ML20195F089
| ML20195F089 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 11/13/1998 |
| From: | Terry C TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TXX-98244, NUDOCS 9811190192 | |
| Download: ML20195F089 (7) | |
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Log # TXX-98244
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File # 10010-r
-C-916 (3/4.1)
'7tlELECTRIC 916 (3/4.5)
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. November 13,1998 LC.LasseDrry.
I Senior Hee Pmident c
& PrincipalNuclear OBicer J 1
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Ul S.; Nuclear' Regulatory Commission
.: Attn: Document Control Desk 4
Washington, DC - 205551 1
SUBJECT:
~-. COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)
DOCKET NOS. 50-445 AND 50-446 SUPPLEMENT TO THE RESPONSE TO THE NRC REQUEST FOR ADDITIONAL INFORMATION ON LICENSE AMENDMENT REQUEST 96-06
. REF:
1)' TU Electric Letter, logged TXX-96434, from C. L. Terry to the NRC dated August 2,-1996
- 2) SNRC Letter from the T. J. Polich, NRR, to C. L. Terry, dated ~ July 30,1998 ~
~ 3) TU Electric Letter, logged TXX-98215, from C. L. Terry to the NRC dated October 2,1998
' Gentlemen:
. License (NPF-87) and CPSES Unit 2 Operating License (NPF-89) by incorporating changes that would increase the outage time' allowed for a centrifugal charging pump to
.be out of service from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 7. days for CPSES Units 1 and 2.- Per Reference 2, TU Electric submitted a response to a request for additional information regarding R
~ License Amendment Request 96-06. Provided herein (Attachment 2) are supplemental clarifications to the response provided in Reference 3.. Attachment 1 is the affidavit for
- this information supporting License Amendment Request 96-06.
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If you have any questions regarding the attached information, please contact MrcJ.' D.' Seawright at (254) 897-0140.
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. 9811190192'981113 E'
PDR ADOCK 050004457 P
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COMANCHE PEAK STEAM ELECTRIC STATION i
P.o. Box 1002. Glen Rose, Texas 76043 1002
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.Page 2 of 2 '
This communication contains no new commitments regarding CPSES Units 1 and 2.
Sincerely, 1
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M jhN C. L. Terry
'JDS/jds
~ Attachments c-Mr. E. W. Merschoff, Region IV Mr. T. J. Polich, NRR Mr. J. l. Tapia, Region IV Resident inspector, CASES Mr. Arthur C. Tate Bureau of Radiation Control-Texas Department of Public Health 1100 West 49th Street Austin, Texas 78704
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,, to TXX-982441 Pag,e 1 of 1.
UNITED STATES OF AMERICA-NUCLEAR REGULATORY COMMISSION
- In the Matter of
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.. Texas Utilities Electric Company-
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Docket Nos. 50-445-
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50-446 i
' (Comanche Peak Steam Electric
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License Nos. NPF-87 Station, Units 1 & 2).
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NPF-89 AFFIDAVIT C. L. Terry being duly sworn, hereby deposes and says that he is the Senior Vice President and Prinicipal Nuclear Officer TU Electric, the licensee herein; that he is duly -
-i authorized to sign and file with the Nuclear Regulatory Commission this supplement to the Request for Additional Information regarding License Amendment Request 96-06; i
that he is familiar with the content thereof; and that the matters set forth therein are true '
j and correct to the best of his knowledge, information and belief.
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i C. L. Terry
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Senior Vice Presidenbahd Principal Nuclear Officer STATE OF TEXAS
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COUNTY OF Sea"N'd// ))
Subscribed and sworn to before me, on this /J// day of 7me C
.1998.
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/24W Notary Public
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SUSAN C. GRAVA1T
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NOTARY PUBLIC J
STATE OF TEXAS H
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j, kt/ Commnsion Emim 3-2M001 4 m-m
, to TXX 98244:
Page 1 of 4
'. Requested supplementalinformation on the CPSES CCP AOT RAI response Tier.1: ' Risk'imnact and PRA Validity -
- Clarification:
In the earlier response, TU Electric stated that there is no difference in instantaneous.
Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) between preventive maintenance and corrective maintenance for either internal or external events.
' Clarify how the' common cause failure of a centrifugal charging pump (CCP) was -
l considered in that analysis and how, in general, the CCP common cause failures are included in the results. Supplement the discussion of Instantaneous CDF and LERF
. given a CCP is out of service to discuss the difference in results between preventive maintenance and corrective maintenance from the perspective of common cause failure.
TU Electric Response:
.The common cause failu're parameters for the CCPs were calculated using the Multiple
)'
Greek Letter (MGL) model developed by Pickard, Lowe and Garrick, Inc. (PLG). These
' parameters were then used to quantify the effect of common cause events, including the P
CCPs. The Bayes Theorem was applied to combine the actual common cause failure -
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data from industry experience with engineering judgment from experts to estimate the j'
MGL parameters. The resultant MGL parameters for CCPs ( standby pumps) are: beta (two pumps fall to start on demand) = 0.0359 and beta (two pumps fail to operate after starting) = 0.00177.
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'.The basis for the earlier response to this question is the way common cause failure of a f
CCP is treated in the CPSES PRA model. The PRA modelincludes the common cause
' failure mode of a CCP in addition to the normal failure modes associated with the CCP (e.g., fails to start, test and maintenance, etc). Thus, using the model, common cause it
- failures of a CCP can occur coincident with any other of the failure modes and not only with a corrective maintenance unavailability. The results of the CCP study are based on
- pre-generated cutsets. Given the low failure probability of the common cause basic t
1 event and the accident sequence modeling, common cause failure of the CCP is not
. included in the pre-generated results. [For CPSES, a truncation limit of 1E-09 was used based on modules and the resulting cutset typically includes cutsets down to several
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orders of magnitude below the truncation limit when the modules are expanded.] Thus, common cause is explicitly modeled in the fault tree, however, for the CCPs, it is appropriately truncated in the results.
However, to estimate the contribution of the truncated common cause failure cutsets to the instantaneous CDF, the CCP common cause failure value was added to the module value for the CCP and the cutsets requantified. The instantaneous CDF increased from 4.79E-05 to 4.81E-05. Thus, it can be seen that the effect of common cause failure is
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very small and the use of the pre-generated cutsets to estimate the instantaneous CDF is appropriate. This shows that for the cases in question, namely corrective maintenance or
. preventive maintenance unavailability, the effect of common cause failure of the opposite train is included in the model and its contribution is insignificant to the instantaneous CDF.
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. to TXX 98244
. Page 2 of 4 l
Tier 2:
Restriction on High Risk Configuration Clarification:
Expand the response to address / describe what type of restrictions, or compensatory actions, e.g., TS and plant administrative procedures, would be in place to control out of service activities on the higher risk equipment listed in the response, and thus.
avold/ reduce potential risk-significant configurations. Discuss the development of the matrix and how it is used. Provide a brief description of the Safety Monitor and the schedule for putting it in service.
- TU Electric Response
- Plant Administrative Means to Control Out of Service Activities CPSES'uses a philosophy that during a given work week, planned maintenance will be limited to a given train / channel. That is, if a train A work week is scheduled, typically, no train B work will be scheduled during that period. By procedure, it is the responsibility of the Central Organization for Reliable Power Support (CORPS) team manager (that is, the
. Individual charged with planning and scheduling on-line and outage maintenance) to
. consider reliability, availability and other performance criteria when making work scheduling decisions affecting plant SSCs. This manager is also responsible for ensuring that safety assessment processes are incorporated and implemented during preparation
. and implementation phases of at-power and outage scheduling. The CORPS team is responsible for reviewing the cumulative effect on plant safety due to taking multiple
. systems out of service by performing a safety assessment. The safety assessment involves either a schedule review by the risk and reliability engineers or the use of -
screening guidelines, usually both.
Rheussion of Screening Guidelines and the Matrix in Control Out of Service Activities The screening guidelines used in the on-line maintenance safety assessment are based on a matrix approach that uses input from the PRA. The screening methodology recognizes that there are three main elements that control overall plant risk: events that could lead to reactor trip, events that affect the availability of systems required to mitigate the effects of transients and accidents, and events that affect systems required to maintain containment integrity. The screening process asks questions related to these
' elements and based on the outcome, makes a determination whether the events in question are more or less important to plant risk.
