ML20140D798
| ML20140D798 | |
| Person / Time | |
|---|---|
| Issue date: | 03/21/1986 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Asselstine, Palladino, Roberts NRC COMMISSION (OCM) |
| Shared Package | |
| ML20140D804 | List: |
| References | |
| NUDOCS 8603260497 | |
| Download: ML20140D798 (2) | |
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[*g UNITED STATES 8 n NUCLEAR REGULATORY COMMISSION
- j WASHINGTON. D. C. 20555
\...../ NAR 211986 MEMORANDUM FOR: Chairman Palladino Comissioner Roberts Comissioner Asselstine Comissioner Bernthal Comissioner Zech FROM: Victor Stello, Jr.
Acting Executive Director for Operations
SUBJECT:
B&W DESIGN REASSESSMENT On January 16, 1986 I discussed, with the senior staff, management actions that we should take to improve operations ac a result of insights gained from the Davis-Besse and (to a limited extent) the Rancho Seco events. As indicated in my February 6 memorandum to you, one of the principal decisions reached as a result of those discussions was that a reassessment of the B&W design should be undertaken in the light of the cumulative operating experience with the B&W-type facilities to date. NRR was assigned the lead role in developing the overall plan for such a reassessment effort, and the goal established for completion of the reassessment was about the end of 1986. Enclosed for your information is the original NRC reassessment program plan of B&W design that was promptly developed by NRR in consultation with the other NRC offices before we decided to encourage the B&W Owners' Group (BWOG) to take the leadership role in this matter.
We subsequently contacted the BWOG and the NSSS Vendor in connection with the reassessment, and encouraged them to assume a strong leadership role in accomplishing key aspects of the overall effort required, where such involve-ment would be considered appropriate. We did this in consideration of
_ expertise and resource availability, and in recognition of the fundamental responsibility of the utility members of the BWOG for the proper design of the operating plants. In that context, we have provided the original NRC plan to the BWOG for their consideration. Copies of correspondence exchanged with I.he group in this mattar ere also enclosed for your information.
A meeting is now planned on April 8, at which the BWOG is to present to the staff a plan developed by that group for addressing concerns related to the frequency of trips and the ecmplexity of ' post-trip responses in B&W plants.
The staff will review the BUOG reassessment plan and reach final agreement with the BWOG regarding Ge BWOG reasmessment program. These interactions will enable the staff to establish the final hRC course of action and schedule to be followed in completing the overail reassessment effort. I will keep you informed regarding the progress of interactions with the BWOG in this matter and the culmination of staff's planning efforts. The staff is, of course, 4 6, h
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.. 't already proceeding to the extent possible in those areas which properly lie within the sole purview of NRC in order to expedite completion of this important task.
Original signed by Victor Stelley Victor Stello, Jr.
Acting Executive Director for Operations
Enclosures:
- 1. Ltr. Crutchfield to Tucker (BWOG) dtd 3/13/86 w/ Enclosure
- 2. Ltr. Tucker (BWOG) to Stello dtd 2/13/86 Distribution: cc: SECY VStello OGC JHSniezek OPE JConran DCrutchfield -
JTaylor, B&W HTucker, BWOG DEDROGR cf Central File PDR HDenton TRehm JRoe ED0 r/f
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+ UNITED STATES E[o fo o NUCLEAR REGULATORY COMMISSION Enclosure 1 y, .; wAssincrow. o. c. 2osss
% ...,* March 13,1986 Mr. Hal Tucker, Chairman Babcock & Wilcox Owners Group Duke Power Company .
