ML19296A761
| ML19296A761 | |
| Person / Time | |
|---|---|
| Issue date: | 02/08/1980 |
| From: | Scinto J NRC OFFICE OF THE EXECUTIVE LEGAL DIRECTOR (OELD) |
| To: | Vollmer R Office of Nuclear Reactor Regulation |
| References | |
| RTR-REGGD-01.046, RTR-REGGD-1.046 NUDOCS 8002190012 | |
| Download: ML19296A761 (3) | |
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%' u.....f February 8, 1980 MEMORANDUM FOR; Richard H. Vollmer, Acting Assistant Director for Systematic Evaluation Program, D0R FROM:
Joseph F. Scinto, Deputy Director Hearing Division
SUBJECT:
INTERPRETATION OF GENERAL CRITERION 4, 10 CFR 50, APPENDIX A, " ENVIRONMENTAL AND MISSILE DESIGN BASES" In your memorandum to Mr. Christenbury dated January 16, 1980, you requested a legal opinion as to the acceptability of using on a limited basis a combina-tion of increased periodic inspections and state-of-the-art leakage detection to " satisfy" General Design Criterion 4 for pipe breaks inside containment for those situations in which relocation of equipment and installation of pipe restraints are impractical.
You pointed out that this approach was deemed acceptable in the review of pipe breaks outside containment that was performed by the Division of Operating Reactors in 1975. You stated that the Staff believes that this approach would provide " appropriate protection" in accord-ance with GDC 4 for pipe breaks inside containment because it reduces the probability of a " pipe break"
" pipe whip" event by providing assurance that the integrity of the piping system has not been degraded by operations.
Mr. Cutchin of this office and I have ' looked into your request.
General Design Criterion (GDC) 4 imposes two requirements on " structures systems and components finportant to safety." The first is that they "shall be designed to accommodate the effects of and to be compatible with the environmental conditions associated with nonnal operation... and postulated accidents" (emphasis added). The second requirement is that they "shall be appropriately protected against dynamic effects, including the effects of
... pipe whipping..." (emphasis added). Your memorandum deals solely with this second requirement.
To respond specifically to your question as to the legal requirements of the provisions of GDC 4 as it applies to pipe whipping; this requirement is satisfied when each structure, system and component important to safety is appropriately protected against pipe whipping, etc. This is a question of fact. However, your memorandum does not provide a factually sufficient basis to advise you on whether the opinion you offer is sufficiently supported to 8 002190 O Q,:,,
be a satisfactory implementation of the pipe whip requirement of GDC 4.
Specifically, your memorandum does not deal factually with what appears to be a conflict between the basis you give and the discussion in Regulatory Guide 1.46, " Protection Against Pipe Whip Inside Containment," which sets forth guidance for postulating pipe breaks and providing protection against pipe whip.
Regulatory Guide 1.46 calls for provision of measures for protection against pipe whipping except for situations where (1) the piping is isolated or restrained by protective barriers such as concrete encasement; or (2) where a whipping pipe cannot damage any system, structure or component important to safety.
Regulatory Guide 1.46 calls for breaks to be postulated at terminal ends of piping runs and at intermediate locations where stress intensity or cumulative usage factors exceed specified levels.
In the discussion, Regulatory Guide 1.46 states:
Piping locations where breaks are not postulated nor protection provided are restricted to those locations whose probability of failure is sufficiently low as to be acceptable without the need for restraints.
Regulatory Guide 1.46 also states that:
The limits on stress intensity and cumulative usage factor selected to determine piping break locations are based on the assumption that, despite the accepted conservatism in the ASME Code piping design rules, the system piping may suffer structural degradation of an unanticipated nature in service or may have its design margins unknowingly reduced by faulty design, improperly controlled fabrication, installation errors, or unexpected modes of operation.
Thus, Regulatory Guide 1.46 addresses not only unanticipated piping system degradation caused by nonnal operation but also unknown reductions in design margins caused by faulty design, improperly controlled fabrication, installation errors, or unexpected modes of operation.
Having considered those possibilities, the Staff in Regulatory Guide 1.46 appears to have selected limits on stress intensity and cumulative usage factors which would result in pipe breaks being
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assumed at those locations at which the probability of piping failure is not sufficiently low to allow the piping system to be found to be acceptable without restraints.
It is not clear that a combination of increased periodic inspections and state-of-the-art leakage detection would make the probability of piping failure sufficiently low in situations in which by applying the guidance of Regulatory Guide 1.46 the probability of a break could not be assumed to be sufficiently low to allow the piping system to be found to be acceptable without restraints since your memorandum addressed only piping degradation resultigg from operations. Unknown reductions in design margins caused by faulty design, improperly controlled fabrication, installation errors, or unexpected modes of operation are not. discussed in your memorandun. Nor is there any discussion in your memorandum of the magnitudes of the stress intensity and cumulative usage factors at the locations where installation of restraints is impractical and where you intend to substitute surveillance for restraint.
While Regulatory Guides are only guides, the Staff cannot disregard the factual information contained in the guides. The apparent conflict between the views expressed in your memorandum and the views expressed in Regulatory Guide 1.46 must be explained before we can advise you on the adequacy of your proposed method of satisfying GDC 4.
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I have asked Mr. Cutchin to assist you, to the extent he can reasonably do so, if you wish to pursue this matter further.
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Joseph F. Scinto, Deputy Director Hearing Division Internal Distribution:
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