ML20058L996
| ML20058L996 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 08/06/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20058K167 | List: |
| References | |
| NUDOCS 9008090166 | |
| Download: ML20058L996 (10) | |
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i UMTED STATES 8 NUCLEAR REGULATORY COMMISSION
/s nAsmworow, o, c. ms ENCLOSURE l' k ...* y L
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION' RELATING TO STATION BLACK 0UT l
COMMONWEALTH EDISON COMPANY BRAIDWOOD STATION. UNIT NOS. 1 AND 2 DOCKET N05. STN 50-456 AND STN 50-457 L 1.0' INTRODUCTION
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l L On July 21, 1988, the Code of Federal Regulations 10 CFR Part 50, was amended 1 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 SB0 of specified duration, requires licensees to submit information as defined in 10 CFR Part 50.63 and requires licensees to provide a plan and schedule for
-r con-formance to the SB0 rule. The SB0 rule further requires that the baseline '
l assumptions, anelysis and related information be available for NRC review. - '
Guidance for conformance to the 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, "Su i
dated December 27,1989(pplementalQuestions/Answersand.MajorAssumptions,"
issued to the industry by NUMARC January 4,1990).
TofacilitatatheNRCstaff's(hereafterreferredtoasstaff)reviewof 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 Alter-nate AC (AAC) power source and the other format is for use by plants proposing an AC independent response. 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 .
- ihe results and maintain docu-mentation that supports the stated results.
Compliance to the SB0 rule is veri-fied by a review of the licensee's submit- )
tal, an audit review of the supporting documentation as deemed necessary, )
- and possible. followup NRC inspections to en-sure that the licensee has imple- I mented the appropriate hardware and/or procedure modifications that will be a required to comply with the SB0 rule.
l The Braidwood Station has proposed using existing emergency diesel generators i (EDGs)asanAACpowersourceandhassubmitteditsresponseintheapplicable !
generic response format. The licensee's original response was provided by a j l
- Nuclear Management and Resources Council, Inc. f 9008090166 900806 PDR i P
ADOCK 05000454 '
PDC l
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' letter from M. H. Richter (Comonwealth Edison) to T. E. Murley (NRC) dated April 17, 1989. In addition, the licensee provided a response to the NUMARC 87-00 Supplemental Questions / Answers by a letter from M. H. Richter to T. E.
Murley dated March 29, 1990. The licensee respo .es were reviewed by Science Applicatior.sIntctnationalCorporation(SAIC)undercontracttotheNRC. The results of the review cre documented by a SAIC Technical Evaluation Report (TER),
SAIC-90/1043, "Braidwood Station Units 1 and 2 Station Blackout Evaluation,"
dated June 14,1990(AttachmentNo.1).
2.0 EVALUATION
' After reviewing the licensee's 580 submittal and the SAIC TER, the staff concurs ,
with the conclusions as identified in the SAIC TER (refer to Attachment No.1 for details of the review). Based on this review, the staff findings and recom-l mendations are summarized as follows.
2.1 Station Blackout Duration The licensee has calculated a minimum acce) table station blackout duration of <
4-hours based on an offsite power design claracteristic group of "P1," an-
~ Emergency AC configuration group "C," and an EDG reliability target of .95.
After reviewing the available information in the licensee's submittal RG 1.155 NUMARC87-00andSAIC' STER,thestaffagreeswiththelicensee'sevaluationof, a 4-hour SB0 coping duration based upon the offsite power design characteristic group being "P ". The offsite power design characteristic group of "P " was 3
selected based upon the assumption that Braidwood Station had not ex)effenced
.any grid-related events exceeding once per 20 years. However, for tie reasons discussed in the SAIC TER, this assumption cannot be confirmed. If the expected frequency of grid-related events at Braidwood Station exceeds once per 20 years, it would be classified as offsite power design group characteristic group "P~" instead of "P " As a result, the Braidwood Station coping duration I
wouldch$ngefroma4-hobr.to 8-hour or 16-hour depending upon the EDG reli-l- ability target selected. j l
Recommendation: The licensee should verify that the grid related events that '
have occurred at Braidwood Station since its commercial operation date are not symptomatic of underlying or growing grid instability, and are hot indicative of a loss-of-offsite power frequency greater than once in 20 years.
