ML14184A796
| ML14184A796 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 02/04/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML14184A794 | List: |
| References | |
| NUDOCS 9102110202 | |
| Download: ML14184A796 (10) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY-EVALJATION-REPORT-BY-.THE-OFFICE -OF-NUCLEAR--REACTOR-REGULATION CAROLINA-POWER-&-LIGHT-COMPANY HI-8 -ROBINSON-STEAM-ELECTRIC-PLANTL-UNIT-N9. 2 STATION-9LACKOUT-EVALUATION DOCKET NO.-50-261
1.0 INTRODUCTION
On July 21, 1988, the Code of Federal Regulations 10 CFR Part 50 was amended to include a new section 50.63 entitled, "Loss of All Alternating Current Power,"
(Station Blackout). The station blackout (SBO) rule requires that each light water-cooled nuclear power plant be able to withstand and recover from an SBO of a specified duration. The SBO rule also requires licensees to submit informa tion as defined in part 50.63 and to provide a plan and schedule for conformance to the SBO rule. The SB0 rule further requires that the baseline assumptions, analysis and related information be available for NRC review. Guidance for conformance to the SBO rule is provided by (1) Regulatory Guide (RG) 1.155, Station Blackout, (2) NUMARC 87-00, Guidelines and Technical Bases for NUMARC Initiatives Addressing Station Blackout at Light Water Reactors, and (3) NUMARC 87-00 Supplemental Questions/Answers agd Major Assumptions dated December 27, 1989 (issued to the industry by NUMARC January 4, 1990).
To facilitate the Nuclear Regulatory Commission (NRC) staff's (hereafter referred to as staff) review of licensee responses to the SB0 rule, the staff endorsed two generic response formats. One response format is for use by plants proposing to use an Alternate AC (AAC) power source and the other format is for use by plants proposing an AC independent approach. The generic response formats provide the staff with a summary of the results from the licensee's analysis of the plant's SB0 coping capability. The licensees are expected to verify the accuracy of the results and maintain documentation that supports the stated results. Compliance to the SBO rule is verified by a review of the licensee's submittal, an audit review of the supporting documentation as deemed necessary, and possible follow-up NRC inspections to ensure that the licensee has implemented the appropriate hardware and/or procedure modifications that will be required to comply with the SB0 rule.
Carolina Power & Light (CP&L or the licensee) has proposed using an Appendix R dedicated safe shutdown (DSD) diesel generator as an AAC power source and has submitted its response in the applicable generic response format.
The licensee's initial response to the SBO rule was provided by a letter from M. A. McDuffie, dated March 3, 1989, to the NRC's Document Control Desk. A supplemental submittal in response to a NUMARC letter was submitted by a letter
- Nuclear Management and Resources Council, Inc.
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-2 from A. B. Cutter, dated March 30, 1990, to NRC's Document Control Desk. This was followed by a teleconference between representatives of the licensee and the NRC staff on August 8, 1990, and a follow-up response was provided by a letter from S. D. Floyd to A. S. Gill of the NRC, datedAugust 30, 1990. The licensee's responses were reviewed by Science Applications International Corp oration (SAIC) under contract to the NRC. The results of the review are docu nented by a SAIC Technical Evaluation Report (TER) SAIC-90/1379, "H. B. ROBINSON STEAM ELECTRIC PLANT,-UNIT 2, STATION BLACKOUT EVALUATTON," dated November 21, 1990, (Attachment 1 to this document).
2.0 EVALUATION After reviewing the licensee's submittals and the SAIC TER, the staff concurs with the conclusions as identified in the SAIC TER (refer to Attachment 1 for details). The staff findings and recommendations are summarized as follows:
2.1. Station Blackout Duration The licensee has calculated a minimum acceptable station blackout (SBO) duration of 8-hours based on a plant AC power design characteristic Group P2, an emer gency AC (EAC) power configuration Group C and a target Emergency Diesel Generator (EDG) reliability of 0.95. The Group C EAC classification is based on two EDGs nut credited as AAC power supplies, with one of the two EDGs required to operate safe shutdown equipment following a loss of offsite power.
The target EDG reliability was based on H.B. Robinson Steam Electric Plant, Unit No. 2 (Robinson 2), having an average EDG reliability greater than 0.95 over the last 100 demands. The P2 grouping is based on an independence of offsite power classification Group 13, a severe weather (SW) classification Group 2, and an extremely severe weather (ESW) classification Group 3.
The staff agrees with the licensee's determinations above except for the ESW classification. The staff has classified the ESW group for Robinson 2 as Group 4. However, this does not change the required coping duration for Robinson 2, and does not affect the licensee's coping analyses.
