ML20059F337
| ML20059F337 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/29/1990 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20058K974 | List: |
| References | |
| NUDOCS 9009110183 | |
| Download: ML20059F337 (14) | |
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'l ENCLOSURE 1 w
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MILLSTONE 1 STATION
- STATION BLACKOUT SAFETY EVALUATION REPORT 1.0l INTRODUCTION
On July 21, 1988, the Code of Federal Regulations 10CFR Part 50, was amended to w
include a new Section 50.63, entitled " Loss of All Alternating Current Power,"
(StationBlackout)..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 con-formance to-the SB0 rule. The SB0 rule further requires that the baseline assumptions, analysis and related information be available for NRC review.
Guidance for conformance to the rule is provided by (1) Regulatory Guide (RG)
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J.155, Station Blackout, (2) NUMARC 87-00, Guidelines and Technical Bases for HUMARC Initiatives Addressing Station Blackout at Light Water Reactors', and
-(3)NUMARC87-00SupplementalQuestions/AnswersandMajorAssumptionsdated D'ecember 27,1989-(issued to the industry by NUMARC January 4,1990).
To' facilitate the NRC staff c '.nereafter referred to as staff) review of licensee responses to the SB0 rule,
'a staff endorsed 2 generic response formats. One response, format is for use by plants proposing to use an Alternate AC (AAC) power 4
tource and the other format is for=use by plants proposing an AC independent response. The generic response formats provide the staff with a summary 'f the o
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 docu-
' mentation that supports the stated results. Compliance to the SB0 rule is veri-fied by-a review of the licensee's submittal, an audit review of the supporting documentation as deemed necessary, and possible followup NRC inspections to en-sure that the licensee has implemented the appropriate hardware and/or procedure modifications that will be required to comply with the SB0 rulo.
- The M111stor.e 1 Station has proposed using Millstone Unit 2 existing emergency diesel generators (non-blacked out emergency ac power sources) as an AAC power
- Nuclear Management and Resources Council, Inc.
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[j source and has submitted its response in the applicable generic response format.
The licensee's original response was provided by a letter from E. J. Mroczka
,y (NortheastUtilities) tot.E.Murley(NRC)datedApril17,andMay 30, 1989.
In addition, the~ licensee provided a response to the NUMARC 87-00 Supplemental Questions / Answers by a letter from E. J. Mroczka to T. E. Murley dated March 30, 19 7.The licensee responses were reviewed by Science. Applications International
- Cor, ation(SAIC)undercontracttotheNRC. Millstone I was one of the plants selected by the NRC for a site audit review. The site audit was performed by a-joint NRC/SAIC team headed by a NRC staff member on July 18-21, 1989.
The re-suits of the review and site audit are documented by a SAIC Technical Evaluation Report (TER),SAIC-89/1154,"MillstoneNuclearPowerStation-UnitNo.1, Station Blackout Evaluation," dated July 18,1990(AttachmentNo.1).
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- 2.0 EVALUATION:
After reviewing the licensee's SB0 submittal and the SAIC TER and in considera-tion of the information obtained by the~NRC staff.during the site audit review, the staff concurs with the conclusions as identified in the SAIC TER (refer.to-L AttachmentNo.1fordetailsofthereview). Based on this review, the staff
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l findings and recomendations are summarized as follows.
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' 2.1 Station Blackout Duration l
L The licensee has calculated a minimum acceptable station blackout duration of 8
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L hours based on an offsite power design characteristic group of "P3", an Emergency AC (EAC) power configuration group "C", and an EAC power sources (one EDG and one L
gas turbine) reliability target of 0.975. The target reliability was based on Millstone Unit 1 EAC power sources having a unit average reliability greater
'than 0.95 over the last 100 demands. The P3 grouping is based on an independence of offsit'e power classification of Group "I3", a severe weather'(SW) classifica-tion of Group "5" and an extremely severe weather (ESW) classification of s
Group "5".
After reviewing the available information in the licensee's. 0mittal, RG 1.155, NUMARC 87-00 and SAIC's TER, the staff agrees with the licensee's evaluation of
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ia 8, hour SB0 coping duration.
2.2; Alternate AC (AAC) Power Source 2
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The licensee has proposed using the existing EDGs in non-blackout (NBO) Unit 2
'as an AAC' power source to operate systems necessary for the required SB0 coping duration and. recovery therefrom.
