ML20062A375
| ML20062A375 | |
| Person / Time | |
|---|---|
| Issue date: | 07/14/1982 |
| From: | Serkiz A Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20062A368 | List: |
| References | |
| REF-GTECI-A-01, REF-GTECI-A-43, REF-GTECI-ES, REF-GTECI-PI, TASK-A-01, TASK-A-1, TASK-OR NUDOCS 8208030704 | |
| Download: ML20062A375 (2) | |
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RESOLUTION OF USI ' A-1, " WATER HAMMER" by A. W. Serkiz, Task Manager U.S. Nuclear Regulatory Comission Division of Safety Technology, NRR 2nd International Topical Conference on Nuclear Reactor Thermal Hydraulics Jan. 11-14, 1983, Santa Barbara, CA
. ABSTRACT.
Water hammer events are large~ hydraulic loads which are the result of steam bubble collapse, steam-driven slugs of water, pump startup into voided lines and rapid
. valve closures. Since 1968, about 150 water hammer events have been reported in nuclear power plants. The increasing frequency of water hammer events noted in the early.1970's (which'also correlates with~an upsurge ~in plants being' brought bn-line) raised sufficient safety concerns to result'.in designation of~this phenomena as an Unresolved Safety Issue A-1, Water Hammer in 1979. 5idc~ that e
time, the NRC staff with the help of subcontractors has develo' ped a. potential resolution of this issue.
In the course of resolution, several approaches were used, including an analytic sclution. This paper presents conclusions reached and development of the NRC staff position.
Examination of plant, reported water hammer events reveals tne following findings:
(a) principal reported damage has been failures in snubbers and pipe hangers, (b) approximately one-half of the reported events have occurred during pre-opeiational testing and the first year of commercial operation (which suggests a learning process), (c) only approximately one-third of the operating reactors have reported water hammer related events, (d) cited causes are about equally related to operational effects and design mismatches. The results of close~
l examinations of' operating experience reveal that water hamer is less signi-ficant as a safety concern than previously viewed.
In addition, safety systems have not been disabled.
8208030704 820714 PDR GTECI GESA-43 PDR
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2 The perspective gained is as follows:
totsi elimination of water hammer will not be possible in view of the coexistence of steam, water and voids inherent to the operation of nuclear power plants; the prediction of occurrences in all plant systems, under all possible operational scenarios 'is also not' feasible;
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finally, code analysis capabilities are limited with respect to predicting certain two-phase phenomena (i.e., steam-pocket collapse). The calculational approach was tried and did not succeed in resolving this safety issue; The resolution developed for USI A-1 is based on recognition that water hammer events will occur, and that preventive measures can be taken. Key elements in reducing frequency and severity of water hammer can be summarized as:' (1) increase operator awareness, (2) assure adequate plant operation.and maintenance procedures are in effect, (3) utilize surveillance instrumentation to detect voids in systems having a history of water hammer occurrences, (4) incorporate design features (e.g., J-tubes in steam generator feed ring, jockey pump keep-fill systems in BWR's) which have demonstrated success in eliminating water hammer events, (5) address the design requirements associated with preventing water hammer through l
use of experience gained. This paper expands on these points and details the proposed method of implementation.
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