ML20206C218
| ML20206C218 | |
| Person / Time | |
|---|---|
| Issue date: | 03/18/1986 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Asselstine NRC COMMISSION (OCM) |
| Shared Package | |
| ML19302B456 | List: |
| References | |
| FRN-51FR12502, RULE-PR-50 AB76-2-36, NUDOCS 8606190400 | |
| Download: ML20206C218 (8) | |
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NAR 181986 MEMORANDUM FOR:
Comissioner Asselstine Victor Stello, Jr.
FROM:
Acting Executive Director for Operations FINAL RULE TO MODIFY GENERAL DESIGN CRITERION 4 0F
SUBJECT:
APPENDIX A, 10 CFR PART 50 (SECY 86-4)
In response to your March 6 memorandum. I have provided a sumary of the regulatory analysis provided with the GDC-4 proposal, and I will also address your specific questions in the memorandum.
10 CFR 50.109 clearly defines a backfit as a change in staff position that meets certain timing criteria (Section (a)(1)).However, 50.109(a)(2) a The GDC-4 just as clearly and as such is a backfit.
indicate that the " systematic and documented analysis" and a determination based on that analysis is required for those backfits which it {the Comission)
As OGC has recently written, the backfit seeks to impose (emphasis added).
rule was framed with no contemplation of addressing relaxations inT requirements.
control the imposition of changes in requirements which were thought by the staff to increase safety, but for which there often had been an inadequate We consider that for proposed staff positions, analysis and justification.
including rule changes, which the NRC would not impose, the essential requirements of 50.109 that the Connission make a determination of substantial increase in protection, with costs justified, and based on an analysis in We do plan however, that staff accordance with 50.109(c), are not operative.
regulatory analyses will be completed to the degree necessary for the senior staff, CRGR, and where appropriate, the Comission, to rationally deliberate Such work and make recomendations on the merit of any generic proposal.
should not be considered to be necessary to meet the requirements of 50.109.
Appropriate regulatory analyses of this type were completed to support the development of the GDC-4 proposal.
The passages quoted in your memorandum were from the Statement of Considerat accompanying the rule and they reflect the intent and understanding of backfit problem I have just described.
Tourtellotte on many occasions over the several years of backfit rule development, I believe I understand the concepts and the directions taken in the writing of the revised 50.109.
The first passage quoted from 50 FR 38103 must be read with the realization that the new or modified interpretiition referred to is assumed to be one which was proposed to be imposed by the staff.
23,1986 Memorandum, M. Malsch to Connissioner Asselstine, January 1
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The second passage quoted refers to a new Comission interpretation of a risk The threshold for a specific plant or a generic surrogate for several plants.
"no undue risk" threshold would be an absolute risk level associated with a plant above which the plant risk to the public would be considered unacceptable and some changes would be needed, independent of cost, to bring the plant risk level back down to the undue risk threshold or below. All operating plants are considered to have residual risk levels below the threshold of u the public.no additional public risk, that is, no decrease in current safety, would not affect any plant in such a way as to increase the residual risk of operation.
Thus, no plant which would acceptably incorporate the GDC-4 prooosal changes would suffer an increase in residual risk level, which would bring that plant It is important to understand, closer to a threshold of unacceptable risk.
however, that a proposition to change requirements, with some associated change in risk due to the changed requirements, is quite independent from the perception of an absolute " undue risk" threshold value for a plant or plants.
It is only important to detemine that the proposed change would not add any which already is presumed to present an operating risk that than the " undue risk" threshold. Such is the case with the GDC-4 proposal, an understanding that was developed by the regulatory analysis which is sumarized in the enclosure, To address your question regarding what change in public risks would obtain if a licensee implemented the GDC-4 changes, there is some unquantified likelihood that the risks to the general public would be reduced by a reduced likelihood The calculated best estimate of large pipe rupture (see item 3 in analysis).
increase in public risk is numerically insignificant, ever considering mevimum Further, it is probable unceitainties of several orders of magnitude.
essentially certain that a large decrease in occupational radiation exposure would be realized from the decreased inspection and maintenance related Accepting that as fact, however, exposures incurred over the plant lifetimes.
for a given plant, would not mean that the " undue risk" threshold for that plant is changed - it would mean only that the actual operating risk for that plant would be even lower than before the change, and would be even further below the perceived undue risk threshold for that plant.
