ML091490007

ME0969 & ME0970, RAIs from Apla (PRA Branch) Amendment Request for One-Time Ext of AOT - 72 Hrs to 10 Days

ML091490007
Person / Time
Site:	Susquehanna
Issue date:	05/29/2009
From:	Bhalchandra Vaidya Plant Licensing Branch 1
To:	Filchner D Susquehanna
vaidya B, NRR/Dorl/lpl1-1, 415-3308
References
TAC ME0969, TAC ME0970
Download: ML091490007 (6)

Text

From:

Bhalchandra Vaidya Sent:

Friday, May 29, 2009 7:18 AM To:

'dlfilchner@pplweb.com'; 'Coddington, Cornelius T';

'ckhoffman@pplweb.com' Cc:

Douglas Pickett; John Boska; Richard Guzman; Andrew Howe; Donnie Harrison

Subject:

Susquehanna Units 1 and 2, TAC Nos. ME0969 & ME0970- RAIs from APLA (PRA)

SUBJECT:

PPL Susquehanna, Units 1 and 2. - REQUEST FOR ADDITIONAL INFORMATION (RAIs) RE: License Amendment Request for One-time extension of Allowable Outage Time in TS 3.8.1, LCO ACTION A3, from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 10 days for replacement of Transformer ST-20 (TAC NOS. ME0969 and ME0970)

By letter dated March 24, 2009, supplemented by letters dated April 30 and May 12, you submitted a license amendment request for One-time extension of Allowable Outage Time in TS 3.8.1, LCO ACTION A3, from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 10 days for replacement of Transformer ST-20.

The PRA Licensing Branch identified a number of areas where additional information is needed to complete our review, as provided below:

References:

1. Letter, W. H. Spence to U. S. Nuclear Regulatory Commission, Susquehanna Steam Electric Station Amendment Request No. 305 to Unit 1 License NPF-14 and Amendment Request No. 276 to Unit 2 License NPF-22: One-Time Extension to Technical Specification 3.8.1 Allowable Completion Time for Offsite AC Circuits, PLA-6480, March 24, 2009.

2. Letter, W. H. Spence to U. S. Nuclear Regulatory Commission, Susquehanna Steam Electric Station Amendment Request No. 305 to Unit 1 License NPF-14 and Amendment Request No. 276 to Unit 2 License NPF-22: One-Time Extension to Technical Specification 3.8.1 PRA Supplemental Information, PLA-6505, April 30, 2009.

===

RAIs:

1. Section 4.2.1.1 of the Enclosure of Reference 1 identifies that the loss of offsite power (LOOP) initiation frequency is explicitly calculated by a fault tree which is capable of assessing the impact of an out-of-service transformer. Section 4.2.1.2 identifies that the impact of the transformer is evaluated in the plant-centered LOOP initiating event. The licensee is requested to provide additional details of this model for the staff to better understand the cause-effect relationship of the out-of-service transformer and the plant-centered LOOP frequency for this application:

a. Identify the transformer failure modes, failure probabilities, treatment of common cause failure of transformers, and the calculated frequencies for plant-centered LOOP when both transformers are available and when one transformer is unavailable.

b. Typically, a fault tree model for an initiator involving two redundant components must assume a mean-time-to-repair applicable in the model when one transformer fails, after which the redundancy is re-established. This is established in the mission time of the remaining operable component. In this case, the calculations should not assume any repair of the out-of-service transformer, because the calculation is based on the core

damage frequency (CDF) over an entire year while in the outage configuration, and then the 10-day exposure time is used to calculate the incremental conditional core damage probability (ICCDP). Confirm that no credit has been taken for repair and restoration of ST No. 20 in the fault tree calculation of the plant-centered LOOP frequency for this application.

c. Identify whether credit is taken in the PRA model for restoration of offsite power given a plant-centered LOOP as the initiating event, and if so, provide the nonrecovery probability, its basis, and its applicability to the specific configuration which will exist during the 10-day outage.

