ML17157B020

Safety Evaluation Finding That Licensee Submittals Do Not Conform W/Station Blackout Rule & Guidance of Reg Guide 1.155.Recommends That Licensee Reevaluate Areas of Concern Identified

ML17157B020
Person / Time
Site:	Susquehanna
Issue date:	01/14/1992
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML17157B019	List: ML17157B018 ML17157B020 ML20091J115
References
RTR-REGGD-01.155, RTR-REGGD-1.155 NUDOCS 9201240044
Download: ML17157B020 (18)

Text

t Ie (g% htCy~

C+

fpo n0 4

C v

Cy 4y

%y*y4 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, O. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION STATION BLACKOUT RULE PENNSYLVANIA POWER AND LIGHT COMPANY t

SUS UEHANNA STEAM ELECTRIC STATION UNITS 1

AND 2 DOCKET NOS. 50-387/388

1.0 INTRODUCTION

e On July 21, 1988, the Code of Federal Regulations, 10 CFR 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 lfght-water-cooled nuclear power plant be able to withstand and recover from an SBO of specified duration, requires licensees to submit information as defined in 10 CFR 50.63, and requires licensees to provide a plan and schedule for conformance to the SBO Rule.

The SBO Rule further requires that the baseline assumptions,

analyses, 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) the Nuclear Manage'ment and Resources

Council, Inc.,

(NUMARC) 87-00, Guidelines and Technical Bases for NUMARC Initiative Addressing Station Blackout at Light Mater Reactors, and (3)

NUMARC 87-00 Sup-plemental guestfons/Answers and Major Assumptions dated December 27, 1989, (issued to the industry by NUMARC on January 4, 1990).

To facilitate:-.%he 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 generic response formats provide the staff with a suIImIary of the results from the licensee's analysis of the

'7201240044 920114 l

PDR ADOCK 05000387 P

PDR

)

0

plant's SBO 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 imple-mented the appropriate hardware and/or procedure modifications that will be required to comply with the SBO Rule.

The Susquehanna Steam Electric Station has proposed coping independent of an alternate ac power source for the SBO coping duration of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

This SBO evaluation is based upon the responses provided by letters from H.

W. Keiser of Pennsylvania Power and Light Company to the U.S. Nuclear Regulatory Comnission, dated Apri 1 17, 19S9, April 17, 1990, February 27, 1991, and the licensee's responses, dated August 1, 1991, to questions discussed during a

June 14, 1991, telephone conference.

The licensee's responses were reviewed by SAIC under contract to the NRC.

The results of the review are documented in the SAIC Technical Evaluation Report (TER), SAIC-91/6671, "Susquehanna Steam Electric Station, Units 1 and 2, Station Blackout Evaluation," dated October 1, 1991, (Attachment No., 1).

2. 0 EVALUATION After reviewing the licensee's SBO submittals 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's 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 offsite power design characteristic Group "Pl," an emergency AC (EAC) power configuration Group "B," and a target emergency diesel generator (EDG) reliability of 0.95.

The target EDG reliability is based on Susquehanna having an average EDG reliability greater than 0.95 over the last 100 demands.

The "Pl" grouping is based on an independence of offsite power classification Group "I 1/2,"

a severe weather (SW) classification Group "2," and an extremely severe weather (ESW) classification Group "2."

The calculation performed by the licensee for the expected frequency due to ESW ccndi:ion as Group "2" was based on a normalized heioht of 30 feet above the ground.

The licensee should have based its calculation on a normalized height of 30 meters.

Therefore, as noted in the attached SAIC TER, the expected frequency of LOOPs due to ESW condition is Group "3.".

The licensee's EAC classification as Group "B" was based on four EDGs A, 8, C, and D at the site, two of which are necessary to achieve and maintain a safe shutdown for both units.

The staff's analysis indicates that three-out-of-four EDGs are required to power the LOOP shutdown loads for both units.

