ML030590156
| ML030590156 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 02/27/2003 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Moroney B, NRR/DLPM, 415-3974 | |
| Shared Package | |
| ml030660105 | List: |
| References | |
| TAC KC0042, Y020030008 | |
| Download: ML030590156 (8) | |
Text
ATTACHMENT 4 ACTION PLAN FOR ADDRESSING DAVIS-BESSE LESSONS LEARNED TASK FORCE RECOMMENDATIONS REGARDING ASSESSMENT OF BARRIER INTEGRITY REQUIREMENTS Last Update: Initial Update (2/27/03)
Lead Division: RES/DET Supporting Divisions: DRAA,DSARE Supporting Offices: NRR, Regions TAC No.
Description KC0042 Develop and implement action plans based on recommendations of the Davis-Besse reactor vessel head degradation Lessons-Learned Task Force (LLTF)
Milestone Date (T=Target)
(C=Complete)
Lead Support Part I: Leakage 1.
Review PWR TS to identify plants that have non-standard RCPB leakage requirements [LLTF 3.3.4(9):High]
7/03 (T)
NRR/DRIP 2.
Review plant alarm response procedure requirements for leakage monitoring systems and assess their adequacy for identification of RCPB leakage [LLTF 3.2.1(3):High]
3/04 (T)
NRR/DIPM RES/DET 3.
Re-evaluate basis for RCS leakage requirements and assess the capabilities of currently used and state-of-the-art leakage detection systems [LLTF 3.2.1(1):High, 3.1.5(1):High]
7/04 (T)
RES/DET RES/DRAA RES/DSARE NRR/DSSA NRR/DE NRR/DRIP NRR/DIPM 4.
Develop recommendations for inspection guidance pertaining to RCS unidentified leakage that includes action levels to trigger increasing levels of NRC interaction with licensees in response to increasing levels of unidentified RCS leakage
[LLTF 3.2.1(2):High]
1/05 (T)
NRR/DIPM RES/DET NRR/DE NRR/DSSA
Milestone Date (T=Target)
(C=Complete)
Lead Support 5.
Develop recommendations for (1) improving plant procedures for identifying RCPB leakage, (2) consistent TS, and (3) use of on-line, enhanced leakage detection systems on critical components [LLTF 3.1.5(1):High, 3.2.1(1):High, 3.2.1(3):High, 3.3.4(9):High]
3/05 (T)
NRR/DIPM NRR/DRIP RES/DET NRR/DE RES/DRAA NRR/DSSA NRR/DLPM 6.
Use appropriate regulatory tools to implement improved requirements
[LLTF 3.2.1(1):High]
TBD NRR/DRIP RES/DRAA RES/DSARE RES/DET NRR/DSSA NRR/DE NRR/DLPM Part II. Performance Indicators (PI) 1.
Develop and implement improved barrier integrity PI based on current requirements and measurements
[LLTF 3.3.3.(3):High]
6/04 (T)
NRR/DIPM RES/DRAA RES/DET NRR/DE NRR/DSSA Regions 2.
Develop and, if feasible, implement an additional PI capable of tracking the number, duration, and rate of primary system leaks. [LLTF 3.3.3.(3):High]
12/05 (T)
NRR/DIPM RES/DRAA RES/DET NRR/DE NRR/DSSA Regions 3.
Determine feasibility of establishing a risk-informed barrier integrity PI [LLTF 3.3.3.(3):High]
6/05 (T)
RES/DRAA NRR/DIPM NRR/DSSA NRR/DE RES/DET Regions 4.
Evaluate the need to modify existing barrier integrity PIs based on potential new requirements for RCS leakage from Part 1 [LLTF 3.3.3.(3):High]
TBD NRR/DIPM RES/DRAA RES/DET NRR/DE NRR/DSSA Regions
Description:
The Reactor Pressure Vessel Head degradation event at the Davis Besse Nuclear Power Station has many safety implications. One concern is the integrity of the reactor coolant pressure boundary. This action plan was developed to improve some of the requirements intended to ensure an effective barrier to the release of radioactivity. This plan describes the required actions, milestones schedules, identifies responsible parties, and estimates resource requirements.