2.2 Alternate AC Power Source The licensee has proposed an existing Appendix R DSD diesel generator as an AAC power source to operate systems necessary for the required coping duration of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> and recovery therefrom.
2.2.1 General staff position on AAC power sources The definition in 10 CFR 50.2, RG.1.155, and NUMARC 87-00, defines the AAC power source in terms of four attributes (1) connections to the offsite or the onsite AC power systems, (2) minimum potential for common cause failure with the offsite power sources or the onsite emergency AC power sources, (3) timely availability, and (4) required capacity arid reliability. More specifically, in regard to the fourth attribute, the SBO rule reads as follows:
-3 (4) Has sufficient capacity and reliability for operation of all systems required for coping with station blackout and for the time required to bring and maintain the plant in safe shutdown (non-design basis accident).
In view of the variety of types, capacities, and capabilities of power sources proposed as AAC sources by various licensees, the staff has characterized pro posed AAC power sources as being either optimum, fully capable, or partially capable. This characterization, which relates only to the capacity attribute cited above, was necessary in order to facilitate the staff review of licensee responses to the SBO rule. It does not invalidate or revoke any of the require ments or guidance applicable to AAC power sources.
An optimum AAC power source design is one that is capable of powering simultane cusly both safety trains of rormal safe shutdown systems and equipment. Such a design, following actuation of the AAC source, would provide completely re dundant normal safe shutdown capability during an SBO and recovery therefrom from the main control room.
A fully capable AAC power source design is one that is capable of powering at least one complete safety train of normal safe shutdown systems and equipment.
This includes decay heat removal, battery charging,.HVAC (heating, ventilation and air conditioning), emergency lighting, and the associated controls and instrumentation. Thus, although redundant capability is not available, a fully capable AAC source would enable attainment of safe shutdown during an SBO and recovery therefrom from the main control room.
A minimally capable AAC power source design is one that is not capable of power ing all (or any) normal safety-train-related safe shutdown equipment; but it is capable of powering specific equipment that in conjunction with extensive manual operator actions both inside and outside of the control room is adequate for attaining safe shutdown during an SBO. Appendix R diesels proposed as an AAC source are examples of minimally capable AAC sources. With this design, oper ability of the main control room could not be assured unless the batteries were sized to operate for the SBO duration, or battery charging capability was pro vided by the AAC source.
2.2. 1.1 Connestabi4yty-.ef-AAC-owe-r-sources The basic criteria governing the connectability of an AAC power source are con tained in 10 CFR 50.2 (the AAC source should be connectable to, but normally not connected to, the offsite or onsite emergency AC power systems), and 10 CFR 50.63 (SBO should not assume a concurrent single failure or design basis accident on the blacked out unit). Therefore, as a minimum, an AAC source need only be connectable to one set of safe shutdown equipment regaroless.of whether that equipment is part of a safety train or not.
2.2.2 Propoed-AAC--pow-sar-ce The licensee has proposed using the Appendix R DSD diesel generator as the AAC power source for an SBO. The licensee has stated that the AAC power source is available within one hour from the 'onset of an SBO event, has sufficient capac-
-4 ity and capability to operate systems necessary for coping with an SBO for a duration of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, and has capability to bring and maintain the plant in safe shutaown. The licensee has also.statea that the AAC source meets the criteria of NUMARC 87-00, Appendix B.
The proposed AAC source is a 4.16 kV, 2450kW, self-contained diesel generator.
The licensee stated during the teleconference that the unit is tested weekly under a surveillance procedure and the reliability exceeds 95%. The licensee has stated that a test will be conducted to demonstrate the ability of the pro posed AAC source to power the SBO loads within one hour.
The staff assessment of the capacity and connectability of the proposed AAC source indicates that it fails into the minimally capable category as discussed in Section 2.2.1 above and meets the connectability requirements of Section 2.2.1.1 above. The proposed AAC source is normally in standby and does not power any safety-train-related safe shutdown buses.
However, in conjunction with some manual operator actions outside the control room, it is capable of powering specific loads (Appendix R loads) that are able to shut down the plant (hot standby) during an SBO.
Recommenda-tion:
The licensee, in accordance with their stated commitment, should test the AAC source to show that it can be started and connected to the safe shutdown loads within one hour. The test results should be included in the documentation supporting the SBO submittals that is to be maintained by the licensee.
2.3 Station-Blackout -Copin-Caab4Ii-ty The characteristics of the following plant systems and components were reviewed to assure that the systems have the availability, adequacy, and capability to achieve and maintain a safe shutdown and to recover from an SBO for an 8-hour coping duration.
