Letter Sequence Approval |
---|
|
|
MONTHYEARML20244D6331986-01-15015 January 1986 Forwards SER Providing Risk Perspective of Util Proposal to Increase Allotted Outage Time from 3 to 7 Days for safety- Related Sys,Per Review of Util PRA (WCAP-10526).Review Results Listed Project stage: Approval 1986-01-15
[Table View] |
Similar Documents at Byron |
---|
Category:INTERNAL OR EXTERNAL MEMORANDUM
MONTHYEARML20211K8611999-09-0101 September 1999 Informs That There Has Been Some Confusion Re Recently Issued ODCM Generic Section Rev Which Needs to Be Clarified. Clarifications Are Listed ML20210P1361999-08-0404 August 1999 Notification of 990817 Meeting with Util in Rockville, Maryland to Discuss Status of Licensing Actions Submitted by Comm Ed & Plan for Proposed Licensing Workshop ML20206U2721999-05-13013 May 1999 Revised Notification of 990527 Meeting with Util in Lisle,Il to Discuss Results of Licensee Evaluation on Potential Chilling Effect Concern within Working Environ & Use of Overtime within Operations Dept Organization at Plant ML20206E9331999-05-0303 May 1999 Notification of 990524 Meeting with Commonwealth Edison,Co in Rockville,Md to Discuss Technical Issues Related to Proposed re-rack of SFPs at Braidwood Station & Byron Station ML20206U2801999-04-28028 April 1999 Notification of 990527 Meeting with Util in Lisle,Il to Discuss Results of Licensee Evaluation on Potential Chilling Effect Concern within Working Environ & Use of Overtime within Operations Dept Organization at Byron Station ML20155G4661998-11-0303 November 1998 Forwards Exam Repts 50-454/98-301(OL) & 50-455/98-301(OL) Administered on 980914-22 with as-given Written Exam Attached for Processing Through Nudocs & Distribution to NRC Staff,Including NRC PDR ML20155F6291998-11-0303 November 1998 Forwards Facility Outline & Initial Exam Submittal for Operator Licensing Exam Administered Wk of 980914 ML20197C8041998-09-0202 September 1998 Informs That Braidwood Station Concurs with Proposed Encl Response to NRC Re RPV Integrity at Braidwood & Byron Stations ML20151V2951998-09-0202 September 1998 Informs That Braidwood Station Concurs with Encl Proposed 980904 Util Response to NRC Re IPEEE ML20197C8301998-09-0101 September 1998 Informs That Rev 2 to Calculation BYR98-109/BRW-98-339-E Has Been Reviewed & Found Acceptable for Transmittal to Nrc. Draft Util Ltr Re Thermo-Lag Ampacity Derating Factor Calculation,Encl ML20237D4331998-08-21021 August 1998 Notification of 980903 & 04 Meetings W/Util in Rockville,Md to Discuss Technical Issues Related to Byron & Braidwood Improved Std TSs Conversion,Including Section 3.3,beyond Scope Issues,Closeout Packages & Amends to Current TSs ML20249A2231998-06-12012 June 1998 Notification of 980625-26 Meeting W/Util in Rockville,Md to Discuss Technical Issues Re Byron & Braidwood Improved Std TSs Conversion ML20217E3881998-04-23023 April 1998 Notification of 980506 & 07 Meetings W/Util in Rockville,Md to Discuss Technical Issues Re Plants Improved STS Conversion ML20217H5421998-03-31031 March 1998 Discusses Completion of SG Replacement Proj at Plant,Unit 1. Plant Resumed Power Operation on 980308 ML20216H3401998-03-17017 March 1998 Notification of 980331-0402 Meeting W/Util in Rockville,Md to Discuss Reviewer Comments on Byron & Braidwood Improved Std TS Submittal ML20216H6971998-03-17017 March 1998 Notification of 980326 Meeting W/Commonwealth Edison Co in Lisle,Il to Discuss Comed Request to Consolidate near-site Emergency Operations Facility Into Single Central EOF ML20203G8551998-02-23023 February 1998 Notification of 980305 Meeting W/Util in Rockville,Md to Discuss Status of Byron & Braidwood Licensing Issues ML20203C3621997-11-25025 November 1997 Revised Notification W/New Starting Time of Meeting W/Ceco on 971215 in Rockville,Maryland to Discuss Review Schedule Byron & Braidwood Improved TS Conversion & Supplemental Submittals ML20202E5831997-11-25025 November 1997 Notification of 971215 Meeting