ML20207P324
| ML20207P324 | |
| Person / Time | |
|---|---|
| Issue date: | 11/21/1986 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | |
| Shared Package | |
| ML20207P321 | List: |
| References | |
| FOIA-86-834, TASK-PII, TASK-SE SECY-86-349, NUDOCS 8701150409 | |
| Download: ML20207P324 (8) | |
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POLICY ISSUE (In OrmatIOn)
November 21, 1986 SECY-86-349 For:
The Commissioners t
From:
Victor Stello, Jr.
Executive Director for Operations
Subject:
BA. LANCE OF PLANT
Purpose:
To describe the balance-of-plant programs currently underway and those planned for the future.
Issue:
Recent operational events and studies by the NRC Staff and industry have shown that poor balance-of-plant perfomance can increase the risk to public health and safety by in-creasing the frequency of transients which challenge plant safety sysiems and by increasing the complexity of plant response to off-normal conditions.
Discussion:
Background
There is no single universally-accepted definition for what l
constitutes balance-of-plant (80p) systems, and components.
1 A commonly accepted definition for B0P includes all safety-related and non-safety-related items and structures of the facility described in the FSAR and not supplied by the MSSS vendor. The discussions in this paper will be limited to non-safety-related B0P items, a subset of those systems, structures and. components that previously were judged to be within the Important-to-Safety envelope presented in SECY 86-164. Particular attention is given to B0P equipment in steam and power conversion systems such as condensate, feedwater and turbine control systems, the failure of which pose direct challenges for safety systems. The staff in SECY-E6-164 proposed to the Commission options for clari-fying the term important-to-safety and scope of equipment that is subject to NRC regulation under 10 CFP 50.
Contact:
G. Holahan, NRR 497-4420 F. Miller, IE 49?-9677 fD//1
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The safety significance of B0P items, as well'as safety-related items, can be related to two aspects of challenges-to reactor safety. The first aspect relates to the fre-quency of challenges to the safety systems caused by B0P malfunctions such as those caused by a failure of a feed-water regulating valve that results in steam generator low level reactor trip and emergency feedwater system actuation.
The second aspect relates to the effect of B0P on the efficacy of safety-related systems and the operators to control the reactor or mitigate the consequences of chal-lenges to the safety systems given the potential compli-cations that may arise from B0P. An example of this would be the failure of turbine bypass systems which could com-plicate recovery during a plant transient.
Trips at U.S. light water reactors during the past several years have been evaluated by the Office for Analysis and Evaluation of Operational Data (AE00) for trends and pat-terns. Factors which have been evaluated include the ex-tent to which hardware or human failures were involved, whether testing, calibration or maintenance was involved, whether plant age, type, AE, or NSSS is significant, which systems or components were most frequently involved, and what were the dominant operating power ranges. These studies have shown that operational problems within the BOP (i.e., feedwater/ steam and turbine generator) have caused many challenges to the reactor safety systems. The feedwater system was the single system most responsible for unplanned reactor trips above 15% power during 1984 and 1985.
The importance of increased attention to B0P equipment was emphasized in an EDO memorandum dated November 26, 1985, on NRC lessons learned frcm the Davis-Besse loss of feedwater event of June 9,1985. There appears in some instances to be a relaxation or laxity on the part of utility management and workers and shortcomings in maintenance, surveillance, quality control, and design configuration control programs on non-safety equipment or POP equipment outside " reactor spaces." Some licensees have indicated that they place BOP modifications and maintenance work low in priority because of prior commitments to perfonning work on safety-related items.
In view of the experience discussed above, this paper focuses on the steam and power conversion 80P systems that present significant challenges to safety-related systems.
Current NRC Activities The staff activities related to the BOP and the bases for these activities are described in the following four sections.
3 (1) Licensing Peview As part of the licensing review process, at both the Construction Permit stage and the Operating License stage, the staff requires applicants to provide significant in-
. formation on the plant design. Staff guidance on the t.