2.3.1 Condensa1te-.ventory-for-decay-heat-removal1 The licensee's Technical Specifications require a minimum condensate storage tank level of 35,000 gallons. The licensee initially calculated that 28,600 gallons of water are required to cope with an SBO for one hour. A revised calculation indicated that 33,500 gallons (includes makeup of 4,900 gallons for shrinkage in steam generators) would be required. After the first hour, the AAC source can power one service water pump to provide an additional seven hours of cooling water to the steam generators through the steam driven auxil iary feedwater (AFW) pump via a service water system cross connection to the AFW system. After reviewing the licensee's response to the SBO rule, and the SAIC TER, the staff agrees with the TER that there is sufficient condensate water to cope with and recover from an SBO for the 8-hour coping duration.
2.3.2 Class4E-Battery-apacity The licensee stated that the Class 1E batteries have sufficient capacity to supply the SBO loads for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and that after 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> the battery chargers would be powered from MCC-5 which is supplied from the proposed AAC source.
-5 As discussed in the attached TER, a previous evaluation by the NRC showed that Battery B was not sufficiently sized for a one hour duty cycle, considering the design margin and aging factor. Also, the licensee indicated in their August 30, 1990, submittal that the B battery will not be charged by the AAC source.
Although one train of instrumentation and plant control is gencrally aaEquate to meet SBO guidance, the licensee needs to verify that this is sufficient for Robinson 2.
Reommendation: The licensee should reevaluate the adequacy of the B battery to power te necessary SBO loads for one hour considering the aging factor and an allowance for additional loads that may be added. Also, the licensee should confirm that the B battery is not needed after one hour for the SBO scenario and what steps, if any, will be taken to prevent the battery from discharging to the point where reverse polarity could occur. The results of the reevalua tioin ana confirmation should be included in the documentation supporting the SBO submittals that is to be maintained by the licensee.
2.3.3 Cempressed-air The licensee stated that the air-operated valves that are required to cope with an SBO are the steam generator power operated relief valves (PORVs); that when compressed air is not available, backup nitrogen gas supplies and hose connec tions for temporary hook-up can be provided to operate the PORVs with nitrogen; and that Procedure DSP-010 provides instructions for this temporary hookup.
The licensee also stated that after the AAC source is operational, one instru ment air compressor could be started to supply compressed air.
It is not clear whether the licensee intends to implement the nitrogen backup connections during an SB0, and what effort and time would be needed for these connections. Also, as noted in the attached TER, it is not clear from the Updated Final Safety Analysis Report that the air compressor can be made available during an SBO.
Recommendation:
The licensee should describe in detail what specific procedures woul1dbe usedto supply compressed air during an SBO and how the procedures will assure adequate air supply to the PORVs. This documentation should be included in the documentation supporting the SBO submittals that is to be maintained by the licensee.
2.3.4 Ef-fects-of-lss-of-ventilation In his initial submittal, which was based on a 4-hour coping duration, the li censee considered the steam-driven AFW pump and the control room as the only possible areas in which heatup could be a concern during an SBO, but concluded that they were not dominant areas of ccncern (DACs) because the AFW pump was not enclosed and because the calculated heat-up in the control room did not exceed 120 0F. In a subsequent submittal, based on an 8-hour coping duration, the licensee identified the battery room and cable spreading room as DACs, based on steady state temperatures of 145 0F and 121.5 0 F, respectively. However, the licensee determined that there was reasonable assurance of the operability of the equipment in these rooms based on NUMARC 87-00, Appendix F, and the, associated Appendix F Topical Report to NUMARC 87-00. Also, the licensee determined based on an 8-hour coping duration that the control room and steam driven AFW pump room were not DAC'S.
-6 During a subsequent teleconference, the staff advised the licensee that the NUMARC 87-00 methodology for heat-up calculations was not appropriate for an 8-hour coping duration. Therefore, the licensee repeated the calculations using a modified NUMARC methodology for heat-up calculations for events lasting longer than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. The revised temperature (T) values were provided as follows:
Room 0144 New-T CCW pump room 149 0F 151.1 0F Charging pump room 137 0F 137.7 0F Battery room 145 0F 147.1 0F Cable spread room 121.5 0F 122.2 0F Control room - no door open 126.9 0F 128.3 0F Control room - one door open 119.3 0F 120.7 0F Control room - two doors open 114.6 0F The above calculations for the control room assumed an initial control room air temperature before the SBO of 750 F. The staff considers this to be non-conser vative, because the licensee's response to the SBO rule does not provide infor mation as to whether the control room heat-up calculations were performed using an initial temperature corresponding to the maximum bounding design temperature of the control room, including Technical Specification temperature limits.