Post Office B0x 33189 Charlotte, North Carolina' 28242
Dear Mr. Tucker:
SUBJECT:
B&W DESIGN REEXAMINATION In Mr. Stello's letter to you of January 24, 1986, he indicated that there is a need to reexamine the basic design for B&W reactors. On February 5,1986, the staff met with the B&WOG. Part of this meeting dealt with the Owners Group's response to the January 24, 1986 letter. You indicated that it is logical for the Owners Group to serve in a leadership role in resolving the NRC's concern. You also indicated that the Owners Group is willing to work with the NRC on this program. On February 13, 1986, you provided your response to the January 24, 1986 letter. In that response, you noted that the Owners
- Group would take the lead in a planned effort to define concerns related to the frequency of reactor trips and the complexity of the post-trip responses in B&W plants. You noted that such a plan would be available to be discussed with the staff during the first week of April. You also noted that the Owners Group intends to work interactively with the staff on this plan.
The staff has prepared a plan that includes those items that the staff believes are necessary to carry out the reexamination. A copy of the staff's plan is enclosed and has been given to Mr. Taylor of Babcock and Wilcox~. Identified in the plan are those items that we expect the Owners Group would take the lead in or play a major role in completing. Those items that the Owners Group are not doing, such as a emparison with other PWRs, will be handled by the staff.
We intend to meet with the Owners Group in April to discuss their plans.
As a result, there could be changes in our plan.
. Sincerely, b d $ -- '
enn s M. Crutchfiel , s st nt Director for Technical Suppor Divir. ion of PWR Licensing-B
Enclosure:
As stated k -
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ENCLOSURE 1-NRC REASSESSMENT PROGRAM
. INTRODUCTION Since the TMI-2 accident, there has been a growin~9 realization of the sensitivity of Babcock and Wilcox (B&W) plants to operational transients. By letter dated January 24, 1986, the Acting E00 informed the Chairman of the Babcock and Wilcox Owners Group (B&WOG) that a number of recent events at B&W designed reactors lead us to conclude that there is a need to re-examine the basic design requirements for B&W reactors.
This Task Action Plan outlines the scope that the staff believes is needed to accomplish the reassessment. NRR has been assigned the responsibility to provide overall direction of thsi effort with support from the Regions and all appropriate NRC offices. It is likely that the B&WOG will play a major role in carrying out a large part of this reassessment but that there will be areas that the staff feels need to be evaluated, that the Owners Group will not be doing.
- 1. OBJECTIVE The overall objective of the generic evaluation is to reassess the basic design requirements and operational characteristics of.the B&W nuclear reactors. Also, the study will compare the overall safety of the B&W reactors to other PWRs.
- 2. DISCUSSION To achieve the objectives discussed above, a Task Action Plan has been developed that -includes both deterministic and probabilistic assessments, an integrated evaluation to identify potential improvements to reduce the frequency and complexity of anticipated operational transients, and thereby improve the overall safety of the B&W reactor, and identification of potential revised licensing criteria. D. Crutchfield, Assistant Director for Technical Support, Division of PWR Licensing-B, NRR has been designated as the senior staff manager responsible for this program. Enclosure I lists the Regional and appropriate Office contacts.
Figure 1 shows the major tasks and the interfaces between tasks.
An overview of the tasks shown in Figure 1 is discussed in the follcwing paragraphs.
- 3. SCOPE AND CONTENT OF TASKS The study and required informatior, will be based on the following B&W designed plants for which utilities hold operating licenses:
Arkansas Nuclear One, Unit 1 (AN0-1) - (Arkansas Power & Light Company)
Crystal River, Unit 3 - (Florida Power Corporation)
Davis-Besse, Unit 1 - (Toledo Edison Company)
Oconee, Units 1, 2 and 3 - (Duke Power Company)
Rancho Seco, Unit 1 - (Sacramento Municipal Utility District)
Three Mile Island, Units 1 and 2 (Metropolitan Edison Company)
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- The main focus of the study will be the generic assessment of B&W designed reactors and the identification of potential improvements as related to reducing the frequency and severity of anticipated operational occurrences, and thereby improve the overall safety of the B&W reactors. In addition, representative Combustion Engineering (CE) and Westinghouse (W) PWR designs will be selected and compared with the B&W PWR design to assess the relative plant' dynamic behavior that would result when confronted with similar anticipated operational occurrences, as well as their overall safety.