Finally, you provided sample quotations fron the proposal which would seem to indicate that the rulemaking would require licensees to implement something.
It is indeed the staff position that licensees must provide analyses to verify the safety of the GDC-4 changes if they would implement such changes in their plants, but only if the licensees first elect to adopt the permitted changes, an election which is not required by the rulemaking.
Notwithstanding the views expressed here on the evolution of and meaning of the backfit rule, the staff will prepare analyses for proposed relaxations or increases in staff positions whether such positions are to be elective or It is through such documented analyses that the senior staff and CRGR imposed.
But my point is that such will rationally deliberate the merits of proposals.
analyses and specific findings thereon are in some cases no more than internal staff procedures, not required to be documented in order to meet the letter of 50.109.
A b'l6 - Z PDR The substance of the proposed GDC-4 change is to provide a purely elective opportunity for licensees to improve their plant design and 10 CFR 50.109 was not written to decrease in cccupational radiation exposure.The burden of proof for licensee elected or deal with this kind of change.
proposed change to the licensee's licensing basis has always licensee.
rule on its head.
I am pleased to be able to share these views with you, and am prepared to discuss this further with you at your convenience.
original signed by
. Victor stellop,,
Victor Stello, Jr.
Acting Executive Director for Operations
Enclosure:
i As Stated cc: Chaiman Palladino I
Comissioner Roberts Comissioner Bernthal f
Comissioner Zech l
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SUMMARY
OF REGULATORY ANALY$15 Limited Scope Modification to General Design Criteria 4 1.
Statement of the specific objectives that the proposed backfit is designed to achieve.
i This rulemaking offers licensees and applicents new options not previously available while imposing no additional requirements.
However, physical features at operating plants, plants under construction and in future designs can be impacted when the conditions of the rule are satisfied.
Specifically, licensees and applicants can at their own choosing decide to undertake investigstions to demonstrate that PWR primary loop piping systems meet NRC acceptance criteria for applying leak-before-break technology.
Only when NRC acceptance criteria are met will assurance be provided that the risks of pipe ruptures are at least as low as under the current licensing basis.
Successful demonstration will allow elimination of dynamic effects associated with PWR prirary loop pipe rupture from the design basis while not influencing requirements for environmental qualification of electrical and mechanical equipment, containment design or emergency core cooling system perfomance. When dynamic effects are eliminated, certain plant hardware (such as pipe whip restraints and jet impingement shields) need not be installed and other related changes can take place.
In particular, internals and supports of pipe connected components, such as steam generators, and reactor coolant pumps need not be designed for the dynamic effects associated with pipe rupture.
Pressurizations in cavities, compartments and subcompartments which are not part of the containment system can also be eliminated under this ruleraking action.
Safety benefits result from the application of this rule, but are not quantified. The rule is not mandatory; however it is expected that economic and other considerations will lead many applicants and licensees to elect to implement the rule,
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PDR 2.
General description of the activity that would be required by the licensee or applicant in order to complete the backfit.
In order for licensees or applicants to take advantage of leak-before-break technology in pWR primary loops they must provide sufficient information to satisfy stringent NRC leak-before-break acceptance criteria.
For example, materials test data must be available to support the leak-before-break evaluation.
The acceptance criteria require leakage detection systems which are diverse, reliable, redundant and sensitive such that a margin of a factor of 10 exists on undetected leakage from the crack assumed in the fracture mechanics analyses.
Applicants or licensees electing to implement leak-before-break technology may need to upgrade or improve existing leakage detection systems, although it is possible that some plants may have adequate leakage detection systems already.