The matrix consists of a series of tables that identify the initiating events and the mitigating systems, and a table that shows pre-analyzed configurations. The pre-analyzed configurations were developed based on a review of the 12 week rolling schedule using various configurations of systems. The systems listed in the tables are those used in the CPSES PRA for accident mitigation. Using the PRA, these systems are i
further categorized into most risk significant systems and a table is provided in the matrix
.j listing them. The on-line maintenance safety assessment process asks a series of questions about a planned or emergent maintenance activity to determine how it relates to the systems on the matrix tables,in particular noting the cumulative effect of an activity with other such activities. Typically, if an activity window includes activities that f
' involve two of the mitigating systems and those activities have not been pre-analyzed, the cumulative effect of the activities will be classified as potentially significant and the
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activities will be evaluated further by risk and reliability engineers. The work control 1
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. to TXX 98244 i
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.Page 3 of 4 instructions provide that:
j WHEN work activities do not fit into Risk Categories 3 or 4 by use of the Screening Guidelines For On-Line Maintenance Safety Assessment (e.g., they are not part of an evaluated combination in the Risk Matrix), THEN these work activities should be evaluated by the Risk and Reliability Engineers or the On-Line Maintenance Safety Assessment software [This anticipates Safety Monitor which is described below] for risk categorization. Alternatively, the work may be rescheduled so that it is classified into Risk Category 3 or 4.
The review by the risk and reliability engineers may involve interacting with the PRA l
model to quantify the risk level. Depending on the results of this evaluation, the activity is classified into one of the risk _ categories and appropriate action taken. [The bases for the risk categories and their development are discussed in the' original response. These categories are based on core damage frequency. However, the threshold for medium risk category (category 3) corresponds to a RAW of approximately 2 to 3 and the threshold for the high-medium risk category (categorv 2) corresponds to a RAW of l
approximately 10 to 12.]
Thus, if a CCP was out of service for maintenance and another activity involving one of the other mitigating systems was contemplated, if the activity had not been pre-analyzed, the risk and reliability engineers would perform the evaluation and place it in the appropriate category. For example, if the other contemplated activity involved one of the important systems identified in the earlier response to this question, the cumulative effect would place the combined activity in one of the higher risk categories, in this case, the -
work controlinstructions provide the following:
IE the work activities are classified as Risk Categories 1 or 2, THEN the CORPS team
. scheduling supervisor should ensure that EITHER the Weekly Surveillance / Work Plan is modified, QR confer with plant management to prescribe required actions.
This may include deferring the work until plant conditions are more favorable (i.e.,
power reduction or plant shutdown) or compensatory measures to reduce the level of risk.
Discussion of the Safetv Monitor The Safety Monitorru is a trade name for an on-line computerized risk monitor developed by NUS/Scientech for CPSES and several other nuclear utilities. This risk monitor is an extension of the risk assessment screening guidelines and matrix currently employed at models the plant for all modes of operation and provides l
CPSES. The Safety Monitorru F
the users with the capability to assess the impact of on line maintenance activities on L
core damage frequency and large, early release frequency.
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.Once completed and implemented, the Safety Monitor will have the capability to assess ru the risk of individual configurations either planned or emergent. Like the existing guidelines and matrices, the associated risk from any configuration will be binned into
. one of three groups. These are: Green or low, Yellow or medium and Red or high. These f
bins can be directly correlated back to the screening guidelines and matrix. That is, Green equates to Category 4, Yellow to Category 3 and Red to Categories 2 and 1. The transition points between the various bins is the same as those used in the screening i
guidelines and matrix which are discussed in the earlier response. However, unlike the i
screening guidelines and matrix, the Safety MonitorTu will requantify the PRA model using 5
plant configuration and equipment out-of-service as input parameters.
CPSES is currently completing the verification and validation of the Safety Monitor code ru 4
p-l Attachment'2 to TXX 98244
=Page4Lof4-D. '
and the linked PRA model. Once complste (scheduled for the last quarter of '98), the Safety Monitor will be used in parallel with the screening guidelines and matrix over ru several months. Following this testing and shakedown period, the plan is to
- proceduralize the use of the Safety Monitor as an alternative method for required risk ru assessments.
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