Historical
Background:
In March, 2002, while conducting inspections in response to Bulletin 2001-01, the Davis-Besse Nuclear Power Station identified three control rod drive mechanism (CRDM) nozzles with indications of axial cracking, which were through-wall, and resulted in reactor coolant pressure boundary leakage. During the nozzle repair activities, the licensee removed boric acid deposits from the RVH, and conducted a visual examination of the area, which identified a 7 inch by 4-to-5 inch cavity on the downhill side of nozzle 3, down to the stainless steel cladding. The extent of the damage indicated that it occurred over an extended period and that the licensees programs to inspect the reactor pressure vessel (RPV) head and to identify and correct boric acid leakage were ineffective.
One of the NRC follow-up actions to the Davis-Besse event was formation of a Lessons Learned Task Force (LLTF). The LLTF conducted an independent evaluation of the NRCs regulatory processes related to assuring reactor vessel head integrity in order to identify and recommend areas of improvement applicable to the NRC and the industry. A report summarizing their findings and recommendations was published on September 30, 2002. The report contains several consolidated lists of recommendations. The LLTF report was reviewed by a Review Team (RT), consisting of several senior management personnel appointed by the EDO. The RT issued a report on November 26, 2002, endorsing all but two of the LLTF recommendations, and placing them into four overarching groups. On January 3, 2003, the EDO issued a memo to the Director, NRR, and the Director, RES, tasking them with developing a plan for accomplishing these recommendations. This action plan addresses the Group 4 recommendations of the Davis-Besse Lessons Learned Task Force Review Team regarding the Assessment of Barrier Integrity Requirements. The 6 high priority recommendations in the Assessment of Barrier Integrity Requirements grouping are included in this Action Plan. The LLTF recommendations are listed in the attached Table 1, and have been identified under the appropriate milestone(s).
Proposed Actions: The specific LLTF recommendations within this category are focused on reviewing and improving leakage detection requirements. However, simply improving leakage detection and lowering allowable leakage may not be sufficient to provide increased assurance of reactor coolant pressure boundary (RCPB) integrity. Leakage monitoring assumes that the pressure boundary will fail only under a leak-before-break (LBB) scenario. Small leak rates associated with tight stress corrosion cracks or cracks which may be partially plugged are not necessarily associated with small flaws in the RCPB. Therefore, the scope of this action plan also includes methods which may be capable of detecting crack initiation and monitoring crack growth before a through-wall crack develops and leakage occurs. Other degradation modes, such as boric acid corrosion and erosion-corrosion, which can lead to failure without leakage as a precursor will also be considered.
First, a comprehensive review and evaluation of plant experiences and current leakage detection systems will be performed. A similar study was performed by Argonne National Laboratory in the late 1980s. This task would essentially be to update that work. The technical bases for the current requirements on leak rates will also be reviewed. If changes should be made to leak rate limits, the impacts of these changes to other plant systems and analyses need to be identified. An evaluation of state-of-the-art systems capable of detecting leaks and cracks will also be completed. This evaluation includes, but is not limited to, acoustic emission technology. An evaluation will also be done to determine if leak rates can be correlated to unacceptable levels of degradation. It should be noted that this evaluation will be more difficult for tight stress-corrosion cracks which typically have low leak rates. Results of these reviews and analyses will then be used to develop an updated basis for leak rate requirements. Once this basis is complete, recommendations will then be made for improving leak rate limits, plant alarm response procedures, TS, and inspection guidance. Then a determination will be made to select which recommendations should be imposed as new requirements. The appropriate regulatory tools and procedures will be used to develop and implement these new requirements. A regulatory analysis will probably be needed to help establish the appropriate leakage criteria. It may not be possible or practical to implement leakage requirements small enough to preclude failure. Therefore, a regulatory impact analysis will be necessary to establish appropriate risk-informed leakage limits.
