NUREG-1109, Recommends That Final Station Blackout Rule,As Contained in Encl Fr Notice & Reg Guide,Providing Method Acceptable to Comply W/Rule,Be Issued in Order to Implement Final Resolution of USI A-44: Difference between revisions

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#REDIRECT [[NUREG-1109, Summary of 870305 Meeting in Bethesda,Md W/Nuclear Utility Group on Station Blackout Re Status of Four Initiatives Proposed by Industry to Resolve Station Blackout Issue, USI A-44 & Dates for Future Meetings on Initiatives 2 & 4]]
| number = ML20245A518
| issue date = 04/06/1987
| title = Recommends That Final Station Blackout Rule,As Contained in Encl Fr Notice & Reg Guide,Providing Method Acceptable to Comply W/Rule,Be Issued in Order to Implement Final Resolution of USI A-44
| author name = Denton H
| author affiliation = NRC OFFICE OF NUCLEAR REACTOR REGULATION (NRR)
| addressee name = Zerbe J
| addressee affiliation = NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
| docket =
| license number =
| contact person =
| case reference number = REF-GTECI-A-44, REF-GTECI-EL, RTR-NUREG-1032, RTR-NUREG-1109, TASK-A-44, TASK-OR
| document report number = AB38-2, NUDOCS 8704140502
| package number = ML20245A520
| document type = INTERNAL OR EXTERNAL MEMORANDUM, MEMORANDUMS-CORRESPONDENCE
| page count = 63
}}
 
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                        ' MEMORANDUM FOR:      Johr F. Zerbe, Acting Deputy Executive Director for. Regional Operations and Generi_c Requirements FROM:                Harold R. Denton, Director Office of Nuclear Reactor Regulation
 
==SUBJECT:==
CRGR REVIEW OF FINAL RESOLUTION OF USI A-44,
                                              ~ STATION BLACK 0UT
 
==References:==
        '1. ' Memorandum for V. Stello from H. Denton, March 6,1984.
: 2. Memorandum for W. Dircks from V. Stello, May.8, 1984
: 3. SECY-85-163, May.6, 1985.
: 4. SECY-85-163A, Sept. 4 1985
: 5. SECY-86-28, Jan. 28, 1986.
: 6. . Memorandum for V. Stello from S. Chilk, March 5,1986..
                                            -7. 51' FR 9829,- March 21,1986.
: 8. 51 FR _11494, April 3,1986.
9., Letter to Chairman Palladino from J. H. Miller, NUMARC,
                                                  . June 17, 1986.
: 10. Memorandum for T.'Speis from W. Minners,' August:7. 1986.
: 11. Memorandum for T. Speis from A. Rubin, Sept. 4, 1986,
: 12. Memorandum for T. Speis from A. Rubin, Oct. 8, 1986.
: 13. Meinorandum for T. Speis from A. Rubin, Dec. 24, 1986.
: 14. Memorandum for T. Speis from A. Rubin, March 17,.1987.
The staff has completed its assessment of Unresolved Safety' Issue A-44 and has developed a final position, including rulemaking, to resolve this issue. The final resolution-is a rule and regulatory guide on station blackout based on
                    . draft NUREG-1109, and draft NUREG-1032, which were issued for public comment.
Enclosures 1 through 4 respectively contain the final versions of these                  -
documents, which have been revised to respond to public comments. The most                  j significant changes to these documents based on the public comments are summarized in Enclosure 5.
The rule requires all nuclear power plants to be able to cope with a station blackout for a specified duration and to have procedures to withstand and                    i recover from such an event. ' The regulatory guide provides guidance on                    l acceptable plant-specific coping durations to comply with the rule. The acceptable coping durations are based on plant design and site-related I-                  characteristics that affect the reliability of offsite and onsite emergency ac power systems.
I One significant change from the proposed rule is that the requirement for                    l licensees to determine their plant's maximum station blackout coping                        j capability has been deleted. The ability to cope for an acceptable duration,                  I as specified in the final rule, would provide adequate protection of the public and safety from station blackout events.                                              ]
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The proposed technical resolution of USI A-44 was submitted to the CRGR for review in March 1984_(Ref. 1), and CRGR minutes and recommendations on the proposed resolution were issued in May 1984 (Ref. 2). The proposed station blackout rule was submitted to the Commission along with the staff's evaluation of a proposal by the Nuclear Utility Group on Station Blackout (NUGSBO) to resolve USI A-44, and the backfit analysis for the ' staff's proposed resolution (References 3 through 5). The Commission voted 5-0 to issue the proposed rule for public comment (Ref. 6). The proposed rule and associated draft regulatory guide on station blackout were subsequently issued for public comment (References 7 and 8), and the 90-day public comment period ended on June 19, 1986. The Coninission received 53 letters commenting on the proposed rule. These comments and responses to the public comments are discussed in the Supplementary Information Section of the Federal Register notice (Enclosure 1).
One letter from the Nuclear Utility Management and Resources Committee (NUMARC) included four initiatives endorsed by industry to address the "more important contributors to station blackout" (Ref. 9). These initiatives consist of the following:
: 1. Each utility will review their site (s) against the criteria specified in NUREG-1109, and if the site (s) fall into the category of an eight-hour site after utilizing all power sources available, the utility will take actions to reduce the site (s) contribution to the overall risk of station blackout. Non-hardware changes will be made within one year. Hardware changes will be made within a reasonable time thereafter.
: 2. Each utility will implement procedures at each of its site (s) for:
: a. coping with a station blackout event,
: b. restoration of ac power following a station blackout event, and                                                          i
: c. preparing the plant. for severe weather conditions, such as hurricanes and tornados to reduce the likelihood and consequences of a loss of offsite power and to reduce the overall risk of a station blackout event.
: 3. Each utility will, if applicable, reduce or eliminate cold fast-starts of                                                      1 emergency diesel generators for testing through changes to technical specifications or other appropriate means.                                                                                      l l
: 4. Each utility will monitor emergency ac power unavailability utilizing data utilities provided to INP0 on a regular basis.
The staff has participated in a series of meetings to discuss NUMARC's initiatives with representatives of NUGSB0 (Ref.10-14). (NUGSB0 provides                                                              i technical support to NUMARC on this issue.) These initiatives include some of the same elements which are included in the staff's resolution of USI A-44 However, at this time, final guidelines and details of all the NUMARC initiatives are not available to the staff. Draft guidelines for several of the                                                                    I initiatives have been discussed with the staff.                                                                                        t t
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Based on these discussions one significant difference between the NUMARC and the staff positions is that the NUMARC initiatives do not include assessments i
'            to determine that plants can cope with a station blackout for any specific duration. Without such an assessment, it is difficult to see how adequate procedures could be developed to ensure that a plant could cope with a station blackout. Furthermore, without knowledge of the capability to cope with a station blackout for a specific period, such as 4 or 8 hours, the risk is indeterminate.
To implement the final resolution of USI A.44, NRR recommends the following actions be taken:
: 1. Issue the final station blackout rule as contained in the Federal Register notice (Enclosure 1).
: 2. Issue the regulatory guide on station blackout (Enclosure 2) which provides a method acceptable to the staff to comply with the rule.
The    factors and considerations          that support          these recommendations,                                                                            inclu the backfit/value-impact  analysis, are documented    in NUREG-1109                                                          (Enclosure 3 with additional supporting technical analyses provided in NUREG-1032 (Enclosure 4). Results of these analysis support the determination that implementing the final resolution of USI A-44 would provide a substantial increase in the overall protection of the public health and safety, and the direct and indirect costs of implementation are justified in view of this increased protection.
The recommended actions above are Category 2, and do not warrant accelerated actions. In order to meet the schedule requested by the EDO, completion of CRGR review, including receipt of any comments, is requested by June 1,1987.
In accordance with CRGR operating procedures, I am enclosing 15 copies of the CRGR package for your review. For further information on this issue, contact                                                                                              i Alan Rubin at x28303.
L ., d i ' ' ' A                                                                                                '
{ ij. t. c . 4n Harold R. Denton, Director Office of Nuclear Reactor Regulation
 
==Enclosures:==
 
1
: 1. Federal Register Notice
: 2. Station Blackout Regulatory Guide
: 3. NUREG-1109
: 4. NUREG_1032
: 5. Significant Changes to USI A_44 Package                Distribution: See next page
            *See previous concurrence.
                                                                /~m                                                                                      ,
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DATE :03/30/87      :04/01/87    :04/01/87      :04/01/87    4/%/87                                    :                                Q/87                :
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J. Sniezek/H. Denton E. Beckjord 6-27-If T. Speis B. Sheron W. Minners K. Kniel P. Norian A. Rubin P. Barnowsky J. Flack E. Lois S. Crockett N. Anderson J. Jackson L. Sofer S. Trely C. Belote DSR0 C/F RSIB R/F Central Files
                                                                                                                                                                'l 1
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ENCLOSURE 1 Federal Register Notice of Final Rulemaking NUCLEAR REGULATORY COMMISSION 10 CFR Part 50 Station Blackout                                        ,
AGENCY:    Nuclear Regulatory Commission.
ACTION:    Final rule.
 
==SUMMARY==
:  The Nuclear Regulatory Commission is amending its regulations to require that light-water-cooled nuclear power plants be capable of withstanding a total loss of alternating current (ac) electric power (called " station black-out") for a specified duration and maintaining reactor core cooling during that period. This requirement is based on information developed under the Commission's study of Unresolved Safety Issue A-44, " Station Blackout." The amendment is intended to provide further assurance that a station blackout (loss of both offsite power and onsite emergency ac power systems) will not                                i adversely affect the public health and safety.
EFFECTIVE DATE:
FOR FURTHER INFORMATION CONTACT:    Alan Rubin, Division of Safety Review and Oversight, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, DC 20555, Telephone: (301) 492-8303.                                              !
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SUPPLEMENTARY INFORMATION:                                                        l
 
===Background===
The alternating current (ac) electric power for essential and nonessential          l service in a nuclear power plant is supplied primarily by offsite power.
Redundant onsite emergency ac power systems are also provided in the event that all offsite power sources are lost. These systems provide power for various        {
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safety functions, including reactor core decay heat removal and containment heat removal, which are essential for preserving the integrity of the reactor f
core and the containment building, respectively. The reactor core decay heat can also be removed for a limited time period by safety systems that are            f independent of ac power.
j The term " station blackout" means the loss of offsite ac power to the essential and nonessential electrical buses concurrent with turbine trip and the unavailability of the redundant onsite emergency ac power systems (e.g., as a result of units out of service for maintenance or repair, failure to start on        i demand, or failure to continue to run after start). If a station blackout persists for a time beyond the capability of the ac-independent systems to            I remove decay heat, core melt and containment failure could result.
The Commission's existing regulations establish requirements for the design and testing of onsite and offsite electric power systems that are intended to reduce the probability of losing all ac power to an acceptable level. (See General Design Criteria 17 and 18, 10 CFR Part 50, Appendix A.) The existing
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regulations do not require explicitly that nuclear power plants be designed to        f assure that core cooling can be maintained for any specified period of loss of        1 all ac power.
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                          '/        .
As operating experience has accumulated, the concern has arisen that the reliability'of both the onsite and offsite emergency ac power systems might be j
less than originally anticipated, even for designs that meet the requirements l
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of General Design Criteria 17 and 18.      Many operating plants have experienced a total loss of offsite power, and more occurrences can be expected in the future. Also, operating experience with onsite emergency power systems has included many. instances when diesel generators failed to start. In a few cases, there has been a complete loss of both the offsite and the onsite ac power systems. During these events, ac power was restored in a short time without any serious consequences.
In 1975, the results of the Reactor Safety Study (WASH-1400) showed that station blackout could be an important contributor to the total risk from nuclear power plant accidents. Although this total risk was found to be small, the relative importance of the station blackout accident was established.
Subsequently, the Commission designated the issue of station blackout as an Unresolved Safety Issue (USI); a Task Action plan (TAP A-44) was issued in July 1980, and studies were initiated to determine whether additional safety requirements were needed. Factors considered in the analysis of risk from station blackout included: (1) the likelihood and duration of the loss of offsite power; (2) the reliability of the onsite ac power system; and (3) the potential for severe accident sequences after a loss of all ac power, including consideration of the capability to remove core decay heat without ac power for
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a limited time period.
l The technical findings of the staff's studies of the station blackout issue are presented in NUREG-1032, " Evaluation of Station Blackout Accidents at Nuclear Power Plants, Technical Findings Related to Unresolved Safety Issue A-44."(1)
Additional information is provided in supporting contractor reports:
NUREG/CR-3226, " Station Blackout Accident Analyses" published in May 1983; NUREG/CR-2989, Reliability of Emergency AC Power Systems at Nuclear Power (1) Draft NUREG-1032 was issued for public comment on June15, 1985.
 