The three-out-of-four EDG requirement places the site in an EAC power configu-ration of Group "D."

The i'nformation in NSAC-108, indicates that the EDGs at Susquehanna experienced an average of 90 valid starts per diesel and have reliability levels of higher than 0.99.

Originally, the licensee selected an EDG target reliability of 0.975 based on EDG reliability data for the last 100 demands which was greater than 0.95.

However, the licensee revised its position and reduced the minimum required EDG reliability target value from 0.975 to 0.950.

In accordance with RG 1.155, the EDG target reliabi lity of either 0.95 or 0.975 is acceptable.

Based on the ESV and SW grouping provided in NUMARC 87-00, the plant is in the offsite power design characteristic Group "P2," with an EAC classification of Group "D," thus requiring an EDG target reliability of 0;975 and an 8-hour coping duration in accordance with NUHARC 87-00, Table 3-8.

Recommendations; The licensee needs to change the EDG reliability target from 0.95 to 0.975 and the coping duration from 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

I

e 2.2 Station Blackout Co in Ca abilit As discussed

above, the staff has determined that the plant must be able to cope with an 0-hour SBO event.

Therefore, 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 the plant in a safe shutdown and to recover from an SBO for an 8-hour coping duration.

Recommendation:

The licensee needs to conform to an 8-hour coping duration arid increase the EDG reliabi lity target from 0.95 to 0.975.

2.2.1 Condensate Inventor for Deca Heat Removal The licensee stated that 117,626 gallons of water are required to cope with a 4-hour SBO event which -includes the, condensate necessary for decay heat removal (72,841 gallons),

RCP seal leakage (22,500 gallons),

and blowdown (22,285 gallons).

The plant Technical Specifications (TS) require a minimum of 135,000 gallons of water to be maintained in the condensate storage tank.

This TS required capacity exceeds the amount of water necessary for coping with a 4-hour SBO event.

The licensee further stated that there is a minimum of 270,000 gallons of water maintained in the refueling water storage tank (RWST) which can be manually connected to refill the CST during an SBO event.

Based on its review, the staff.determines that the minimum coping duration for an SBO event at the Susquehanna plant is 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> (see Section 2.1).-

However,'uring the course of the review, the staff's consultant performed an indepen-dent analysis which indicates that approximately 174,000 gallons of water would be required for an 8-hour SBO event at the Susqueha'nna plant.

Therefore, the staff concludes that there is sufficient water at the Susquehanna plant to cope with an 8-hour SBO event, providing that the licensee will establish a

procedure to refill the CST from the RWST during an SBO event.

Recommendation:

The licensee should provide a procedure to refill the CST from the RWST during an SBO event.

2.2.2 Class 1E Batter Ca acit The licensee-stated'hat a battery capacity calculation was performed which verified that the station Class-1E batteries (125V and 250V) have sufficient capacity to meet SBO loads for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> assuming loads not needed to cope with an SBO are stripped.

The licensee further stated that these loads are iden-tified in plant procedures.

In its SBO coping assessment, the licensee stated that the current 125V dc battery cells will be upgraded from nine positive plates to ten positive plates following each unit's refueling outage later this year.

In addition, the licensee stated that a portable ac generator has been installed which is designed to provide ac power to the "A" and "B" channel battery chargers in the event of an extended SBO.

The licensee estimates that the generator can be connected within 1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> to the plant ac distribution system.

Once tied to the battery chargers, the diesel is expected to function for at least 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br />.

In addition,=the licensee stated that a plant modifi-cation is under evaluation to install a non-Class 1E,battery to carry all non-Class 1E loads, thus permanently removing these loads from batteries 1D650 and 1D660 and thereby increasing the capacity available to the SBO load to ensure at least a 4-hour capacity.

Our review indicates that the licensee did not assume any diesel generator field flash attempts as part of its first minute random load.

However, the inclusion of a diesel generator field flash load assignment will not change the final result.

