ML20195J297
| ML20195J297 | |
| Person / Time | |
|---|---|
| Issue date: | 06/14/1999 |
| From: | Travers W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Powers D Advisory Committee on Reactor Safeguards |
| References | |
| RULE-PR-50-MISC, RULE-PR-72-MISC NUDOCS 9906180160 | |
| Download: ML20195J297 (8) | |
Text
b g "E4 7
gf q
UNITED STATES l
NUCLEAR REGULATORY COMMISSION
\\...glf WASHINGTON, D.C. 20666 4 001
~
June 14, 1999 Dr. Dana A. Powers, Chairman Advisory Committee on Reactor Safeguards i
U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
SUBJECT:
FINAL RULE - REVISIONS TO 10 CFR PARTS 50 AND 72, REQUIREMENTS CONCERNING CHANGES, TESTS, AND EXPERIMENTS i
Dear Dr. Powers:
In a letter uated May 17,1999, on the above subject, the Advisoiy Committee on Reactor Safeguards stated that it tupported issuance of the final rule, subject to resolution of various comments and concems. As discussed during the briefing on May 5,1999, the schedule established for the final rule package did not allow time for consideration of most of these comments before SECY-99-130, dated May 12,1999, was issued forwarding the final rule to the Commission.
In the letter, the Committee raised fourissues. First, the Committee recommended that the language for criterion (vii) be revised to " result in a fission product barrier being altered by a change in its design basis limit or a likely reduction in the margin between the design basis limit and the failure point." The staff-proposed criterion deals with changes affecting the facility when the response of a barrier would exceed its design basis limit or where the limit itself is affected by the change. The basis for this proposal is that the limits are established at a point that integrity of the barrier is maintained, having taken into account uncertainties and the need to provide margin to the point atwhich failure could occur. The staff believes that the first part of the criterion proposed by the Committee is similar to the staff's criterion of " limit being rJtered," since the staff would expect that the limit would only be altered if there was a change to the barrier, or to the understanding about how the barrier responds to particular i
events. The situation that the second part of the Committee's proposed revision seemed to
{
address is a change that affects the barrier in which the limit remains the same, but for which f
the failure point may have moved closer to the limit than was previously contemplated. The specific example mentioned was installation of a hardened vent where the containment barrier i
capability is reduced by introducing the ability to open the containment barrier before reaching its failure point. There would be some interpretation issues arising from use of the terms g/0)
"likely" and " margin." The staff concludes that the specific example would likely be addressed by other evaluation criteria, such as a more than minimal increase in consequences in those situations in which the vent would be planned for use under design basis accident conditions.
Therefore, the staff does not recommend adoption of the altemate criterion.
g The second issue concemed the subjectivity associated with basing enforcement discretion on whether the matter required " substantial review." In SECY-99-130, the staff further discussed how " substantial review" would be determined. As noted, this determination relates only to whether discretion would be exercised, not whether there is a violation. Further, the determination is another way of judging the significance of the failure to seek NRC review of a
& Ib h i
7 g^ )9e& k4 c1,/
t PDR PR L 4-1PT 50 9906180160 990614
'3 50 MISC PDR 8
- 7. LI1-lhI 4
/
Dr. Dana Powers '
change. A change made without prior NRC review but that clearly meets NRC requirements is of less concem than a change that is sufficiently novel or complex that it is not readily apparent whether NRC requirements have been met, and thus requires NRC review of its merits.
The third issue concemed criterion (viii) on evaluation methods. The Committee recommended that " minimal departures" be allowed to preclude the criterion from becoming a "zero change" standard. The sta*. was also concemed about the potential impact of a zero change standard, and thus developed the language of " departure" to provide ways by which a licensee could make changes to methods without NRC approval under certain con,ditions. For instance, if the new method that the licensee wishes to use has been approved, it could be used even if there were more than " minimal" effects upon the results. The staff did not incorporate the term " minimal" because of difficulties in defining its meaning for the spectrum of possible analyses that might be included. The staff acknowledges that guidance will help ensure a clear understanding of " essentially the same" and intends to work c;osely with the industry and other stakeholders to develop guidance on both evaluation methods and input l
parameters.