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Plants" published in July 1983; NUREG/CR-3992, " Collection and Evaluation of Complete and Partial losses of Offsite Power at Nuclear Power Plants" published in February 1985; and NUREG-CR 4347, " Emergency Diesel Generator Operating Experience, 1981-1983" published in December 1985.(2) The major results of these studies are given below.
Losses of offsite power can be characterized as those resulting from plant-centered faults, utility grid blackout, and severc weather-induced failures of offsite power sources. Based on operating experience, the frequency of total losses of offsite power in operating nuclear power plants was found to be about one per 10 site years. The median restoration time was about one-half hour, and 90 percent of the offsite power losses were restored within approximately 3 hours (NUREG/CR-3992).
The review of a number of representative designs of onsite emergency ac power systems has indicated a variety of potentially important failure causes. However, no single improvement was identified that could result in a significant improvement in overall diesel generator reliability. Data obtained from operating experience in the period from 1976 to 1980 showed that the typical individual emergency diesel generator failure rate was about 2.5 x 10-2 per demand (i.e., one chance of failure in 40 demands), and that the emergency ac power system unavailability for a plant which has two emergency diesel generators, one of which was required for decay heat removal, was about 2 x 10 -3 per demand (NUREG/CR-2989).
(2) Copies of these NUREGS are available for public inspection and copying for a fee at the NRC Public Document Room at 1717 H Street, NW, Washington, DC 20555. Copies may also be purchased through the U.S. Government Printing Office by calling (202) 275-2060 or by writing to the Superintendent of Documents, U.S. Government Printing Office, P. O. Box 37682, Washington, DC 20013-7082.
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Compared to the data.in NUREG/CR-2989, updated estimates of emergency diesel generator failure rates indicated that diesel generator reliability has improved somewhat from 1976 to 1983. For the period 1981 to 1983, the mean failure rate for all demands was-about 2.0 x 10 ~2 per demand (i.e. , one chance of failure in 50 demands).
However, the data also indicate that the probability of diesel generator failures during actual demands (i.e., during losses of offsite power) is greater than that during surveillance tests I
(NUREG/CR-4347)!.                                    l:'
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                                                                                                      ' Given the occurrence of a station blackout, the likelihood of resultant core damage or core melt is dependent on the reliability and capability of decay heat removal systems that are not dependent on ac power. If sufficient ac-independent capability exists, additional time will be available to restore ac power needed for long-term cooling'(NUREG/CR-3226).
It was determined by reviewing design, operational, and site-dependent factors that the expected frequency of core damage resulting from station blackout events could be maintained near 10-5 per reactor year with reedily achievable diesel generator f
reliabilities, provided that plants are designed to cope with station blackout for a specified duration. The duration for a specific plant            .l I
is based on a comparison of the plant's characteristics to those factors that have been identified as the main contributors to risk from station blackout (NUREG-1032).
As a result of the station blackout studies, improved guidance will be provided to licensees regarding maintaining minimum emergency diesel generator 1
reliability to minimize the probability of losing all ac power.                                                                                  In addition, the Commission is amending its regulations by adding a new S50.63 and by adding                                                                                  .
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* a new final paragraph to General Design Criterion 17, Appendix A of 10 CFR Part 50, to require that all nuclear power plants be capable of coping with a station blackout for some specified period of time. The period of time for a specific plant will be determined based on a comparison of the individual plant's design with factors that have been identified as the main contributors to risk of core damage resulting from station blackout.
These factors, which vary significantly from plant to plant because of considerable differences in design of plant electric power systems as well as site specific considerations, include: (1) redundancy of onsite emergency ac power sources (i.e., number of sources minus the number needed for decay heat removal), (2) reliability of onsite emergency ac power sources (usually diesel generators), (3) frequency of loss of offsite power, and (4) probable time to restore offsite power. The frequency of loss of, and time to restore, offsite power are related to grid and switchyard reliabilities, historical weather data for severe storms, and the availability of nearby alternate power sources (e.g., gas turbines). Experience has shown that long duration offsite power outages are caused primarily by severe storms (hurricanes, ice, snow, etc.).
The objective of the rule is to reduce the risk of severe accidents resulting from station blackout by maintaining highly reliable ac electric power systems                t and, as additional defense-in-depth, assuring that plants can cope with a station blackout for some period of time. The rule requires all plants to be j
able to cope with a station blackout for a specified acceptable duration selected on a plant specific basis. All licensees and applicants are required j
to assess the capability of their plants to cope with a station blackout (i.e., determine that the plant can maintain core cooling with ac power unavailable for an acceptable period of time), and to have procedures and training to cope with such an event.
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i On the basis of station blackout studies conducted for USI A-44, and presented in the reports referenced above, the NRC staff has developed a draf t regulatory guide entitled " Station Blackout,"(3) which presents guidance on (1) main-taining a high level of reliability for emergency diesel generators, (2) developing procedures and training to restore offsite and onsite emergency ac power should either one or both become unavailable, and (3) selecting a plant-specific acceptable station blackout duration which the plant would be capable of surviving without core damage. Application of the methods in this guide would result in selection of an acceptable station blackout duration (e.g. , 4 or 8 hours) depending on the specific plant design and site-related characteristics. However, applicants and licensees could propose alternative methods to that specified in the regulatory guide in order to justify other acceptable durations for station blackout capability.
Based on the rule and regulatory guide, those plants with an already low risk from station blackout would be required to withstand a station blackout for a relatively short period of time and probably would need few, if any, modifi-cations as a result of the rule. Plants with currently higher risk from station blackout would be required to withstand somewhat longer duration blackouts. Depending on their existing capability, these plants might need to make hardware modifications (such as increasing station battery capacity or condensate storage tank capacity) in order to cope with the longer station blackout duration. The rule requires licensees to develop, in consultation with the Office of Nuclear Reactor Regulation, plant-specific schedules for implementation of any needed modifications.
(3) A notice of availability and request for comments on the draft regulatory guide was published in the Federal Register on April 3, 1986 (51 FR 11494).
Free single copies of the draft regulatory guide may be obtained by writing to the Distribution Section Division of Information Support Services, U.S. Nuclear Regulatory Commission, Washington, DC 20555.
 
l y 61              .'
Proposed Rule On March 21, 1986, the Commission published a proposed rule in the Federal Register (51 FR 9829) that would require (1) light-water-cooled nuclear power plants to be capable of cuping with a station blackout for a specified duration, and (2) licensees to determine the maximum duration for which their plants as currently designed are able to cope with a station blackout. A 90-day comment period expired on June 19, 1986.
On April 3, 1986 (13 days after the proposed rule was published), the NRC published in the Federal Register (51 FR 11494) a notice of availability and request for comments on a draft regulatory guide entitled " Station Blackout" (Task SI 501-4). This draft guide provided guidance for licensees to comply with the proposed station blackout rule. Many letters commenting on the proposed rule also included comments on the draft' regulatory guide. Responses to these comments provided below address the public comments on the draft guide as well ac on the proposed rule.
Comments on the Proposed Rule i
                                .The Commisaion received 53 letters commenting on the proposed rule.(4)
Forty-five of these were from the nuclear industry, comprised of electric utilities, consortiums of electric utilities, vendors, a trade association, and an archite.;t/ engineering firm.      Other letters were submitted by the Union of Concerned Scientists (UCS), the Department of Nuclear Safety of the State of Illinois (IDNS), a representative of the Professional Reactor Operator Society, a citizens group, a consultant, and three individuals. Largely, the industry (4) Copies of these letters are available for public inspection and copying for a fee at the NRC Public Room at 1717 H Street, NW, Washington, DC.
 
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comments were opposed to generic rulemaking to resolve the station blackout issue. The Nuclear Utilities Management and Resources Committee (NUMARC) sub-  !
mitted, along with its comments on the proposed rule, a set of industry ini-tiatives that it believes would resolve this issue without rulemaking.
Thirty-nine of the industry letters supported NUMARC's submittal. On the other hand, UCS, IDNS, and the citizens group' supported the Commission's objective in the proposed rule, but did not believe the rule and guidance associated with the rule went far enough to reduce the possibility of a serious accident that could be initiated by a total loss of alternating current (ac) power.
                                . Every letter was reviewed and considered by the staff in formulating the final resolution of USI A-44. Because of the large number of comments, it was not practical to prepare formal responses to each one separately. However, since        "
many comments were on similar subjects, the discussion and response to the          !
comments has been grouped into the following subjects:(5)
                                  /
: 1. Quality Classification of Modifications.
(
: 2. Whether the Backfit Analysis Adequately Implements the Backfit Rule.
3.
Cost-Benefit and Whether S50.63 Meets the " Substantial Increase in the Overall Protection of the Public Health and Safety."
j
: 4. Whether NRC Should Require Substar.?ial Improvements in Safety that Go Beyond Those Proposed in this Rulemaking.
: 5. The Need for Generic Rulemaking.                                              i (5) The first four subjects are ones on which the Commissioners specifically requested public comments when the proposed rule was published, l
: 6.      Applicability of the Proposed S50.63 to Specific Plants.
: 7.      Plant-Specific Features and Capabilities.
: 8.      The Source Term Used to Estimate Consequences.
: 9.      Specificity on the Extent of Required Coping Studies.
: 10. Acceptable Duration for Coping with a Station Blackout.
11.
Credit for Alternate or Diverse AC Power Sources.
: 12.      Trends on the Reliability of AC Power Sources.
: 13.      Sharing of Emergency Diesel Generators Between Units at Multi-Unit Sites.
14.
Clarification of the Definitions of Station Blackout and Diesel Generator Failure.
: 15.      Specificity and Clarification of Requirements.
: 16.      Technical Comments on NUREG-1032.
: 17. Relationship of USI A-44 to Other NRC Generic Issues.
: 18. An Alternative of Plant-Specific Probabilistic Assessments.
: 19. Procedures and Operator Actions During Station Blackout.
: 20. Schedule Provisions in the Proposed S50.63.
: 21. Industry Initiatives
 
    <c;            :.
The comments and responses to each of these subjects are presented on the following pages.
: 1. Quality Classification of Modifications The Commission requested comments on whether the staff should give further consideration to upgrading to safety grade the plant modifications needed (if any) to meet the proposed rule. Upgrading to safety grade would further ensure appropriate licensee attention is paid to maintaining equipment in a high state of operability and reliability.
Comments - The prevailing view by industry on this subject is represented by the following comments submitted by NUMARC:
Quality Classification is Unnecessary - Equipment used to prevent or respond to a station blackout should be sufficiently available and operable to meet its required function. To this extent, the Commission's desire that appropriate attention be paid to maintaining a sufficiently high state of operability and reliability is appropriate. The point of departure begins with the method for achieving this objective.
Specifically, by itself, a " safety grade" classification scheme does not solely equate with high states of equipment operability and reliability.
Such classification systems too often can become a documentation exercise more than a process for providing the requisite level of system functionality.
Duquesne Light agreed with this view and expressed the following comments:
Any plant modifications or additional equipment required to meet the proposed rule should not be specified safety grade. For equipment which is to be manually started and placed in service for testing or in the event of a loss of power condition there is no necessity for specifying safety grade since adequate reliability can be obtained through normal surveillance testing and the proper maintenance of commercial power plant equipment.
The cost difference in safety grade vs. commercial grade modifications is significant and must be emphasized.
 
