ML17223B020

Draft Safety Evaluation Re Station Blackout

ML17223B020
Person / Time
Site:	Saint Lucie
Issue date:	11/21/1990
From:	Office of Nuclear Reactor Regulation
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ML17223B019	List: ML17223B018 ML17223B020 ML17308A504
References
NUDOCS 9012030037
Download: ML17223B020 (18)

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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 DRAFT SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO STATION BLACKOUT TO FACILITY OPERATING LICENSE NO. DPR-67 FLORIDA POWER 8I LIGHT COMPANY ST.

LUCIE PLANT UNIT NO.

1 DOCKET NO. 50-335 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 SBO rule further requ.ires that the baseline assumptions, analysis and related information be available for NRC review.

Guidance for con-formance 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 Supple-mental guestions/Answers and Major Assumptions dated December 27, 1989 (issued to the industry by Nuclear Management and Resources Council, Inc.

(NUMARC) January 4,

1990).

To facilitate the NRC staff's (hereafter referred to as staff) review of licensee responses to the SBO 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 response.

The gener ic response formats provide the staff with a summary of the results from the licensee's analysis of the plant's SBO 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 SBO rule 'is veri-fied 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 pro-cedure modifications that will be required to comply with the SBO rule.

Staff review of SBO submittals can be limited to a review of the licensee's sub-mittal and need not include a concurrent site audit review of the supporting documentation.

However, a limited number of site audit reviews were performed to obtain a benchmark for licensee conformance with the documentation require-ments of the SBO rule.

St. Lucie was one of the plants selected by the NRC for a site audit review.

9012030037 901121 PDR ADOCK 05000335 F

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The licensee's responses to the. SBO rule was provided by letters (L-89-145) from W. F.

Conway to U.

S." Nuclear Regulatory Commission, dated April 17, 1989 and March 7, 1990.

The licensee response was reviewed by Science Applications International Corporation (SAIC) under contract to the NRC.

The site audit was performed by a joint NRC/SAIC team headed by.a NRC. staff member on October 17-19, 1989.

The results of the review and site audit are documented by a SAIC Tech-nical Evaluation Report (TER) SAIC-89/1643, "St. Lucie, Unit 1, Station Blackout Evaluation," dated August 17, 1990 (Attachment 1).

Paragraph (b) of 10 CFR 50.63 exempts certain plants from the requirement to sub-mit information in response to the SBO rule if the capability to withstand statirn blackout was specifically addressed in the operating license proceeding ard was specifically approved by the NRC.

St. Lucie Unit 2 meets this requirement because the issue of SBO was considered by the Atomic Safety Licensing Appeal Board (ALAB-603) and plant specific analysis (UFSAR Section 15.10) was performed by the licensee

,which demonstrated that the plant could successfully withstand a complete loss of all AC power for at least 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

Therefore, this review is limited to St. Lucie 1.

However, further discussion of Unit 2 SBO withstand capability is included in Section 3.0 of this Safety Evaluation in order to provide a more comprehensive treatment of SBO at the St. Lucie site.

2.0 EVALUATION After reviewing the licensee s

SBO 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 Attachment No.

1 for details of the review).

Based on this review, the staff findings and recommendations are summarized as follows.

2.1 Station Blackout Duration The licensee has calculated a minimum acceptable SBO duration of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> based on a plant AC power design characteristic group "P2", an emergency AC (EAC)

Power configuration Group "A", and a target Emergency Diesel Generator (EDG) reliability of 0.95.

The target EDG reliability was based on each St. Lucie EGG having a reliability greater than 0.95 over the last 100 demands.

The "P2" grouping is based on an independence of offsite power classification of Group "I2", a severe weather (SW) classification of Group "1" and an extremely severe weather (ESW) classification of Group "4".

For the reasons discussed in the attached SAIC TER, the staff disagrees with the licensee's determination of several of the items used to determine the required SBO duration.

The staff agrees with the licensee's classification of the independence of offsite power as Group I2 provided that each startup transformer has sufficient capacity to supply the loss of offsite power (LOOP) loads of one division of both units. If the startup transformers do not have this capacity requirement, the classification of the independence of qffsite power would be Group I3.

However, this alone does not change the -"P3 " classifi-cation or the required coping duration.

The staff classifies the ESW classifi-cation group as Group 5 insteadof ESW Group 4, which results in a plant AC power design characteristic Group "P3*".

Also, the staff classifies the EAC power configuration as Group "C".