The fourth issue concemed the discussion in the Statement of Considerations (SOC) for minimalincreases in consequences. The Committee stated that the staff-proposed guidance of "10% of the difference between the calculated value and the regulatory value" lacked sufficient justification and that the staff should discuss the management of incremental changes. The staff stated in the SOC that10 percent was a value chosen to allow some flexibility yet at the same time restrict changes from consuming all remaining " margin" to the regulatory values without the opportunity for NRC review. Although the specific value of 10 percent is a matter of judgment, the staff does believe that it is consistent with the " minimal" philosophy desired by the Commission, that is, of being more than " negligible" but less than "significant." Further, since the 10 percent applies to the remaining " margin," incremental changes can result in the consequences approaching, but not exceeding the regulatory values.
Finally, in its letter, the Committee noted some specific changes to the draft SOC, which the staff included in the paper us forwarded to the Commission.
The staff is awaiting Commission guidance on SECY 99-130. As the staff develops its Regulatory Guide in this area, it will continue to discuss important issues with the Committee.
Sincerely William D. Travers Executive Director for Operations cc: Chairman Jackson Commissioner Dieus Commissioner Diaz Commissioner McGaffigan Commissioner Merrifield SECY
ch ngs. A changs m:d3 without prior NRC rsvi:w but that cisarly mxts NRC r:quiramants is of l;ss concem thin a changs that is sufficiantly novel or complex that it is not readily apparent whether NRC requirements have been met, and thus requires NRC review of its merits.
The third issue concemed criterion (viii) on evaluation methods. The Committee recommended that " minimal departures" be allowed to preclude the criterion from becoming a "zero change" standard. The staff was also concemed about the potential impact of e zero change standard, and thus developed the language of " departure" to provide ways by which a licensee could make changes to methods without NRC approval under certain conditions. For instance, if the new method that the licensee wishes to use has been approved, it could be used even if there were more than " minimal" effects upon the results. The staff did not incorporate the term " minimal" because of difficulties in defining its meaning for the spectrum i
of possible analyses that might be included. The staff acknowledges that guidance will help ensure a clear understanding of " essentially the same" and intends to work closely with the industry and other stakeholders to develop guidance on both evaluation methods and input parameters.
The fourth issue concemed the discussion in the Statement of Considerations (SOC) for minimal increases in consequences. The Committee stated that the staff-proposed guidance of "10% of the difference between the calculated value and the regulatory value" lacked sufficient justification and that the staff should discuss the management of incremental changes. The staff stated in the SOC that 10 percent was a value chosen to allow some.
flexibility yet at the same time restrict changes from consuming all remaining " margin" to the regulatory values without the opportunity for NRC review. Although the specific value of 10 percent is a matter of judgment, the staff does believe that it is consistent with the " minimal" philosophy desired by the Commission, that is, of being more than " negligible" but less than "significant." Further, since the 10 percent applies to the remaining " margin," incremental changes can result in the consequences approaching, but not exceeding the regulatory values.
Finally, in its letter, the Committee noted sorne specific changes to the draft SOC, which the staff included in the paper as forwarded to the Commission.
The staff is awaiting Commission guidance on SECY 99-130. As the staff develops its Regulatory Guide in this area, it will continue to disgss important, issues with the Committee.
y a.m William D. Travers Executive Director for Operations cc: Chairrr,an Jackson Commissioner Dieus Commissioner Diaz Commissioner McGaffigen DISTRIBUTION: See attached page Commissioner Merrifield DOCUMENT NAME: G:\\PGEB\\EMM\\G990254 SECY
- See previous concurrence OFFICE '
RGEB: DRIP
- TECH. EDITOR SC:RGEB: DRIP
- C:RGEB*
NAME EMcKenna:sw BCalure*
FAkstulewicz CCarpeer F
DATE 5/27/99 5/28/99 5 /27/99 5/27/9)I Eh OFFICE '
D: DRIP
- ADIP
- D:NRR*
NAME DMatthews WKane SCollins WTk ers DATE 6 / 3 /99 6 /8 /99 6 /8 /99 6/jb9
DISTRIBUTION: Green Ticket 19990254 Dated June 14. 1999 Central File (w/ incoming)(GT 19990254)
PUBLIC (w/ incoming)(GT 19990254)
EDO r/f (w/ incoming)(GT 19990254)
NRR MAILROOM (w/ incoming)(GT 19990254)
RGEB r/f (w/ incoming)(GT 199990254)
WDTravers FMiraglia, Jr.