Modifications of the licensed plant design of operating plants may involve an unreviewed safety question under 10 CFR 50.59.
Where it is determined that an unreviewed safety question is involved, licensees of operating plants desiring to make modifications should submit a license amendment for NRC approval in accordance with revised GDC-4 A simple removal of pipe whip restraints and jet impingement barriers would not involve an unrevir.ed ufety question.
However, modification to component internals and supports would involve an unreviewed safety question.
Applicants for operating licenses seeking to modify design features to take advantage of revised CbC-4 are required to reflect the revised design in an amendment to the pending FSAR.
If the design change modifies design criteria set forth in the PSAR, an amendment to the applicable construction permit may also be necessary.
l 3.
Potential change in risk to the public from the accidental offsite release of radioactive materials.
Best estimate increases in public risks are a total of.003 man-rem over the lifetime of a population of 85 PWR primary loops.
This is an insignificant risk increase even under uncertainty, since a several order
bb7b-2 PDPs of magnitude variation in one direction would still yield a relatively insignificant predicted risk.
These best estimates are themselves con-servative, since they consider only the potential for protective devices to mitigate accidents.
Thus, according to these best estimate calcula-tions, when the accident mitigation potential is removed, public risk increases.
Regarding the calculated risk increase, the contractor (LLNL) that prepared the Regulatory Analysis for this rulemaking noted that:
L "Many experts believe, however, that the proposed rule change could
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conceivably _ reduce public risk, arguing that pipe whip restraints and jet impingement barriers may actually decrease the reliability of piping systems by limiting access to pipe welds, therefore reducing the effectiveness of in-service inspection, and by potentially restricting the l
movenent of piping during routine operation and thus increasing pipe f
stresses caused by restraint of thertnal expansion. This latter situation l
could occur, for example, if pipe whip restraints (which are designed to j
accomodate thermal expansion displacements measured during preoperational plant testing) were to be installed incorrectly.
In this value-impact assessment, however, we have assumed that restraints are installed as designed and have not attempted to quantify any effect that avoidance of fl possible pipe birding might have on public risk.
Similarly, we have not I
attempted to take credit for increased piping reliability due to improved effectiveness of in-service inspection." (UCID-20397) 4 Potential impact on radiological exposure to facility employees.
6 For the population of 85 PWRs (considering only primary coolant loops),
net occupational exposures are reduced by 34,000 man-rem over the h
I remaining life of the plants.
These are real increases in safety, as opposed to probabilistic estimates of risk increase discussed in item 3 above.
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PDR 5.
Installation and continuing costs associated with the backfit including the cost of facility down times for the cost of construction delay.
For the 85 PWRs operating or under construction and considering only the primary coolant loops, cost savings of about $200 million result.
6.
The potential safety impact of changes in plant or operational conplexity including the effect on other proposed and existing regulatory requirements.
The rule is calculated to improve safety and increase the effectiveness of inservice inspection, reduce worker radiation exposures and positively impact construction and maintenance economics. This rulemaking allows the removal of counterproductive hardware from the plant and leads to signifi-cantly less complexity in plant operations.
Fire protection is enhanced since visibility and movement about the plant is improved.
Thennal efficiency is also improved since insulation may now be added to sections of high energy piping which previously, because of pipe whip restraints, had no pipe insulation.
7.
The estimate resource burden on the NRC associated with the proposed backfit; and the availability of such resources.
it is estimated that two to four NRC man years of effort (to review industry initiatives) are needed to respond to actions taken under the Limited Scope GDC-4 Rule.
8.
The potential impact of differences in facility type, design or age on the relevancy and practicality of the proposed backfit.
i; The Limited Scope GDC-4 Rule speaks only to PWR primary coolant loop piping. Age is not a factor in implementing ttis rule. Value-impacts are more in future plants and less in operating plants.
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Pm 9.
Whether the proposed backfit is interim or final and if interim, the justification for imposing the proposed backfit on an interim basis.
Any backfits under the Limited Scope GDC-4 modificetion are final.
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