ML20154N700
| ML20154N700 | |
| Person / Time | |
|---|---|
| Issue date: | 03/13/1986 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Tucker H BABCOCK & WILCOX OPERATING PLANTS OWNERS GROUP, DUKE POWER CO. |
| Shared Package | |
| ML20151Z072 | List: |
| References | |
| NUDOCS 8603180392 | |
| Download: ML20154N700 (7) | |
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Mr. Hal Tucker, Chairman Babcock & Wilcox Owners Group Duke Power Company Post Office 80x 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 88W reactors. On February 5,1986, the staff met with the B&WOG. Part of this meeting dealt with the Osners 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 respa se-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 comparison 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.
4 Sincerely, W/
Dennis M. Crutchfield, Assistant Director for Technical Support l Division of PWR Licensing-B I
Enclosure:
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t ENCLOSURE 1 NRC REASSESSMENT PROGRAM INTRODUCTION Since the TMI-2 accident, there has been a growing realization of the sensitivity of Babcock and Wilcox (B&W) plants to operational transients. By letter dated Janua ry 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-8, NRR has been designated as the senior staff manager responsible for this program. Enclosure 1 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 following pa ragra phs.
- 3. SCOPE AND CONTENT OF TASKS The study and required information will be based on the following B&W designed plants for which utilities hold operating licenses:
Arkansas Nuclear One, Unit 1 (ANO-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 1 weaknesses. The review should include, but should not be limited to, the l 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. 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, BW0G, NRC).
i 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.
l 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 Information (*)
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 previcus 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 he developed 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.
3.6 Assess B&W PRA's 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 Turbine trip Loss of offsite power ,
PORV or code safety relief valve open Steam generator tube failure '
Small break LOCA 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, consequential equipment malfunctions, operator errors of commission, as well as omission, will be considered. The evaluations should determine:
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- 1. The proximity to a regulatory limit,
- 2. The availability of systems and components to provide mitigation, The information (i.e., procedures, training, and control room 3.
instrumentation) available to the operators, and
- 4. The time frames within which the operator must act to keep the event i under control.
j 3.10 Identify Additional Safety Concerns I 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 j 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 1 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 i j number of analysts.
! 3.11 Reaional Operations Experience Feedback i
This task is aimed at utilizing the experience, judgements and concerns coming i from the NRC's Regional staff, particularly the Resident Inspectors. These i individuals have extensive first-hand knowledge of B&W reactor operations, procedures and design-relatej deficiencies that must weigh in the NRC's overall evaluation of the adequacy of the B&W plants.
i j 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 transients,
- 3. Items that improve the operator's ability to manage transients, and
, 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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