MKnapp PNorry JBlaha GTracy JMitchell KCyr SBurns ACRS r/f SCollins RZimmerman BSheron WKane WBrach, NMSS PBrochman, NMSS DMatthews SNewberry
^CCarpenter FAkstufewicz EMcKenna MManahan, (G19990254)
)
RLaskin (EMail/RSL) l
of 1:ss cone:rn thin a changs that is suffici:ntly nov:1 or compl:x that it is not readily apparnnt wh:th:r NRC rcquir:m:nts h:va b::n mat. end thus rcquires NRC revi:w of its marits.
Tne third issue concerned criterion (viii) on evaluation methods. The Committee recommended that " minimal departures" be allowed to preclude the criterion from becoming a "zero change" standard. The staff was also concerned about the potentialimpact of a zero change standard, and thus developed the language of " departure" to provide ways by which a licensee could make changes to methods without NRC approval under certain conditions. For instance, if the new method that the licensee wishes to use has been approved, itcould be used even if there were more than " minimal" effects upon the results. The staff did liot incorporate the term
" minimal" because of difficulties in defining its meaning for the ectrum of possible analyses that might be included. The staff acknowledges that guidanc will help ensure a clear understanding of " essentially the same" and intends to wor losely with the industry and other stakeholders to develop guidance on both evaluation met ds and input parameters.
The fourth issue concerned the discussion in the Stat ent of Considerations (SOC) for minimalincreases in consequences. The Committe stated that the staff-proposed guidance of "10% of the difference between the calculated val and the regulatory value" lacked sufficient justification and that the staff should discuss the anagement of incremental changes. The staff stated in the SOC that 10 percent was a v ue chosen to allow some flexibility yet at the same time restrict changes from consuming remaining " margin" to the regulatory values without the opportunity for NRC review. A!t ough the specific value of 10 percent is a matter of judgment, the staff does believe that it is nsistent with the " minimal" philosophy desired by the Commission, that is, of being more tha negligible" but less than "significant." Further, since the 10 percent applies to the remainin " margin," incremental changes can result in the consequences approaching, but not xceeding the regu'atory values, j
Finally, in its letter, the Committe noted some specific changes to the draft SOC, which the staff included in the paper as fo arded to the Commission.
4 Sincerely, William D. Travers Executive Director for Operations cc: Chairman Jackso Commissioner picus CommissionepDiaz Commission r McGaffigan Commissio er Merrifield SECY DISTRIBUTI N: See attached page DOCUMENT NAME: G:\\PGEB\\EMM\\g990254 *See previous concurrence OFFICE RGEB: DRIP TECH. EDITOR SC:RGEB: DRIP,
C:RGEB*
NAME EMcKenMN BCalure FAkstulewiDC CCarpenter DATE 5/27/99 5/28/99 Jil2749,9 5/27/99 Dd
)D NRh OFFICE D:DRIL,
ADIP A
EDO NAME DMad N WKane [ft[Uns WTravers 6 @/99
/
/99 DATE 6 / 3/99 f /8/99
/
OFFICIAL OFFICE COPY
th;t th3 d:t:rminition th:t requiram:nts era mat can only b3 mada following " substantial rsvi w" of th3 m:rits of tha chinga.
