ML20151L089
| ML20151L089 | |
| Person / Time | |
|---|---|
| Issue date: | 08/05/1985 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Stello V Committee To Review Generic Requirements |
| Shared Package | |
| ML20151L097 | List: |
| References | |
| REF-GTECI-A-49, REF-GTECI-RV, TASK-A-49, TASK-OR NUDOCS 8508090665 | |
| Download: ML20151L089 (3) | |
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August 5, 1985 MEMORANDUM FOR: Victor Stello, Jr., Chairman Comittee to Review Generic Requirements FRO *: Harold R. Denton, Director Office of Nuclea' Reactor Regulation SUBJE:i: CRGR REVIEW OF F:0 POSED REGULATORY GUTCE FOR DLANT-SPECIFIC ANALYSES REGUIRED BY THE PRESSURI:'E0 THERMAL SHOCK RULE (USI A-49)
The Final PTS Rule recently accreved by the Ccmission recuires that licen:ees must perfore a plant-specific DTS risk analysis tnree years before exceeding the screening criterien specified in the rule, if the licensee wishes to justify centinued operatien beyond the screening criterion. The supolementary information section of the Notice of Final Rulemaking notes that the staff is developing guidance on the content of the required plant-soecific analyses and on the acceptance criteria the staff will use in reviewing the analyses. The rule specifies that no licensee is recuired to submit an analysis sooner than one year af ter publication o' that guidance.
The staff has developed the recuired gu1 dance in the form cf a proposed Regulatory Guide (Enclosure 1). I request CRGR review prior to issuance of the Guide for public cement.
The CRGR consicered the proposed Pressurized therinal Shock (PTS) rule at meeting nutoer 38, and the cemittee's recomendations were given in minutes cated May 31, 1983. Suosequent to incorporation of public coments received in response to publication of tne proposed rule in the Federal Peoister on February /,1984, the CRGR reviewed tne proposed Final pts rule at meeting numoer 70, with results given in minutes dated hovember 7, 1984 The Comittee recomended "that the EDO forward the proposed final rule for*
Comission approval." That was done on February 20, 1985 (SECY-85-60) and the Final PTS Rule was approved by the Ccmission on June 20, 1985.
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o 'L e August 5, 1985 The staff developed the technioues recommended in the proposed Regulatory Guide during its direction and participation in three prototype, plant-specific PTS PRA analyses performed at Oak Ridge National Lacoratory (ORNL) as part of the program for resolution of USI A-49. These three analyses constitute the most detailed, thorough analyses of this type performed to date, and the lessons learned in their performance are incorporated in the Guide. Descriptions are included of the recommended methods for assembling details of a plant's design (and to what level those details should be included), using event tree methodologies to identify and group potential PTS events, calculating the severity of the events, and integrating the results to obtain vessel through-wall crack frequency, core melt frequency, risks in terms of person-rem exposures, and fatalities. The staff believes that use of this Guide by licensees will enable them to efficiently perform analyses that will produce results in the form needed for evaluating conformance with the regulations.
The proposed Guide also discusses criteria that would be used by the staff in judging the acceptability of continued operation beyond the PTS screening criteria, based on the plant-specific analyses submitted by licensees.
The calculated mean frequency of reactor vessel through wall crack pene-tration is proposed as the principal acceptance criterion because the staff's analyses predict that there is a high likelihood of oressure vessel failure and core damage in the event of such cracks. Core damage events have potential oublic health and safety consequences that are difficult to analyze with certainty, and also would have severe economic impacts upon the licensee and the public who will pay for cleanup and replacement power.
A value of 5 x 10-6 mean frequency per reactor year was selected as a goal, considering that pressure vessel failure is not part of the design basis of the plant. When the various (unquantifiable) biases that are inherent in the analyses are taken into account at least qualitatively, such as the imolicit assumotion that " core damage" is eouivalent to " core melt", this value probably results in a core melt mean frequency close to one per million reactor years.
The proposed Guide also indicates that the calculations of risk in terms of predicted core melt frecuency, person-rem exposure, and early and late
- fatalities will be considered in judging acceptability of continued i l operation. Since the NRC's safety goals are currently being developed, the l Guide simply states that the results of the plant-specific PTS risk analyses will be compared with whatever goals are in place or in general use by the j NRC at the time the plant-specific PT5 analyses are required. !
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-3 August 5, 1985 The proposed Reg. Guide is included as Er. closure 1. The required Regulatory Analysis is included as Enclosure 2, and the CRGR standard format information is included as Enclosure 3.
We have identitied USI A-49 (whose final resolution requires publication of
- this Reg. Guide) as a Category 2 action.
- For further infomation on this subject, contact Karl Kniel Chief, Generic IssuesBranch(x27359)orR. Woods,USIA-49TaskManager(x24714).
Harold R. Denton, Director Office of Nuclear Reactor Regulation
Enclosures:
- 1. Proposed Regulatory Guide
- 2. Regulatory Analysis
- 3. Background Information for CRGR Review of USI A-49 related Reg. Guide Distribution Central file GIB Rdg DST CHRON A-49 file RWoods Woods CHRON KKniel FSchroeder TSpeis DE1senhut
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