ML20237C203
| ML20237C203 | |
| Person / Time | |
|---|---|
| Issue date: | 08/26/1996 |
| From: | Speis T NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Thadani A NRC (Affiliation Not Assigned) |
| Shared Package | |
| ML20237C196 | List: |
| References | |
| FOIA-98-300, REF-GTECI-166, REF-GTECI-NI, TASK-166, TASK-OR NUDOCS 9808210022 | |
| Download: ML20237C203 (2) | |
Text
- 42 0 k UNITED STATES j NUCLEAR REGULATORY COMMISSION
( WASHINGTON, D.C. 2000H001
- / August 26, 1996 NEMORAIERSI T0: Ashok C. Thadani, Associate Director for Technical Review Office of Nuclear Reactor Regulation FRON: Themis p. Spels, Deputy Director Office of Nuclear Regulatory Research
SUBJECT:
SDIERIC SAFETY ISSUE (451)-166, " ADEQUACY 0F FATIGUE LIFE OF
, NETAL COMP 0NENT5' REFERDICE: Nemo to T. Speis from A. Thadant, dated June 3, 1996
,Your reference memo about generic safety issue (SSI)-166, fatigue of metal components was received. He have considered the suggestion of transferring responsibility for management of $51-166 to RES, and accept the responsibility to work on it.
The risk of failure from fatigue of various reactor coolant system components was studied under 451-78, "Nonitoring of Fatigue Transient Limits for the Reactor Coolant system." This specific concern was substaned by NRA's Fatigue
(' Action plan (FAp), now completed as documented in SECY-96-246. Under 45I-78, a study was completed that showed very small risk from fatigue failure of the primary coolant pressure boundary components. The Advisory Casumittee for Reactor safeguards (ACRS) agreed with the conclusion and considered 65I-78 resolved; howevet, these fatigue analyses assumed a 40-year plant life.
Because the ,sta,ff is required to document resolution of any generic issue for a proposed life extension period, the staff is currently performing a fatigue anapis for extended plant life up to 60 years.
This ing work on SSI-78 and residual work on 851-166 will now be carried on by ' under a new G5I-190, " Fatigue Evaluation of Metal Components for 60-year p1 t !*fe."
Schedule and Milestones for 85I-190
- 1. Extend the RES risk study to cover a potential 60-year plant life.
Completion Date: September, 1996
- 2. Develop a staff position in cognizance with the appropriate IstR technical staff.
Completion Date: January, 1997 Meet with CRSR, if necessary, to discuss the license renewal
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recannendations in the staff position paper.
Completion Date: April, 1997 i i 9808210022 980818 i PDR FOIA HEROUX98-300 PM l
1 A. Thadani 4. Meet with ACRS to discuss the license renewal recossendations in the staff position paper.
Completion Date: June, 1997 cc: W. Russell, INtA D. Norrison L. Shao C. Serpan K. Shaukat CONTACT: S. Khalid Shaukat, RES 415-6592 DISTRI N T1 5: *See previous concurrences 6518 Reading File l 1
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June 3, 1996 I ~ '/g ' h Thents P. Spets, Deputy Director j
, MOORANCUM TO:
Office of Nuclear Regulatory Research
( FROM: Ashok C. Thadant, Associate Director /s/
I k for Technical Review Office of Nuclear Reactor Regulation SU8 JECT: ACTIVITIES LEADING TO RESOLUTION OF GENERIC SAFETY ISSUE 166 l Issues concerning fatigue of metal components were designated as Generic Safety Issue (GSI) 166, " Adequacy of Fatigue Life of Metal Components." In response to Commission-direction (June 28, 1993, memorandum, to J. M. Taylor
- and W. C. Parler dealing, in part, with SECY 91-049 , NRR developed the
- Fatigue Action Plan (FAP) to address technical conce)rns regarding the original licensing basis fatigue criteria used to evaluate the reactor coolant pressure boundary components of operating plants. Because GSI 166 incorporated the FAP effort, the GSI was assigned to NRR.
The completion of the FAP was documented in SECY 95-245 (Completion of the Fatigue Action Plan). In SECY 95-245, the staff concluded that no immediate actions were' required to deal with the issues addressed by the FAP. The conclusion was based, in part, on a risk assessment of reactor coolant
! pressure boundary components performed by RES under GSI-78, " Monitoring of Design Basis Transient Fatigue Limits for Reactor Coolant System." However, the conclusion was based on an assessment of the fatigue issues for the
, current plant design life. The procedures for the resolution of GSIs require l that the resolution also consider a license renewal period of 20 years.
( The RES risk study that contributed to the completion of the FAP addressed a 40-year plant life. The NRR staff and the RES staff have discussed an extension of the previous risk study and developed the attached action plan to l address this effort. The RES staff agreed to the transfer of lead l responsibility and the approach described in the action plan. The purpose of l the action plan is to develop the specific recommendations applicable to an extended period of operation for license renewal in order to resolve GSI-166.
The major effort of the proposed action plan involves the extension of the RES risk study which you are currently undertaking. It should ba noted that, in '
accordance with the License Renewal Rule (10 CFR 54), licensees seeking ,
renewal of their license will be required to demonstrate that the effects of j aging (including fatigue) will be adequately managed for their facility. NRR j will be respons<ble for these reviews.