The opposite point of view was taken by the IDNS.
No credit should be given for the capability of equipment to respond to a station blackout unless that equipment was originally designed, constructed, inspected, performance tested, qualified, certified for the intended safety-related purpose, and the equipment is maintained to the highest industry safety standards.
Gulf States Utilities commented.
The proposed rule does not provide sufficient direction on the quality classification  of plant modifications that may be required to meet the rule. ...the quality  classification of plant modifications implemented to meet the proposed rule should be commensurate with classification of the system they support.
Response - The proposed S50.63 does not specifically address the topic of safety classification of modifications, but guidance is given in the regulatory guide on station blackout as well as in a draft American Nuclear Society standard, ANS 58.12 entitled, " Criteria for Establishing Response Capability for Loss of All AC Power (Station Blackout) at Light Water Reactor Nuclear Power Plants," Draft Revision 5, March 1987. Neither of these documents specify that equipment modifications needed to meet the proposed rule be safety grade. However, the equipment must meet certain quality assurance criteria to ensure a high level of reliability and operability during station blackout events.
Based on technical analyses performed for USI A-44 and public comments received, there are insufficient bases to require that modifications be seismically qualified and/or meet the single failure criterion. Therefore, the Commission would not require that modifications to meet the station black-                        !
out rule be safety grade. However, the Commission believes that licensees should pay diligent attention to quality assurance, in order to maintain highly reliable equipment to comply with the station blackout rule.
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5 2.
Whether the Backfit Analysis Adequately Implements the Backfit Rule In addition to comments on the merits of the proposed rule, the Commission specifically requested comments on whether the backfit analysis for this rule adequately implements the Backfit Rule, 10 CFR 50.109.
Comments - The Commission received two differing views in response to this request.
On one hand, NUMARC expressed the view that the proposed rule does                                  l
        - not meet the backfit rule standard because the analysis of the factors set                                        >
forth in S50.109(c) were not adequately considered by the staff. Specifically, i
NUMARC stated --
: 1. Installation and Continuing Costs Associated With the Backfit Have Been Underestimated.
: 2. Potential Impacts on Radiological Exposure of Facility Employees Should Be Further Addressed.
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3.
The Relationship to Proposed and Existing Regulatory                                                l Requirements Should Be Considered Further.                                                          s 4.
Potential Impacts of Differences in Facility, Type, Design or Age Should Be Considered Further.
5.
The Reduction in Risk from Offsite Releases to the Public Has Been Overestimated.
On the other hand, the Ohio Citizens for Responsible Energy (OCRE) and UCS commented that the backfit rule should not apply to the proposed rule. OCRE took the position that " application of the backfit rule to [NRC] rulemakings is plainly illegal," and the Commission is not empowered to consider costs to licensees in deciding whether to impose new requirements. UCS commented that the cost benefit analysis should not be applied in this case because safety improvements are needed to secure compliance with existing NRC regu-lations, specifically General Design Criterion 17, Electric Power Systems                                            i (Appendix A to 10 CFR Part 50).
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Response - NUMARC's comments on the backfit analysis were taken into account by   1 the staff in revising the draft version of NUREG-1109, and a separate appendix that addresses the factors in S50.109(c) was added to that report. All but Item 2 above are on the same subjects as letters from other commenters            (
1 and are' discussed in more detail under subjects 3 (Item 1), 6 (Item 4), 8 (Item 5), and 17 (Item 3) in this section. NUMARC's Item 2, the potential y
impact on radiological exposure of facility employees, would need to be assessed in detail only if it were a major factor in the value-impact analysis.    !
The offect of radiological exposure on facility employees, if any, would be extremely small in comparison to the reduction in radiological exposure to the public from accident avoidance-Therefore, this factor would have no impact on the overall value-impact analysis.
                                                                                                    )
In response to the OCRE's comments, the Commission follows a specific process by which rules are formally promulgated, but it is not prevented from imposing internal controls on the rulenaking process. For new requirements, the Commission believes that it is empowered to consider the costs of incremental safety improvements wherever those improvements go beyond the level of safety necessary to ensure no undue risk to the public and safety. GDC 17 requires that nuclear power plants have redundant and reliable electrical supply systems.        Each operating plant has such systems, and the Commission has made an adjudicative finding that all operating plants comply with GDC 17; otherwise, a license would not have been issued authorizing operation.
The issue in this rulemaking is whether some additional protection is needed beyond that already provided to comply with existing requirements. This does not imply that operating plants are unsafe. The Commission is entitled to inquire, and seek public comment, on whether additional safety measures should be imposed where the benefit to public health and safety outweighs the cost of the improvements.
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: 3. Cost-Benefit Analysis and Whether $50.63 Meets the " Substantial Increase in the Overall Protection of the Public Health and Safety" Chairman Zech and Commissioner Roberts requested comments on the analysis of cost benefit, value impact, and safety improvements and the station blackout standing on the overall risk (e.g., is the reduction of risk only a small percentage of the overall risk, or is it a major component of an already small risk?) Chairman Zech and Commissioner Roberts were particularly interested in specific comments assessing whether or not this proposal meets the " substantial increase in the overall protection of the public health and safety..."
threshold now required by the backfit rule.
Comments - (A) One of the major comments by industry on the cost-benefit analysis was that the costs of implementing the proposed requirements have been underestimated. NUMARC and the Atomic Industrial Forum (AIF) commented that the cost estimates for hardware modifications reported in NUREG/CR-3840,
                                                        " Cost Analysis for Potential Modifications to Enhance the Ability of a Nuclear Plant to Endure Station Blackout," were too low. Commonwealth Edi:on and other utilities felt that performance of an analysis to determine the maximum duration a nuclear plant could cope with a station blackout would be substantially costlier than what is estimated in NUREG-1109.                          Industry also expressed concern that the interpretations associated with the proposed rule could lead to sub-stantial costs above those addressed by the NRC staff in its backfit analysis.
AIF commented that "The estimate of 120 NRC man-hours per plant [for NRC review) ... appears inadequate to account for technical review and evaluation of the determination of maximum coping capability and of the description of station blackout procedures which the rule would require each licensee to submit."
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(B).Several commenters expressed the view that the NRC failed to consider all l        the risks associated with a station blackout in its value-impact assessment.
1 UCS thought independent failures, in addition to failures that lead to a station blackout, should be included. One individual stated that "both NRC reports [NUREG-1109 and NUREG-1032] are completely deficient in that neither look at sabotage." OCRE commented that seismic events should also be considered.
l-      .(C) With respect to safety improvements and overall risk, different points of-view were expressed. On one hand, NUMARC commented --
While the risk reduction might be large [for a] limited number of plants, the risk reduction associated with the majority of plants will be small.
Thus, as a general matter, the reductions in risk offered by the proposed rule constitue a small percentage of the overall risk, a risk which is already small (and acceptable).
AIF stated that there is no standard by which to conclude that " substantial additional protection will be realized."
A different view was expressed by UCS who stated that " station blackout is clearly a major component of the total risk posed by operating nuclear plants.
The magnitude of the total risk is largely unknowable due to the enormous uncertainty which surrounds probabilistic assessments."
Response - (A) In order to adequately respond to industry's comments above, the staff and NRC contractors reviewed the cost estimates associated with imple-menting the station blackout rule. Based on this review, the estimated costs for hardware modifications were reviewed and are in the range of from 20 percent to almost 140 percent greater than the estimates in NUREG/CR-3840, depending on the specific modification considered. On average, the cost estimates for hardware backfit were found to be approximately 80 percent greater than estimated in NUREG/CR-3840. However, the cost estimates in NUREG/CR-3840 were not used by the staff in the value-impact analysis in the draft version of NUREG-1109 where estimates approximately 100 percent greater
 
than the NUREG/CR-3840 estimates were used. Therefore, the revised cost estimates used in the final _value-impact analysis are not significantly different from the estimates used in the draft version.
Industry's comments on the costs to assess a plant's capability to cope with a station blackout were based on the proposed rule that required an assessment of the maximum coping capability and the potentially unbounded nature of such an assessment. Based on public comments, the Commission has revised the final rule to modify the requirement for licensees to determine the maximum coping capability. (See response to public comments in subject number 9.) Instead, a coping assessment is required only for a specific duration. The cost for such a study is estimated to be from 70 to 100 percent higher than the original estimates by the staff, and these revised costs are used in the final value-impact analysis.
The staff revised its estimate of the resource burden on NRC for review from 120 to 175 person-hours per reactor. This revision was based on technical review required for other comparable NRC activities.
(B) The technical analyses performed for USI A-44 indicated that the contribution to core damage frequency from independent failures, in addition to failures that must occur to get to a station blackout, is low. Likewise, results of USI A-44 studies and other probabilistic risk assessments have shown that, for station blackout sequences, the contribution to core damage frequency from seismic events is low.
Sabotage can not be analyzed adequately on a probabilistic basis.      Even though sabotage was not explicitly considered in the staff's value-impact analysis, it is discussed in NUREG-1109 under other considerations.      These considerations support the conclusion that a station blackout rule will provide a substantial safety benefit.
 
f(          .
,                                                                        (C) The revised value-impact analysis performed for the resolution of USI A                  indicates that there are substantial benefits in terms of reduced core damage frequency and reduced risk'to the public that. result from the station blackout rule, and the costs are warranted in light of these benefits. The best estimate for the overall value-impact ratio is 2,400 person-rem per million dollars. Even if those plants.with the highest risk (and therefore the greatest risk reduction) were not considered, the value-impact ratio for the remaining plants is still favorable (i.e. , about 1,500 person-rem per million dollars).
Recent analyses performed for NUREG-1150, " Reactor Risk Reference Document,"
indicate that station blackout is a dominant risk contributor to overall risk for most of the six plants analyzed. These results support the comment by UCS in response to the Commissioner's request for comments on this subject.
4.
Whether NRC Should Require Substantial Improvements in Safety that Go Beyond Those Proposed in this Rulemaking Commissioner Asselstine requested comments on whether the NRC should require        j substantial improvements in safety with respect to station blackout, like those l
being accomplished in some other countries, which can be achieved at reasonable cost and which go beyond those proposed in this rulemaking.                        '
Comments - NRC received eight letters that included comments on this subject.
                                                                                                  )
Five of these were from the nuclear industry, none of which felt that the 1
approach to station blackout taken in European countries should be used to i
justify safety improvements that go beyond the proposed $50.63. The main justification for industry's argument is that foreign countries may have reasons for requiring activities that differ from, or exceed, those in the U. S.
For example, Washington Public Power Supply Systems (WPPSS) commented, "It is not apparent that the details of U.S. grid stabilities and onsite power      1 reliabilities are substantially similar enough to those found abroad to warrant a simple adoption of these [ European] measures."
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In another comment from industry on this subject, NUMARC stated that there are several reasons why many of the features for coping with a station blackout in new French nuclear power plants may already exist at most U.S. plants. In fact, they said, "The French approach to station blackout does not appear to depart significantly from current regulatory approaches in the U.S." Similarly, AIF stated, "The assertions of extensive station blackout coping capability at foreign (notably European) nuclear power plants are not sufficiently substant-iated to serve as even part of the basis for the proposed requirements."
Three other letters (UCS, OCRE and IDNS) supported the NRC rulemaking to require all plants to be able to cope with a station blackout, but urged the l
Commission to go beyond the proposed rule.            IONS stated that --
I The goal of ho]ging the expected frequency of core damage from station blackout to 10 per reactor year is not sufficiently stringent.
relatively modest modifications to the proposed rule, a frequency of 10With _7 appears achievable at reasonable cost. Specifically, the rule should require no less than 20 hours decay heat removal capacity instead of only                                                i four or eight hours in the proposed rule, in the event of a blackout.
Reponse - The staff agrees with industry's comments that foreign countries may have valid reasons for imposing requirements that differ from or exceed                                                      ;
those in the U.S. For example, it appears that there is a higher frequency of losses of offsite power in France than in the U.S. This experience, along with French safety objectives, led the French to design their new standard nuclear power plants to be able to cope with a very long duration station blackout (i.e., up to three days). The French safety approach and their station                                                          I blackout design features are documented in NUREG-1206, " Analysis of French (Paluel) Pressurized Water Reactor Design Differences Compared to Current U.S.
PWR Designs," June 1986.
The Commission believes that the staff has adequately considered foreign approaches to station blackout in developing the resolution of USI A-44. It has not been shown that more stringent requirements would be cost beneficial.
Although the rule requires plants to be able to cope with station blackout for a specific duration, that duration is not specified in the rule. Guidance to
 
determine an acceptable duration is included in the station blackout regulatory guide. This guidance should apply to most plants, but if there were adequate justification, different requirements (either more or less stringent than the regulatory guide) could be applied to specific plants.
: 5. The Need for Generic Rulemaking Comments - Five letters from the nuclear industry commented that generic rulemaking is not necessary to resolve the station blackout issue. Their reasons for this issue were as follows:
A generic rulemaking is inappropriate since the historic number of sites experiencing a loss of all offsite power is small. (Texas Utilities)
The station blackout issue should be handled on a plant-specific basis and does not need to be resolved by generic rulemaking. Each plant has unique probability for a loss-of power event based on transmission system, location of plant, and onsite power systems. (Duquesne Light)
The Commission need not pursue generic rulemaking in order to resolve a non generic issue. In the proposed station blackout rule, the number of plants of concern is acknowledged to be limited. (NUMARC)
Station blackout has been found not to be a generic issue. Station blackout risk is plant specific and, according to the staff's own analyses, the proposal requirements are expected to result in modifications at no more than a few facilities, if at any. Requiring all licensees to undertake extensive analyses under the provisions of the proposed rules when only a small group of plants may have a need for remedial action is not appropriate. (AIF)
Response - The Commission believes that a rule is appropriate to ensure that station blackout is addressed at all nuclear power plants. The plant-specific features that contribute to risk for station blackout (e.g., diesel generator configuration, probability of loss of offsite power) are considered in the station blackout regulatory guide to determine an acceptable coping duration for each plant. Even though not all sites have experienced a loss of offsite power, there is not sufficient assurance that such events would not occur in the future. Since historic experience has shown that a total loss of
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l offsite power occurs about once every 10 site years, and many nuclear plants have operated for less than 10 years, it is not surprising that some plants      l have experienced a loss of offsite power while others have not.
Even though it is likely that many plants will not need hardware modifications to comply with the rule, the assessment of station blackout coping capability for a specific duration and implementation of associated procedures will effect a safety benefit for all plants. The " limited number of plants of concern" in NUMARC's letter refers to those plants having the highest risk from station blackout (i.e., those that would need hardware modifications). Without a generically applied assessment, these plants can not be identified. Even excluding these plants from consideration, the staff's analysis has shown that the improvements in safety associated with the rule are cost beneficial.
: 6. Applicability of the Proposed $50.63 to Specific Plants Comments - Four letters included comments or questions regarding the applicability of the rule to specific plants.      For example, does the rule apply to high temperature gas cooled reactors (i.e., Fort St. Vrain)? What about TMI-2 or plants that are near completion but will not have an operating license prior to the amendment's effective date? Houston Power and Lighting Company wrote --
Proposed Section 50.63 provides schedular guidance for implementing station blackout-related modifications on plants that already hold oper-ating licensees or will be licensed to operate prior to the effective date of the amendment. Plants who may be NT0L's [near-term operating license]
but will not be licensed prior to the amendment's effective date should be accorded the same compliance period under parts (c) and (d) of this section. Otherwise this proposed rule could be interpreted to imply that plants not licensed prior to the effective amendment date must comply with    ;
the rule and make all necessary modifications prior to receiving an 0.L.
[ operating license). The rule should be amended to address plants which      !
are scheduled to receive an 0.L. within a short time following imple-        i mentation of this rule.
Response - Rather than identifying specific plants for which the rule does not apply, 650.63(a) specifies when it does apply (i.e. , "each light-water-cooled nuclear power plant licensed to operate"). Since Fort St. Vrain is an
 
t HTGR, the generic rule would not apply.
Station blackout will be considered individually for that plant based on its unique design. Since TMI-2 is not licensed to operate, likewise, the rule would not apply to that plant. A sentence has been added to $50.63(a) to take into account the comment on NT0Ls.
Applicants for operating licenses as of the date the rule is issued are required to comply with the rule on the same schedule as those plants already licensed to operate or before an operating license is issued, whichever is later.
: 7. Plant-Specific Features and Capabilities Comments - A number of utilities described plant specific features and capabilities that reduced the risk posed by a station blackout event compared to the staff's analysis.      Examples of such features are given below.
Availability of alternate, independent ac power sources such as diesel generators, gas turbines, or nearby " black start" ac power      -
sources.
I Extremely reliable offsite power supplies because of multiple
      ,        right of-ways or underground feeders to back up above ground transmission lines.
Dedicated shutdown systems and associated diesel generators to meet the fire. protection requirements of Appendix R to 10 CFR Part 50.
1 Common or shared systems between two units at multi-unit sites such as de power, auxiliary feedwater, or diesel generators.
t i
Response - The analyses performed for USI A-44 clearly show that plant-specific            [
features do affect the risk from station blackout, and the station blackout                3 f
regulatory guide takes this into account in providing guidance on different acceptable coping durations depending on the most significant of these                      l h
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I features. Those plants with extremely reliable offsite and onsite ac power supplies need only have a very short (e.g. , 2-hour) coping duration to be acceptable. Plants that have a dedicated shutdown system with its own inde-pendent power supply could take credit for this system to cope with a station blackout. The regulatory guide has been clarified to give credit for alternate              ,
ac power supplies (see response to subject 11). Therefore, the Commission                  l believes that for almost all sites, plant specific differences have been adequately accounted for in the resolution of USI A-44, but the door is open to licensees who believe their plants have additional capability that should be considered by the staff in demonstrating compliance with the rule.
: 8. The Source Term Used to Estimate Consequences Comments - Letters from NUMARC and others in the industry commented that the consequences of offsite releases that would result from a station blackout event are overestimated, and new source term information would lead to the prediction of much lower consequences for this event. Several commenters felt that the approach taken by the staff to estimate consequences of a station blackout event -- decreasing the estimated consequences of the SST1 siting source term from NUREG-CR/2723, " Estimates of the Financial Consequences of Nuclear Power Reactor Accidents" (September 1982), by a factor of three -- was improper.
AIF felt that " implementation of any requirements resulting from the resolution of USI A-44 should be deferred until the results of the source term research can be taken into account." They based this statement on the premise that if the consequences used in the staff's value-impact analysis were reduced by a factor of 10, none of the alternatives would be feasible.
UCS expressed a different point of view in their letter which said
      "... available evidence indicates that the consequences of an accident involving station blackout may be even worse than those estimated either in WASH-1400 or the NRC's more recent studies."
 
i 1                                                        3 Response - NRC has had an extensive research effort underway since about 1981 to evaluate severe accident source terms. The staff has reviewed the results of this research to take into account the public comments received on this subject. Since there is still a great deal of uncertainty regarding source l:
terms and associated consequences, the staff revised its value-impact analysis for USI A-44 considering a range of estimates for consequences of a station l
blackout.
i      The NRC research on severe 1 accident source. terms has resulted in the develop-ment of significan.t new analytical tools by NRC contractors, as discussed in NUREG-0956, " Reassessment of the Technical Bases for Estimating Source Terms,"
July 1986. . The analytical methods developed, generally referred to as the
          -Source ' Term Code Package (STCP), have been used to analyze a number of severe accident sequences for five reference plants, namely:                                    Peach Bottom, a BWR Mark I design; Sequoyah, a PWR ice condenser; Surry, a PWR witq a sub-atmo-I spheric containment; Grand Gulf, a BWR with a Mark III contamment; and Zion, a PWR with a large dry containment (NUREG-1150, " Reactor Risk Reference Document," Draft for Comment, February 1987).
The results of these analyses show that releases from station blackout sequences can be expected to vary significantly depending upon the plant and the specific sequence. Although generalizations are difficult, it appears that calculations using the STCP yield release fractions for most of the                                            '
sequences range from about one third of an SST1 release (for the case of Surry, without condensation) to roughly one order of magnitude less than this. However, the uncertainties in our present understanding also do not preclude the possibility of a large release, approaching that of the SST1 estimate.
To determine the consequences in terms of person-rem, given the above range of Felease fractions, data taken from NUREG/CR-2723 indicate that the variations in person-rem associated with releases of magnitude SST1, SST2 and SST3, are virtually identical to the variations in latent cancer fatalities for the same
 
o.~
I three releases. Hence, the estimated change in latent cancer fatalities with
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release fractions provides a reliable indication of change in person-rem as i
well.
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Table 10 in NUREG/CR-2723 presents variations in estimated latent cancer fatalities associated with changes in SST1 release fractions (for all elements except noble gases).
This table shows that a release fraction of one third of an SST1 release would yield a value of about 50 percent of the latent cancer    !
fatalities (and person rem) of an SST1 release. Similarly, a release fraction of one third of an SST1 release would yield an estimated person rem of about 15 percent of that associated with an SSTI release. Consequently, for value-impact calculations, the staff estimated the range of consequences of station blackout, in terms of person-rem, to be from 0.15 to 0.5 of the estimated person rem of an SST1 release. As noted, the original value-impact analysis was based on 0.3 times the estimated person-rem of an SST1 release. l With regard to a possible delay in the resolution of USI A-44 until "better" source terms become available, key considerations appear to be when better source terms are likely to become available, and to what degree uncertainties in phenomenology as well as differences between investigators will be resolved. Although research on source terms is expected to continue well into 1
the future, improvements in our knowledge are expected to be largely I
)        evolutionary beyond this point, in that the major phenomena appear to have j        been accounted for, at least in a first-order fashion, both in NRC as well as I        industry models. Resolution and narrowing of the remaining uncertainties would also benefit from improved experiments and analytical models that are likely to become available gradually. For these reasons, significantly better source terms than those presently available are likely to be forthcoming only
!      after a number of years. Since the range of severe accident source terms and L
consequences suggested above from estimating station blackout sequences is sufficiently broad to cover likely improvements in source term knowledge, the resolution of USI A-44 should not be delayed.
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x p                            9.                                    Specificity on the Extent of Required Coping Studies Comments - Several letters by industry expressed concern that the studies necessary to demonstrate that a plant can cope with a station blackout are not c
well defined and could potentially be unbounded. These comments focused on two main points. First, the proposed rule required plants to determine the maximum                                                                                                                                                                                                      )
i duration the plant could cope with a station blackout, yet the draft regulatory                                                                                                                                                                                                      {
i guide included specific guidance on acceptable coping durations (e.g., 4 or 8 hours).                                          Determining the maximum duration, rather than assessing the plant's j
capability for a specific acceptable duration, could be an open ended requirement. Along these lines, NUMARC stated --
Unless the required coping demonstration is specifically bounded by clearly stated definitions, assumptions, and criteria, there could conceivably be hundreds of supporting special effects analyses which licensees may have to consider as a result of the exercise of discretion by individual staff reviewers. Under the rule as proposed, licensees cannot ascertain the ultimate requirements they will be expected to meet (including the potential plant modifications they will need to make) to demonstrate compliance.
i Second, industry also commented on the potential open endedness of analyses to determine the operability of equipment in environmental conditions resulting from a station blackout (e.g., without heating, ventilation, and air condition-ing).                                          Unless these analyses were well defined, industry felt the analyses could be much more costly than estimated by the staff. However, NUMARC made the following statement relating to the need for detailed prescriptive require-ments by NRC that appears to contradict their earlier statement.
The point .... is not that regulations must be prescriptive by their very nature.                  Prescriptive regulations, which outline in detail exactly what i
I steps are required by licensees to satisfy a proposed regulation, are, in many instances, unnecessary and counterproductive.                                                                                                                                                                                                      '
i Response - With regard to proposed requirement to determine the plant's maximum duration for coping with station blackout, the staff agrees with the industry comments.                                          First of all, it would be difficult to adequately define " maximum w_____.______._____._        _______.___________________________.___.__m.___                  _ _ _ _ . _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ . _ _ _ _ _ _ _ _ . - _ . . _ . _ - . _ _ _ . _ _ _        - . _ _ _ _ _ _ _ - . _ _ _ . _ _ _ .                  -______-___..--______-_____._2
 
duration" in this sense. Second, as long as licensees determine that their plants can cope with a station blackout for a specified " acceptable" duration, the additional safety benefits of further assessments are marginally smaller, but the costs could be significantly higher. Therefore, the rule and regulatory guide have been revised accordingly to delete the requirement for licensees to-determine a plant's maximum coping capability.
With regard to the comments on assessments to determine equipment operability during a station blackout, the staff feels strongly that such assessments are necessary to determine a plant's response to station blackout. By deleting the requirement to determine a plants " maximum" coping capability, the assessment of equipment operability would not be as costl3 as assumed by industry.
Guidance on acceptable coping assessments is provided in the station blackout regulatory guide. Also, additional work was done by an American Nuclear Society working group to develop a draft standard ANS 58.12. " Criteria for Establishing Response Capability for Loss of All ac Power (Station Blackout) at Light Water Reactor Nuclear Power Plants." Efforts such as this could provide additional definitions, criteria, and standards for licensees' assessments of equipment operability without the need for " prescriptive regulations" by NRC.
In order to evaluate further industry's comments on this subject, NRC requested Sandia National Laboratories to identify specific tasks necessary to determine operability of equipment during a station blackout, and estimate the cost to perform these tasks. Results of this study were used in the revised value-impact analysis performed for this issue (" Equipment Operability During Station BlackoutEvents," SAND 87-0750).
: 10. Acceptable Duration for Coping with a Station Blackout Comments - Several comments with differing views were directed at guidance in the draft regulatory guide on acceptable station blackout coping durations in order for plants to comply with the proposed rule.
 