Based on these characteristics, the required coping duration is 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> for an EDG reliability target of 0.95, or 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> for an EDG reliability target'f 0.975.

Recommendation:

The licensee should veri y that the Unit 2 auxiliary or

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h division of Unit 2 and LOOP loads of one division of Unit I, and there is an approved procedure to power the buses of one division of both units from an oper-able Unit 2 auxi liary or startup transformer.

This verification should be included in the documentation supporting

.he SBO submittal.

2.2 Alternate AC (AAC) Power Source 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 SBO coping duration and recovery therefrom.

2.2.1 General staff osition on AAC ower sources The definition in 10 CFR 550.2, RG 1.155 and NUMARC 87-00 define AAC power source in terms of four attributes: (I) connections to the offsite or the onsite AC power systems, (2) minimum potential for common cause failure with offsite power or the onsite emergency AC power sources, (3) timely availability, and (4) re-quired capacity and reliability.

More specifically, in regard to the fourth attribute, the SBO rule reads as follows:

"(4)

Has sufficient capacity and reliability for operation'f 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 simultan-eously both safety trains of normal safe shutdown systems and equipmert.

Such a design, following actuation of the AAC source, would provide completely re-dundant normal safe shutdown capability during an SBO and recovery'herefrom 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.

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I 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 critical for attaining safe shutdown during an SBO.

Appendix R diesels proposed as an AAC source are examples of minimally capable AAC sources.

llith this design, opera-bility 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 EDGs used as AAC ower sources The guidance on the use of existing emergency diesel generators (EDGs) at multi-unit sites as AAC power sources is documented in the SBO rule, 10 CFR 550.63, RG 1.155 Position C.3.3.5 and NUMARC 87-00 (Section 2.3.1(3).

This guidance is further explained in NUMARC 87-00 Supplemental guestions and Answers dated December 27, 1989, under questions 3.4 and B.3.

The SBO rule states:

"At multi-unit sites, where the combination of emergency ac power sources exceeds the minimum redundancy requirements for safe shutdown (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 qualify as an AAC source, there must be an EDG available in the non-blackout (NBO) unit'that is in addition to the number of EDGs required to meet the minimum EDG redundancy requirement for powering a normal safe shutdown for a loss of offsite power (LOOP) event.

Thus, the EDG's in a two-uni:t site with two 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 redun-dancy but where each EDG is of sufficient capacity to fully'power all the normal LOOP loads of the NBO unit, and also has sufficient excess capacity for powering the required, safe shutdown loads of the SBO unit.

In recognition of the existence of this type of situation, the staff has interpreted the excess EDG redundancy requirement of the SBO rule to allow EDGs just meeting the minimum EDG redundancy requirements to qualify as AAC sources on the basis of excess

capacity, provided the other applicable requirements for AAC sources are also met.

The NRC's basic position on the use of EDGs as AAC'power sources on the basis of excess capacity is that such excess capacity should not be attained by load shed'-

ding in the NBO unit which 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 NBO unit.

The staff position is therefore that the normal equipment compliment should remain available with adequate EDG capacity for use

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The NBO 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 NBO 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 SBO rule in another unit.

Each unit must meet, the SBO rule on its own merits without reducing another unit's capability to respond to its own potential problems.

Therefore,'

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 SBO rule AAC source option require-ments.

Further measures are required such as a,separate AAC source or a coping analysis which shows the plant can cope with and recover from SBO for the required, duration.

2.2.1.2 Connectabilit of AAC ower 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),

10 CFR 50.63 (SBO should not assume a concurrent single failure or design basis accident),

and in Appendix A of 10 CFR Part 50 (The single failure criterion and the independence requirements apply to the non-blackout

[NBO] 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 or excess capacity 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 SBO can occur in either unit, and that the single failure in the NBO unit can be on either one of its EDGs or on its respective safety bus.,

2.2.2 Pro osed AAC ower source The St. Lucie Plant is a two-unit site with two dedicated EDGs to each unit.

The licensee proposes to install a 4160V connection between safety busses 1AB of Unit I and 2AB of Unit 2 (see SAIC TER Figure I for details) to permit one of the EDGs of the non-blacked unit to be used as an alternate AC (AAC) source for the blacked out unit.

Either of the two EDGs of one unit can be connected to either of the safety busses of the other unit. The licensee stated that each of the Unit 2 EDGs has sufficient capacity to power the required loads of both units.