In view of the foregoing, we are hereby transferring responsibility for j management of GSI-166 to RES. Although the schedule may require reevaluating, t the attached action plan can be used as the basis to update GSI-166 in the Generic Issues Management Control System (NUREG-0933).
Attachment:
'As stated 4 CONTACT: R. Wessaan, NRR/DE *See previous concurrences ;
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r LICENSE RENEWAL FATIGUE ACTION PLAN lk Description During the development of criteria for the evaluation of applications for license renewal, the staff identified technical issues related to the fatigue design of reactor coolant ~ pressure boundary components that were applicable to license renewal. Subsequent discussions within the staff and between the staff and the industry identified that the issues were also applicable to current operating plants. The technical issues were designated Generic Safety .
Issue (GSI) 166, Adequacy:of Fatigue Life:of Metal Components." The NRR staff developed the Fatigue Action Plan (FAP) to address these issues for operating l plants. On September 25, 1995, the staff informed the Commission of its conclusion that no additional actions to address the fatigue issues at current operating plants were necessary at this time (SECY-95-245). However, the staff indicated it would consider, as part of the resolution of GSI-166, the need for license renewal applicants to evaluate a sample of components with ,
high fatigue usage for any extended period of operation for license renewal. J Historical Backaround Reactor coolant pressure boundary components of many older plants were designed to codes, such as ANSI B31.1, that did not require an explicit component fatigue analysis. Because the ASME Code currently requires a fatigue evaluation of the components of the reactor coolant pressure boundary, this led to a question regarding the fattgue resistance of these older vintage
[( plants. In addition, some test data indicate that the effects of the LWR environments could significantly reduce the fatigue resistance of materials.
The ASME Code design fatigue curves were based primarily on strain-controlled fatigue tests of small polished specimens at room temperature in air.
Although factors of safety were applied to the best-fit curves to cover effects such as size and data scatter, some of the test data indicate that these factors of safety may not be adequate to encompass the environmental effects.
In order to assess the significance of the fatigue issues an evaluation of a ;
sample of reactor coolant pressure boundary components from several plants was perfomed. These evaluations used interim fatigue curves that accounted for i the environmental test data. The evaluations indicated that the majority of l the sample components in both older and newer plants could be shown to meet the ASME Code fatigue criteria for the current plant design life when curves i that accounted for environmental effects were used. The components that did i not meet the ASME Code fatigue criteria for the current design life were piping components and piping nozzles. When an extended period of operation i for l< cense renewal was considered, additional components in the sample ,
exceeded the ASME Code fatigue critertav Although the staff believed that the fatigue limit could be met for most of the components if additional measured i plant transient data or detailed analyses had been used in the evaluations, the staff believed that it would be more difficult to meet the fatigue limit for an extended period of operation associated with license renewal.
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( The Office of Nuclear Regulatory Research (RES) performed a risk assessment of reactor coolant pressure boundary components under GSI-78, " Monitoring of Design Basis Transient Fatigue Limits for Reactor Coolant System." The risk assessment indicated that risk due to a piping contponent failure was low. The risk assessment used the results of previous studies which indicated that there is a relatively low probability of piping system failure given a crack has been initiated in the piping. The previous studies were based on stresses that the piping system was projected to be subjected to during its design lifetime. In order to apply the risk study to license ranewal, it needs to be ~
updated to address a 60-year design life. The results of the risk study will be used in the formulation of the staff recommendation for license renewal.
(The updated risk study can also fom the basis for the resolution of GSI-78 for license renewal).
Proonsed Actions Perfom a risk assessment of high fatigue usage components identified in NUREG/CR-6260 for a 60-year design life. The risk assessment will use the computer code PC PRAISE to generate failure probabilities for the high fatigue usage components. Using the results of the risk assessment, develop a recommendation for a 60-year operational period. The recommendation will address whether applicants for a renewed license should be requested to evaluate a sample.of components at their facilities using fatigue curves which account for environmental effects.
(F. Reaulatory Assessment .
Based on the FAP it was determined that no new requirements could be justified for operating facilities based ch their current design lives. The issue being addressed is whether additional effort is required for an extended period of operation for licensee renewal. Since there are rio plants currently operating beyond their original design lives, there is no immediate safety concern while this issue is being addressed.
Schedule and Milestones
- 1. Obtain the results from the Fatigue Action Plan (FAP).
Completion Date: September 1995
- 2. Extend the RES risk study to cover a potential 60-year plant life. The l study will consider the component stresses obtained in the FAP study.
Completion Date: September 1996: ;
- 3. Based on the risk study in Item 2 above, develop a staff position paper providing reconnendations regarding the use of the environmental fatigue data in a license renewal assessment of reactor coolant pressure boundary components for a 60-year operational period.
Completion Date: December 1996 4
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- 4. Meet with the CRGR, if necessary, to discuss the license renewal recommendations in the staff position paper.
Completion Date: March 1997
- 5. Meet with the ACRS to discuss the license renewal recommendations in the staff position paper.
Completion Date: May 1997 -
References SECY 93-049 SRM, Chilk to Taylor and Parler, June 28, 1993 SECY 94-191 NUREG/CR-6280 SECY 95-245 ACRS letter to Chairman Jackson, October 16, 1995
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