Also, as noted in the attached TER, the staff considers the above calculations (New T) as non-conservative because a linear temperature rise is assumed across the wall thickness.
Such an assumption for the concrete wall is not realistic because the inner wall surface will heat up more rapidly than the outer surface (due to the time lag of heat transfer across the wall) and, there fore, would not absorb as much heat from the air mass as is assumed by the non conservative calculation.
The licensee analyzed the heat-up within containment assuming a 300 gpm pump seal leakage rate and using Figure 32 of Westinghouse Owners Group Background Document ECA-0.0 that enviromnentally the licensee stated is applicable to Robinson 2. The resulting heat-up to 155 0F, assun.irn an T1sitial temperature of 120 0 F, was well below the 219'F "Loss of All AC Power", qualified (EQ) temperature.
The licensee did not state that their procedures would include a provision to open the cabinet doors in the control room.
Recommendations: (1) The licensee should re-evaluate the temperature rises in the above identified areas, other than containment, using conservative initial temperatures, corresponding to the maximum bounding design temperatures includ ing the Technical Specification temperature limits, and confirm that there is a reasonable assurance of SBO equipment operability in these areas during an 8-hour SBO, and (2) the licensee should include in their SBO procedures a provi sion to open the control room cabinet doors within 30 minutes after the onset of an 580. These evaluations and verifications and any resulting modification should be included in the documentation supporting the SBO submittals that is to be maintained by the licensee.
-7 2.3.5 Containment-i.solation The licensee stated in their submittal that the plant list of containment isola tion valves had been reviewed to verify that valves which must be capable of being closed or that must be operated (cycled) under SB0 conditions can be posi tioned (with indication) independent of the preferred and emergency onsite AC power supplies. The licensee identified two residual heat removal (RHR) pump suction valves of concern whose positions need to be verified. These valves (SI-860B and 8618) are required to be procedurally closed under all normal modes of plant operation. Access to these valves is controlled by a locked barrier under security control, and if both valves were inadvertently left open, the refueling water storage tark would begin to drain into containment. The con tainment water level is checked each shift independently by two individuals.
However, the licensee has not provided information on how he intends to detect the missposition of these RHR system valves during power operation to ensure that appropriate containment integrity can be maintained during the 8-hour SB0 duration.
Recommendation: The licensee should provide a means to detect the misposition or SI-80B Sor SI-867B during normal operation and provide for corresponding corrective measures to maintain appropriate containment integrity during the 8-hour SB0 duration. The evaluation and proposed actions addressing the above should be included in the documentation supporting the SBO submittal that is to be maintained by the licensee.
2.3.6 Reaster-cooln-inventory The licensee asserted that an' evaluation has been performed to assess the ade quacy of the reactor coolant inventory, and that no makeup systems, other than those available under SB0 conditions, are required to prevent core uncovery for the 8-hour coping duration. The staff agrees with the SAIC TEP that the assumed RCS leakage of 100 gpm (2F gpm per reactor coolant pump and 25 gpm for Technical Specification allowable RCS leakage) will not result in core uncovery during an 8-hour SBO event, if a 77 gpm charging pump is kept operating when the AAC power source is established 'within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> following the SBO. This staff conclusion is based on a fact that with a charging pump continuously operating for 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> after its initiation from the AAC power source, an estimated total loss of RCS inventory is less than 17,000 gallons and thus the RCS will have more than a 53,000 gallon inventory at the end of the SB0 event.
The reactor coolant inventory evaluation, as discussed above, was based on the guidance provided in NUMARC 87-00 of 25 gpm per reactor coolant pump (RCP) seal leakage for pressurized water reactors. The 25 gpm value was agreed to between NUMARC and the staff pending resolution of Generic Issue (GI 23. If the final resolution of GI-23 defines higher RCP leakage rates than assumed for this evaluation, the licensee should be aware of the potential impact of this resolution on their analyses and actions addressing conformance to the SBO rule.
2.4 Procedures_-nd-Traing The licensee stated that the AC power restoration, severe weather, and SBO response procedures have been or would be reviewed and modified to meet the guidelines of NUMARC 87-00, Section 4. Also, procedural changes associated
-8 with any modifications that may be required for coping with an SBO will be im plemented to ensure that all the provisions of NUMARC 87-00, Section 7, are included.
The staff did not review the procedures or proposed procedure modifications.