In support of this, the licensee provided (during the site audit review) the NBO loads (Unit 2) as 1954kW and SBO loads (Unit I) as 897kW (i.e., total EDG loading of,2851kW).

The AAC power source would be available to power the loads within

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't 10 minutes following the confirmation that an SBO has occurred.

The licensee has committed to performing a test to demonstrate that the AAC power source can power the SBO loads within ten minutes.

The staff finds that the licensee evaluation of LOOP loads (NBO unit) is not consistent with the staff position stated above (Section 2.2.1.1),

since loads such as auxiliary feed pump, residual heat removal pump, instrument air compres-sor, etc.,

were not included in the LOOP loads.

Therefore, to assess whether the Unit 2 EDGs have true excess capacity to qualify as an AAC power source for Unit I in accordance with the above stated

guidance, the staff referred to the St. Lucie UFSAR.

Attachment I (SAIC TER) documents the LOOP loads of the Unit 2 (NBO unit) as 2802.5kW (based on Table 8.3-2 of the Unit 2 UFSAR) and the cor-rected SBO loads of the Unit I (black out unit) as 1133.5kW.

This tabulation indicates a total load of 3936kW for the NBO and SBO unit which is essentially equal to the 3935kW (2000HR) rating of each of the Unit 2 EDGs.

This indicates that the Unit 2 EDGs qualify as AAC sources for Unit I on the basis of excess capacity but with no margin available.

The staff finds this to be acceptable provided that no additional loads are required for the SBO scenario beyond those that have been identified.

The staff finds that the AAC power source for St.

Lucie Unit I satisfies the connectability requirements of Section 2.2.1.2.

The staff assessment indicates that the proposed AAC power source for Unit I falls into the fully capable category as discussed in Section 2.2.1.

Recommendation:

The licensee should confirm and include in the documentation ppPPg SBO b itt 1 th t:

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d SBO loads on Unit 1 are within the Unit 2 EDG's 2000HR rating based on the above guidance (Section 2.2.1.1);

and 2) no additional SBO loads are required than those already identified.

Also 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 Co in Ca abilit 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 recover from the SBO for a 4-hour coping duration.

2.3.1 Condensate inventor for deca heat removal The licensee's Technical Specifications require a minimum condensate storage tank level of 116,000 gallons in Unit 1 and 307,000 gallons in Unit 2.

Using NUMARC 87-00 methodology, approximately 62,000 gallons are required to cope with an SBO for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

The attached TER indicates that approximately 98,000 gallons of condensate would be required for either unit--during an 8-hour SBO event.

In either case, the CST capacity exceeds the required condensate inventory.

The staff therefore concludes that there is sufficient condensate water to cope with an SBO of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

In addition, the excess inventory available in the CST is available for SBO recovery.

2.3.2 Class 1E batter ca acity The AAC source will be available to power the battery chargers in approximately 10 minutes.

Adequate battery capacity is not considered to be a concern under these conditions and the licensee was not required to perform any additional calculations to meet the requirements of the SBO rule.

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'The licensee has stated that air-operated valves needed to cope with an SBO are supported by diesel-driven air compressors which will continue to operate during an SBO.

The staff therefore concludes that there is reasonable assurance that such valves will remain operable.

2.3.4 Effects of loss of ventilation The licensee did not perform any calculations pertaining to loss of venti lation since the AAC source wi 1,1 be available within approximately 10 minutes to power the necessary ventilation equipment.

However, not all ventilation equipment wi 11 be powered by the AAC source during an SBO.

The licensee indicated that additional studies will be made to assure that these areas will not overh'eat during an SBO.

Recommendation:

The licensee should complete the ventilation studies and include the studies and the results in the documentation supporting the SBO submittal.

The licensee should implement any procedure changes and modifications that are required to assure adequate ventilation is maintained, in the areas containing SBO equipment, for the required coping duration.

2.3.5 Containment isolation The licensee did not address containment isolation since the AAC source will be available to power one of the blacked-out unit safety busses within approx-imately 10 minutes.

The licensee was not required to address containment isolation if the AAC source is available within 10 minutes.

Since power is available to one division of safe shutdown equipment, it is assumed that the AAC source provides power to the appropriate isolation valves to assure containment integrity during an SBO.

2.3.6 Reactor coolant inventor The licensee plans to use one charging pump to maintain reactor coolant inventory.'he charging pump wi 11 be powered by the AAC source within 10 minutes and has a

capacity of 44 gpm.

