;=ted =:t :f p1=t in g: frs; th: p=tel:ted =:id =0.
(43) Loss or. severe degradation of a layer in the defense-in-depth concept (e.g., one mode of core cooling or containment cooling).
(64) Issues for which solutions of widely differing costs may be applicable to different classes of plants or various plants are otherwise affected in vastly different ways.
(b)
Factors related to uncertainties stemming from an incomplete or imprecise data base for the priority formula:
(1) Uncertainty bounds, imbalance in uncertainty factors, certainty of cost to fix versus uncertainty that safety is really improved and the true extent of such improvement.
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(2) Situations where uncertainty is extraordinarily large-(in accident probability, consequences, or cost, or any or all of these).
(3) Problems which are ill-defined and problems for which solutions are not evident so that at least the resources necessary to understand the problem are assignedf (4) The potential for a proposed change to affect more than one accident or transient. sequence, thus affecting risk to a greater or lesser degree than assessed in the description of the issue; notably, the potential for a new safety decrement, or increase in risk, due to unidentified effects of a proposed change, or addedcomplexity,orforotherreasons]
.(5) Circumstances imparting unusual significance to accident consequences (such as ingestion-pathway effects) or mitigating measures (such as evacuation) that are not directly included in the public dose calculationsi 0Q22[91 25 NUREG-0933
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