W/Commonwealth Edison Co in Rockville,Md to Review Schedule for Listed Plants Improved Std TS Conversion & Supplemental Submittals ML20236N5111997-10-22022 October 1997 Fowards Staff Response to 960912 TIA Re Containment Spray Additive Sys Conformance W/Design Basis & Tss.Analysis Concluded That 2,400-2,600 Ppm in RWST Acceptable ML20217K8271997-10-16016 October 1997 Notification of 971024 Meeting W/Util to Discuss Results of Comed Investigation Into Sensitivity of Proposed voltage- Dependent Growth Rates to Binning Strategy for ODSCC Indicators ML20217D4261997-09-30030 September 1997 Informs of Scheduled Visits W/Nuclear Services at Gpu on Nov 14th & Visit at Commonwealth Edison on Dec 3rd & Would Like to Receive Any Info Available.Supporting Documentation Encl ML20217E1591997-09-26026 September 1997 Notification of 971001 Meeting W/Ceco in Rockville,Maryland to Discuss Licensee Plans for SG Replacement Program at Byron,Unit 1 ML20217B3901997-09-23023 September 1997 Forwards Questions Re Ceco Submittal of Revised SG Tube Rupture Analysis for Byron,Unit 1 & Braidwood,Unit 1 ML20210S8461997-09-0202 September 1997 Notification of 970904 Meeting W/Util in Rockville,Md to Discuss Comed Methodology,Including Assumptions for Calculating Radiation Exposure Doses Resulting from Predicted SG Tube Leakage in Event of Msb ML20217Q9531997-08-28028 August 1997 Notification of 970904 Meeting W/Util in Rockville,Md to Discuss CE Methodology,Including Assumptions for Calculating Radiation Exposure Doses Resulting from Predicted SG Tube Leakage in Event of Msb ML20210L7831997-08-18018 August 1997 Notification of 970826 Meeting W/Util in Rockville,Md to Discuss Comeds Methodology Including Assumptions for Calculating Radiation Exposure Doses Resulting from Predicted SG Tube Leakage in Event of Main Steamline Break ML20149L1901997-07-22022 July 1997 Notification of 970723 Meeting W/Commonwealth Edison Co in Rockville,Md to Discuss Results of Spring 1997,Braidwood,1 SG Tube Eddy Current Insp.Time of Meeting Rescheduled ML20149F2731997-07-0303 July 1997 Notification of 970723 Meeting W/Util in Rockville,Md to Discuss Results of Spring 1997 Plant,Unit 1 SG Tube Eddy Current Insp Including Determination of Impact of Data ML20138D2781997-04-28028 April 1997 Notification of 970430 Meeting W/Util in Rockville,Md to Discuss Results of EC Insps of Plant SGs Conducted During Present Refueling Outage ML20217D5461997-04-18018 April 1997 Forwards Partially Withheld Background Briefing Package in Preparation for 970425 Meeting Between Comed & Commission IA-97-178, Forwards Partially Withheld Background Briefing Package in Preparation for 970425 Meeting Between Comed & Commission1997-04-18018 April 1997 Forwards Partially Withheld Background Briefing Package in Preparation for 970425 Meeting Between Comed & Commission ML20147J2391997-04-0909 April 1997 Notification of Meeting on 970416 W/Util in Rockville,Md to Discuss Overall Response & Present Addl Details Re Performance Indicators Used to Monitor Performance Stations ML20138J7671997-02-0505 February 1997 Informs That NRC Plans to Administer Generic Fundamentals Exam Section of Written Operator Licenseing Exam on 970409. Ltr W/Copy to Chief,Operator Licensing Branch Must Be Submitted to Listed Address in Order to Register Personnel ML20149M6901997-01-19019 January 1997 Notification of 970128 Meeting W/Commonwealth Edison Co to Discuss Licensee Proposed Program for Use of Mixed Oxide Fuel ML20133J4821997-01-15015 January 1997 Notification of 970123 Meeting W/Licensees in Rockville,Md to Discuss Contents of Plants TS Conversion Submittal, Provide Staff Comments Based on Initial Screening Review & Discuss Review Schedule ML20133J5811997-01-15015 January 1997 Notification of 970122 Meeting W/Util in Rockville,Md to Discuss Licensee Status of Program for Replacement & Operation of New SG at Byron 1 & Braidwood 1 ML20135D8861996-12-0505 December 1996 Notification of 961219 Meeting