As discussed in the attached

TER, a leakage rate of 112 gpm was assumed based on data from similar plants.

If this assumption is correct, the staff agrees with the conclusion reached in the TER that for a net loss of 68 gpm, there is reasonable assurance that the reactor coolant inventory will be adequate during an SBO of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

The reactor coolant inventory evaluation as discussed above was based on the guidance provided in NUMARC 87-00 of 25 m

er reactor coolant um s (RCP) seal leaka e for ressurized water reactors.

T e 25 gpm va ue was agree to etween

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NUMARC and the'staff pending resolution of Generic Issue (GI) 23. If the final resolution of GI-23 defines higher RCP leakage rate 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.

Recommendation:

The licensee should evaluate and confirm, and include this h

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EBO bi<<i, h<<h be adequate RCS inventory to ensure continued core cooling for the required SBO duration and recovery therefrom.

2.4 Procedures and Trainin The licensee has committed to the issuance of new and revised procedures, in-cluding the associated training required to implement the procedures.

The proposed procedural and training modifications were not reviewed in detail but the staff expects the licensee to maintain these procedures to ensure an appropriate response to an SBO event.

2.5 Pro osed Modifications As discussed in paragraph 2.2 above, the licensee is adding a 4160V cross-tie between the safety busses of Units 1 and 2 so that one of the two EDGs of either unit can be used a's an AAC source for an SBO of the other unit.

This 4160V cross-tie wi 11 have sufficient capacity to power the shutdown loads of the blacked-out unit and will be installed underground or be within buildings such that it will not be exposed to weather-related events.

Physical separation of the cross-tie will conform with the separation criteria of the plant's licensing basis.

The licensee stated that procedure changes, will be completed within 1 year of the notification from the NRC staff per 10 CFR 50.63(c)(3).

The staff finds that the proposed modification serves as a part of the AAC source implementa-tion and meets the applicable guidelines of RG 1.155 and NUMARC 87-00, Appendix B.

Recommendations:

The licensee should provide a full description, including the f

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d mentation supporting the SBO submittals that is to be maintained by the licensee.

2.6 gualit Assurance And Technical S ecifications The licensee has committed to incorporate all equipment used to cope with an SBO and not covered by current gA programs into a gA program that meets the guidance of RG 1.155, Appendix A.

The staff finds this to be acceptable.

The Technical Specifications for the SBO equipment are currently being con-sidered generically by the NRC in the context of the Technical Specification Improvement Program and remains an open item at this time.

However, the staff would expect that the plant pro'cedures will reflect the appropriate testing and surveillance requirements to ensure the operability of the necessary SBO equip-ment. If the staff later determines that TS regarding the SBO equipment is war-

ranted, the licensee will be notified of the implementation requirements.

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2.7 EDG Reliability Pro ram The licensee's submittal on SBO did not specifically address the commitment to implement an EDG reliability to conform to the guidance of RG 1.155, Position 1.2.

However, during the site audit review, the licensee stated that their reliability program would meet these guidelines.

Recommendation:

The licensee should implement an EDG reliability program which g

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!.2. if EDG 1i biii y p rently exists, the program should be evaluated and adjusted in accordance with RG 1.155.

Confirmation that such a program is in place or will be implemented should be included in the documentation supporting the SBO submittals that is to be maintained by the licensee.

2.8 Sco e 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 scheduled for later implementation.

However, based on our review of the licensee supporting documentation and SBO audit, 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 SBO rule.

Additional items may be added as a result of the staff review of the actions taken by the licensee in response to this SE.

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, d.

EDG reliability program meets, as a minimum, the guidelines of RG 1.155, e.

Equipment and components required to cope with an SBO are incorporated in a gA program that meets the guidance of RG 1.155, Appendix A, f.

Review of the heating and ventilation calculations when they are completed for the dominant areas of concern during an SBO to assure that the systems and equipment therein are operable under the SBO conditions, and g.

Actions taken pertaining to the specific recommendations noted in this SE.

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IC 3.0 St. Lucie Unit 2 SBO Withstand Ca ability As noted in Section 1.0 of this SE, paragraph (b) of 10 CFR 50.63 exempts certain plants from the requirement to submit information in response to the SBO rule if the capability to withstand station blackout was specifically addressed in the operating license proceeding and was specifically approved by the NRC.