/
l
- The third concern related to criterion (viii) on evaluation methods. The Committee /
recommended that " minimal departures" be allowed to avoid this becoming a "z change" standard. The staff was also concerned about the potentialimpact of a "zero ange" standard, and thus developed the language of " departure" to provide ways by which icensee could make changes to methods without NRC approval under certain conditio. Forinstance,if the new method that the licensee wishes to use has been approved, it co be used even if there were more than " minimal" effects upon the results. The staff did no ncorporate the term
" minimal" because of difficulties in defining its meaning for the sp rum of possible analyses that might be included.- The staff acknowledges that guidance 11 need to be provided to ensure a clear understanding of " essentially the same" and i nds to work closely with the industry and other stakeholders to develop guidance on evaluation methods and input parameters.
The fourth issue related to the discussion in the Stat ent of Considerations (soc) for minimal increases in consequences. The Committee stat that the staff-proposed guidance of "10% of tho difference between the calculated value and e regulatory value" lacked sufficient justification and that the staff should discuss t management of incremental changes. The staff stated in the soc that ten percent was alue chosen to allow some flexibility yet at the same time restrict changes from consumin all remaining " margin" to the regulatory values without the opportunity for NRC review.
ile the specific value of ten percent is a matter of
' judgment, the staff does believe it is co istent with the " minimal" philosophy desired by the Commission, of being more than "neg ' ible" but less than "significant." Further, since the ten J
percent applies to the remaining "m in," incremental changes can result in the consequences approaching, but not exceeding th egulatory values.
Finally, the letter noted some sp cific changes to the draft soc that the staff agreed to include
{
in the paper as forwarded to t Commission, which was done.
Sincerely, William D. Travers Executive Director for Operations cc: Chairman Jacks Commissioner icus Commission Diaz Commissio r McGaffigan Commissi er Merrifield SECY DISTRIBUTION: See attached page DOCUMENT NAME: G:\\EMM\\g990254 OFFICE RGQB: DRIP TECH. EDITOR SC:RGEB: DRIP C:RGEB,,
NAME-EMcN b w FAkstulewicz Mntf s
DATE 4/f/99
/ /99
/ /99
%/99 OFFICE D: DRIP ADIP D:NRR EDO NAME-DMatthews WKane SCollins WTravers DATE
/ /99
/ /99
/ /99
/
/99 OFFICIAL OFFICE COPY
C EDO Principal ~ Correspondence Control
,FROMs DUE t06/15/99 EDO CONTROL: G19990254 DOC DT: 05/17/99 j
FINAL REPLY:
D2nn A. Powers, ACRS J
TOs Chairman Jackson
,.FOR SIGNATURE OF :
- GRN CRC NO: 99-0471 s
Travers, EDO DESCs.
ROUTING:
PROPOSED FINAL RULE - REVISIONS TO 10 CFR PARTS 50 Travers
'AND 72 CONCERNING CHANGES, TESTS, AND EXPERIMENTS Knapp Miraglia Norry Blaha Burns DATES 05/19/99 Thadani, RES Paperiello,NMSS ASSIGNED TO:
CONTACT:
Lieberman, OE Mitchell, OEDO NRR Collins ACRS File SPECIAL INSTRUCTIONS OR REMARKS:
Raf. G19990156.
Prepare response to ACRS for EDO signature.
Add
-Commissioners and SECY as cc's.
USE SUBJECT LINE IN RESPONSE.
b h h U' kY y;etfaud: w M M99 Acnon D
WE Mf
'7' f DUE T0 i chh3 ggg defM h bl== h %
m
L l
L OFFICE OF THE SECRETARY CORRESPONDENCE CONTROL TICKET PAPER NUMBER:
CRC-99-0471 LOGGING DATE: May 18 99 ACTION OFFICE:
EDO i
. AUTHOR:
DANA POWERS
. AFFILIATION:
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS ADDRESSEE:
' CHAIRMAN' JACKSON LETTER DATE:
May'17 99 FILE CODE: OM-7 ACRS.