2.2 Alterna'et AC (AAC) Power Source The licensee has proposed an AAC power source to operate systems necessary for the required SB0 coping duration and recovery therefrom. I 2.2.1 General Staff Position on AAC Power Sources The definition in 10 CFR $50.2, RG 1.155 and NUMARC 87-00, define AAC power source in terms of four attributes: (1)connectionstotheoffsiteorthe onsite AC power systems, (2) minimum potential for common cause failure with
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l offsite power or the onsite emergency AC power sourcos, (3) timely availa-bility, and (4) required capacity and reliability. More specifically, in regard to the fourth attribute, the SB0 rule reads as follows:
'(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 shut-dM<n(non-designbasisaccident)."
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 SB0 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, simultan-eously, both safety trains of normal 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 powering all (or any) normal safety train related safe shutdown equipment; but, it is capable of powering specific equipment that, in conjunction with extensive nanual operator actions both inside and outside of the control room, is critical-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 SB0 duration, or battery charging capability was provided by the AAC source.
7.2.1.1 EDGs Used as AAC Power Sources The guidance on the use of existing emergency diesel generators (EDGs) as AAC power sources is documented in the station blackout rule 10 CFR 650.63, RG 1.155, Puntion C.3.3.5, and NUMARC 87-00 (Section 2.3.1(3)). This guidance is further explained in NUMARC 87-00 Supplemental Questions and Answers dated December 27, 1989, under questions 3.4 and B.3. The station blackout rule states:
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"At multi-unit sites where the combination of emergency ac power '
sources exceeds the m,inimum redundancy requirements for safe shut-down (non-DBA) of all units, the remaining emergency ac power sources may be used as alternate ac power sources provided they meet the applicable requirements."
The rule statement requires minimum redundancy. This means that in order to qualif l
-(NBO) y as an AAC source, there must be an EDG available in the non-blacko imum EDG redundanc of offsite power (yLOOP req) event.uirement Thus, thefor EDG's powering in aa two normal unit safe shutdown site with two for a loss dedicated EDG's per unit would not qualify as AAC sources because the two EDGs per unit just meet the minimum redundancy requirement, i.e., there is no excess- !
EDG.
- However, there are some plants at two unit sites which just meet minimum re-dundancy but where each EDG is of sufficient capacity to fully power all the normal LOOP loads of the NB0 unit, and also has sufficient excess capacity for powering the required safe shutdown loads of the 5B0 unit. In recogni-l tion of the existence of this type of situation, the staff has interpreted the l
l excess EDG redundancy requirement of the SB0 rule to allow EDGs just mecting the minimum EDG redundancy requirements, to qualify as AAC sources on the basis of l excess capacity, provided the other applicable requirements for AAC sources are l
also met.
The NRC's basic position on the use of EDGs as AAC nwer sources on the basis of excess capacity is that such excess ca >acity should not be attained by load shedding in the non-blackout (NBO) unit w11ch results in a degradation of.its normally available safe shutdown capability for the LOOP condition. Any actions that would add to the burden of operators that are already in a high stress environment, such as load. switching or disablement of information readouts or alarms in the control room, are considered to be a degradation of normal safe shutdown capability for LOOP in the NB0 unit. The staff position is, therefore, that the normal equi) ment com311 ment should remain available with adequata EDG capacity for use s1ould it become necessary. The HBO unit should have the capability for hot shutdown / hot standby forced cooling, cooldown and depressurization as required. While additional events are not explicitly being postulated,-it is not prudent to diminish the capability of the NB0 unit to mitigate problems should they arise. It is not in the interest of safety to reduce the capability to handle various eventualities in one unit for the purpose of meeting the SB0 rule in another unit. Each unit must meet the SB0 rule on its own merits without reducing another unit's capability to respond to
! its own potential problems.
Therefore, a multi-unit site with the dedicated EDGs just meeting the minimum redundancy requirement but not having the excess capacity defined above for qualifying as an AAC source does not meet the SB0 rule AAC source option requirements. Further measures are required such as a separate AAC source or a coping analysis which shows the plant can cope with and recover from SB0 for the required duration.
