ML18100A458
| ML18100A458 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 06/25/1993 |
| From: | Newton R WESTINGHOUSE OPERATING PLANTS OWNERS GROUP |
| To: | WESTINGHOUSE OPERATING PLANTS OWNERS GROUP |
| References | |
| GL-93-04, GL-93-4, OG-93-39, NUDOCS 9307120128 | |
| Download: ML18100A458 (8) | |
Text
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Subject:
Westinghouse Owners Group J!S.GULATORY RESPONSE GROUP WOG Effort Related to Salem Rod Control System Event (GL 93-04) Update
- Westinghouse and the Westinghouse owners Group (WOG) Regulatory Response Group (RRG) met on Thursday, June 24, to develop a generic action plan to assist all Westinghouse licensees in responding to NRC Generic Letter 93.04. The following is a status of the WOO initiatives with respect to the generic assessment of the Rod Control System failure event at Salem Unit 2.
Generic: Letter 93-04 Summary Pursuant to the requirements of 10 CFR 50.S4 (t)t the NRC has issued Generic Letter 93-04, "Rod C.Ontrol System Failure and Withdrawal of Rod control Custer ~mblies." The letter was issued on Monday, June 21, 1993 and addressed to all licensees with the Westinghouse Rod Control System (except Haddam Neck) for action and to all other licensees for information.
The generic letter requires that within 45 days from the date of the generic letter, eacb addressee provide an assessment of wheiher or not the licensing basis for each facility is still satisfied whh regard to the requirements for system response to a single failure in the Rod Control System (GDC 2S for most plants). If the* assessment indicates that the licensing basis is not satisfied,. describe compensatory short-term actions consistent with the guidelines contained in the generic leuer, and within 90 days, provide a plan and schedule for long-term resolution.
The WOO members will be requested to endorse the programs outlined in this letter which are aimed at developing a generic response for the licensees to utilize as part of their plant-specific response to the generic letter.
070031
JUN ~~ '93 14:40 F'R(:iE. 003 l .
Update to NSAL 93-007 Westinghouse issued Nuclear Safety Advisory Letter 93-07 on June 11. 1993. During the Last two weeks, additional thought has gone into the appropriate licensing interpretation of the current understanding of the Salem failure event Given that the failure will result in identical current orders to an the rods in the selected bank, other effects have been postulated to address why the entire bank did not behave in a similar marmcr. As a result. the Westinghouse position on GDC~2S. as stated in Westinghouse Nuclear Safety Advisory Letter 93-007, has been revised. Specifically, the determination in the Assessment of Failure Scenarios (pg 8) that GDC 25 is not met is not the current intetpretation of the position of Westinghouse and the WOO. As stated in the June 14 NRC meeting, the Salem event is still considered to be an infrequent fault (COndition Im. based on probability and thus, satisfying the DNB design limit is not the appropriate licensing criteria. The WOG, and Westinghouse. believe that the intent of GDC 25 continues to be met. The position of the NRC as indicated in the Generic Letter (93-004) is that the specified acceptable fuel design limits (SAFDL) referred to in GDC-25 is the minimum DNBR limit Westinghouse and the WOG RRG believe that the design philosophy behind rhe classification of events. based on probability of occurrence and severity of consequences. indicates that it is appropriate to consider a small amount of fuel damage vs the DNBR limit as the acceptance criteria for a low probability event.
To address the potential consequences of an asymmetric rod withdrawal. Westinghouse is confident that. using current methods. all plants would be able to show that the ANS Condition m acceptance criteria would continue to be met (i.e.* no more than a small fraction of fuel will experience DNB -
less than 5% ). Westinghouse also believes that it is imponant to pursue the possibility of the acceptability of a small fraction of fuel failure for these events while investigating the likelihood of occurrence of a single or multiple asymmetric rod withdrawal.* The programs outlined below will provide the technical and analytical bases to support this position and provide interim assurance that the DNBR will be greater than the design limit while long-tenn solutions are pursued.
1n addition, in the Review of Failure History at U.S. Westinghouse Plants section of NSAL 93-007, the number and types of failures is incorrect. The failure breakdown in the second paragraph should be "Of rhe 34 reported failures, 24 caused. the rods to ~main as positioned. S failures resulted in dropped rod(s). 2 failures were step cowiter failures. and 3 (including the Salem event) failures resulted in misalignment of the rods." The fifth paragraph in that same section should be changed to the following, "This event is thus considered no worse than an infrequent f3u.lt using ANSI standard
.S 1.1 .to correlate the calculated probability of occurrence to the FSAR accident category definitions.
For an event to become* an 'incident of moderate frequency,' the frequency would have to be in the range of lE-01 evenrs per year. Thus. additional misalignments would have had to occur to reach the upper bound of a Condition 1Il event (i.e.* to move to a Condition II event)."
General Discussion At the June 14, 1993 WOO Regulatory Response Group presentation to the NRC on the generic assessment of the Salem event. it was stated that the expected response to the single failure is a RCCA group or bank movement. nus would include the failure that occurred at Salem. The e:itplanatton for why only one RCCA moved at Salem will be provided as part of The generic assessment. Also discussed with the NRC was the consideration that this event has very low probability and should be classified as a Condition m event with associated acceptmce criteria. Actual operating and failure experience will help substantiate this statement of event frequency.
Generic Letter 93-04 included the following sentence just before the paragraph on the Westinghouse Nuclear Safety Advisory Letter, The analysis discussed by the Westinghouse Owners Group indicated that fuel failures could result from single failures identified as a result of the Salem event." Tilis is a NRC conclusion apparently developed by combining two parts of the presentation material. The safety analysis discussed with the NRC was not attributed to the rod control system single failure. but was an analysis intended to bound the safety significance of single or multiple rod withdrawals from power or from subcriticai initial reactor conditions.
Another consideration presented by the WOO RRG was that the rod control system failures were detectable when rod motion occurs. The operator would *detect abnormal rod motion as a result of nonnal plant operation at power, during periodic technical specification surveillance tests on control rod movement. or during other manual operation of the rod control system. It was concluded that from a generic standpoint. the rod control system is considered operable if the control rods move as required and technical specification requirements are met An operability determination on the Rod Control System is not typically required because it is not a safety system. but rather the operability determination is made on the ability of the control rods to perform their safety function, i.e** fall into the reactor upon demand. Given that the postulated failure is detectable, Westinghouse believes that the Rod Control System failure does not have to be considered coincident with any other Chapter 15(14) accident. Note that it still must be addressed as an initiating event A meeting will be scheduled with the NRC on July 8/9 to provide the NRC with a status of WOG activities. the intended direction of those activities, and to request a 15 day extension to the 45 day reporting requirement in order to permit utilities time to incorporate the results Of the WOG programs.
Attendance at this meeting is tentatively limited to members of the RRG and additional requests should be discussed with Mr. Roger Newton. RRG Chairman.
WOG Plans and Schedule This section identifies the activities that the WOG RRG intends to sponsor during the next 6 weeks.
Each is described in some detail and a single comprehensive schedule is attached. The schedules for both Westinghouse and the licensees are extremely aggressive and will require dedicated cooperation from each licensee. It is the intent of the WOO RRG to request an additional 15 days for the licensee response at the July 8/9 NRC meeting. The necessity for the extension is based on the ability of Westinghouse and the Licensees to pertbnn all the various actions within the alloued time.
The programs discussed below will be documented in lWo WOO Project Authorizations yet to be issued. These will be issued by June 30. 1993 with the voting to be completed by July 7. 1993.
- 1. SURVEY In the next several weeks. the WOO. through Westinghouse, will be conducting.a survey.
1bis survey is in response to the WOG commitment made to the NRC to evaluate the equipment perfoimance history of the Rod Control System and to suppon the initial detennina:tion of the probability of occurrence for the postulated failures. This survey will involve the collection and analysis of component failure data in the Rod Control System logic cabinets during startup, rod surveillance testing, and power operation. The components that will be analyzed .include logic cabinet components such as printed. circuit boards. DC power supplies, and loose wiring and connectors within the logic cabinet. The events of particular interest a.re those where the control rods did not move consistently when demanded. including movement from the bottom of the core and misalignment. The data collection is to span the time from initial plant startup through May 1993.
Failures of rods to move properly and failures of components (i.e., not out-of-tolerance conditions but failures in which the component would not be able to perform its function) will be analyzed. In this instance, failures are de.fined ~ replaced components or repairs with at least one component replaced (such as a chip on a printed circuit board).
The survey will be mailed from the Westinghouse WOG Project Office on Friday, June 25.
Licensees need to respond with as much information as possible by July 15. Tue most Critical items (supervisory and slave cycler cards) are identified in the survey. A preliminary repon will be issued by July 23. The final repon will be issued by July 30.
- 2. TESTING The purpose* of the Rod Control System test program is to determine the type of motion that can occur when Control Rod Drive Mechanisms (CRDMs) are. subjected to corrupted current orders under varying conditions. A test team will be assembled from WOG, PSE&G. and Westinghouse, including design expertise in the Rod Control System and CRDMs. Tests will be performed on a Rod Control System (Logic Cabinet, Power Cabinet and one or more CRDMs) installed in a test facility. Tests to be conducted include baseline cycle tests. latching tests. rod displacement tests~ load tests, and current onier timing tests. The test program, ~
currently designed, is anticipated to be completed. over an 80 day tiIIle frame. Once rhe Project Authorization is completed and approved. and the testing site is confinned, the schedule will be integrated. into the master schedule. It is recognized that portions of the program will not be completed prior to the 45/60 day reporting requirement.
A generic failure assessment will be performed to determine whether other single point failures can occur in the Rod Control System that corrupt the CRDM coil current orders. Of concem are only those comipted current orders that could. possibly produce motion of less rhan a group of control rods. The analysis would revise or supplement *the existing Failure Modes and Effects Analysis (WCAP-8976). The schedule for completion of the generic failure assessment will be included* with the overall test program.
- 3. ACCIDENT ANALYSIS As pan of the WOO initiative, the Analysis Subcommittee will be sponsoring a generic approach to demonstrate that all Westinghouse plants satisfy GDC 25 (or its equivalent). The purpose of this program is to analyze a series of asymmetric rod withdrawal c~ from both subcritical and power conditions to demonmate that the Condition II DNB design basis will remain met. Current codes and NRC-approved methodologies are not sufficient to make that determination. As a result, the approach will use a three-dimensional spatial kinetics/systems transient code (LOFTS/SPNOV A) to show that. in 3-D. the localized power peaking is not as severe as current codes would predict. This code/methodology is not yet approved by the US NRC, but is approved for use in the United Kingdom (UK) by their regulatory agency. The analytical work will be conducted by the National Nuclear Corporation (NNC) - the UK Westinghouse licemee. Given that the UK regularor is similar to the US NRC in philosophy and level of review detail. this approach should provide additional ~ranee that all Westinghouse plants continue to satisfy GDC 2.5.
To address those plants that either do not use Westinghouse fuel or do their own* safety analyses. Westinghouse will be providing a brief suivey foIUl to gather the required neutronics panuneters to ensure that the "generic" sensitivity studies are ~sentative of all Westinghouse plants.
The schedule for this program is the following: the draft project authorization is due out on Friday, Jwte 25. The final is due out by June 30 through the Westinghouse WOG Project Office. A phone vote will then be conducted. 1be draft analysis report will be issued for comment by July 23 with the final report being issued by July 30.
- 4. WESTINGHOUSE TECHNICAL BULLETIN Westinghouse is currently working on the draft Technical Bulletin that will describe the Rod Control System failure event in detail. The Technical Bulletin will also provide guidance in detennining the functionality of the rod deviation alarm, a recommended action in NSAL 93-007.
- 5. GENERIC RESPONSE TO THE SALEM COMPENSATORY ACTIONS The WOG will also be sponsoring a generic assessment of the plant~specific compensatocy actiom committed to by Salem as a precondition for plant startup. Each compensatory action will. be identified. reviewed, and a conclusion made as to whether or not the action should be implemented by the remainder of Westinghouse plants. The preliminary detennination is that a sufficient technical ~s exists such that none of the Salem compensatOry actions needs to be inlplemented. Peruiing release by Public Seivice Electric & Gas, a copy of the Salem Justification of Continued Operation will also be attached. A copy of typical normal and coI?Upted Rod Control System current traces will also be provided. This action will be completed by Friday, July 2.
- 6. GENERIC RESPONSE TO GL 93-04 The WOG will be issuing a comprehensive report summarizing all the various activities that can be referenced in each licensee* s response. The WOG report will provide a technical b~is for the determination that every Westinghouse plant continues to meet the requirements for system response to a single failure in the Rod Control System {GDC 25 for most plants) and provide some level of guidance as to the content and format of the individual licensee respome. The defeme will focus on 1) the root cause of the*Salem event. 2) the probability or likelihood that the fault in the ROd Control System could result in .all rods in a bank not behaving in a siwilar manner, 3) the expected symptomatic response if it does occur, and 4) a best-estimate analytical, argument that. even if the fault were to cx:cur. every plant would continue to satisfy the DNB design basis.
The draft of this report will be issued to utilities by July 23 with the* final report issued. by July 30.
WOG Delil'erables A comprehensive schedule hM been developed and is contained in Attachment 1. All milestones and
. deliverables are highlighted.
Strategy Tue WOO, with support from Westinghouse, will $SesS the Salem event to show rhat no single failure (without other effects) can result in single or asymmetric rod movement. The approach will include discussions on Rod Control System failure rates/types and probability of occunence through the equipment SUIVey, expected/predicted movement under failure conditions from the testing program, and the ability to detect such a failure. Ultimately, it is expected. that all Westinghouse planrs will continue to satisfy GDC 2S (or its equivalent). As additional suppon. best estimate analyses will be petform~d to demonstrate that all plants can continue to satisfy their DNB design basis.
The primary technical contact at Westinghouse is Mr. Mark .Proviano {412) 374-5651. The WOG Project Office Interface is Mr. J. DaVid Campbell (412) 374- 6206. Additional information will be provided as it becomes available .
. Very truly yours*
. Roger A. Newton. Chainnan Regulatory Response Group Westinghouse Owners Group cc: WOO Steering Committee Regulatory Response Group C.K. McCoy, Georgia Power J.P. O'Hanlon. Virginia Power S.R. Tritch, W N.J. Liparulo, YI.
K.J. Voytell, "Ji_
- Attachment 1
,I June 25: WOO RRG update letter WOO/Westinghouse RCS survey issued Draft project authorization faxed for review June 30: Final project authorization issued for WOO vote Neuttonics analysis survey issued to non-Westinghouse scope plants July 2: Generic response to Salem compensatory actions July 7: WOO project authorizations telephone votes completed Start of Testing Program (Day l)
Westinghouse Technical Bulletin issued July 8: NRC meeting in Rockville. Maryland July 9: NRC meeting in Rockville. Maryland (alternate date)
Neutronics analysis survey returned to Westinghouse July 15: RCS survey response due to Westinghouse July 23: Draft RCS failure survey report issued Draft generic response to Generic Letter 93-004 issued Draft accident analysis report issued July 27: Start of actual testing (Day 21)
July 30: Final RCS failure survey report issued final accident analysis report issued Final generic. response to Generic Letter 93-004 issued
August 5:
Original due date to NRC . ~*
August 20: Proposed extended NRC due date (pending .NRC approval)
August 25: Completion of testing (Day 50)
September 9: Draft test report issued (Day 65)
September 24: Final test report issued (Day 80)
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