                                                ~    ..
l Washington Public Power Supply commented that "it should be possible for q
certain utilities to demonstrate [an acceptable] zero hour blackout."
One individual recommended "that a 30 minute period be a margin, and that no duration under 4 hours be accepted by the staff." NucleDyne Engineering          i commented that " advanced reactors should require the capability to safely withstand a station blackout of at least 8 hours," and IDNS wrote that "the    j rule should require no less than 20 hours decay heat removal capability          {
instead of only 4 or 8 hours."
z Response - Although a diversity of comments was received on this subject, none provided supporting analysis or information to back up the opinions expressed.
However, the staff did re-analyze the estimated risk from station blackout events for different plant- and site-related characteristics and revised its guidance on acceptable coping durations accordingly based on a goal of limiting the average contribution to core damage from station blackout to about 10 5 per reactor year. Most plants would still need a 4- or 8-hour coping capability. Those few plants with the most redundant onsite emergency ac power system, coincident with significantly lower than average expected frequency of loss of offsite power would need only a 2-hour capability to be acceptable.
Any plant with minimum redundancy in the onsite emergency ac power system coincident with low reliability and a significantly higher than average expected frequency of loss of offsite power would need to substantially improve its ac power reliability or be able to cope with a station blackout for more than 8 hours.
11.
Credit for Alternate or Diverse AC Power Sources Comments - Ten letters from the utility industry commented that more credit
                                                                                          )
should be allowed for the availability of alternate power sources such as onsite gas turbines. The two comments below represent the utilities' viewpoint.
          /
 
i The station blackout rule should be clarified to allow credit for diverse and very reliable offsite power sources or diverse and very reliable onsite electrical generation. (Public Service Company of Colorado)
The option of providing an additional alternate source of ac power is eliminated by [the proposed resolution]. The inconsistency in this approach nuclear        can best power        be understood by considering an example at a generic station.
If the licensee were to provide an additional independent diesel generator capable of providing the necessary ac power to prevent station blackout, the licensee without            ... would still be required to withstand at least 4 hours ac power.
They would receive no credit for the additional diesel generator in the coping analysis.
If the licensee were to use that same diesel engine to power a charging pump, even though it would be of less significance to mitigation of reactor core damage than the diesel generator, the licensee could take credit for it in coping with the blackout.
i Since a diesel charging pump will not provide for equipment loading flexibility, lighting, ventilation, instrumentation, etc., it is          ,
obviously of lower value than an additional source of ac power. The fixed category approach taken in [the proposed resolution], however, will not permit taking credit for the same diesel engine when used as a generator through the actual reliability for the machine is the same. (Toledo Edison)
(
I Response - The proposed resolution did not intend to ignore the alternative              I of adding additional power sources or taking credit for such sources if they already exist.
For example, as specified in the regulatory guide, if a licensee added an emergency diesel generator to one of its plants that had minimum redundancy in the onsite emergency ac power sytem, the acceptable station blackout coping duration could be reduced. For some plants, however,                1 i
adding a diesel generator would not result in a reduction in the acceptable coping duration, and the point made by Toledo Edison is a valid one. The regulatory guide has been revised to clarify that alternate power sources may be given credit to comply with the rule provided that certain criteria are                  !
met (e.g., independence, diversity, high reliability, maintenance, and testing).                t I
 
l l
: 12. Trends on the Reliability of AC Power Sources 1
Comments - Five letters included comments on the reliability of ac power sources.
Four letters from industry felt that improved ac power reliability              ]
{
should be factored into the staff's technical analysis. Examples of these                      j comments include the following:
              "... the frequency of loss of offsite power activities has been decreasing..." (Washington Public Power Supply System);                                  j
              "... offsite power availability in the absence of regulation has significantly improved over the past decade." (Southern California Edison Company);
              "[NUREG/CR-4347] ... shows an improvement in diesel generator reliability over  that shown Electric);  and in the earlier document [NUREG/CR-2989)." (General
              " Typically the reliability of onsite power systems increases during the first few years following startup." (Gulf States Utilities)
IDNS on the other hand felt that potential vulnerabilities still exist in                      1 onsite emergency ac power systems, and licensees should demonstrate that they have taken steps to reduce the probability of loss of ac power.
Response - The staff and its contractors have extensively analyzed the industry experience and trends in ac power reliability as documented in NUREG-1032,                    j NUREG/CR-2989, NUREG/CR-3992, and NUREG/CR-4347.
Trends have shown that two aspects of ac power reliability have improved somewhat -- the reduced frequency of losses of offsite power due to plant-centered events, and a slight improvement in average diesel generator reliability from 1976 through i    1983. These factors have been taken into account in the staff's analyses and the resolution of USI A-44. However, data also demonstrate that there are practical limits on ac power reliability, and the defense-in-depth approach of being able to cope with a station blackout is warranted.
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l i                        *
: 13. Sharing of Emergency Diesel Generators Between Units at Multi-Unit Sites.
Comments - Several letters from industry stated that some plants with two units on a site have the capability to crosstie electrical buses between units and therefore have improved flexibility in providing ac power. Since the magnitude                                                                                                                      :
i of the electrical loads necessary to provide core cooling during a station                                                                                                                          j blackout is significantly less than that required for a design basis accident, it could be possible to provide ac power to both units at the site using only a                                                                                                                  ,
single diesel generator.                                                                                                                                                                            l Response - The proposed rule and draft regulatory guide do not prohibit the approach discussed above.                                                              If licensees can demonstrate that such crosstie capability exists; procedures are in place to accomplish the crosstie and shed nonessential loads, if necessary; and no NRC regulations are violated (such as separation and independence), then credit would be given for this capability as shown in the station blackout regulatory guide (e.g., reduced acceptable station blackout coping durations for greater diesel generator redundancy).                                                                                                                                                                                        !
: 14. Clarification of the Definitions of Station Blackout and Diesel Generator Failures.                                                                                                                                                                            1 Comments - (A) Three letters from the utility industry recommended that the                                                                                                                          l definition of station blackout in 650.2 should be clarified to exclude ac power from the station batteries through inverters. This source of ac power from the station batteries would be available in the event of a loss of both the offsite and onsite emergency ac power sources (i.e. , diesel generators).                                                                                                                                    j (B) Several industry letters commented that the definition of diesel generator failure should be clarified, particularly with respect to the treatment of short-term failures that can be recovered quickly.                                                                          A letter from Sargent and Lundy Engineers commented that --
    - - _ _ - - _ _ -                      _ _ _ - _ - _ _ _ _ _ _ _ _ _ _                        _ _ _ _ _ - _ _ _        _- ____-____- ____        __      . _ _ _ - _ _ _ _ _ . _ = _ _ _ _ _ _ _ - - - _ _ _ _ _ _ _ _ - .
 
i I
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A definition of failure on demand for emergency diesel generators needs to be provided. Under the context of a station blackout, a diesel generator which fails to start automatically upon detection of an offsite power loss, but is successfully started manually from the main control room or from the local control panel, should not be considered a failure on demand.
1 Response - (A) The staff agrees with comment A and revised the definition of                          '
station blackout accordingly.
(B) Based on actual experience, failures of diesel generators to start due to failures in the auto-start system make up less than 20 percent of all diesel generator failures.
Therefore, discounting these failures would not have a significant imput of overall diesel generator reliability statistics.
However, the staff agrees in principle with comment B and has clarified the station blackout regulatory guide so that auto-start failures of diesel generators n'eed not be counted in determining the failure rate if the diesel generator is capable of being started manually immediately after it does not start automatically.
: 15. Specificity and Clarification of Requirements Comments - Public comments were received regarding the specificity and clarifi-cation of the proposed rule and draft regulatory guide. These ranged from general to specific comments as the following two excerpts indicate:                                  l l
We are concerned that, if the proposed rule is adopted, the staff will promulgate regulatory guidance criteria which will be unrealistic and excessive, i.e., compounding the event with other accidents, imposing                            i passive failure criteria, applying seismic, environmental qualification and other qualifications to equipment that could otherwise be used in response to such an event, etc. (Maine Yankee Atomic Power Company)
Definitions of P1 and P2 [in Table 3 of the draft Regulatory Guide] use frequency of extremely severe weather and severe weather interchangeably, thus creating confusion in the definition. (Washington Public Supply System) l l                                          -              -        ----- --- --_    -- -------
 
Response - Some of the comments on this subject relate to other subjects discussed elsewhere in this section. Some comments were quite specific while others were general in nature or expressed views that were not substantiated with backup material.
The staff has taken these comments into consideration and revised and clarified the rule and regulatory guide accordingly. Work,      ;
such as that undertaken by the American Nuclear Society to develop an ANS standard on station blackout, could provide additional criteria and guidance for licensees to follow to comply with the station blackout rule.    (See discussion in subject 9).
: 16. Technical Comments on NUREG-1032 Comments - In addition to comments on the proposed rule and draft regulatory guide, several letters contained comments on the staff's draft technical          !
report, NUREG-1032, " Evaluation of Station Blackout Accidents at Nuclear Power Plants."
Response - NUREG-1032 was issued in draft form for public comment in May 1985 (b0FR24332). The comments received were reviewed and considered by the staff and resulted in a re-evaluation of the technical analysis. Details of s
the specific comments and responses are not presented here.      Rather, an appendix will be added to the final version of NUREG-1032 to adoress the public comments.      In general, the overall conclusions on the risk from station blackout events did not change significantly. One of the major changes resulting from the re-analysis was a revision to the definitions of plant characteristics, especially the clustering of plants into site and weather-related groups (Appendix A in NUREG-1032).      These changes are reflected in revisions to the guidance in the station blackout regulatory guide to determine plant-specific acceptable station blackout coping durations.
r
                                                                                              )
i
: 17. Relationship of USI A-44 to Other NRC Generic Issues Comments - The major public comment regarding the relationship of USI A-44 to other NRC generic safety issues was that the proposed rule may not be necessary or should be postponed because of ongoing work to resolve related generic issues.
Some comments were general in nature such as the following one from Southern California Edison Company:
Promulgation of a final station blackout rulemaking at this time will unnecessarily complicate the final resolution of related generic technical issues... The NRC must develop and implement a program to coordinate the resolution  of all power-related individual proposed  rule.      generic issues prior to finalizing any AIF suggested that the implementation of any requirements for station blackout j
be deferred until the requirements from USI A-45, Shutdown Decay Heat Removal Requirements, are known and until the effect of source term changes can be evaluated.
NUMARC mentioned specific proposed and existing regulatory requirements that should be considered because they could reduce the need for a station blackout rule (e.g., B-56, Diesel Generator Reliability and GI 23, Reactor Coolant Pump Seal Failures). Other related issues mentioned in the public comments were A-30, Adequacy of Safety Related DC Power Supplies, and implementation of safe shutdown facilities to meet the fire protection requirements of Appendix R.
Response - The question that needs to be addressed is "should a requirement be imposed now to reduce risk, or should it be postponed until related issues are resolved sometime in the future?" Potentially, this could result in sub-stantial delays and thereby not resolving generic safety issues in a timely manner.
The staff has considered the resolution of USI A-44 in light of the related issues mentioned in the comments.      Although these issues are identified as separate tasks within NRC, they are all managed in a well            '
established program that coordinates all related issues. A brief discussion i
1 L ______- -__________________ _
 
of the most relevant issues is presented below.
(Additional infe- ' ion is provided in NUREG-1109, " Regulatory Analysis for the Resolution of Unresolved Safety Issue A-44, Station Blackout.")
Although the recommendations that might result from the resolution of USI A-45 have not yet been issued, only recommendations that involve new or improved decay heat removal systems that are ac power independent or include a separate independent ac power supply would have an effect on USI A-44. Such a new additional system would receive the appropriate credit within the USI A-44 resolution by either changing the emergency ac power configuration group or providing the ability to cope with a station blackout. Well before plant modifications, if any, will be implemented to comply with the station blackout rule, the proposed technical resolution of USI A-45 will be published for public comment.
Those plants needing hardware modifications for station blackout could be reevaluated before any actual modifications are made so that any contemplated design changes following from the resolution of USI A-45 can be considered at the same time.
Maintaining emergency diesel generator reliability, the purpose of B-56, is an integral and necessary part of the resolution of USI A-44. However, the Commission believes that additional defense-in-depth is necessary to adequately protect the public health and safety.
Likewise, the resolution of GI 23 is necessary to assure the adequacy of reactor coolant pump seal integrity in the event of a station blackout.
Although the resolution of this issue is necessary, by itself it is not sufficient to ensure the adequate protection of the public health and safety from station blackout events.
I i
Some licensees have implemented dedicated shutdown systems that are independent of normal and emergency ac power to meet Appendix R requirements. If appli-cable, these features would be credited in the resolution of USI A-44 by providing the capability to cope with a station blackout.
l l
 
s Thus, the resolution of USI A-44 is coordinated with related generic issues, and implementation of a Yinal resolution should not be delayed further.
(Response to comments on the effect of source term changes is included in subject number 8.)
: 18.                        An Alternative of Plant-Specific Probabilistic Assessments Comments - Several utilities suggested that, in lieu of the requirements in the rule, licensees should be permitted to submit plant-specific evaluations to demonstrate that the frequency of core damage from stati m blackout events is 10 per reactor year or less. In a similar vein, the suggestion was made that NRC should specify a target level of reliability for ac power systems in order to satisfy NRC's criteria for core damage frequeracy. A few licensees submitted limited probabilistic assessments to show that for some plants station blackout could have a very small probability of severe consequences.
Response - The Commission does not preclude licensees from submitting probabilistic assessments to support a determination that the plant's station blackout coping duration could be less than that specified in the regulatory guide on station blackout. However, the Commission recognizes the potential drawbacks of relying on this approach on an industry-wide basis for the reasons given below.
One detrimental aspect of reliability-based regulation is that it tends to lead to much staff review of the reliability analysis and much discussion with licensees or applicants regarding the adequacy of the analysis in lieu of concentrating on the adequacy of the design. The Commission's experience shows that there is a strong emphasis on fine tuning the model and the data base in order to achieve results directed solely at meeting the numerical criterion.
Also, the Commission does not have any mechanism in place to assure that the reliability analysis would still be applicable over the life of the plant.              The Commission's experience to date in implementing reliability goals and the i
w_        - _ - - - _ - - _ - - - -
 
uncertainties associated with the present state of-the-art in reliability and risk analysis, lead us to believe that defense-in-depth, via specific deterministic criteria, is still warranted.
                    '19. Procedures and Operator Actions During Station Blackout Comments - (A) Several letters from industry commented that, in response to Generic Letter 81-04, " Emergency Procedures and Training for Station Blackout Events," dated February 21, 1981, utilities already have procedures in place to prepare plant operations for station blackout events. Owners groups have established generic guidance for station blackout operating procedures for licensees to use in developing plant-specific procedures. A representative of the Professional Reactor Operator Society, commented that --
i Generic procedures are used by most operating facilities. These procedures are not carried into adequate depth of specific power plant operations. The industry has relied too heavily on generic procedures and has not given a real look at what specific steps must be taken.
Extrapolation of these procedures must be required. Specific maintenance procedures must be established and followed.
(B) Other comments on procedures related to the timeliness of operator actions, both inside and outside the control room. Houston Lighting and Power suggested that --
In Section 3.1 (Part 6), [of the regulatory guide] the first sentence should be revised to read, ' Consideration should be given to timely operator actions both inside and outside of the control room that ...',
so that credit can be taken for existing equipment that may not have actuation and control from the control room.
Illinois Power Company recommended that --
                        . .. Section C.3.3, Item 3.a, of the proposed regulatory guide should be modified to read:
- _ - _ _ _ - _                                                                                                    \
 
                                            -          a. The system should be capable of being actuated and controlled from the control room, or if other means of control are required (e.g. ,
manual jumping of control logics or manual operation of valves), it should be demonstrated that these steps can be carried out in a timely fashion.
Response - (A) Licensees may take credit for station blackout procedures already in place to comply with the station blackout rule. However, for the most part, these procedures were developed without having the benefit of a plant-specific assessment to determine whether a plant could withstand a station blackout for a specific duration. Therefore, these procedures may need to be modified after licensees have determined an acceptable station blackout coping duration and evaluated their plant's response to a station blackout of this duration.
(B) The staff agrees with the comments related to operator actions outside the control room, and the regulatory guide was revised accordingly.
: 20. Schedule Provisions in the Proposed 650.63 Comments - Two letters contained comments on the proposed schedule in 650.63.
OCRE felt the scheduling provisions in the proposed rule were far too generous.
One individual recommended that the schedule be modified to require licensees to submit, within 9 months of the date of the amendment, a list of modifications along with a proposed schedule to implement those modifications. (According to the proposed rule, licensees would not have to submit a schedule for implementing equipment modifications until after the staff received and reviewed licensees' submittals on their plant's acceptable station blackout duration.)
Response - The staff agreed in part with these comments, and the schedule was revised accordingly. S50.63(c)(iv) now requires that licensees submit within 9 months after the rule is issued a list of equipment modifications and a proposed schedule for implementing them.        A final schedule would be developed after NRC has reviewed the licensees' submittal of their plant's acceptable station blackout duration.
: 21. Industry Initiatives Comments - In addition to comments on the proposed rule, NUMARC endorsed the following four initiatives to address the more important contributors to station blackout:
1.
Each utility will review their. site (s) against the criteria specified in NUREG-1109, and if the site (s) fall into the category of an eight-hour site after utilizing all power sources available, the utility will take actions to reduce the site (s) contribution to the overall risk of station blackout. Non-hardware changes will be made within one year. Hardware changes will be made within a reasonable time thereafter.
: 2. Each utility will implement procedures at each of its site (s) for:
,                        a. coping with a station blackout event b.
restoration of ac power following a station blackout event, and
: c. preparing the plant for severe weather conditions, such as hurricanes and tornados to reduce the overall risk of a station blackout event.
: 3. Each utility will, if applicable, reduce or eliminate cold fast-starts of emergency diesel generators for testing through changes to technical specifications or other appropriate means.
4.
Each utility will monitor emergency ac power unavailability utilizing data utilities provide to INP0 on a regular basis.
NUMARC opposed generic rulemaking and felt that these initiatives would resolve the station blackout issue.
Response - These initiatives include some of the same elements that are included in the NRC resolution of USI A-44. However, at the time this response was written, details of the NUMARC initiatives were not available to the NRC staff.
This made it difficult for the staff to evaluate the benefits of the                j industry program.      For example, the industry initiatives do not include                    i
{
assessments to determine that plants can cope with a station blackout for any                  j E_________.--__--_------
 
w period of time.
Even so, an attempt was made to estimate the likely impact this initiative would have compared to the station blackout rule and regulatory guide.
The largest risk reduction associated with the industry program would probably result from NUMARC's initiative number one. Assuming that implementing this initiative would result in licensees taking actions to reduce the risk from station blackout for those plants that fall into the category of needing an 8-hour coping ce.pability, the staff estimated the value-impact ratio for the remaining plants. The estimated total cost for these plants to comply with the resolution of USI A-44 is $42 million; the estimated reduction in risk to the public for these plants is 61,000 person rem; and therefore, the overall value-impact ratio is approximately 1,500 person-rem per million dollars. This analysis supports the conclusion that although the industry initiatives would provide benefits in terms of reducing risk from station blackout events, the recommended resolution provides greater benefits that are cost effective.
Finding of no Significant Environmental Impact Availability The Commission has determined under the National Environmental Policy Act of 1969, as amended, and the Commission's rules in Subpart A of CFR Part 51, that this rule is not a major Federal action significantly affecting the quality of the human environment, and therefore, an environmental impact statement is not required. There are not any adverse environmental impacts as a result of the rule because there is no additional radiological exposure to the general public or plant employees, and plant shutdown is not required so there are no additional environmental impacts as a result of the need for replacement power.                                                                                                    {
The environmental assessment and finding of no significant impact on    I which this determination is based are available for inspection and copying for a fee at the NRC Public Document Room 1717 H Street, NW, Washington, DC.                                    t Single copies of the environmental assessment and the finding of no significant
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . . _ _ _ _ _ _ _            _                              _                        _.A.
 
impact are available from Mr. Warren Minners, Office of Nuclear Reactor Regulation, U. S. Nuclear Regulatory Commission, Washington, DC 20555, Telephone:    (301) 492-7827.
Paperwork Reduction Act Statement
                          'This final rule amends information collection requirements that are subject to the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.). These requirements were approved by the Office of Management and Budget approval number 3150-0011.
4 Regulatory Analysis The Commission has prepared a regulatory analysis on this final regulation.
                        -The analysis examines the costs and benefits of the alternatives considered by the Commission. A copy of the regulatory analysis, NUREG-1109, " Regulatory /
Backfit Analysis for the Resolution of Unresolved Safety Issue A-44, Station Blackout is available for inspection and copying for a fee at the NRC Public Document Room, 1717 H Street, NW, Washington, DC 20555.      Copies of NUREG-1109 i
may be obtained by vriting the Distribution Section, Room P-1304, Division of Information Support Services, U. S. Nuclear Regulatory Commission, Washington, DC 20555.
Regulatory Flexibility Certification As required by the Regulatory Flexibility Act (5 U.S.C. 605(b)), the Commission certifies that this rule does not have a significant economic impact on a substantial number of small entities. The rule requires that nuclear power plants be able to withstand a total loss of ac power for a specified time duration and maintain reactor core cooling during that period. These facilities are licensed under the provisions of 10 CFR 50.21(b) and 10 CFR 50.22. The companies that own these facilities do not fall within the scope of i
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                      "small entities" as set forth in the Regulatory Flexibility Act or the small business size standards set forth in regulations issued by the Small Business Administration in 13 CFR Part 121.
List of Subjects in 10 CFR Part 50
            ' Antitrust, Classified information, Fire prevention, Incorporation by reference, Intergovernmental relations, Nuclear powerp' lants and reactors, Penalty, Radiation protection, Reactor siting criteria, Reporting and recordkeeping requirements.
For the reasons set out in the preamble and under the authority of the Atomic Energy Act of 1954, as amended, the Energy Reorganization Act of 1974, as amended, and 5 U.S.C. 553, the NRC is adopting the following amendments to 10 CFR Part 50.
Part 50 - Domestic Licensing of Production and Utilization Facilities
: 1. The authority citation for Part 50 is revised to read as follows:
AUTHORITY:                  Secs. 102, 103, 104, 105, 161, 182, 183, 186, 189, 68 Stat. 936, 937, 938, 948, 953, 954, 955, 956, as amended, sec. 234, 83 Stat. 1244, as amended (42'U.S.C. 2132, 2133, 2134, 2135, 2201, 2232, 2233, 2236, 2239, 2282); secs. 201, as amended, 202, 206, 88 Stat. 1242, as amended, 1244, 1246, (42 U.S.C. 5841, 5842, 5846).
Section 50.7 also issued under Pub. L. 95-601, sec. 10, 92 Stat. 2951 (42 U.S.C. 5851). Sections 50.10 also issued under secs. 101, 185, 68 Stat.
936, 955, as amended (42 U.S.C. 2131, 2235); sec 102, Pub. L. 91-190, 83 Stat. 853-(42 U.S.C. 4332). Sections 50.23, 50.35, 50.55, 50.56 also issued under sec. 185, 68 Stat. 955 (42 U.S.C. 2235). Sections 50.33a, 50.55a and Appendix Q also issued under sec. 102, Pub. L. 91-190, 83 Stat. 853 (42 U.S.C.
4332) Sections 50.34 and 50.54 also issued under sec. 204, 88 Stat. 1245 (42                          i
 
