ML19275A422
| ML19275A422 | |
| Person / Time | |
|---|---|
| Issue date: | 09/18/1979 |
| From: | Gamble R Office of Nuclear Reactor Regulation |
| To: | Rachel Johnson Office of Nuclear Reactor Regulation |
| References | |
| REF-GTECI-A-11, REF-GTECI-RV, TASK-A-11, TASK-OR NUDOCS 7910040375 | |
| Download: ML19275A422 (3) | |
Text
POR Generic Task No. A-11
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September 18, 1979 DUM FOR:
R. E. Johnson, Task Manager A-ll FROM:
R. M. Gamble
SUBJECT:
ANNEALING FEASIBILITY FOR REACTOR PRESSURE VESSELS HAVING MARGINAL FRACTURE TOUGHNESS As part of the Annealing Feasibility Task contained in TAP A-ll, I recently visited EPRI and NRL to discuss the status of their annealing programs. The following sumarizes information obtained during these visits and presents some comments concerning the annealing programs, and J-R test procedures and resulting data relative to completing and implementing A-ll.
I.
Annealing Program Status Sumary A.
EP'll The EPRI annealing program is being conducted by Westinghouse and is quite comprehensive. The program includes (1) systems analyses to detennine the system contraints that might restrict reactor vessel annealing and (2) materials tests to detennine the efficiency of annealing processes in restoring material toughness. The EPRI program is in its initial stages and few results are available. Currently, the main program conclusion is that wet annealing (at 650 F) of the reactor vessel in Westinghouse 3 and 4 loop plants is feasible with minor system modifications, while wet annealing in Westinghouse 2 loop plants is feasible only with major system modifications. Wet annealing in 2, 3 and 4 loop Westinghouse plants can be accomplished only by removing the core from the vessel. This later finding by Westinghouse precludes obtaining much of the advantage previously associated with wet annealing.
Systems feasibility studies are now in progress for a potentially more effective, dry anneal at 750 F.
The EPRI program is scheduled for completion in mid 1980.
B.
NRL The NRL program is sponsored by RES and focuses on testing to define the material toughness recovery associated with various annealing conditions. NRL has conducted fracture toughness tests for specimens annealed at 650*F and 750*F. The results from Charpy V-notch tests for specimens annealed at 650 F indicate that annealing following an irradiation of 1019 n/cm2 produces significant, but not total, toughness recovery; however, the recovery is lost after a reirradiation of about 3 x 1018 n/cm. Results from Charpy V-notch tests for soecimens 2
annealed at 750 F again indicate significant toughness recovery 1095
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R. E. Johnson from annealing with subsequent loss of toughness upon reirradiation.
For a 750'F anneal, tne reirradiation necessar{8to eliminate the 2
toughness recovery is extended to about 7 x 10 n/cm,
NRL also is just completing their first phase of testing to obtain J-R curves. These J-R curves are being obtained for materials subjected to various irradiation, annealing and reirradiation schemes. For these tests all annealing is perfonned at 750*F. The results obtained from the currently available J-R curves indicate the same general trends observed with the C data. A second phase of the annealing study to y
investigate additiohal annealing strategies is now being planned by RES and NRL.
II. Comments A.
Annealing Based on a review of the initial NRL data, it appears possible to achiave significant toughness recovery from annealing, particularly at 750 F.
However, m annealing strategy that can be endorsed by the NRC for licensing aralication is certainly not now available and probably won't be aw.ili.ble for at least a year.
In fact, an effective annealing strategy can only be devised after A-ll is completed and the appropriate safety criterica is defined. The annealing procedure and the asscciated experimental development and verification should be tailored to ensure that the defined safety criterion is achieved and maintained within the physical constraints of the reactor systems.
Continued testing without a defined safety goal and knowledge of system constraints seems nonproductive. The EPRI program seems to recognize this concept since they are apparently attempting to develop a generalized recovery relationship that can be applied to a range of criteria. While the EPRI approach is the right direction it is an ambitious attempt and may prove difficult to achieve.
B.
Testing Procedures and Results The available J-R curves for irradiated weld metal generally indicate that accurate, repeatable data can be obtained.
However, anomalies have been observed. These anomalies are typically detected ir, J values TC and not in the T values. Licensing criteria based on J will be difficult to impMent because of the problems encountered kn defining I
J e
Since T likely will be the basis for NRC IIben.tperimentally. sing criteria for vesseggtwith low upper shelf materials, the d being generated appear to be acceptable for licensing application.
While good T data can be obtained, testing in a hot cell to obtain mat J-R curves is not yet routine.
It is probably desirable to have some standard to which various test results can be compared. This can be accomplished for future testing by using the load displacement record analysis method developed by Washington University.
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R. E. Johnson III. Recommendations A.
The second phase of the NRL annealing feasibility study including the definition of the irradiation and annealing sequences should be delayed until after the licensing criterion for low upper shelf materials has been developed. The testing should then be tailored to ensure the means are available to meet our criterion, should the implementation phase of A-11' indicate that annealing is necessary for certain plants.
This effort should also be closely coordinated with the EPRI program.
B.
The irradiated test data described in Milt Vagins July 12, 1979 memorandum should be sufficient to allow us to develop a generic licensing criterion. Consequently, we should delay, for a brief period, the testing of the remaining specimens, especially the larger ones, until we review this initial data, and develop the licensing criterion. The remaining tests can then be tailored to fill in any gaps or answer questions that may surface.
C.
Attempts should be made wher.ever possible to provide an extra specimen for analysis of load displacement records using the Washington University method. This type and analysis will provide a QA type check until the J-R curve development is more or less routine in various labs.
JW.
R. M. Gamble, Section N der Materials Integrity Section Materials Engineering Branch Division of Systems Safety cc: Central Files C. Serpan NRR Reading File P. Albrecht S. Hanauer M. Vagins M. Aycock R. Gamble D. Eisenhut V. Noonan L. Shao J. Strosnider P. Kapo R. Klecker W. Hazelton J. Knight P. Check S. Pawlicki W. Regan J. Watt S. Varga P. Randall 1095
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