- 2. 2.1 -
General staff position on AAC power sources o
The definition in 10CFR 950.2, RG 1.155 and NUMARC 87-00 define AAC power source j
in terms of four attributes: (1) connections to the offsite or the onsite AC' 4
powersystems,(2)minimumpotential.forcommoncausefailurewithoffsitepower Lor the onsito emergency AC power sources, (3) timely availability, and (4).re-g quired capacity and reliability. tiore specifically, in regard to the fourth J
attribute, the SB0 rule reads as follows:
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"(4) 'Has sufficient capacity and reliability for operation of all systems required for coping with station blackout and'for b
the: time required to bring and maintain the plant in u fe stut-down-(non-design basis accident)."
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In view of the variety of types,. capacities and capabilities of power sources L
proposed as AAC sources by various licensees, the staff has characterized pro-L posed AAC power sources as being either optimum, fully capable or partially I
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.
5 An optimum AAC power source design is one that is capable of powering simultan-h eously both safety trains of normal safe shutdown systems and equipment. Such
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l a design, followiEg actuation of the AAC source, would provide completely.re-4 dundant normal safe shutdown capebility during an SB0 and recovery therefrom y
from the main control room.
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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.
i 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 i
capable AAC-source would enable attainment of safe shutdown during an SB0 and recovery therefrom from.the main control room.
A minimally capable AAC power source design is one that is not capable of l
- powering 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 cri?
for attaining safe shutdown durug an SBO. Appendix R diesels proposed as -
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source are examples of minimally capable AAC. sources. With this design, opet ability of the main-control' room could not be assured unless the batteries were sized to operate tur the SB0 duration, or battery charging capability was provided by the AAC source.
2.2.1.1 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 550.63, RG-1.155PositionC.3.3.5andNUMARC87-00(Section2.3.1(3). This guidance is further expleined in NUMARC 87-00 Supplemental Questions and Answers dated December 27, 1989, under questions 3.4 and B.3.
The-station blackout rule
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s "At multi-unit sites, where the combination of emergency ac power l
sources exceeds the minimum redundancy requirements for safe shut-down (non-DBA) of all units, the remaining emergency ac power sources i
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may be used as alternate ac power sources provided they meet-the applicable r:quirements."
The rule statement requires minimum redundancy. This means that in order to qualify-as an AAC source, there must be an EDG available in the non-blackout (NBO)unitthatisinadditiontothenumberofEDGsrequiredtomeetthemin-imum EDG redundancy requirement for powering a normal. safe shutdown 1or a loss "L.
t ofoffsitepower(LOOP) event. Thus, the EDG's in a.two unit site with two dedicated EDG's per unit would not qualify as AAC sources because the two EDGs
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per unit just meet the minimum redundancy requirement, i.e., there is no excess t
EDG.
g 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 SB0 unit.
In recogni-tion of the existence of this type of situation, the staff has interpreted the L
excess EDG redund4ncy requirement of the SB0 rule to allow EDGs just meeting the L
minimum EDG redundancy requirements, to qualify as AAC sources on the basis.of I
l excess capacity, provided the other applicable requirements for AAC sources are
-j also met.
L The NRC's basic position on the use of EDGs as AAC power sources on the-basis of
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excess capacity is that such excess capacity should ~not be' attained by load shed-ding in the NB0 unit which results in a degradation of its normally_available safe shutdown capability for the loss-of-offsite-power (LOOP) condition. Any
. actions that would add to the burden of operators that are already in a high l-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 equipment compliment should remain available with adequate EDG
_ capacity for use should it become necessary. The NB0 unit should have the cap-ability for hot shutdown / hot standby forced cooling, cooldown and depressuriza-tion-as required. While additional events are not explicitly being postulated,
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it is not prudent to diminish the capability of the NB0 unit to mitigate problems t
should they aris_e.
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 I
redundancy requirement but not having the excess capacity defined above sfor.
qualifying as an AAC source does not meet the SB0 rule AAC source option require-ments.
Further measures are required such as a separate AAC source or a coping' l
analysis which shows the plant can cope with and recover from SB0 for. the required duration.
2.2.1.2 Co'nnectability of AAC power sources -
The basic criteria governing the connectability of an AAC power source are contained in 10CFR 50.2 (The AAC source should be connectable to but normally not. connected to the offsite or onsite emergency AC power systems),10CFR 50.63
~(SB0 should not assume a concurrent single failure or design basis accident.),
and in Appendix A of 10CFR 50 (The single failure criterion and-the independence L
requirements apply to the NB0 unit.). Therefore, in a one unit site as a mini-mum 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 l
the AAC:. source is an excess redundancy EDG or an independent power source, j
b However, at a two-(or more) unit site where the EDGs meet the AAC~ source excess redundancy or excess capacity criterion,'one intertie circuit between units is L
acceptable provided it is separately connectable to each' safety (EDG). bus in
.both1 units. This follows from the application of the above criteria and the l-assumptions that must be taken that an SB0 can occur in either unit, and that the single failure in the NB0 unit can be on either one of its EDGs or on its 0
' respective safety bus.
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,1 2.2.2 Proposed AAC power source The proposed AAC source for~ Unit 1 is either one of the EDGs of. Unit 2 which can be cross tied between Units 1 and 2.
The cross-tie is configured such that either ofthetwoEDGsfromUnit2canpoweranon-Class 1Ebus(14H)thatcanthenpro-vide power to Unit 1.
The licensee has stated that this power source is avail-able within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> from the onset of an SB0 event and has sufficient capacity
- and capability to operate all systems necessary for coping with an SB0 for a-i duration of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to achieve and maintain the plant in safe shutdown (hot standby).
The licensee also stated that the AAC power source meets the assump-tions in-Section 2.3.1 of NUMARC 87-00.
Based on the staff evaluation and evaluation documented in Attachment 1 (SAIC TER),
the Millstone Unit 1 and 2 emergency AC power sources just meet minimum redundancy-
= requirements. tiowever, Unit 2 EDGs have sufficient capacity and the required
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connectability to qualify as AAC sources for Unit 1.
Our assessment of the proposedAACpowersource(Unit 2EDGs)indicatesthatitfallsintothemini-mally capable AAC power source category cited above.
However, the AAC configuration does not meet the guidance of NUMARC 87-00 Appendix B, items 3,9 and 12 in one respect. -Appendix B of NUMARC 87-00 states that AAC' components should be enclosed within structures and that exposed cables should be buried. The staff has' determined that these requirements are necessary to ensure that the AAC source components (cross-tie) are not affected by the same.
3 weather related and switchyard events that may have contributed to the 580. A -
review of the Millstone Unit 1 submittals has shown (refer to Attachment 1) that the 14H bus and the associated power lines could be affected by these weather related and switchyard events.
Should the cross-tie fail as a result of these events, there would be no means to provide power to the blacked out unit and sub-sequently, the ability to safely shutdown the blacked out unit would be lost.
Therefore, it is the staff's position that the 14H bus.and the cross connecting n
power cables should be enclosed in a structure (modified in accordance with NUMARC 87-00, Appendix B) to minimize the vulnerability of the AAC cross-connect to weather related and switchyard events.
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furthermore, the NUMARC 87-00, Appendix B guidance states that the AAC system should be demonstrated by initial test to be capable of powering the necessary.
3 equipment within one hour and should be capable of maintaining voltage and Lfrequency within the limits of established industry standards.
1 Recommendation:
- 1) The 14H bus and cross connecting cables should be modified' in.accordance with RG 1.155 ano NUMARC 87-00, Appendix B to ensure the oper--
ability of the AAC source and its components, and 2) The licensee should conduct the appropriate AAC tests in accordance with the guidance of NUMARC 87-00, Appendix B,' item B.12.
2.3 Station Blackout Coping Capability L
The characteristics of the following plant systems and components were reviewed to assure that the systems have the avai'1 ability, adequacy and capability to achieve and maintain a safe shutdown and recover from an SB0 for an 8-hour coping duration.
2.3.1 Condensate inventory for decay heat removal h
The. licensee's submittal states that a total of 132,000 gallons of water are
. required for decay heat removal and reactor cooldown for.the proposed SB0 dura-tion of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. The minimum permissible level from two fire water tanks per Technical Specifications provides a useable volume of 378,000 gallons of water which exceeds the required quantity for coping with an 8-hour SBO. The staff,
.therefore, concludes that there is sufficient condensate water to cope with an SB0 of eight hours.