2.2.1.2 Connectability of AAC Power Sources The basic criteria governing the connectability of an AAC power source are contained 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); 10 CFR 50.63 (SB0 should not assume a concurrent single failure or design basis accident); and in Appendix A of 10 CFR 50 (the single failure criterion and the independence requirements apply to the NB0 unit). Therefore, in a one unit site, as a minimum, an AAC source need only be connectable to one set of safe shutdown equipment, regardless of whether that equipment is part of a safety train or not, or whether the AAC source is an excess redundancy EDG, or an independent power source.
However, at a two (or more) unit site where the EDGs meet the AAC source excess redundancy criterion, one intertie circuit between units is acceptable provided it is separately connectable to each safety (EDG) bus in both units. This follows from the application of the above criteria and the assumptions that must.
be taken that an SB0 can occur in either unit, and that the single failure in the HBO unit can be on either one of its EDGs or on its respective safety bus.
2.2.2 Proposed AAC Power Source The Braidwood Station is a two unit site with two dedicated EDGs per unit.
The proposed AAC power source for the blacked out unit is a cross-tied EDG from the NB0 unit. There are two manual cross-ties between the units. One manual' crosstie exists between Division 11 of Unit I and Division 21 of Unit 2. The second manual cross-tie exists between Division 12 of Unit 1 and Division 22 of Unit 2. .
The licensee's submittal states that the EDG/AAC source is available within 10 minutes of the onset of the SB0 event, and has sufficient capability to provide power for safe shutdown of both units for a 4-hour SB0 duration. The licensee's submittal did not specifically denote any equipment to be load shed in order to achieve this EDG capability. '
However, during a teleconference on February 26, 1990, the licensee stated that the auxiliary feedwater (AFW) motor driven pump and the component cooling water pumps will not be powered from the EDG of the NB0 unit in order'to conserve cap-acity in the FDG for qualifying it as an AAC for the blacked-out unit. In addition, the licensee stated that a load management scheme will be implemented in order to power the needed equipment for safe shutdown operation of the blacked-out unit and NB0 unit. The staff has reviewed the licensees proposed actions and find that they do not conform to the guidance on the use of exist-ing EDGs on the basis of excess capacity as an AAC power source as documented in10CFR550.63;RG1.155,PositionC.3.3.5;NUMARC87-00,Section2.3.1(3);
and NUMARC 87-00, Supplemental Questions and Answers, dated December 27, 1989.
After reviewing the SAIC TER and the licensee's proposed actions for crediting existing NB0 units EDGs as an AAC source, the staff has determined that the pro-posed AAC source does not meet the requirements of 10 CFR 550.63.
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Recomendation: The licensee should undertake further measures such as pro-viding a separate AAC power source or a coping analysis which shows that the plant can cope with, and recover from, an 580 for the required duration inde-pendent of AC power.
2.3 Station Blackout Coping Capability l 2.3.1 Condensate Inventory for Decay Heat Removal The sisanaly(CST) and shown that tosufficient providewater is available in thelicensee condensatehas perforined decay heat removal for storage tank SB0 duration.
After reviewing the licensee's submittal and the SAIC TER, the staff agrees l with the licensee's assessment that the plant has adequate condensate inventory j for a 4-hour SB0 duration. In addition, the eveess inventory available in the CST is available for 580 recovery.
2.3.2 Class 1E Battery Capacity The licensee did not submit battery capacity assessment based on the assumptions that: (1) the AAC ,
SB0 event, and (2) the powerAAC source is available within 10 minutes of the onset of an battery chargers. However, power source will power one division of Class 1Ebas i
AAC power source does not meet the requirements of 10 CFR 550.63. Therefore, the staff does not agree with the licensec's conclusion that battery assessment is not required.
Recommendation: The licensee is required'to conduct an assessment to verify that the battery has suffi-ient capacity to power s11 normal battery-backed monitoring I and electrical systems and controls for the required SB0 duration and recovery therefrom, or provide battery charging from an independent AAC power source.