2. Section 4.2.1.1 of the Enclosure of Reference 1 identifies the configuration of the onsite AC power sources. The licensee is requested to provide additional details regarding PRA modeling of these systems:

a. Describe the applicability of common cause failures between the four emergency diesel generators and the fifth diesel generator, and if appropriate, the basis for not assessing any common cause failure of the fifth diesel generator.

b. It is stated that the fifth diesel generator may be placed into service within 90 minutes; provide the human error probability used in the PRA for this action, and the basis of the calculation, including availability of procedures, and the capability to accomplish the task using only on-shift staff and pre-staged tools and equipment.

c. There is no discussion of the assumptions regarding timing of the use of the 480V portable diesel generator. Discuss the use of this equipment with regards to the time required to place it into service and how it is credited in the PRA; provide the human error probability used in the PRA for this action, and the basis of the calculation, including availability of procedures, and the capability to accomplish the task using only on-shift staff and pre-staged tools and equipment.

d. Describe how the human error dependency for aligning the fifth diesel generator and the portable diesel generator is addressed in the PRA model, if the PRA credits both recovery actions in the same cutset.

e. Describe the sensitivity of the risk results to crediting the fifth diesel generator and the portable diesel generator.

f. Describe any assumptions in the PRA regarding repair of diesel generators. If repairs are credited, describe how the human error dependency between those repairs and the actions to align the fifth diesel generator and the portable diesel generator are addressed, if the PRA credits both repairs and recovery actions in the same cutset.

g. One of the open findings and observations (F&O) from the 2003 peer review (Attachment 4 of Reference 1) addressed the age of the plant-specific failure data used in the PRA model, and identified 1999 as the end of the data period. The disposition of this F&O states that the diesel generators use plant-specific data, but did not identify if more recent data was applied. Identify what plant-specific failure data has been used for the diesel generators in this application; if recent (post-1999) data is not incorporated, then describe the diesel generator performance over this 10-year period and justify that the PRA model failure probabilities are appropriate for this application.

3. The licensee described the approach applied to the quantitative evaluation of fire risk for this application (Section 4.2.1.2 of the Enclosure to Reference 1, Attachment 1 of Reference 2).

The licensee is requested to provide the following additional information/clarifications:

a. Reference 1 states that an assumption is made that all fires not manually suppressed progress to a large fire which damages all cables and equipment in the zone.

Reference 2 (Question #2, Quantification of Fire Risk) states that fire risk considers both the probability of nonsupression and the probability of a fire progressing to a large fire. Reference 2 (Question #2, Assumptions) also states that all fires progress to large

fires. Reconcile these three statements and clearly identify the assumption made relating to suppression and the magnitude of fires.

b. References 1 and 2 state that an assumption is made when a fire zone includes cables affecting both ST No. 20 (the out-of-service transformer) and ST No. 10 (the sole remaining transformer providing offsite AC power to both units), the risk metrics were doubled to account for ST No. 20 being unavailable. Confirm that this assumption is consistent with the response to RAI 1a, above, regarding the change in frequency of plant-centered LOOP events for the one transformer available configuration.

c. The fire risk is only presented for unit 1. There is no discussion in either of the submittals to address the applicability of these risk results to unit 2, and the basis for that conclusion, including the assessment of any unit 2 specific configuration issues which could affect the fire risk calculations. Confirm the applicability and basis for the unit 1 fire risk calculations to unit 2.

d. Reference 2 (Attachment 1, Question 2, General Approach) states that an assumption is made that cables fail open. This may be nonconservative for zones containing cables for normally closed circuit breakers connecting ST No. 10 to the plant electrical busses, in that an open circuit failure might leave the breaker closed, but a short circuit failure could result in spurious actuation of the breakers, interrupting offsite power. Provide an assessment and disposition of the potential for and failure impacts of spurious breaker actuations for the available offsite circuits.

4. Reference 1 provides a qualitative assessment and disposition of seismic events and external fires and floods, but does not address other external events (transportation and nearby facility accidents, toxic gas, high winds and tornadoes). Provide a disposition of these events for this application. (The staff has accepted that such events are not significant contributors to risk if the plant design conforms to the 1975 Standard Review Plan criteria, which is typically discussed in the Individual Plant Examination of External Events.)

5. Reference 1 Attachment 3 identifies a regulatory commitment (#4) addressing the availability of systems and components which are associated with the licensees tier 2 evaluation of potentially risk-significant configurations in accordance with Regulatory Guide (RG) 1.177. The licensee is requested to address the following concerns:

a. The commitment wording is that the listed systems and components will be required to be available during the ST No. 20 replacement, and then states Elective maintenance will not be performed and then identifies actions to be taken if the system or component is unavailable due to causes other than elective maintenance.