2.3.2-Class -1E battery capacity h
The licensee has d'etermined that there is sufficient battery capacity for one hour at which time the AAC source and station battery "A" will provide the
'necessary power.
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'n The staff agrees with the licensee's assessment contingent'on confirmation'of
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thefollowing:(,
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Since'thecalculationsusedactualcurrent. values-(ammeter readings) instead of nameplate ratings, any change to present plant de loading will require a reevaluation of battery capacity (referto-SAICTER).
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The actual ammeter readings are acceptable provided that they are the maximum values taken over a pu lod of testing and-not from a-one time test.
3)
The normal battery-backed plant monitoring and electrical system 1
controis in-the control = room for at least one safety train will remain operational during an SB0. These are considered to be; essential for successful coping with and recovery from an SBO.
- Recommendation: :The documentation, supporting the SB0 submittals that is to be' maintained by the licensee should include confirmation of the items identified-above.-
4 2.3.3 Compressed air Theilicensee stated that no air operated valves other than the automatic depres-surizationvalves,(ADVs)arereliedupontocopewithanSB0foran8 hour
- duration.
1The staff finds that each ADV is connected' torthe drywell nitrogen-header and.
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~has an ' accumulator'with sufficient nitrogen capacity for several cycles of' valve -
operation during the first hour of SB0 duration and upon initiation of the AAC c
source,;the normal nitrogen supply is available and ADV accumulators'are recharged to cope'with the remaining SB0 duration.
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i 2.3.4 Effects of loss of ventilation Th~ licensee-analyzed the affects of SB0 steady state air temperatures for plant areas containing SBO~ equipment. With compensatory procedural actions, the licensee stated that steady state room air temperatures can be maintained within
-limits to provide reasonable assurance of SB0 equipment operability (refer
.toAttachment1fordetails).
The staff agrees with the licensee's stated results except in.the following areas:
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- 1) the isolation condensor area (the Reactor Building), and 2) the control room.
The staff-concurs with SAIC's assessment of the deficiencies as identified in-for the above mentioned areas.
Reconsnendation: The licensee should reevaluate the effects of loss of ventila-tion for the' areas identified in this section and correct the deficiencies.
If the licensee's reevaluation shows that additional procedure changes or hardware modifications!are necessary to ensure equipment operability in the above mentioned
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-areas, then the licensee should implement the appropriate procedure ~ changes or y
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. modifications accordingly.. The licensee should maintain these analyses in the 1
documentation. supporting the SB0 submittal.
In addition, in the control room, L
Li cabinet doors. should 'be opened within 30 minutes from the onset of.SB0.to pro-
-vide adequate air mixing to maintain cabinet temperatures in equilibrium with the control room temperature and plant procedures should be 'evised accordingly.
2.3.5-Containment isolation The licensee has reviewed the plant list of-containn.ent isolation valves to verify-which valves must be capable of being closed or cycled during an SB0 event.
Based on this review, the licensee has identified procedures that will'be modified to ensure that appropriate containment integrity will be maintained.
.The staff finds the licensee's assessment and proposed procedure changes'to be consistent with the guidance of RG 1.155 and NUMARC 87-00 and are acceptable.
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-2.3.6 Reactor coolant inventory 1
The licensee has performed analysis and has stated that there is sufficient RCS linventory during the first hour of SB0 duration and, thereafter, the-AAC power j
source is on line to ensure RCS make-up and core cooling for the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> SB0 duration.
The'sta.ff agrees with the licensee's assessment that adequate RCS inventory-4 will-be maintained and finds it acceptable (refer to Attachment 1 for details).
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2.4 Procedures and Training a
E 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 P
of this.SER.
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y The' proposed procedure modifications indicated above were nct reviewed,.but the!
-i staff expects the licensee to maintain and implement'these-procedures. including
= any others.:that may be required to ensure an effective response to an SB0 event.
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Although personnel training requirements for an SBO response.were not specifically 4
addressed.by.the' licensee's submittal,.the staff expects'the licensee to imple-
. ment the appropriate: training to ensure an effective response to the SB0.