In general, Tasks 3.1 through 3.11 involve a spectrum of assessments, each of which should identify potential system, human factors, operations or analysis improvements aimed at increasing the perceived level of safety of the B&W reactors. Task 3.12 performs an integrated evaluation of all these improvements, without regard to cost / benefit judgements. Tasks identified with an asterisk are those where the Owner's Group is likely to take a lead or play a major. role in completing.
3.1 Review Operating Events (*) .
This activity will consist of the re-review of past B&W operational occurrences.
The intent of this effort is to look at these events as a set of operational experiences that may indicate common problems, deficiencies, or system weaknesses. The review should include, but should not be limited to, the applicable Licensee Event Reports (LERs), Inspection and Enforcement (IE)
Bulletins, Circulars and Notices and other information involving anticipated operational occurrences and related failures at each of the operating B&W plants, and for other PWR vendor plants. Existing compilations of data will be used where possible. This information will be. input to Item 3.3, below.
3.2 Identify Problems, Root Causes, and Sensitive Systems (*)
The results of the review of B&W operating reactor events will be used to identify problem areas, complications during the events. root causes and sensitive systems. This review should also identify any human factors problems, including operator errors, procedural deficiencies or control room inadequacies. The reviews should rely, to the maximum extent possible, on existing reviews (i.e., industry, BWOG, NRC).
During this review, special attention should be given to the individual items to determine if the particular problem is within the plant's licensing basis.
This determination will be used in later assessments.
Once the set of problems, root causes and sensitive systems is determined, the degree that these items would be the same for Westinghouse or CE reactors should be determined. Similarly, this determination should rely to the maximum extent possible, on existing reviews. Where reviews do not exist, the assessment should rely on engineering judgements as opposed to a detailed review of other NSSS reactor's experience.'
- Tasks identified with an asterisk are those where the Owner's Group is likely to play a major role in completing.
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3.3 Obtain B&W Plant-Specific Design Infomation (*)
The objectives of this task are to: (1) assemble B&W plant system information (e.g., EFIC, SFRCS, AFW, valve positions on loss of ICS power, etc.), and (2) compile and compare operating B&W plant features. The information obtained from Item 3.2 above should be used as guidance in defining system information to be gathered.
3.4 Compile and Assess Previous Staff Reviews of Anticipated Operational Occurrences and the Status of Implementation (*)
The objectives of this task are to: (1) compile the results of previous reviews of B&W operational occurrences, and (2) summarize the status of the implemen-tation of modifications at each B&W plant resulting from the requirements /
recommendations developed during the previous reviews. Reviews of events beginning with the March 20, 1978 Rancho Seco " light bulb" event should be considered.
A detailed list of those events to be reviewed should be deveioped.at the beginning of this task by the lead organization.
3.5 Review Existing Plant Probabilistic Risk Assessment (*)
The objective of this task is to' assemble and review existing PRA's that have been performed for B&W plants and other PWR facilities. An assessment of the input data should be performed to verify that it is consistent with actual B&W data.
. The objectives of this task are to: (1) assess the probability of core melt at B&W plants considering observed operating events, and (2) compare core melt probability among.the B&W plants. B&W plant-specific probabilities should be used in the evaluations. Existing plant PRA's (e.g., Midland, Oconee) should be used as tools in developing the task objectives.
3.7 Compare B&W and Other PWR PRA's The objective of this task is to make a limited comparison of the core melt probability at B&W plants with other PWRs using the results of the PRAs.