The staff assumes that the intent of this commitment is that the systems and components will be available unless an unplanned failure occurs, and that no elective maintenance, preventive maintenance, planned testing, or any other activity which is not absolutely required to be performed during the transformer outage will be conducted.

Reword this commitment to be less ambiguous.

b. The commitment includes a risk evaluation of any emergent unavailability of the systems and components to determine if the basis for the proposed one-time change to LCO 3.8.1 remains valid. The intent of the tier 2 evaluation recommended in RG 1.177 is

to specifically identify and prohibit such high risk configurations, not to commit to evaluate the risk if such configurations occur; that is the scope of the tier 3 process.

Based on the risk significance of the fifth diesel generator and the portable diesel generator determined in the response to RAI 2e, above, and the risk significance of the other systems and components in the scope of commitment #4, it may be appropriate for the TS to directly include the requirement for availability of some of the systems and components during the extended outage of ST No. 20, and to provide for an immediate plant shutdown if these components are unavailable. Assess the risk impacts of the unavailability of these systems and components, and if appropriate, provide the appropriate TS control in the one-time amendment changes.

c. The unavailability of the emergency diesel generators during the ST No. 20 outage appears to be addressed by existing plant Technical Specification (TS) action requirements (TS 3.8.1, Condition D) which would apply when a diesel generator and an offsite circuit are both unavailable. It is unnecessary to make any additional commitment for such components, and the licensee may wish to remove the diesel generators from the list.

6. Section 4.2.1.2 of the Enclosure of Reference 1 includes a section on dual unit shutdown issues. The licensee is requested to address the following concerns related to shared diesel generators:

a. The standby diesel generators are not identified as a common system that may be needed for both units to shutdown. It is not clear if the diesel generators are dedicated to a unit, or if not, how the electrical loads between units are split amongst the four diesel generators. It is also not clear whether the failure of more than one diesel generator still permits both units to safely shutdown. The FSAR chapter 8 states that failure of one of four diesel generators still permits safe shutdown of both units.

Describe the configuration of the electrical system as it pertains to sharing of diesel generators between the units.

b. For dual unit plants with shared systems, if a common initiating event will challenge both units to safely shutdown simultaneously, the PRA must not credit the same equipment for mitigating the event in both units. Describe how the SSES PRA model addressed shared systems for this application for the case of a plant-centered LOOP (such as a failure of the ST No. 10 transformer), where both units lose offsite power and must rely upon the shared onsite diesel generators.

You requested approval of the amendment request by September 1, 2009. A full and complete response must be received by June 30, 2009, in order to be able to support this schedule.

If you have any questions and/or need clarifications, please contact me.

Bhalchandra K. Vaidya Licensing Project Manager NRC/NRR/DORL/LPL1-1 (301)-415-3308 (O) bhalchandra.vaidya@nrc.gov E-mail Properties

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Subject:

Susquehanna Units 1 and 2, TAC Nos. ME0969 & ME0970- RAIs from APLA (PRA)

Sent Date: 05/29/2009 6:56:03 AM Received Date: 05/29/2009 7:17:00 AM From: Bhalchandra Vaidya Created By: Bhalchandra.Vaidya@nrc.gov Recipients:

dlfilchner@pplweb.com ('dlfilchner@pplweb.com')

Tracking Status: None ctcoddington@pplweb.com ('Coddington, Cornelius T')

Tracking Status: None ckhoffman@pplweb.com ('ckhoffman@pplweb.com')

Tracking Status: None Douglas.Pickett@nrc.gov (Douglas Pickett)

Tracking Status: None John.Boska@nrc.gov (John Boska)

Tracking Status: None Richard.Guzman@nrc.gov (Richard Guzman)

Tracking Status: None Andrew.Howe@nrc.gov (Andrew Howe)

Tracking Status: None Donnie.Harrison@nrc.gov (Donnie Harrison)

Tracking Status: None Post Office:

Files Size Date & Time MESSAGE 39603 05/29/2009 Options Expiration Date:

Priority: olImportanceNormal ReplyRequested: False Return Notification: False Sensitivity: olNormal Recipients received: