ML25195A188
| ML25195A188 | |
| Person / Time | |
|---|---|
| Issue date: | 08/16/1979 |
| From: | Carbon M Advisory Committee on Reactor Safeguards |
| To: | Hendrie J NRC/Chairman |
| References | |
| Download: ML25195A188 (1) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION ADVISORY COMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, D. C. 20555 August 16, 1979 Honorable Joseph M. Hendrie Chairman U.S. Nuclear Regulatory Commission Washington, D.C.
20555
SUBJECT:
PIPE CRACKING IN LIGHT WATER RFACTCRS
Dear Dr. Hendrie:
There have been a significant nl.lnber of occurrences of pipe cracking in boiling water reactors (BWRs), the Duane Aroold incident in 1978 representing the most severe example thus far.
For pressurized water reactors (FWRs), leaks and dete-rioration of steam generator tubing have been significant problems and recently, cracking of a related but ll'lpredicted type has been found in EWR steam generator feedwater oozzles.
'Ihe Nuclear Regulatory Commission's Pipe Crack Sttrly Group issued a report in 1975 (NUREX:i-75/067) which reviewed EWR pipe cracking and made recanmendations to reduce the incidence and severity of cracking. A second report (NUREX:i-0531) was issued in early 1979 which again examined the status of the incidence of pipe cracking and made further recamnendations, primarily related to the in-fluence of the choice of material and to the p:,tential for inservice inspection.
The ACRS believes that it is appropriate to extend the scope of the NRC Staff review beyond that examined in NUREX;-0531.
'Ihe relatively high frequency of EWR pipe cracking stggests that there may be a significant probability of a loss of coolant accident (LOCA), particularly a small LOCA, and that it may be relevant to examine, in greater depth than usual, a range of matters inclt..rling the following:
- 1. 'Ihe reliability of the safety features needed to cope with soch an event.
- 2. 'Ihe p:,ssibility of determining the location of a leak or break more rapidly and more directly than is now the practice.
- 3. 'Ihe ~equacy of operational procedures for soch LOCAs, incltrling combinations of circumstances that could arise in connection with soch an event.
Furthermore, the seeming long-time existence of large, deep cracks in the re-circulation pipes at Duane Aroold stggests that a range of possible accident initiators soch as water hammer, earthquakes or other p:,tential sources of 2637
Honorable JoseJil M. Hendrie 2 -
August 16, 1979 large additional forces could lead to a previously tmexplored accident soch as concurrent multiple failures.
If so, consideration may have to be given to further analysis of the course of such an event in order to ascertain what, if any, additional measures are needed to reduce the probability of the accident or to mitigate its consequences.
'Ihe presence of the large, multiple cracks at Duane Arnold in sections of the pipe in which no inservice inspection was required, points to a need for a comprehensive reexamination of all safety-related piping systems for similar or equivalent design, fabrication or construction flaws, as well as the adequacy of the NRC requirements for inservice inspection. Furthermore, high priority should be given by both the industry and the NRC to the early implementation of improved crack detection capability.
Some types of cracking in PWRs and a-ms can be retarded through the control of water purity. For example, most foreign cl"ld some danestic B-lRs deaerate the primary coolant during reactor startup. 'Ihe NRC Staff is considering a regulatory guide on this matter. A progran should be initiated to develop optiml.lTl water specifications, particularly in the areas of BWR primary coolant and PWR secondary coolant.
Sincerely yours, Olairman References
- 1. NUREXi-75/067, "Technical Report -- Investigation and Evaluation of Cracking of Cracking in Austenitic Stainless Steel Piping in Boiling Water Reactor Plants," Pipe Crack Study Group, U.S. -Nuclear Regulatory Commission, O::tober 1975.
- 2.
NUREXi-0531, "Investigation and Evaluation of Stress-Corrosion Cracking in Piping of Light Water Reactor Plants~* Pipe Crack Stooy Group, U.S. Nuclear Regulatory Commission, February 1979.
- 3. "Metallurgical Investigation of Cracking in a Reactor Vessel Nozzle, Safe-End, Final Report," Southwest Research Institute, dated December 26 1978.
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