The 125V dc batteries for the A and B channels do not have sufficient capacity to last 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

However, if the licensee were to use the portable ac-generator to provide charging to these batteries, the batteries would have sufficient capacity.

This requires.that the portable ac generator

P I0 0

1e meets the criteria in Appenoix B of NUHARC 87-00 and that it be added to the list of SBO equipment.

The division I 250V batteries (in Units 1 and 2) support RCIC op'eration and the licensee intends tc use RCIC to cope during an SBO.

The licensee's data indicate that the Unit 1 250V dc (1D650) battery is insufficient to support the operation of RCIC during the. full 8-hour SBO duration.

The division II 250V batteries support HPCI operation.

These batteries are not of concern because HPCI operation is required only during the first few minutes of an SBO event.

Based on the above, we conclude that, except for the Unit 1 250V dc (1D650) battery, all other Class-IE batteries have sufficient capability or backup charging capability to support the required loads during an 8-hour SBO event.

Recommehdation:

The licensee should add the portable ac generator to the list of SBO equipment, provide procedures for its utilization, and apply to it an appropriate gA progr'am.

The portable ac generator should meet the criteria in Appendix B of HUNARC 87-00.

Also, the licensee should replace battery 1D650 with a higher capacity=battery or provide charging capability to the existing battery to extend its support for the 8-hour SBO duration, and recovery thereafter.

The licensee should include all the analyses and related information in supporting documentation that is to be maintained by the licensee for possible staff review.

2.2.3 C~ddi The licensee stated that the air operated valves (steam relief valves) needed 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 /> have sufficient backup sources independent of the preferred and blacked out unit's Class 1E power supplies and that no valves require manual operation.

e Based on its review, the staff finds that the steam relief valves which will be used for plant depressurization are accumulator-backed with sufficient capacity for an 8-hour SBG event.

Therefore, the 'staff concludes that the Susquehanna plant will have sufficient compressed air to cope with an 8-hour SBO event.

I 2.2.4 Effects of Loss of Ventilation The licensee has performed plant-specific analyses to determine the effects of loss of ventilation and identified the HPCI room, RCIC room, and the main steam tunnel as the only dominant areas of concern (DACs).

The calculated temperature in the control room (which includes four relay rooms) during an SBO event did not exceed 120'F.

Therefore, the control room was not identified as a

DAC.

The licensee's calculations were based on a 4-hour coping duration.

As discussed in Section 2.1, the staff has determined that the plant must be able to cope. with an 8-hour SBO event.

In addition, during the course of its review, the staff's consultant found that the licensee used the COTTAP computer code for conducting all calculations of 4-hour room heat-up analyses.

The review of these analyses resulted in-questions regarding the following three aspects of the evaluation:

input, methodology, and results, which are discussed in greater detail below.

A number of input values used in the room heat-up calculations have not been technically justified, are inconsistent for different calculations, or are non-conservative from the viewpoint of maximizing the room temperature response.

These parameters are:

init'ial room temperature, initial room humidity, concrete thermal conductivity, maximum allowable control room cabinet temperature, and constant control room boundary temperature.

The licensee needs to either provide adequate technical justification for selecting these parameter values or perform a reanalysis using more conservative values for SBO room heat-up during an SBO.

The room heat-up analysis relies on the COTTAP computer code which is not generally used in the nuclear industry.

The licensee did not present any information regarding the meth'odology inherent in COTTAP nor any indication as to whether COTTAP has been benchmarked for subcompartment heat-up calculations similar to the SBO case.

There is also no evidence as to whether COTTAP is maintained and controlled under an appropriate computer software quality assurance program.

There was no evidence of any independent review and approval by the licensee of the COTTAP calculation files provided for this SBO review.

In addition, the licensee did not provide any technical justifi-cation for modelling a very large number of interconnected rooms in a single COTTAP calculation as being conservative for determining each room's SBO temp'erature response.