4       I U.S.C. 5844). Sections 50.58, 50.91, and 50.92 also issued under Pub. L.
97-415, 96 Stat. 2073 (42 U. S. C. 2239). Section 50.78 also issued under sec.
122,68 Stat. 939 (42 U.S.C. 2152). Sections 50.80-50.81 also issued under sec. 184, 68 Stat. 954, as amended (42 U.S.C. 2234). Section 50.103 also issued under sec. 108, 68 Stat. 955 (42 U.S.C. 2237).
For the purposes of sec. 223, 68 Stat. 958, as amended (42 U.S.C. 2273);
50.10(a), (b), and (c) and 50.44, 50.46, 50.48, 50.54, and 50.80(a) are issued under sec. 161b, 68 Stat. 948, as amended (42 U.S.C. 2201(b)); 50.10(b) and (c), and 50.54 are issued under sec. 1611, 68 Stat. 949, as amended (42 U.S.C.
2201(i)); and 50.55(e), 50.59(b), 50.70, 50.71, 50.72, 50.73, and 50.78 are issued under sec. 1610, 68 Stat. 950, as amended (42 U.S.C. 2201(o)).
: 2. In S50.2, a definition of " station blackout" is added in the alphabetical sequence to read as follows:
650.2 Definitions
                  " Station blackout" means the complete loss of alternating current (ac) electric power to the essential and nonessential switchgear buses in a nuclear power plant (i.e., loss of power from the offsite electric power system concurrent with turbine trip and unavailability of the onsite emergency ac power system). Station blackout does not include the loss of available ac power to buses fed by station batteries through inverters.
: 3. A new S50.63 is added to read as follows:
650.63 Loss of all alternating current power.
(a) Requirements. Each light-water-cooled nuclear power plant licensed to operate must be able to withstand and recover from a station blackout as      ,
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defined in 650.2 for a specified duration in accordance with the requirements in paragraph (e) of General Design Criterion 17 of Appendix A of this part.
Applicants for operating licenses as of [ insert the effect date of this amend-ment] must comply with this rule on the same schedule as those plants already licensed to operate or before an operating license is issued, whichever is later.
(b) Limitation of Scope. Paragraphs (c) and (d) of this section do not apply to those plants licensed to operate prior to [ insert the effective date of this amendment] if the capability to withstand station blackout was considered in the operating license proceeding and a specified duration was accepted as the licensing basis for the facility.
(c) Implementation - Determination of Station Blackout Duration.
(1) For each light-water-cooled nuclere power plant licensed to operate on or before [ insert the effective date of this amendment], the licensee shall submit to the Director of the Office of Nuclear Reactor Regulation by [ insert a date 270 days after the effective date of this amendment]:
(i) A proposed station blackout duration to be used in determining compliance with paragraph (e) of General Design Criterion 17 of Appendix A of this part, including a justification for the selection based on --
(A) The redundancy of the onsite emergency ac power sources; (B) The reliability of the onsite emergency ac power sources; (C) The expected frequency of loss of offsite power; and (D) The probable time needed to restore offsite power; (ii) An identification of the factors, if any, that limit the capability of the plant to meet the requirements of paragraph (e) of Criterion 17 for the specified station blackout duration proposed in the response to paragraph (c)(1)(i) of this section;
 
    ,                                            i
                                                                                                      .r                                              .,
(iii) A description of the procedures that have been established for station blackout events for the duration determined in paragraph (c)(1)(i) of this section and for recovery therefrom; and (iv) A list of modifications to equipment and associated procedures necessary, if any, to meet the requirements of paragraph (e) of Criterion 17 for the specified station blackout duration determined in paragraph (c)(1)(i) of this section, and a proposed schedule for implementing the stated modifications.
j (2) After consideration of the information submitted in accordance with        ;
paragraph (c)(1) of this section, the Director, Office of Nuclear Reactor              !
Regulation, will notify the licensee of the Director's determination of the specified station blackout duration to be used in determining compliance with paragraph (e) of General Design Criterion 17 of Appendix A of this part.
(d) Implementation - Schedule for Implementing Equipment Modifications.
                                                          ' (1) For each light-water-cooled nuclear power plant licensed to operate on or before [ insert the effective date of this amendment], the licensee shall, within 180 days of the notification provided in accordance with paragraph (c)(2) of this section, submit to the Director of the Office of Nuclear Reactor          I Regulation a schedule for implementing any equipment and associated procedure modifications necessary to meet the requirements of paragraph (e) of General Design Criterion 17 of Appendix A of this part. This submittal must include an explanation of the schedule and a justification if the schedule does not provide for completion of the modifications within two years of the notification provided in accordance with paragraph (c)(2) of this section.
(2) The licensee and the NRC staff shall mutually agree upon a final              i schedule for implementing modifications necessary to comply with the requirements of paragraph (e) of Criterion 17.                                            l
 
                                                                                                                          )
: 4.                                In Appendix A, General Design Criterion 17 is revised read as follows:
APPENDIX A--General Design Criteria for Nuclear Power Plants II.                                Protection by Multiple Fission Product Barriers Criterion 17-Electric power systems. (a) An onsite electric power system and an offsite electric power system shall be provided to permit functioning of structures, systems, and components important to safety. The safety function for each system (assuming the other system is not functioning) shall be to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents.
(b) The onsite electric supplies, including the batteries, and onsite electric distribution system, shall have sufficient independence, redundancy, and testability to perform their safety functions assuming a single failure.
(c) Electric power from the transmission network to the onsita electric distribution system shall be supplied by two physically independent circuits                                      !
(not necessarily on separate rights of way) designed and located so as to minimize the extent practical the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions. A switchyard common to both circuits is acceptable. Each of these circuits shall be designed to be available in sufficient time following a loss of all onsite alternating current power supplies and the other offsite electric power circuit, to assure that specific acceptable fuel design limits and design l
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conditions of the reactor coolant pressure boundary are not exceeded.        One of these circuits shall'be designed to be available within a few seconds following a loss-of-coolant accident to assure that core cooling, containment integrity, .
and other vital safety functions are maintained.
(d) Provisions shall be included to minimize the probability of losing electric power from any of the remaining supplies as a result of, or coincident with, the loss of power generated by the nuclear power unit, the loss of power from the transmission network, or the loss of power from the onsite electric power supplies.
(e) The reactor core and associated coolant, control, and protection systems, including the station batteries, shall provide sufficient capacity and capability to assure that the core is cooled and containment integrity is maintained in the event of a station blackout (as defined in 950.2) for a specified duration.
The following factors shall be considered in specifying the station blackout duration: (1) the redundancy of the onsite emergency ac power sources, (2) the reliability of the onsite emergency ac power sources, (3) the expected frequency of loss of offsite power, and (4) the probable time needed to restore offsite power.
Dated at Washington, DC, this      day of            1987.
For the Nuclear Regulatory Commission.
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l Samuel J. Chilk Secretary of the Commission.
Underlined text indicates additional praragraph to GDC 17.
 
l                                                                                                                l BACKFIT ANALYSIS                                                      1 l                  Analysis and Determination That The Rulemaking to Amend 10 CFR 50 Concerning Station Blackout Complies With The Backfit Rule 10 CFR 50.109 The Commission's existing regulations establish requirements for the design and testing of onsite and offsite electrical power systems (10 CFR Part 50, Appendix A, General Design Criteria 17 and 18). However, as operating experi-ence has accumulated, the concern has arisen regarding the reliability of both the off'$ite and onsite emergency ac power systems. These systems provide power for various safety systems including reactor core decay heat removal and con-lainment heat removal which are essential for preserving the integrity of the reactor core and the containment building, respectively. In numerous instances emergency diesel generators have failed to start and run during tests conducted at operating plants. In addition, a number of operating plants have experienced a total loss of offsite electric power, and more such occurrences are expected.
Existing regulations do not require explicitly that nuclear power plants be designed to withstand the loss of all ac power for any specified period.
This issue has been studied by the staff as part of Unresolved Safety Issue (USI) A-44, " Station Blackout." Both deterministic and probabilistic analyses were performed to determine the timing and consequences of various accident sequences and to identify the dominant factors affecting the likelihood of core melt accidents from station blackout. These studies indicate that station blackout can be a significant contributor to the overall plant risk. Conse-quently, the Commission is amending its regulations to require that plants be capable of withstanding a total loss of ac power for a specified duration and to maintain reactor core cooling during that period.
An analysis of the benefits and costs of implementing the station blackout rule is presented NUREG-1109, " Regulatory /Backfit Analysis for the Resolution
 
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f-                                                      of Unresolved Safety Issue A-44, Station Blackout."6 The estimated benefit from implementing the station blackout rule is a reduction in the freque%cy of core damage per reactor year due to station blackout and the associated risk of offsite radioactive releases. The risk reduction for 100 operating reactors is estimated to be 145,000 person-rems.
The cost for licensees to comply with the rule would vary depending on the existing capability of each plant to cope with a station blackout, as well as the specified station blackout duration for that plant. The costs would be primarily for licensees to assess the plant's capability to cope with a station blackout, (2) to develop procedures, (3) to improve diesel generator reliability if the reliability falls below certain levels, and (4) to retrofit plants with additional components or systems, as necessary, to meet the requirements.
The estimated total cost for 100 operating reactors to comply with the resolu-tion of USI A-44 is about $60 million. The average cost per reactor would be around $600,000, ranging from $350,000, if only a station blackout assessment and procedures and training are necessary, to a maximum of about $4 million if substantial modifications are needed, including requalification of a diesel generator.
The overall value-impact ratio, not including accident avoidance costs, is about 2,400 person-rems averted per million dollars. If the net cost, which includes the cost savings from accident avoidance (i.e., cleanup and repair of onsite damages and replacement power following an accident) were used, the overall value-impact ratio would improve significantly to about 6,100 person-rems averted per million dollars.
i 6 Draft NUREG-1109 was issued for public comment in January 1986.        Copies of this report are available for inspection and copying for a fee at the NRC Public Document Room, 1717 H Street, NW, Washington, DC 20555.
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This analysis supports a determination that a substantial increase in the pro-tection of the public health and safety will be derived from backfitting the I
requirements in the station blackout rule, and the backfit is justified in view of the direct and indirect costs of implementing the rule. This does not imply that operating plants are unsafe. Rather, the rule will provide additional protection beyond that already provided to comply with currently existing re-quirements, and the benefit to public health and safety outweighs the cost of the improvements.
The preceding quantitative value-impact analysis was one of the factors considered in evaluating the rule, but other factors also played a part in the decision-                                                            i making process. Probabilistic risk assessment (PRA) studies performed for this USI, as well as some plant-specific PRAs, have shown that station blackout can be a significant contributor to core melt frequency, and, with consideration of containment failure, station blackout events can represent an important contri-butor to reactor risk. In general, active systems required for containment heat removal are unavailable during station blackout. Therefore, the offsite risk is higher from a core melt resulting from a station blackout than it is from many other accident scenarios.
Although there are licensing requirements and guidance directed at providing reliable offsite and onsite ac power, experience has shown that there are prac-tical limitations in ensuring the reliability of offsite and onsite emergency ac power systems. Potential vulnerabilities to common cause failures associated with design, operational, and environmental factors can affect ac power system reliability. For example, if potential common cause failures of emergency die-sel generators exist (e.g., in service-water or dc power support systems), then                                                          j the estimated core damage frequency from station blackout events can increase significantly. Also, even though recent data indicate that the average emergency diesel generator reliability has improved slightly since 1976, these data also show that diesel generator failure rates during unplanned demand (e.g., following a loss of offsite power) were higher than that during surveillance tests.
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The estimated frequency of core damage from station blackout events is directly proportional to the frequency of the initiating event. Estimates of station blackout frequencies for this USI were based on actual operational experience with credit given for trends showing a reduction in the frequency of losses of offsite power resulting from plant-centered events. This is assumed to be a realistic indicator of future performance. An argument can be made that the future performance will be better than the past. For example, when problems with the offsite power grid arise, they are fixed and, therefore, grid reli-ability should improve. On the other hand, grid power failures may become more frequent because fewer plants are being built, and more power is being trans-mitted among regions, thus placing greater stress on transmission lines.
A number of foreign countries, including France, Britain, Sweden, Germany and Belgium, have taken steps to reduce the risk from station blackout events.
These steps include adding design features to enhance the capability of the plant to cope with a station blackout for a substantial period of time and/or adding redundant and diverse emergency ac power sources.
The factors discussed above support the determination that additional defense in-depth provided by the ability of a plant to cope with station blackout for a specific duration would provide substantial increase in the overall protection                                                                                                  ;
of the public health and safety, and the direct and indirect costs of implemen-tation are justified in view of this increased protection. The Commission has l
considered how this backfit should be prioritized and scheduled in light of other                                                                                                l regulatory activities ongoing at operating nuclear power plants. Station black-out warrants a high priority ranking based on both its status as an " unresolved j
safety issue" and the results and conclusions reached in resolving this issue.                                                                                                    !
As noted in the implementation section of the rule ($50.63(d)), the schedule for equipment modification (if needed to meet the requirements of the rule) shall be mutually agreed upon by the licensee and NRC. Modifications that cannot be scheduled for completion within two years after NRC accepts the licensee's speci-fied station blackout duration must be justified by the licensee.
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l                                                    1 Analysis of 50.109(c) Factors
: 1. Statement of the specific objectives that the backfit is designed to achieve The NRC staff has completed a review and evaluation of information developed over the past six years on Unresolved Safety Issue (USI) A-44, Station Black-out. As a result of these efforts, the NRC is amending 10 CFR Part 50 by adding a new S 50.63, " Station Blackout," and adding a new paragraph (e) to General Design Criterion (GDC) 17, " Electric Power Systems," in Appendix A.
The objective of the station blackout rule is to reduce the risk of severe accidents associated with station blackout by making station blackout a relatively small contributor to total core damage frequency. Specifically, the rule requires all light-water-cooled nuclear power plants to be able to cope with a station blackout for a specified duration and to have procedures and training for such an event. A regulatory guide, to be issued along with the rule, provides an acceptable method to determine the station blackout duration for each plant. The duration is to be determined for each plant based on a comparison of the individual plant design with factors that have been identified as the main contributors to risk of core melt resulting from station blackout. These factors are (1) the redundancy of onsite emergency ac power sources, (2) the reliability of onsite emergency ac power sources, (3) the frequency of loss of offsite power, and (4) the probable time needed to restore offsite power.
: 2. General description of the activity required by the licensee or applicant in order to complete the backfit In order to comply with the resolution of USI A-44, licensees will be required to --
Maintain the reliability of onsite emergency ac power sources at or                                      I above specified acceptable reliability levels.                                                            l
 