The second group of milestones relate to LLTF recommendation 3.3.3(3) regarding the review and improvement of barrier integrity performance indicators (PI). The first phase of the PI action plan continues an ongoing effort to improve the existing barrier integrity PI and will develop an improved barrier integrity PI based on current requirements and measurements taken at plants. The second phase will develop and implement (if feasible) additional barrier integrity PIs which would track the number, duration, and rate of primary system leaks that have been identified but not corrected. In parallel with these efforts, the feasibility of developing a risk-informed barrier integrity PI based on measures other than just reactor coolant system leakage will be researched e.g. reduced wall thickness due to degradation found during inservice inspections. The third phase of the PI action plan will be implemented only if new RCS leakage requirements result from the efforts described in the first group of milestones. If there are new leakage requirements, the barrier integrity PIs implemented in the earlier phases will need to be examined again to determine if they should be modified.
Completion of this action plan may require participation in public meetings and establishing communications with stakeholders. These items will be scheduled as needed.
Originating Documents:
Memorandum from Travers, W.D. to Collins, S. and Thadani, A. C., dated January 3, 2003, Actions Resulting From The Davis-Besse Lessons Learned Task Force Report Recommendations. [ML023640431]
Memorandum from Paperiello, C.J. to Travers, W.D., dated November 26, 2002, Senior Management Review of the Lessons-Learned Report of the Davis-Besse Nuclear Power Station Reactor Pressure Vessel Head. [ML023260433]
Memorandum from Howell, A.T. to Kane, W.F., dated September 30, 2002, Degradation of the Davis-Besse Nuclear Power Station Reactor Pressure Vessel Head Lessons-Learned Report.
[ML022740211]
Regulatory Assessment: The reactor coolant pressure boundary forms one of the 3 defense-in-depth barriers to the release of radioactive products. General Design Criteria 14, 30, and 32 of Appendix A to 10 CFR Part 50 specifiy requirements for the reactor coolant pressure boundary.
GDC 14 states in part that [t]he reactor coolant pressure boundary shall be designed, fabricated, erected, and tested so as to have an extremely low probability of abnormal leakage.
GDC 30 states in part that [m]eans shall be provided for detecting and, to the extent practical, identifying the location of the source of reactor coolant leakage.
GDC 32 states in part that [c]omponents which are part of the reactor coolant pressure boundary shall be designed to permit periodic inspection and testing of important areas and features to assess their structural and leaktight integrity.
In addition, the NRC has developed Regulatory Guide 1.45 Reactor Coolant Pressure Boundary Leakage Detection Systems.
From a practical standpoint, it was recognized that the RCPB cannot be made completely leaktight since some leakage is to be expected from equipment such as pump and valve seals.
Therefore, it becomes important to identify the source of any leaks. Identified leaks, such as from valves or pump seals, should be measured, collected, and isolated so as not to interfere with detection of leakage from an unknown source which could indicate a breach of the RCPB.
Specific limitations on leakage are stated in the Technical Specifications (TS) for each plant. In general, the TS place a limit on unidentified leakage (usually to 1 gpm) and state that continued operation with RCPB leakage is not allowed. In addition Title 10, Section 50.55a of the Code of Federal Regulations requires plants to meet the requirements of the ASME Boiler and Pressure Vessel Code.Section XI (Inservice Inspection of Nuclear Power Plant Components) of this code provides acceptance criteria for flaws found during inspection and evaluation procedures for determining the acceptability of flaws exceeding these standards.
Since the vessel head penetration (VHP) nozzles are considered part of the RCPB and significant degradation of the RPV head occurred at Davis-Besse, the issues raised by this event extend beyond problems of stress corrosion cracking in CRDM nozzles to issues of RCPB integrity in general. Primary water stress corrosion cracking of the VHP nozzles and their associated welds has been experienced by both U.S. and foreign plants. In addition, the degradation mechanism that occurred at Davis-Besse was also known. Therefore, one of the conclusions from the LLTF report was that this incident was preventable, but occurred because of a failure to follow-up and integrate relevant operating experience and other available information.