Finally, the licensee did not provide any evidence of the capability of COTTAP to properly model the thermal response. of the small volume contained within a control room instrumentation cabinet to arrive at the maximum hot spot temperature.

Review of the large number of transient temperature plots from the COTTAP analyses revealed many different temperature trends for different rooms.

Some of these trends did not appear to reflect the expected SBO behavior of a room while others did show an expected trend, but with varying slopes and, in some

cases, oscillatory behavior.

The licensee did not provide a discussion that explained why each room responded the way that it did.

Examination of the results for such a complex model of interconnected rooms is necessary to demonstrate both an understanding of the overall model and the individual room response (greater details on the room heat-up analysis review comments can be found in Section 3.2.4 of the SAIC TER).

Based'on its review and the concerns discussed

above, the staff has not been able to conclude that the effects of loss of ventilation during an SBO event at the Susquehanna plant have been properly evaluated.

Recommendation:

The licensee should:

I) provide additional information and/or technical justification for the initial conditions and assumptions used in the heat-up analysis for each area of concern,

2) with regard to the COTTAP computer code, provide detailed information to address the staff's concerns as discussed in the above evaluation, and 3) re-perform the heat-up analysis for each area of concern and for an 8-hour coping duration taking into account the non-conservatism as identified in the SAIC TER.

2.2.5 Containment Isolation The licensee stated that the plant list of containment isolation valves (CIVs) has been reviewed to verify that valves which must be capable of being closed or that must be operated (cycled) under SBO conditions can be positioned (with indication) independent of the unit's preferred and Class-lE ac power supplies.

The licensee added that no plant modifications'nd/or associated procedure changes were determined to be required to ensure that appropriate containment integrity can be provided under SBO conditions.

During its rev'i'ew, the staff's consultant identified containment isolation valves for penetrations X-203 A, B, C, and D; X-204 A and B; X-205 A and B; X-206 A and B; X-207 A and B; and X-208 A and 8 as requiring valve position indication under SBO conditions.

During a telephone inquiry on June 14, 1991, the licensee stated that, containment isolation can be 'assured for each of the penetrations identified above by isolating all side paths coming off the main path downstream of the penetration.

However, the staff has not been able to verify that the downstream valves identified by the licensee are part of the penetration boundary or that they are in the immediate vicinity of the

~ penetration.

Therefore, the staff has not been able to conclude that the CIV design and operation at the Susquehanna plant have met the guidance described, in RG 1.155.

Recommendation:

The licensee should list the valves identified above in an appropriate procedure and identify the actions necessary to ensure that these valves can be fully closed, if containment isolation is required during an SBO event.

The v'alve closure should be confirmed by position indication (local, mechanical,

remote, process information, etc.).

2.3.6 Reactor Coolant Inventor The licensee stated that the ability to maintain adequate reactor coolant system e

inventory to ensure -that the core is cooled has been assessed for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> using a calculated leakage of 100 gpm.

The licensee intends to use both HPCI and RCIC to maintain RCS inventory during an SBO.

According to the Susquehanna FSAR, the HPCI pump has a rated flow of 5070 gpm at 1172 psia reactor pressure, while the RCIC pump has a rated flow of 6GG gpm.

I As discussed in Section 2.1 of this SER, an 8-hour coping duration is required for the Susquehanna plant and it.is being evaluated by the staff as an 8-hour coping plant.

In its review, the staff's consultant finds that the injection capability of either the HPCI or RCIC system exceeds the amount of water required to remove decay heat and to replenish the assumed RCS leak rate of 61 gpm (18 gpm per pump plus 25 gpm for maximum allowed TS leakage).

Therefore, Susquehanna has sufficient capability to maintain reactor coolant inventory for the 8-hour SBO event.

The 18 gpm recirculation pump seal leak rate was agreed to between NUHARC and the NPC staff pending resolution of Generic Issue (GI) 23. If the final resolution of GI-23 defines higher recirculation pump seal leak rates than assumed for this evaluation, the licensee should be aware of the potential impact of this resolution on its analyses and actions addressing conformance to the SBO Rule.