' necessary information is provided in Regulatory Guide 1.70 i
which calls for information on both the safety-related and non-safety related features of the plant including the 4
BOP. The staff licensing review is based on the imple-mentation of the Comission's Pegulations (primarily the General Design Criteria,10 CFR 50 Appendix A) using guid-4 ance documented in the Standard Review Plan which covers j
many 80P areas, such as Steam and Power Conversion Systems (Chapter 10).
In the Shoreham Licensing hearing the NRR j
management estimated that approximately 25 percent of the l
staff licensing review time was devoted to non-safety-related areas which include the BOP.
(A large part of these non-safety-related licensing reviews is aimed at
'i other than steam and power conversion systems; that is, they relate to such things as safeguards, environmental issuesandradiologicalcontrols.)
l The staff review in the BOP areas generally focuses on those aspects of the design which make the equipment j
"important" from a safety perspective. For example, the
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review of the turbine generator design (SRP Chapter 10.7) focuses on the potential for turbine missiles which could damage safety-related structures, systems or components.
The condensate and feedwater system (SRP Chapter 10.4.7) is J
revfewed to assure the capability to supply adequate feed-t we*ar to transfer heat from the reactor to a heat sink uNer both normal and shutdown conditions. The condensate ara feedvater system is also reviewed with respect to-its potential to adversely impact safety-related equipment (e.g. flood potential, missile potential, and high-energy and mcderate-energy pipe break potential). As part of the operating license process, Technical Specifications are i
issued by the staff. The Technical Specifications impose i
regulatory requirements in many safety-related areas and in i
a few non-safety-related 80P areas, such as fire protec-tion, loose-parts monitoring, and water chemistry.
Technical Specifications usually are not issued on those l
BOP items associated with condensate, feedwater, steam and i
electric power generation.
I (2) Inspection Activities i
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As with licensing reviews, the main emphasis in FPC in-f i
spections is on safety-related sy(e. ems and the licensee's st i
processes to maintain equipment g., control of design changes / modification, surveillance and maintenance).
I Currently, inspection procedures focus for the most part i
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on safety-related systems. There are some instances where inspection program guidance and procedures address 80P systems explicitly.
For example, inspection procedures applicable to the preoperational and startup testing phases call for inspection of feedwater system test procedures and test execution. Some inspection procedures which apply to operating activities (such as maintenance and surveillance) direct inspectors, in selected instances, to include POP systems and coniponents in the sample to be inspected.
Netwithstanding this emphasis in inspection procedures on safety-related equipment, there is inherent flexibility in the inspection program permitting safety significant issues where they exist to be pursued by Inspectors. Hence, licensee activities relating to the design, maintenance, operation and testing of R0P systems and equipment may be examined to the degree they impact on safe operations.
Inspections of steam and power conversion BOP systems are mostly reactive in nature. That is, where there are trips and transients or recurring performance problems with BOP.
systems and equipment which present significant challenges to safety systems, Inspectors will, to varying degrees, explore causes and corrective actions with the licensee.
For example, post-trip reviews may lead to investigations and evaluations of BOP where reactor trips are initiated by BOP equipment failures. Where events such as feedwater i
pump trips recur and the licensee is not identifying and j
dealing with the underlying cause, the inspection process may result in discussions with the licensee and reouests for appropriate licensee actions.
For safety-related systems detailed requirements normally exist in the Regulations and technical specifications.
This is normally not the case for BOP systems. Therefore, the nature of dealings with licensees in the BOP area is more infomal than it is in the area of safety-related equipment. Nonetheless, if a safety problem is identi' fed I
the staff has sufficient authority to cause the licensee to take corrective action.
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Surveys made by the staff indicate that licensees' prac-l tices and operating perfomance vary considerably in the BOP area. Because of this, and because the current lack of i
a highly structured BOP inspectinn program, NRC inspection practices in the B0P area are allowed to vary considerably.