SUBJECT:
PRO FINAL RULE -REVS TO 10 CFR PARTS 50 AND 72 CONCERNING CHANGES, TESTS, AND EXPERIMENTS l
ACTION:
Appropriate
' DISTRIBUTION:
CHAIRMAN, RF SPECIAL HANDLING: NONE CONSTITUENT:
)
NOTES:
DATE DUE:
l 1
l SIGNATURE:
DATE SIGNED:
l AFFILIATION:
i-l EDO --G19990254 t:
p@*urug'o, UNITED STATES 8
NUCLEAR REGULATORY COMMISSION o
f ADVISORY COMMITTEE ON REACTOR SAFEGUARDS O
WASHINGTON, D. C. 20556 May 17,1999 The Honorable Shirley Ann Jackson.
Chairman U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Dear Chairman Jackson:
SUBJECT:
PROPOSED FINAL RULE - REVISIONS TO 10 CFR PARTS 50 AND 72 CONCERNING CHANGES, TESTS, AND EXPERIMENTS During the 462*' meeting of the Advisory Committee on Reactor Safeguards, May 5-8,1999, we met with representatives of th(.4RC staff and the Nuclear Energy Institute (NEI) to discuss the proposed final revisions to 10 CFR 50.59 and related requirements in 10 CFR Parts 50 and 72 concoming changes, tests, and experiments. We previously met with the staff and NEI in March 1999 to discuss SECY-99-054 and issued a report to the Commission on March 22,1999. We also had the benefit of the documents referenced.
CONCLUSIONS AND RECOMMENDATIONS 1.
We recommend issuance of the proposed final rule and conforming changes subject to resolution of our comments and concems.
i 2.
We recommend that criterion (vii) be modified to state " result in a fission product barrier being altered by a change in its design basis limit or a likely reduction in the margin between the design basis limit and the failure point."
3.
We recommend that the " substantial review" criterion regarding escalated enforcement be deleted from the proposed final rule.
]
4.
We are concemed that the current wording in criterion (viii) could result in a "zero increase" constraint for departure from a method of evaluation. We recommend that the rule language be changed to "a minimal departure from a method of evaluation."
DidCUSSION j
The staff and industry are continuing discussions to simplify, clarify, and restore stability to the 10 CFR 50.59 process and its implementation. Progress is being made on resolving issues identified in our March 22,1999 report.
Significant changes to 10 CFR 50.59 proposed by the staff since our meeting in March 1999 are the addition of the following two new criteria:
,_330 $ 2LOl N.frp
(vii) result in a design basis limit for a fission product barrier being exceeded or altered; (viii) result in a departure from a method of evaluation described in the FSAR
[ Final Safety Analysis Report) (as updated) used in establishing the design bases or in the safety analyses.
The new criterion (vii) requires prior NR.C review of any change that would result in a design basis limit related to the fission product barrier being exceeded or altered. We note that the margin provided by the fission product barrier is the margin between its design limit and its failure point., This margin can be reduced not only by a change in the design limit, but also by a change in the failure point. The installation of a hardened vent in a containment is an example of the containment design limit not being changed, but the containment barrier capability being reduced by introducing the ability to open the containment barrier before reaching its failure pressure. It is appropriate for the NRC staff to review such a possible reduction in capability before it is implemented by a licensee. Criterion (vii) should be revised to preclude such actions from being carried out under 10 CFR 50.59. To do this, criterion (vii) should be modified to state
" result in a fission product barrier being altered by a change in its design basis limit or a likely reduction in the margin between the design basis limit and the failure point."
The new criterion (viii) requires prior NRC review of any change in a methodology or evaluation method that "results in a departure from a method of evaluation described in the FSAR (as upda+.ed) used in establishing the design bases or in the safety analyses." We agree with the staff that it is important to clearly define what is a method of evaluation and what are input parameters to the methods to ensure consistent implementation of new criterion (viii). To avoid introducing a "zero increase" constraint, this criterion should be revised to state "a minimal departure from a method of evaluation." It is important that the staff and the industry work closely to develop guidance on the specific elements and examples of the evaluation methods that would require prior NRC review. They should also work closely in developing guidance for input parameters.