St. Lucie Unit 2 meets this requirement because the issue of SBO was considered by the Atomic Safety Licensing Appeal Board (ALAB-603) and plant-specific analysis (UFSAR Section 15.10) was performed by the licensee which demonstrated that the plant could successfully withstand a complete loss of all AC power for at least 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

In the context of the SBO rule, this would constitute a coping analysis independent of AC power.

The analysis methodology and results are fully described in ALAB-603, 12 NRC at pages 44-65.

The methodology for determination of the SBO duration is not identical to the methodology prescribed by the corresponding guidance for the SBO rule (Position 3.1 of RG 1.155, or Section 3.0 of NUMARC 87-00).

However, the two methodologies are considered to be essentially equivalent since they are derived from the same fundamental basis and differ only in format.

The determination of the 4-hour SBO duration for St. Lucie Unit 2 was based on a probabi 1istic/statistical calculation which combined the probabilities of loss of offsite power and both

EDGs, and the probabilities of not being able to restore either of these sources of AC power within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

The probability values used in this calculation were based on historical experience data at the St. Lucie site.

The combined probability of failure of both EDGs provided by the licensee was 7E-4.

Assuming complete independence, this reduces to a 2.6E-2 failure probability for each EDG, or an equivalent average reliability of 0.974.

The target EDG reliability for St. Lucie Unit.2 required to support the 4-hour SBO duration established during the operating license proceeding is therefore 0.974; and this is essentially identical to the 0.975 target for the EDGs of both units that is required to establish a 4-hour SBO duration for St. Lucie Unit 1, as cited in Section 2.1.

Conformance to the SBO rule for St. Lucie Unit 1 is attained by utilizing the Unit 2 EDGs as an AAC source.

The Unit 2 EDGs qualify as AAC sources on the basis of excess

capacity, as noted in Section 2.2.2.

The St. Lucie EDGs are smaller (3500kW continuous) and would not qualify as an AAC source for Unit 2 on the basis of excess capacity.

However, an acceptable crosstie between units would be available and, although not qualifying as AAC sources, the Unit 1

EDGs do have substantial capacity (650 kW) above their normal LOOP shutdown load which can be used to power some SBO loads in Unit 2, e.g., battery charging or some HVAC, and a charging pump which would significantly improve SBO coping capability in Unit 2.

In summary, the staff concludes that (I) the SBO withstand capability analysis performed for St. Lucie Unit 2 during the license proceeding was essentially equiv-alent to the coping analysis that would have been required under the SBO rule, and (2) the added intertie between Units 1 and 2 with consequent availability of AC power assist from the Unit 1 EDGs for coping with an SBO in Unit 2.

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Recommendation:

The licensee is expected to maintain the reliability of Unit 2 EDGs at 0.974 or greater in accordance with the licensing basis for Unit 2 in regard to the SBO issue.

The licensee is also encouraged to update the SBO coping procedures for Unit 2 to incorporate the enhanced capability provided by the AC intertie between Units 1 and 2.

4.0

SUMMARY

AND CONCLUSIONS The staff has reviewed the licensee's response to the SBO'ule (10 CFR 50.63) and the Technical Evaluation Report (TER) prepared by the staff's consultant, Science Applications International Corporation (SAIC).

The staff and SAIC also jointly conducted a site audit review of some of the supporting documen-tation for the SBO response.

Based on our review, additional analyses and confirmations described in the recommendations provided in this SE need to be completed.

These include the modifications to the 4160V cross-tie between Units 1 and 2; verification that the Unit 2 auxiliary or start-up transformer has sufficient capacity to support the loads of one division of both units; confirmation that the Unit 2 EDGs being proposed as an AAC power source for Unit I have adequate capacity to power the loads of the NBO and SBO units; confirmation that the AAC wi 11 be tested in accordance with NUMARC 87-00, Appendix B, Item B.12; evaluation of heat-up calculations in the identified areas containing equipment and systems needed to cope with an SBO for the required duration; and evaluation of RCS inventory to ensure continued core cooling for the required duration and recovery therefrom.

The licensee should maintain these analyses and other documentation supporting the SBO submittal available for further inspection and assessment as may be undertaken by the NRC to further verify conformance with the SBO rule.

Based on our review of the submittals and site audit, we find the licensee's design 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 modifications including those resulting from the recommendations documented in this SE will be implemented.

The schedule for implementation should also be provided in accordance with 10 CFR 50.63(c)(4).

Dated:

November 21, 1990 Princi al Contributor:

A.

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