W/Util in Rockville,Md to Discuss Licensee Proposal of 961018 & to Delete Plant,Unit 1 mid-cycle SG Insp ML20135C4761996-12-0505 December 1996 Forwards Request for Addl Info Re Application to Amend Licenses Extending Steam Generator Replacement for Byron Unit 1 and Braidwood Unit 1 ML20135D1241996-12-0404 December 1996 Forwards NRC Approved Operator Licensing Exam (Facility Outline & Initial Exam Submittal & as-given Operating Exam) for Tests Administered on 960930-1014 ML20135B4811996-12-0303 December 1996 Forwards Info Re Eddy Current Indications Located on cold-leg Side of Plant SG Tubes ML20210N4271996-12-0202 December 1996 Informs About Drop in Meeting on 961203 for Update on Industry Restructuring & Deregulation,Unicom Strategic Planning & Mixed Oxide Fuel ML20217D5421996-11-27027 November 1996 Forwards Partially Withheld Background Briefing Package in Preparation for 961203 Meeting Between Comed,Nuclear Strategic Services & Chairman Jackson ML20136E6221996-11-19019 November 1996 Informs That Draft in on Operator Activities Affecting Reactivity Being Distributed ML20149L7721996-11-14014 November 1996 Notification of 961114 Meeting W/Util in Rockville,Md to Discuss Methodology & Database Proposed by Comed to Determine Length of Operating Cycle Between SG Tube Eddy Current Insps for Plants,Unit 1 ML20210N3761996-08-12012 August 1996 Informs About Meeting on 960513 to Brief Chairman Jackson on Comed Response to Deregulation ML20217D4761996-07-31031 July 1996 Forwards Background Briefing Package in Prepartion of 960813 Meeting Between Commonwealth Edison Co & Chairman Jackson. Purpose of Visit to Discuss Recent Organizational Changes at Comed & Company Mgt Focus for Immediate Future ML20210N3381996-05-14014 May 1996 Discusses Courtesy Visit to Ceco on 960513 Re Listed Plants ML20210N2681995-11-13013 November 1995 Discusses Paritially Withheld Chairman Briefing by Ceco on 951116 ML20217D5321995-11-0909 November 1995 Forwards Partially Withheld Background Briefing Package in Preparation for 951116 Meeting Between Commission & Senior Comed Mgt.Purpose of Visit to Discuss Performance at Each of Sites & Challenges & Issues Needed to Be Addressed 1999-09-01
[Table view] Category:MEMORANDUMS-CORRESPONDENCE
MONTHYEARML20211K8611999-09-0101 September 1999 Informs That There Has Been Some Confusion Re Recently Issued ODCM Generic Section Rev Which Needs to Be Clarified. Clarifications Are Listed ML20210P1361999-08-0404 August 1999 Notification of 990817 Meeting with Util in Rockville, Maryland to Discuss Status of Licensing Actions Submitted by Comm Ed & Plan for Proposed Licensing Workshop ML20206U2721999-05-13013 May 1999 Revised Notification of 990527 Meeting with Util in Lisle,Il to Discuss Results of Licensee Evaluation on Potential Chilling Effect Concern within Working Environ & Use of Overtime within Operations Dept Organization at Plant ML20206E9331999-05-0303 May 1999 Notification of 990524 Meeting with Commonwealth Edison,Co in Rockville,Md to Discuss Technical Issues Related to Proposed re-rack of SFPs at Braidwood Station & Byron Station ML20206U2801999-04-28028 April 1999 Notification of 990527 Meeting with Util in Lisle,Il to Discuss Results of Licensee Evaluation on Potential Chilling Effect Concern within Working Environ & Use of Overtime within Operations Dept Organization at Byron Station ML20155G4661998-11-0303 November 1998 Forwards Exam Repts 50-454/98-301(OL) & 50-455/98-301(OL) Administered on 980914-22 with as-given Written Exam Attached for Processing Through Nudocs & Distribution to NRC Staff,Including NRC PDR ML20155F6291998-11-0303 November 1998 Forwards Facility Outline & Initial Exam Submittal for Operator Licensing Exam Administered Wk of 980914 ML20151V2951998-09-0202 September 1998 Informs That Braidwood Station Concurs with Encl Proposed 980904 Util Response to NRC Re IPEEE ML20197C8041998-09-0202 September 1998 Informs That Braidwood Station Concurs with Proposed