2.3.3 Compressed Air l
The licensee did not address the compressed air system in his submittal on the l basis that a 10 minute AAC power source would be available. In_the telephone l
conversation on February 26, 1990, the licensee stated that no air operated .
valves will be relied upon to cope with the 580. The auxiliary feedwater (AFW) valves, atmospheric dump valves (ADYs) and main steam safety relief valves (MSSVs) are relied upon for decay heat removal during an SB0. TheADV's(a totaloffour,twoADY'sperdivision)areelectro-hydraulicallyoperatedvalves with manual backup capability. ,
After reviewing the licensee's proposal and the SAIC TER, the staff agrees with i SAIC's asses: ment that the licensee does not have an AAC source that meets the requirements of the SB0 rule (see Section 2.2.2 above) for powering the ADVs needed for decay heat reri. oval. 3
7 Reconnendation: The licensee should provide an acce) table AAC source that 1 meets the sso rule and provides means for powerirg tie ADV's from the control ,
, room, or provide alternate means for achieving decay heat removal during an '
l SB0 event. Whatever method is chosen, the licensee should simulate the proposed ;
procedure and provide the appropriate operator training to ensure the decay heat '
removal can ba adequately maintained.
2.3.4 Effects of Loss of Ventilation ,
The licensee stated in their $80 submittal, that the AAC power source will power theHVACsystemsthatservtthedominantareasofconcern(DAC). As a result, the licensee did not submit a loss of ventilation assessment. NUMARC 87 00 and >
NUMARC supplemental questions and answers (issued by NUMARC on January 4,1990) provide guidance to the licensee for the determination of DACs. The licenser ias referenced the NUMARC guidance and has stated that the HVAC systems that ,
serve the DACs will be powered by the AAC source. However, based on the staff assessmentandSAICTER,theproposedAACpowersource(i.e.,NB0EDGs)does .
i not meet the SB0 rule requirements. Unless a separate AAC source is pro-vided i which powers HVAC for the DACs, the SB0 equipment operability cannot be assured. ,
( Recommendation: The licensee should provide an independent AAC source that provides HVAC systems that serve the DACs or provide an analysis that verifies I
the operability of SB0 equipment will not be degraded for the required SB0 duration and recovery therefrom. '
2.3.5 Containment tsolation The licensee did not address the containment integrity in its submittal. The L. 14ensee stated that: (1) the AAC power tource is available within 10 minutes oftheonsetofanSB0 event,and(2)theAACpowersourcehassufficient i capacity and the capability to power the appropriate containment isolation l valves (CIVs). However, the proposed AAC power source does not qualify as an AAC power source. Unless a separate AAC power source is provided which provides power to the CIVs, the appropriate containment integrity cannot be assured during an SB0 event.
l Recommendation: The licensee should provide an acceptable AAC power source that l provides pcwer to the needed CIVs or provide alternate means to assure appro-
- priate
- vntainment integrity for the required SB0 duration.
2.3.6 Re'a ctb- Coolant Inventory i
- i. The licensee has stated that the AAC power source will power the necessary make-up systems to maintain adequate reactor coolant system (RCS) inventory to ensure that the core is covered for the required SB0 coping duration. However the l proposed AAC source does not qualify as AAC, and therefore, the licensees state-ment that AAC power source will power the necessary make-up systems to maintain I
adequate RCS inventory is not relevant.
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Recommendation: The licensee should provide an independent AAC power source of sutticient capacity and capability to provide power to the make-up systems to maintain adequate RCS Inventory or provide an assessment that there will be ade-quate RCS inventory to ensure continued core cooling for the required 580 dura-tion and recovery therefrom.
l 2,4 Procedures and Training The licensee has stated that the appropriate procedures have been reviewed and modified. Furthermore, the licensee has stated that the changes will meet the guidelines of NUMARC 87-00 and will be implemented one year after the issuance l of this SER.
Although the licensee has completed appropriate procederes, additional procedures mayberequireddepending)uponthelicensee'sproposedresolutionoftheAACpower source (seeSection2.2.2 issue.
The proposed procedure modifications indicated above were not reviewed but the
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staffexsectsthelicenseetomaintainandimplementtheseproceduresIncludingany others t1at may be required as part of the revised responst to ensure an appro-priate response to an SB0 event.
SB0 response were not specifically addressed by the licensee s submittal, th -
staff expects the licensee to implement the appropriate training to ensure an l effective response to the SBO.