The following summarizes some of the specific approaches being taken by the Regional Offices in addition to the reactive POP inspections discussed above, i
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s Some Regional Offices address 80P perfomance and its impact on operational performance in SALP reports.
In one case statistics have been kept on several im-portant performance indicators such as the number of reactor scrams initiated by BOP equipment. Licensee B0P performance is assessed in terms of this informa-tion and underlying problems are identified where they are known.
Inspections are perfomed on modifications and testing of certain selected and reviewed non-safety-related or BOP modifications which are judged to rank high in importance to overall plant safety.
Resident Inspectors in the nomal course of their plant walkthroughs observe material conditions, housekeeping and work ongoing in PDP areas. Where problems are observed, these are brought to the licensee's attention.
In light of available information from PRA studies, IF and the Regions are developing trial programs for inspections to focus more on major risk contributors irrespective of safety classification.
In some cases this is significant in that 80P systems have inter-connections with safety-related systems such that their availability and/or reliability is affected by the BOP portion. Consequently, the staff is develop-ing tabulations from selected existing PRAs that would identify risk-significant systems and components, associated failure mode (s), and identify areas war-ranting more frequent system walkdowns.
Existing PRAs are being utilized to develop information which can be applied to similar plants not covered by a plant-specific PRA.
It must be recognized that 80P inspections are limited in several respects. Priorities in allocation of inspection resources have been oriented to safety related systems and to certain non-safety related systems and activities where there are definite licensing requirements.
(The latter include areas outside the power conversion systems of the plant such as emergency preparedeness, security and safe-guards, radiological controls, environmental monitoring and fire protection.) The general lack of specific require-ments and comitments applicable to P0P power conversion systems presents a challenge to many Inspectors who'are appropriately focused on the question of determining where explicit commitments are not being met by licensees.
Developing issues with respect to BOP and presenting these to the licensee frequently requires a different approach than is taken for safety-related systems.
The gererally less detailed inspection guidance and programs applicable
6 to BOP power conversion items may lead to a less complete and systematic inspection prograri on the part of Region-based and Resident Inspectors. Therefore, in addition to requiring a proper balancing of resources in the inspection of plant systems, achieving an effective B0P inspection effort requires providing good guidance, close supervision and training to Inspectors.
Information on this subject is included in this paper under " Future Plans."
(3) Review of Operating Experience Licensees are required by the Connission's Regulations to
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submit reports to NRC on events involving reactor trips and challenges to the reactor protection systems including actuation of engineered safety features. In addition, as a result of the Salem ATWS event, licensees were required to develop systematic post-trip review programs. Headquarters and Regional staff reviews these reported events and post-trip evaluation results for safety significance and to be sure the root cause of the event is established. Fre-quently the root cause is found to be associated with items in the BOP.
In such cases, the staff has evaluated the 1
significance and anticipated frequency. Where problems are 4
perceived, they are discussed and resolved with the licen-see through the Regional Office or Headquarters contacts.
The reassessment of B&W plant designs, which was initiated in light of operating experience, is addressing to a large extent BOP systems design and performance.
Bulletins or Generic letters requiring license action would i
not normally be issued where BOP problems were identified as a result of the review of operating experience, unless a i
safety problem was clearly involved. The usual practice would be to issue Information Notices to alert licensees of i
potential BOP problems identified from operating experiences.
As mentioned previously, for several years AE00 has ana-lyzed unplanned reactor trips for trends and patterns.
In addition to identifying BOP problems, the AEOD report for 1985 identified hardware failures as the root cause for about 60% of all trips above 15% power; valve failures were determined to be the largest class of component failure (about 30%) with feedwater regulating valves being about 25% of the valve failures.
AEOD is taking a followup step in the analysis of feedwater regulatiro valve failures using data available in the Nuclear Plant Peliability Data System. The valve study is the first of a series of such studies. This type of effort may lead to an insight as to the cause of valve failures.