2.4 Procedures and Trainin The licensee has stated that the appropriate procedures have been reviewed and the changes made as-necessary to meet the guidelines of NUHARC 87.-00, Section 4.

The proposed procedure modifications indicated above were not reviewed, but the staff expects the licensee to maintain and implement these procedures and any others needed to ensure an appropriate response to an SBO event.

Although personnel training. requirements for.an SBO response were not specifically addressed by th'e licensee's submittal, the staff expects the licensee to-implement the appropriate training to assure an effective response to an SBO event.

I

~

0 2.5 Pro osed tlodifications The licensee 'did not identify any modifications as being necessary to assure a 4-hour coping capability. However, as discusse'd in Section 2.1, the staff has determined that an 8-hour coping duration is required.

Therefore, the licensee's plant-specific evaluations as recommended in this SE for battery

capacity, loss of ventilation, and containment isolation need to be reassessed before a determination can be made as to whether or not any plant modifications are necessary to cope with an SBO event.

Recommendation:

The licensee should provide for staff review a full description, including the nature and objectives of any modifications required.

The analyses and related information should also be included in the supporting documentation that is to be maintained by the licensee in support of the SBO submittals.

2.6 ualit Assurance and Technical S ecifications

~

The licensee stated that a quality assurance (gA) program will be developed and incorporated into a plant procedure.

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

However, the staff would expect that the plant procedures will reflect the appropriate testing and surveillance J

r'equirements to ensure the operability of the necessary SBO equipment.

If the staff later determines that a TS rega'rding the SBO equipmept is warranted, the licensee will be notified of the implementation requirements.

'.7 EDG Reliabilit Pro ram The licensee is in the process of implementing a reliability program consistent e

with the guidance of RG 1.155, Position 1.2.

-I2-Recommendation:

The licensee should complete the implementation of an EDG reliability program which meets the guidance of RG 1.155, Section 1.2, and provide a schedule for its completion.

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 evaluation available to NRC.

The staff and its contractor (SAIC) did not perform a

detailed review of the proposed equipment or procedure modifications which are scheduled for later implementation.

Therefore, based on our review of the licensee SBO 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 SBO Rule:

a.

Hardware and procedural modifications, b.

SBO procedures in accordance with RG 1.155, Position 3.4, and NUMARC 87-00; Section 4, c.

Operator staffino and training to follow the identified actions in the SBO 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 guidance of RG 1.155, Appendix A, kaditional areas may be identified following staff review of licensee's revised.

response to the SBO Rule.

3.0 CONCLUSION

S Based on the staff's review of the licensee's submittals and the SAIC TER, I

the stiff finds that the Susquehanna Steam Electric Station does not conform with the SBO Rule and the guidance of RG 1.155, and therefore recommends that the licensee reevaluate the areas of concern that have been identified in this SE.

Guidance for the licensee to review and implemt'.nt the staff's recommendations is provided in RG 1.155, NUMARC 87-00, and the supplementary guidance (NUMARC 87-00 Supplementary guestions/Answers; NUMARC 87-00 Major Assumptions) dated December 27, 1989, which was issued to the industry by NUMARC on January 4, 1990.

The staff's concerns and recommendations identified in this SE should be addressed by the licensee, and a revised response submitted to the NRC within 60 days.

The licensee is expected to ensure that the baseline assumptions of NUMARC 87-00 are applicable to the Susquehanna Steam Electric Station.

Also, the licensee is expected to document all analyses and related information, and verify that these are available for NRC review.

4.'0 ATTACHMENT 1.

SAIC-91/6671, Technical Evaluation Report, Susquehanna Steam Electric Station, Units 1 and 2, Station Blackout Evaluation, October 1, 1991.

Princi al Contributors N. Trehan J. Raleigh

0 0

0