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Develop procedures and training'to restore ac power using nearby power sources if the emergency ac power system and the normal.offsite power sources are unavailable.
Determine the duration'that the plant should be able to withstand a station blackout based on the factors specified in paragraph'(e) of GDC 17.
Evaluate the plant's actual capability to withstand and recover from a station blackout. This evaluation includes:
Verifying the adequacy of station battery power, condensate storage tank capacity, and plant / instrument air for the station blackout duration.
Verifying adequate reactor coolant pump seal integrity for the station blackout. duration so that seal leakage due to lack of seal cooling would not result in a sufficient primary system coolant inventory reduction to lose the ability to cool the core.
Verifying the operability of equipment needed to operate during a station blackout and the recovery from the blackout for environ-mental conditions associated with total loss of ac power (i.e.,
loss of heating, ventilation and air conditioning).
Depending on the plant's existing capability to cope with a station blackout, licensees may or may not need to backfit hardware modifica-                                                                  .
tions (e.g. , adding battery capacity) to comply with the rule. (See item 8 of this analysis for additional discussion.) Licensees will be required to have procedures and training to cope with and recover from a station blackout.                                                                                                                I
: 3. Potential change in the risk to the public from the accidental offsite release of radioactive material
 
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Implementation of the station blackout rule will result in an est.imated total risk reduction to the public ranging from 65,000 to 215,000 person-rems with a best estimate of about 145,000 person rem.
4.
Pot.ential impact on radiological exposure of facility employees For 100 operating reactors, the estimated total reduction in occupational exposure resulting from reduced core damage frequencies and associated post-accident cleanup and repair activities is 1,500 person rem. No in-crease in occupational exposure is expected from operation and maintenance activities associated with the rule. Equipment additions and modifica-tions contemplated do not require work in and around thereactor coolant system and therefore are not expected to result in significant radiation exposure.
5.
Installation and continuing costs associated with'the backfit, including the cost of facility downtime or the cost of construction delay For 100 operating reactors, the total estimated cost associated with the station blackout rule ranges from $42 to $94 million with a best estimate of $60 million. This estimate breaks down as follows:
Estimated number of  Estimated total cost (million dollars)
Activity                                reactors    Best        High    Low Assess plant's capability to 100                      25          40        20 cope with station blackout Develop procedures and                    100          10          15        5 training Improve diesel generator                  10            2.5        4        1. 5 reliability l
Requalify diesel generator                    2            5. 5      11          2.5 Install hardware to increase                27          17          24        13 plantps capability to cope with station blackout Totals                                  60          94      42 L                                                                                                                          l
 
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The potential safety impact of changes in plant or operational complexity, including the relationship to proposed and existing regulatory requirements The rule. requiring plants to be able to cope with a station blackout should not add to plant or operational complexity. The station blackout rule is closely related to several NRC generic programs and proposed and existing regulatory requirements as the following discussion indicates.
Generic Issue B-56, Diesel Generator Reliability The resolution of USI A-44 includes a regulatory guide on station blackout that specifies the following guidance on diesel generator reliability (Task SI 501-4, Sections C1.1. and 2):
The reliable operation of the onsite emergency ac power sources should be ensured by a reliability program, designed to monitor and maintain the reliability of each power source over time at a specified acceptable level and to improve the reliability if that level is not achieved. The reliability program should include surveillance testing, target values for maximum failure rate, and a maintenance program. Surveillance testing should monitor perfor-mance so that if the actual failure rate exceeds the target level, corrective actions can be taken.
The maximum emergency diesel generator failure rate for each diesel generator should be maintained at 0.05 failure per demand. However, for plants having an emergency ac power system [ configuration re-quiring two-out-of-three diesel generators or having a total of            {
two diesel generators shared between two units at a site], the              i i
emergency diesel generator failure rate for each diesel generator          i should be maintained at 0.025 failure per demand or less.
The resolution of B-56 will provide specific guidance for use by the staff or industry to review the adequacy of diesel generator reliability programs consistent with the resolution of USI A-44.
Generic Issue 23, Reactor Coolant Pump Seal Failures Reactor coolant pump (RCP) seal integrity is necessary for maintaining pri-mary system inventory during station blackout conditions. The estimates l
 
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of core damage frequency for station blackout events for USI A-44 assumed that RCP seals would leak at a rate of 20 gallons per minute. Results.of analyses performed for GI 23 will provide the information necessary to determine RCP seal behavior during a station blackout. Should this analysis conclude that there is a high probability that the RCP seals would not      '
leak excessively during a station blackout, then no modifications would be required. If there is a significant probability that RCP seals can leak at rates substantially higher than 20 gallons per minute, then modifications such as an ac-independent RCP seal cooling system 'may be necessary to resolve GI 23. Any proposed backfit resulting from the resolution of GI 23 would need to comply with the backfit rule.
USI A-45, Shutdown Decay Heat Removal Requirements The overall objective of USI A-45 is to evaluate the adequacy of current licensing design requirements to ensure that the nuclear power plants do not pose an unacceptable risk as a result of failure to remove shutdown decay heat. The study includes an assessment of alternative means of shut-down decay heat removal and of diverse " dedicated" systems for this purpose.
Results will include proposed recommendations regarding the desirability of, and possible design requirements for, improvements in existing systems or an alternative dedicated decay heat removal method.
The USI A-44 concern for maintaining adequate core cooling under station blackout conditions can be considered a subset of the overall A-45 issue.
However, there are significant differences in scope between these two issues.
USI A-44 deals with the probability of loss of ac power, the capability to remove decay heat using systems that do not require ac power, and the abil-ity to restore ac power in a timely manner. USI A-45 deals with the overall reliability of the decay heat removal function in terms of response to transients, small break loss-of-coolant accidents, and special emergencies such as fires, floods, seismic events, and sabotage.
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Although the recommendations that might result from the resolution of USI A-45 are not yet final, some could affect the station blackout capa-bility, while others would not. Recommendations that involve a new or improved decay heat removal system that is ac power dependent but that does not include its own dedicated ac power supply would have no effect on USI A-44. Recommendations that involve an additional ac-independent decay heat removal system would have a very modest effect of USI A-44.
Recommendations that involve an additional decay heat removal system with.its own ac power supply would have a significant effect on USI A-44.
Such a new additional system would receive the appropriate credit within the USI A-44 resolution by either changing the emergency ac power config-uration group or providing the ability to cope with a station blackout for an extended period of time. Well before plant modifications, if any, will be implemented to comply with the station blackout rule, the proposed tech-nical resolution of USI A-45 will be published for public comment. Those plants needing hardware modifications for station blackout could be reeval-uated before any actual modifications are made so that any contemplated design changes resulting from the resolution of USI A-45 can be considered at the same time.
Generic Issue A-30, Adequacy of Safety-Related DC Power Supply The analysis performed for USI A-44 assumed that a high level of dc power system reliability would be maintained so that (1) dc power system failures would not be a significant contributor to losses of all ac power and (2) should a station blackout occur, the probability of immediate dc power system failure would be low. Whereas Generic Issue A-30 focuses on enhanc-ing battery reliability, the resolution of USI A-44 is aimed at assuring adequate station battery capacity in the event of a station blackout of a specified duration. Therefore, these two issues are consistent and compatible.
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L Fire Protection Program 10 CFR 50.48 states that each operating nuclear power plant shall have a fire protection plan that satisfies GDC 3.      The fire protection features required to satisfy GDC 3 are specified in Appendix R to 10 CFR 50. They include certain provisions regarding alternative and dedicated shutdown capability.
To meet these provisions, some licensees have added, or plan to add, improved capability to restore power from offsite sources or onsite diesels for the shutdown system. A few plants have installed a safe shut-down facility for fire protection that includes a charging pump powered by its own independent ac power source.
In the event of a station blackout, this system can provide makeup capability to the primary coolant system as well as reactor coolant pump seal cooling. This could be a significant benefit in terms of enhancing the ability of a plant to cope with a station blackout.
Plants that have added equipment to achieve alternate safe shut-down in order to meet Appendix R requirements could take credit for that equipment, if available, for coping with a station blackout event.
7.
The estimated resource burden on the NRC associated with the backfit and the availability of such resources The estimated total cost for NRC review of industry submittals required by the station blackout rule is $1.5 million based on :,ubmittals for 100 reactors and an estimated average of 175 person-hours per reactor.              '
8.
The potential impact of differences in facility type, design, or age on the relevancy and practicality of the backfit The station blackout rule applies to all pressurized water reactors and boiling water reactors.
However, in determining an acceptable station blackout coping capability for each plant, differences in plant charac-teristics relating to ac power reliability (e.g. , number of emergency diesel generators, the reliability of the offsite and onsite emergency ac I
 
-,ria power systems) could result in different acceptable coping capabilities.
For example, plants with an already low risk from station blackout because of multiple, highly reliable ac power sources are required to withstand a station blackout for a relatively short period of time; and few, if any, hardware backfits would be required as a result of the rule. Plants with currently higher risk from station blackout are required to withstand somewhat longer duration blackouts; and, depending on their existing capability, may need some modifications to achieve the longer station                                                                                                                                          j blackout capability.
: 9. Whether the backfit is interim or final and, if interim, the justification for imposing the backfit on an interim basis The station blackout rule is the final resolution of USI A-44; it is not an interim measure.
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