In criterion (ii) of the Statement of Considerations, under " Guidance for likelihood of occurrence of malfunction," the staff states that " Changes that would invalidate requirements for redundancy, diversity, separation, and other such design characteristics, would be considered as 'more than a minimal increase in likelihood of malfunction,' and thus would require prior NRC approval." We agree that such changes should require prior NRC approval. We disagree that such changes are automatically more than a minimalincrease in likelihood of malfunction. We are concerned about forcing the outcome of what should be a probability determination in order to fit the need for NRC review of design basis commitments, in our February 18,1999 report, we questioned whether the reference to probability could be deleted from the definition of minimal changes.
In the discussion section on enforcement, the staff states that "a failure to submit an amendment as required would be considered a Severity Level lil violation if either a) a substantial review is needed by the NRC before it could conclude that the licensee's actions were acceptable or b)
NRC would not have found the licensee's actions acceptable...." We agree with the industry concem that it is unduly subjective to base the decision to issue a Severity 1.evel 111 violation on
3-whether a " substantial review" was needed to determine that the licensee had performed a proper evaluation. We also agree that the " substantial review" criterion is inherently subjechve and that the extent of NRC review needed to verify the adequacy of a licensee's 10 CFR 50.59 safety evaluation is a function of the complexity of the change and the skill of the NRC reviewer.
.in criteria (iii) and (iv) of the Statement of Considerations, the staff states "no more than a minimal increase in consequences if the increase is less than or equal to the more limiting of either 10 percent of the difference between the existing calculated value and the regulatory guideline value (10 CFR Part 100 or GDC [ General Design Criteria]ig as applicable), or has reached the SRP [ Standard Review Plan] guideline value for the particular design basis event."
The rationale for the 10 percent incremental value lacks sumclent justification even though both the staff and industry agree to this approach. We believe there is a need to expand the discussion to clearly justify why 10 percent is the appropriate criterion and how the management of incremental changes will ensure that margins are not adversely reduced by frequent use of this criterion. Some ACRS members feel that because the increase in consequences for either j
an individual change or the cumulative changes is limited by the SRP guideline value, there is i
sufficient assurance that adequate margins are maintained. Some ACRS members feel that the concem over the particular choice of 10 percent is overwrought.
During our discussions of minimal increases in the likelihood of malfunction, the staff agreed to delete the words "for clarity" from the discussion of ' likelihood" as substituted for the term 4
" probability"in criterion (ii) of the Statement of Considerations. The staff also agreed to delete the words " frequency of' from the rule language in 10 CFR 72.48 to make it conform with the proposed rule language in 10 CFR 50.5g.
The industry has begun the process of developing changes to the guidance provided in NEl g6-07, ' Guidelines for 10 CFR 50.5g Safety Evaluations," and is expected to request NRC endorsement in a regulatory guide. We plan to review the proposed NRC regulatory guide.
Additional comments by ACRS member Graham B. Wallis are presented below.
Sincerely, fLt-ustaa 1
Dana A. Powers Chairman Additional Comments by ACRS Member Graham B. Wallis 1.
I am generally in favor of the objective of restoring 10 CFR 50.5g to the condition where it " worked well' in the past. However, once the revised rule is in place, licensees will adapt to it, so thought needs to be given to what the future might be. Neither the staff nor NEl had much to say about the consequences of implementing the revised rule, something that is surely an important part of the case that must be made for any rulemaking.
-. ~. -
2.
Likelihood and frequency have replaced probability in the rule. I don't see how this makes any difference. To conform to the criteria on page 118 of the proposed final rulemaking (Reference 1), the licensee has to assess these likelihoods and frequencies.
The ' qualitative standard" on page 31 appears to be asking for inconsistency in interpretation and I would expect that the regulatory guide will have to provide more specific guidance. A cautious licensee will probably choose to calculate the probabilities of occurrence of an accident or malfunction and evaluate consequences, just as it would now do for use in a PRA. The basic problem of introducing probabilistic language.into a deterministic rule has not gone away.
3.
" Minimal increase" occurs four times in the criteria on p.118 of Reference 1. For criteria (i) and (ii), there is little guidance on interpretation. The argument that " minimal
- subsumes the NEl language of " negligible" does not help. Once " minimal" is in place, licensees will have greater freedom than they asked for with " negligible" in NEl 96-07.
This is not hypothetical; in its April 30,1999 letter (Reference 2), NEl expresses a desire to take advantage of this greater flexibility.
4.
What is a " minimal increase' in criterion (ii)? The examples on pages 36-37 do not help because no measure of" likelihood of occurrence"is used. Discussion of items such as
" redundant motive force, quality, and other requirements" avoids assessment of likelihood of malfunction, which is not determined by these parameters. The key criterion for evaluation in the rule is still remarkably vague, with no indication of the scale on which it is to be measured.
Since minimal is no longer negligible, is it 1 percer,t or 10 percent of the existing likelihood of malfunction? Is it perhaps 1000 percent if the particular item has very little safety significance? Is it some percentage charige or arithmetical value of the resulting change in a more universal measure of importance to safety such as core damage frequency (CDF) or large, early release frequency (LERF)? In the absence of a l
definition for minimal within the context of criterion (ii), one might turn to the discussion of i
criteria (iii) and (iv) on pages 37-41 of Reference 1 where minimalis defined as less than 10 percent of the margin between calculated values and acceptance values. It would seem that a similar definition should apply, for want of any other, to criterion (ii). Then, for example, a plant with a low CDF compared to the acceptable CDF might have a good argument for increasing its CDF by 10 percent of that margin, eventually working up to the level of CDF where regulatory action is warranted.
This
, at a hypotheticalissue. In its April 30,1999 letter, NEl proposes criteria for use in del,og minimal, one of which is "The effect of the change on frequency of an accident can be calculated and would not cause more than a 10 percent increase in the estimated (pre-change) accident frequency."
5.
A succession of 10 percent (or any percent) incremental reductions in nargin eventually effectively reduces that margin to zero. Perhaps it should be stated straightforwardly that the purpose of this rule is to allow incremental approach to acceptance values at a l___
manageable rate. This may be the right policy, but it appears significantly different in philosophy from the idea of minimal change.
6.
The rule sets a precedent for progressive reduction of margins by specified increments.
Now, margins were originally established because of uncertainties in predictions. One stayed a prudent distance away from limits to avoid (qualitative) probability of exceeding them. Reduction in margin makes sense if uncertainty has been sufficiently reduced, so that approach to the limit does not increase the likelihood of stepping over it. I know of no arguments having been presented to show that this uncertainty has actually been reduced.
7.
The rule has an impact, however minimal, on public safety. I realize that there has been
' ample opportunity for public comment, most of which has come from the nuclear industry, to which the NRC has responded. I suggest that it would help relations with the broader public if, when a rule such as this is finally issued, the Statement of Considerations contained a preamble informing an independent observer of what the rule is designed to accomplish and what the expected consequences are.
References:
1.
Memorandum dated April 27,1999, from David B. Matthews, Office of Nuclear Reactor Regulation, to John T. Larkins, ACRS,
Subject:
Request for Review and Endorsement of Final Rulemaking to Revise 10 CFR 50.59 and Related Provisions Conceming q
' Changes, Tests, and Experiments."
2.
Letter dated April 30,1999, from Anthony R. Pietrangelo, Nuclear Energy Institute, to David Matthews, NRC,
Subject:
Issues Conceming the Pending Revisions to 10 CFR 50.59, 3.
Report dated March 22,1999, from Dana A. Powers, Chairman, ACRS, to Shirley Ann Jackson, Chairman, NRC,
Subject:
SECY-99-054, " Plans for Final Rule - Revisions to 10 CFR Parts 50,52, and 72: Requirements Conceming Changes, Tests, and Experiments."
4.
Report dated February 18,1999, from Dana A. Powers, Chairman, ACRS, to Shirley Ann Jackson, Chairman, NRC,
Subject:
List of Questions to be Addressed for Possible Resolution of Key issues Associated with the Proposed Revision to 10 CFR 50.59 (Changes Tests and Experiments).
5.
Nuclear Energy Institute, NEl 96-07, Revision 0, " Guidelines for 10 CFR 50.59 Safety Evaluations," September 1997.
l l
l 1