The staff expects the licensee to maintain and implement these procedures, including any others that may be required, to ensure an appropriate response to an SB0 event. Although personnel training requirements for an SB0 response were not specifically addressed in the licensee's submittals, the staff expects the licensee to implement the appropriate training to ensure an effective response to an SO.
2.5 Preposed-Medifications The licensee stated that the Appendix R DSD system's conduits and electrical ducts, and a battery storage cabinet are external to the existing buildings-arnd will require additional supports to avoid exceeding the allowable stresses under the Uniform Building Code wind loads. Also, some structural changes will be required to the 4160 V switchgear room.
Recommendation:
The licensee should include a full description of the nature and objective of all modifications in the documentation supporting the SB0 submittal that is to be maintained by the licensee.
2.6 Qual4ty-Assurance-ad-Technca1 -Speci-f4ca-tions During the telephone conversation of August 8, 1990, the licensee stated that all the SBO equipment is covered by NRC approved QA programs (10 CFR Part 50, Appendix B or Appendix R).
The Technical Specificatiors tr the SBC equipment are currently being considered generically by the NRC in the context of the Technical Specification Improvement Program and remain an open item at this time. However, the staff would expect that the plant procedures will reflect the appropriate testing and surveillance requirements to ensure the operability of the necessary SBO equipment. If the staff later determines that TS regarding the SBO equipment is warranted, the licensee will be notified of the implementation requirements.
2.7 EDG-Reliability-Program The licensee stated that it is their understanding that the target reliability of 0.95 for the EDGs is to be maintained consistent with the final resolution of GI B-56. The submittals did not specifically address the commitment to implement an EDG reliability program to conform to the guidance of RG 1.155, Position 1.2.
Recommendat44n. It is the staff's position that an EDG reliability program should be developed in accordance with the guidance of RG 1.155, Section 1.2.
Confirmation that such a program is in place or will be implemented should be included in the documentation supporting the SBO submittal that is to be main tained by the licensee.
-9 2.8 Scope-of--Staff-Review The SBO rule (10 CFR 50.63) requires licensees to submit a response containing specifically defined information. It also requires utilities "... to have baseline assumptions, analyses, and related information used in their coping evaluations available for NRC review."
The staff and its contractor (SAIC) did not perform a detailed review of the proposed hardware and procedural modifica tions which are schedule for later implementation. However, based on our review of the licensee's supporting documentation, we have identified the following areas for focus in any follow-up inspection or assessment that may be undertaken by the NRC to verify conformance with the SRO rule. (Additional items may be added as a result of the staff review of the actions taken.by the licensee in response to this SER).
These areas are:
- a. Hardware and procedural modifications,
- b. SBO procedures in accordance with R.G. 1.155, Position 3.4, and NUMARC 87-00, Section 4,
- c. Operator staffing and training to follow the identified actions in the procedures,
- e. Equipment and components required to cope with an SBO are incorporated in a QA program that meets the guidance of RG 1.155, Appendix A, and
- f. Actions taken pertaining to the specific recommendations noted in the SER.
3.0
SUMMARY
-AND-CONCLUSIONS The staff has reviewed the licensee's responses to the SBO rule (10 CFR 50.63) and the Technical Evaluation Report prepared by the staff's consultant, SAIC.
Based on our review, additional analyses and verifications as described in the recommendations provided in this SER need to be completed. These include (1) a test of the proposed AAC power source (the DSD system) to demonstrate that it can power the necessary shutdown loads withir one hour, (2) a calculation and verification that there is adequate battery capacity to power the needed control room instrumentation and controls, calculations and verifications that there are reasonable assurances of SBO equipment operability under heatup conditions in the identified areas of concern using proper initial temperatures, (3) descriptions of the specific procedures for assuring that adequate air is maintained to operate the PORVs, (4) verification that at least one RHR line suction valve can be detected for misposition and corrective measure taken, and (5) a commitment that an EDG reliability program will be developed in accordance with the guidance of RG 1.155 Section 1.2. The licensee should maintain these analyses and confirmations in the documentation supporting the SBO submittal, and maintain this documentation for further inspection and assessment as may be undertaken by the NRC to verify conformance with the SBO rule.
-10 Based on our review of the submittals. The staff finds the licensee's responses and proposed method of dealing with an SBO to be in conformance with the SBO rule contingent upon receipt of confirmation from the licensee within 30 days that the recommendations documented in this SER will be implemented. The schedule for implementation should also be provided in accordance with 10 CFR 50.63(c)(4).
Dated:
PrInc Ce-_ontributor A. loalston