The TS for Davis Besse set a 1 gpm limit for unidentified leakage. In general, unidentified leakage was kept below 0.2 gpm. Despite this conservatism, the leakage eventually caused the degradation found in the vessel head. Therefore, the requirements associated with RCS leakage need to be reviewed and improved as warranted.
Current Status: This is the initial update for this Action Plan, which addresses the Group of recommendations of the Davis-Besse Lessons Learned Task Force Review Team regarding Assessment of Barrier Integrity Requirements.
Potential Problems: N/A Proposed Resolution of Potential Problems: N/A Schedule Changes Since Last Update: This is the initial update.
Resource Expenditure:
As of February 22, 2003, 0.13 FTE have been expended on the TAC listed for this Action Plan.
TAC No.
TAC Status HOURS KC0042 Open 251.7 An estimate of the additional resources needed to complete this action plan are as follows:
FY03 FY04 FY05 FY06 TOTAL FTE
$K FTE
$K FTE
$K FTE
$K FTE
$K NRR 1.3 1.2 1.2 1.2 4.9 REGIONS 0
0 0
0 0
RES 0.8 250 1.7 600 1.4 450 0.5 100 4.4 1,400 Priority: 2 Contacts:
Cayetano Santos Jr., DET, 415-6004 RES Technical Contacts:
Donald Dube, OERAB, 415-5472 NRR/DIPM Lead
Contact:
Jeffrey Jacobson, IIPB, 415-2977 NRR/DRIP Lead
Contact:
Robert Dennig, RORP, 415-1156 NRR/DLPM Lead
Contact:
Brendan Moroney, DLPM, 415-3974
References:
NRC Bulletin 2001-01, Circumferential Cracking of Reactor Pressure Vessel Head Penetration Nozzles, August 3, 2001 Memorandum from Ledyard Marsh, Deputy Director Division of Licensing and Project Management, to John Grobe, Chair, Davis-Besse Reactor Oversight Panel, dated December 6, 2002, Response to Request for Technical Assistance - Risk Assessment of Davis-Besse Reactor Head Degradation (TIA-2002-01) [ML023330284]
10 CFR Part 50 Appendix A NRC Regulatory Guide 1.45 Reactor Coolant Pressure Boundary Leakage Detection Systems NUREG/CR 4813, Assessment of Leak Detection Systems for LWRs, May 1988, Argonne National Laboratory.
Table 1 LLTF Report Recommendations Included in Barrier Integrity Action Plan High Priority RECOMMENDATION NUMBER RECOMMENDATION 3.1.5(1)
The NRC should determine whether PWR plants should install on-line enhanced leakage detection systems on critical plant components, which would be capable of detecting leakage rates of significantly less than 1 gpm.
3.2.1(1)
The NRC should improve the requirements pertaining to RCS unidentified leakage and RCPB leakage to ensure that they are sufficient to: (1) provide the ability to discriminate between RCS unidentified leakage and RCPB leakage; and (2) provide reasonable assurance that plants are not operated at power with RCPB leakage.
3.2.1(2)
The NRC should develop inspection guidance pertaining to RCS unidentified leakage that includes action levels to trigger increasing levels of NRC interaction with licensees in order to assess licensee actions in response to increasing levels of unidentified RCS leakage.
The action level criteria should identify adverse trends in RCS unidentified leakage that could indicate RCPB degradation.
3.2.1(3)
The NRC should inspect plant alarm response procedure requirements for leakage monitoring systems to assess whether they provide adequate guidance for the identification of RCPB leakage.
3.3.3(3)
The NRC should continue ongoing efforts to review and improve the usefulness of the barrier integrity PIs. These review efforts should evaluate the feasibility of establishing a PI which tracks the number, duration, and rate of primary system leaks that have been identified but not corrected.
3.3.4(9)
The NRC should review PWR plant TS to identify plants that have non-standard RCPB leakage requirements and should pursue changes to those TS to make them consistent among all plants.