Encl Response to NRC Re RPV Integrity at Braidwood & Byron Stations ML20197C8301998-09-0101 September 1998 Informs That Rev 2 to Calculation BYR98-109/BRW-98-339-E Has Been Reviewed & Found Acceptable for Transmittal to Nrc. Draft Util Ltr Re Thermo-Lag Ampacity Derating Factor Calculation,Encl ML20237D4331998-08-21021 August 1998 Notification of 980903 & 04 Meetings W/Util in Rockville,Md to Discuss Technical Issues Related to Byron & Braidwood Improved Std TSs Conversion,Including Section 3.3,beyond Scope Issues,Closeout Packages & Amends to Current TSs ML20249A2231998-06-12012 June 1998 Notification of 980625-26 Meeting W/Util in Rockville,Md to Discuss Technical Issues Re Byron & Braidwood Improved Std TSs Conversion ML20217E3881998-04-23023 April 1998 Notification of 980506 & 07 Meetings W/Util in Rockville,Md to Discuss Technical Issues Re Plants Improved STS Conversion ML20217H5421998-03-31031 March 1998 Discusses Completion of SG Replacement Proj at Plant,Unit 1. Plant Resumed Power Operation on 980308 ML20216H3401998-03-17017 March 1998 Notification of 980331-0402 Meeting W/Util in Rockville,Md to Discuss Reviewer Comments on Byron & Braidwood Improved Std TS Submittal ML20216H6971998-03-17017 March 1998 Notification of 980326 Meeting W/Commonwealth Edison Co in Lisle,Il to Discuss Comed Request to Consolidate near-site Emergency Operations Facility Into Single Central EOF ML20203G8551998-02-23023 February 1998 Notification of 980305 Meeting W/Util in Rockville,Md to Discuss Status of Byron & Braidwood Licensing Issues ML20202E5831997-11-25025 November 1997 Notification of 971215 Meeting W/Commonwealth Edison Co in Rockville,Md to Review Schedule for Listed Plants Improved Std TS Conversion & Supplemental Submittals ML20203C3621997-11-25025 November 1997 Revised Notification W/New Starting Time of Meeting W/Ceco on 971215 in Rockville,Maryland to Discuss Review Schedule Byron & Braidwood Improved TS Conversion & Supplemental Submittals ML20236N5111997-10-22022 October 1997 Fowards Staff Response to 960912 TIA Re Containment Spray Additive Sys Conformance W/Design Basis & Tss.Analysis Concluded That 2,400-2,600 Ppm in RWST Acceptable ML20217K8271997-10-16016 October 1997 Notification of 971024 Meeting W/Util to Discuss Results of Comed Investigation Into Sensitivity of Proposed voltage- Dependent Growth Rates to Binning Strategy for ODSCC Indicators ML20217D4261997-09-30030 September 1997 Informs of Scheduled Visits W/Nuclear Services at Gpu on Nov 14th & Visit at Commonwealth Edison on Dec 3rd & Would Like to Receive Any Info Available.Supporting Documentation Encl ML20217E1591997-09-26026 September 1997 Notification of 971001 Meeting W/Ceco in Rockville,Maryland to Discuss Licensee Plans for SG Replacement Program at Byron,Unit 1 ML20217B3901997-09-23023 September 1997 Forwards Questions Re Ceco Submittal of Revised SG Tube Rupture Analysis for Byron,Unit 1 & Braidwood,Unit 1 ML20210S8461997-09-0202 September 1997 Notification of 970904 Meeting W/Util in Rockville,Md to Discuss Comed Methodology,Including Assumptions for Calculating Radiation Exposure Doses Resulting from Predicted SG Tube Leakage in Event of Msb ML20217Q9531997-08-28028 August 1997 Notification of 970904 Meeting W/Util in Rockville,Md to Discuss CE Methodology,Including Assumptions for Calculating Radiation Exposure Doses Resulting from Predicted SG Tube Leakage in Event of Msb ML20210L7831997-08-18018 August 1997 Notification of 970826 Meeting W/Util in Rockville,Md to Discuss Comeds Methodology Including Assumptions for Calculating Radiation Exposure Doses Resulting from Predicted SG Tube Leakage in Event of Main Steamline Break ML20149L1901997-07-22022 July 1997 Notification of 970723 Meeting W/Commonwealth Edison Co in Rockville,Md to Discuss Results of Spring 1997,Braidwood,1 SG Tube Eddy Current Insp.Time of Meeting Rescheduled ML20149F2731997-07-0303 July 1997 Notification of 970723 Meeting W/Util in Rockville,Md