2.5 Proposed Modifications 1
The licensee response to an SB0 does not include proposed modifir.ations to plant i equipment. However in view of the folloking staff positions as documented in thisSER,somemodificationsmayberequired: (1)theproposedAACsobrcedoes notmeettherequirementsof10CFR550.63,(2) the capacity for the nonnal battery-backed monitoring and electrical system controls in the control room has not been assessed for the required duration of an $30 and recovery there-from, (3) the operability of the 580 equipment located in the dominant area of ,
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' concern (control room, auxiliary electrical equipment room and miscellaneous equipment rooms, essential service water cubical, containment air recirculation fans, charging pump cubical, auxiliary feedwater pump area diesel generator i room, battery room, etc.) has not been assessed due to the, loss'of ventilation, I (4) appropriate assessment has not been done to ensure that there will be adequate RCS, inventory to maintain core cooling, and (5) appropriate containment integrity has not been assessed for all appropriate containment isolation valves.
Recommendation: The licensee should provide a full description including the nature and objectives of the equired modifications to meet the SB0 rule and a proposed schedule for implementation, l
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9 2.6 Quality Assurance (QA) and Technical Specifications (TS)
The licensee did not provide any information regarding QA programs and TS for SB0 equipment. However, the licensee has stated that all SB0 equipment is covered by the normal QA program and TS.
Furthermore, TS for the SB0 equipment are currently being considered generically by the NRC in the context of the Technical Specifi. cation Improvement ProJram and remains an open item at this time. However, the staff would expect taat the plant procedures will reflect the appropriate testing and surveillance "c'
requirements to ensure the operability of the necessary SB0 equip-ment. If the staff later detmnines that a TS regarding the 580 equipment is war-ranted, the licensee will be notified of the implementation requirements, i
Recommendation: The licensee should verify that the SB0 equioment is covered by an appropriate QA program consistent with the guidance of kG 1.155. Further, this evaluation should be documented at part of the package supporting the $80 rule response.
2.7 EDG Reliability Program The licensee Unit Nos. I and 2,stated is beingthat the EDG planned reliability consistent with theprogram forRG guidance of Braidwood 1.1 Station $
Section 1.2, and NUMARC 87-00, Appendix D. 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. If an EDG reliability program currently exists, the program should be evaluated and adjusted in accordance with RG 1.155.
2.8 Scope of Staff Review Thestationblackoutrule(10CFR50.63)requireslicenseestosubmitaresponse containing specifically defined information. It also requires utilities to have baseline assumptions analyses and related information used in their copingevaluationavailabletoNRC. Thestaffanditscontractor(SAIC)did not perform a detailed review of the proposed procedure :nodifications which are l scheduled for later implementation after the ecdifications that could result l from the staff recommendations in this SER. Thereicrs, based on our review of i
' the licensee SB0 submittal and FSAR, we have identified the following areas for focus in any follow-up inspection or assessment that may be undertaken by the NRC to further verify conformance with the SB0 rule.
- b. The preparation and the implementation of the plant SB0 procedures in accordance with RG 1.155, Position 3.4, and NUMARC 87-00, Section 4. 1
- c. The requirement for operator staffing and training to follow the identified actions in the SB0 procedures.
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l i d. Quality Assurance programs as applicable to SB0 equipment,
- e. Actions taken pertaining to the specific reconnendations noted in this SER.
Additional areas may be identified following staff review of licensee's revised response to the SB0 rule.
3.0 CONCLUSION
S Based on the staff's review of the licensee's submittals and the SAIC TER, the i staff finds that the Braidwood Station does not conform with the SB0 rule and l the guidance of R.G. 1.155, and therefore recommends that the licensee re-l evaluate the areas of concern that have been identified in this SER. Guidance for the licensee to review and implement the staff's recommendations is provided in RG 1.155, NUMARC 87-00 and the supplementary guidance (NUMARC 87-00, Supple-mentary Questions / Answers; NUKARC 87-00, Major Assumptions) dated December 27, 1989, which was issued to the industry by NUMARC on January 4,1990. The staff's concerns that are identified in this SER should be addressed by the licensee, and a revised response resubmitted to the NRC within 60 days. The licensee is expected to ensure that the baseline assumptions of NUMARC 87-00 are applicable to the Braidwood plant. Also, the licensee is exsected to document all analyses and relcted information, and verify that tiese are available for NRC review.
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