3.8 Perform System Analyses and Sensitivity Checks Against Current Criteria (*)
This task will analyze the plant behavior when it is confronted with postulated failures and perturbations. Sensitivity checks will be included in the analysis to establish the plant response-boundaries and margins. Current licensing criteria will be used in the analyses. For example, in addition to the assumed initiating event, single failures of active components and the effect of loss-of-offsite power would be considered. Some of the events and their postulated consequences that should be included are as follows:
- Tasks identified with an asterisk are those where the Owner's Group is likely to play a major role in completing.
~ Loss of normal feedwater Overcooling followed by repressurization Undercooling Steam generator overfill
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Turbine trip Loss of offsite power PORV or code safety relief va.1ve open Steam generator tube failure Small break LOCA
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Steam line break spurious signal initiation Pressure temperature limit correlations A B&W plant which includes design features," configurations, and capacities that resemble the majority of the B&W plants will be selected as the model for the systems analysis and sensitivity checks. Results of this effort will be applied to the other B&W plants recognizing the plant differences.
The same approach for analyzing behavior in B&W plants will be followed during the performance of.this task for other vendor plants, except that the plant-specific information data base is limited to selected designs and features.
3.9. Evaluate Margins and Sensitivities Beyond Regulatory Objectives This element of the study will determine, based on the identified problems, root causes and sensitive systems, the margins available beyond the classical limits.when scenarios beyond the Standard Review Plan type events are encountered. This assessment will only consider scenarios that are pertinent to the items identified in Task 3.6. For example, this tasks may involve questions regarding how adequately the B&W plants can manage a total loss of feedwater event.
Questions regarding multiple failures. conseque1 tit.1 equipment malfunctions, operator errors of commission, as well as omission, will be considered. The evaluations should determine:
- 1. The proximity to a regulatory limit,
- 2. The availability of systems and components to provide mitigation,
- 3. The information (i.e., procedures, training, and control room instrumentation) available to the operators, and ,
- 4. The ' tine frames within which the operator must act to keep the event under control.
3.10 Identify Additional Safety Concerns The main thrust of this element of .the study effort is to address concerns that do not-readily fall into a particular regulatory area. This element is aimed at describing operational, human factors, system or other concerns that arise in the course of the review of the operational events. For example, in the course of the review of events at B&W reactors, it is apparent that for a given relatively benign loss of feedwater transient, a number of safety systems are.
challenged. A review of a similar initiating' event on a CE or W plant reveals a lesser challenge to safety systems. Although there are no regulatory limits that restrict reliance on safety systems to particular scenarios, the response of the B&W plant systems has become a concern in the engineering judgment of a number of analysts.
3.11 Regional Operations Experience Feedback
-This task is aimed at utilizing the experience, judgements and concerns coming from the.NRC's Regional staff, particularly the Resident Inspectors. These individuals have extensive first-hand knowledge of B&W reactor operations,
. procedures and design-related deficiencies that must weigh in the NRC's overall evaluation of the adequacy of the B&W plants.
The views of present and former Senior Resident Inspectors having experience at B&W reactors should be especially sought. Also, I&E training staff should be involved in this effort since their hands-on experience is invaluable.
A series of Region-based meetings may be the most efficient manner to obtain this information.
3.12 Integrated Assessment to Identify Plant Alternative Improvements This phase of the effort involves a unified assessment of all the recommendations, conclusions and suggestions coming from the above described tasks. Since this could obviously involve a great deal of quantitative and qualitative information, the team should attempt to first organize the various items into sets or groups.
Then, once into groups, the various items should be given a relative priority based on their perceived safety importance. Some possible groups are:
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- 1. Items that are needed in.the plant to meet current regulatory ;
requirements.
- 2. Items that are not necessarily needed for regulatory conformance, but are needed for reducing the plant's susceptability or severe response to transie'nts,
- 3. Items that improve the operator's ability to manage transients, and
- 4. Items that result in B&W plant transient response being comparable to other NSSS transient response.
This phase of the overall effort should not consider the relative costs / benefits of the various recommendations. The items should be considered only in accordance with their perceived safety importance.
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