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q 2.5' Proposed Modifications:
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,The: licensee response to an SB0 does not include proposed modifications to plant-7 tequipment. However, our assessment indicates that some modifications to the:14H '
bus'and cross connecting power cables will be required (see Section 2.2.2); and-4 that mod'ifications-may be required as a result of reevaluation of the effects
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of loss of ventilation for the isolation condensor area and the control room
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The licensee should include a f011 description including the
. Recommendation:1 nature and objectives of.the requirea modificationr identified above~in the-documentation supporting the SB0 submittals that is to be maintained by the H
' licensee.
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Q 2.6 Quality Assurance (0A) and Technical Specifications (TS) p J
L The licensee has stated that all SB0 equipment are either currently covered by.
QA' program or will be covered by a QA program in accordance with the guidance of RG.l.155. The staff finds the proposed licensee actions in this area to be acceptable.
The technical specifications (TS) for the SB0 equipment are currently being con-sidered: generically by the NRC in the context of the Technical Specification L
Improvement Program and remains an open item at this time. However, the staff would-expect thatithe plant procedures will reflect the appropriate testing j
'and surveillance requirements to ensure the operability of the necessary SB0 equip-l~
ment.
If the staff later determines that a TS regarding the SB0 equipment is war-ranted,-the licensee will be notified.of the implementation requirements.
'2.7 EDG Reliability Program-l l?
The licensee's submittal on SB0 did not specifically address a ccmiitment to l
implement a reliability program for the emergency ac power sources (one EDG'and onegasturbine)inaccordancewithRG1.155.
However, during the site audit.
review, the licensee stated that a reliability program for Millstone 1 emergency ac power sources is consistent with the guidance of RG 1.155, Section 1.2 and
. that'if needed, the program will be 6djusted in accordance with regulatory guidance. The staff. finds this commitment to be acceptable.
Recommendation: The licensee should provide confirmation and include in the documentation supporting the SB0 submittals that is to be maintained by the licensee that such a program is in place or will be implemented, o
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- 2.8-Scope of staff review The station blacbut rule (10CFR 50.63) requires _ licensees to submit a response
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containing specifically defined information.
It also requires utilities
"....to ihave baseline assumptions, analyses and related information used in their coping evaluation available to NRC." Thestaffanditscontractor(SAIC)didnotperform a detailed review of the proposed procedure modifications which'are scheduled '
for later implementation, and hardware modification were not' proposed by the
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11cersee. Therefore, based on our review of the licensee supporting documenta-tion and SB0 audit, we have identified the following areas-for focus in any followup inspection or assessment that may be undertaken by the NRC.to further verify conformance with the SB0 rule.
a.
Hardware and procedural modifications, b.
SB0 procedures-in accordance with RG 1.155, Position 3.4, and NUMARC 87-00, Section 4, c.
Operator staffing and training to follow the identified actions in the SB0 procedures,-
d.
EDG reliability program meets as a minimum the guidelines of RG 1.155, e.
Equipment and components required to cope with an SB0 are incorporated in a QA.. program that meets the guidance of RG 1.155,
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-Appendix A, and f.
Actions _taken pertaining to the specific reconnendations noted above in this SER.
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SUMMARY
AND CONCLUSIONS
.The' staff has reviewed the licensee's response to the station blackout (SBO) rule (10 CFR 50.63) and the Technical Evaluation Report (TER) prepared by the
. staff'sconsultant,ScienceApplicationsInternationalCorporation(SAIC). The staff and SAIC also jointly conducted a s'ite audit review of the supporting docu-mentation for the SB0 response. However, based on our review, additional; anal-4
, yses and confirmations described in the recommendations provided in this SER need to be completed. These include the modifications to 14H bus and the heat -
j up' calculations.in the identified areas containing equipment'and systems.needed to cope with an SB0 for 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. The licensec should maintain these analyses and other documentation supporting the SB0 submittal.available for further p
. inspection and assessment' as may be~ undertaken Ly the NRC to further verify conformance with the'SB0 Rule. Based on our review of the submittal and site-audit, we find the licensee's design and proposed method of. dealing with an 530 l
to be in conformance with the SB0 rule contingent upon receipt of confirmation h
. from the licensee within 30 days-that the modifications identified in this SER' E
will be implemented., The schedule for implementation should also be provided inaccordancewith10CFR50.63(c)(4).
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