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A potential limitation of studies of BOP events is that reporting requirements are not the same as they are for safety-related equipment.
To determine the effectiveness of current maintenance practices as they effect the entire plant, including BOP, NRR as part of a Maintenance and Surveillance Program, sent r
an industry survey to eight sites and all Resident Inspectors. Responses were analyzed and NUREG-1?.12 pub-lished June 1986. One of the findings is that most licen-sees limit ouality control activities to safety-related work. Licensees, individually and in organizations such as the B&W Owners Group, were and are continuing to actively work to improve their maintenance programs; therefore, these statistics may no longer be representative. The NRC staff plans to monitor the effectiveness of industry's -
maintenance programs.
(4) Research The Office of Nuclear Regulatory Research (RES) is asses-sing the effectiveness of reliability technology to help achieve and maintain safety throughout a plant's operating lifetime. This approach applies reliability technology to BOP items to ensure a low frequency of transients that challenge safety systems and high safety system reliability / availability when challenged. PRA techniques are being used by RES to identify BOP systems which are important contributors to upset initiations, as in recent 4
work on Pressurized Thermal Shock (USI A-49) and on Safety Implications of Control System Failures (USI A-47).
RES has a Multi-Loop Integral System Test (MIST) program with the obiective of having a scaled version of a B&W reactor coolant system which will be used to obtain high ouality experimental data for verification of computer codes. This progran, among other things, will be used to investigate primary system response to upset conditions in the BOP. Extensive thermal-hydraulic analytical modeling of the primary system and BOP is aimed at assessing which malfunctions, system designs, and operator actions are important. The models will be used to evaluate overcooling transients and accidents which PRA techniques show to be risk dominant.
i Future Plans The staff has conducted a trial performance indicator l
program to develop tools to monitor operational safety of nuclear power plants.
Pased on results of the trial i
program, a prelininary set of indicaters has been recom-i mended to the Commission for implementation. The imple-mented program is anticipated to include supplemental l
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g information including; identification of BOP problems where they result in challeriges to safety systems through tran-sients or added risk due to safety system 'inavailability.
This data will be beneficial in further identifying BOP related problems and aid in guiding inspection efforts.
Several activities to improve the effectiveness of NRC BOP inspections are in progress. A trial inspection program of a selected important 80P system such as the feedwater system which has been shown from experience to be a sig-nificant contributor to plant trips and transients is being developed. The current good inspection practices of the various Pegions are being identified and made visible to the other Regions. During counterpart meetings the subject of BOP inspections will be included for the purpose of exchanging views and information on various Regional experiences. The staff will be evaluating current in-spection guidance in light of the PRA studies discussed above to determine whether a shift in emphasis from safety-related to 80P items is warranted or justified.
Training programs and manuals will be evaluated to de-termine what revisions are needed.
NRR has initiated a contractor study to examine regulatory approaches for the BOP. The initial phase of this study has focused on identification of BOP systems malfunctions that most frequently initiate and complicate transients. A f
draft report on this contractor effort was reviewed and commented on recently by the staff; in accordance with an earlier commitment by PRR, the final report on this con-tractor study will be provided to the Commission for infomation as soon as it is available.
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Conclusion:==
As. indicated by the above mentioned activities, the NRC staff does have current programs and future plans relating to the POP.
In general these activities are less fomal and are given lower priority than safety-related activities. As operating experience and PRAs indicate that there are significant POP areas warranting additional staff attention, such changes will be seriously considered.
In any such decision to shift emphasis and resources, the staff will carefully evaluate the effects of 5
decreasing emphasis and resources in traditional safety-related review areas.
1 tieillo, Jr. 7 Executive Directo for Operations i
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'120555056781 1 19A19819C1901 US NRC NRR DIRECTOR P-428 OC 20555 WASHINGTON 3
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