to Discuss Results of Spring 1997 Plant,Unit 1 SG Tube Eddy Current Insp Including Determination of Impact of Data ML20138D2781997-04-28028 April 1997 Notification of 970430 Meeting W/Util in Rockville,Md to Discuss Results of EC Insps of Plant SGs Conducted During Present Refueling Outage ML20217D5461997-04-18018 April 1997 Forwards Partially Withheld Background Briefing Package in Preparation for 970425 Meeting Between Comed & Commission IA-97-178, Forwards Partially Withheld Background Briefing Package in Preparation for 970425 Meeting Between Comed & Commission1997-04-18018 April 1997 Forwards Partially Withheld Background Briefing Package in Preparation for 970425 Meeting Between Comed & Commission ML20147J2391997-04-0909 April 1997 Notification of Meeting on 970416 W/Util in Rockville,Md to Discuss Overall Response & Present Addl Details Re Performance Indicators Used to Monitor Performance Stations ML20138J7671997-02-0505 February 1997 Informs That NRC Plans to Administer Generic Fundamentals Exam Section of Written Operator Licenseing Exam on 970409. Ltr W/Copy to Chief,Operator Licensing Branch Must Be Submitted to Listed Address in Order to Register Personnel ML20149M6901997-01-19019 January 1997 Notification of 970128 Meeting W/Commonwealth Edison Co to Discuss Licensee Proposed Program for Use of Mixed Oxide Fuel ML20133J5811997-01-15015 January 1997 Notification of 970122 Meeting W/Util in Rockville,Md to Discuss Licensee Status of Program for Replacement & Operation of New SG at Byron 1 & Braidwood 1 ML20133J4821997-01-15015 January 1997 Notification of 970123 Meeting W/Licensees in Rockville,Md to Discuss Contents of Plants TS Conversion Submittal, Provide Staff Comments Based on Initial Screening Review & Discuss Review Schedule ML20135D8861996-12-0505 December 1996 Notification of 961219 Meeting W/Util in Rockville,Md to Discuss Licensee Proposal of 961018 & to Delete Plant,Unit 1 mid-cycle SG Insp ML20135C4761996-12-0505 December 1996 Forwards Request for Addl Info Re Application to Amend Licenses Extending Steam Generator Replacement for Byron Unit 1 and Braidwood Unit 1 ML20135D1241996-12-0404 December 1996 Forwards NRC Approved Operator Licensing Exam (Facility Outline & Initial Exam Submittal & as-given Operating Exam) for Tests Administered on 960930-1014 ML20135B4811996-12-0303 December 1996 Forwards Info Re Eddy Current Indications Located on cold-leg Side of Plant SG Tubes ML20210N4271996-12-0202 December 1996 Informs About Drop in Meeting on 961203 for Update on Industry Restructuring & Deregulation,Unicom Strategic Planning & Mixed Oxide Fuel ML20217D5421996-11-27027 November 1996 Forwards Partially Withheld Background Briefing Package in Preparation for 961203 Meeting Between Comed,Nuclear Strategic Services & Chairman Jackson ML20136E6221996-11-19019 November 1996 Informs That Draft in on Operator Activities Affecting Reactivity Being Distributed ML20149L7721996-11-14014 November 1996 Notification of 961114 Meeting W/Util in Rockville,Md to Discuss Methodology & Database Proposed by Comed to Determine Length of Operating Cycle Between SG Tube Eddy Current Insps for Plants,Unit 1 ML20210N3761996-08-12012 August 1996 Informs About Meeting on 960513 to Brief Chairman Jackson on Comed Response to Deregulation ML20217D4761996-07-31031 July 1996 Forwards Background Briefing Package in Prepartion of 960813 Meeting Between Commonwealth Edison Co & Chairman Jackson. Purpose of Visit to Discuss Recent Organizational Changes at Comed & Company Mgt Focus for Immediate Future ML20210N3381996-05-14014 May 1996 Discusses Courtesy Visit to Ceco on 960513 Re Listed Plants ML20210N2681995-11-13013 November 1995 Discusses Paritially Withheld Chairman Briefing by Ceco on 951116 ML20217D5321995-11-0909 November 1995 Forwards Partially Withheld Background Briefing Package in Preparation for 951116 Meeting Between Commission & Senior Comed Mgt.Purpose of Visit to Discuss Performance at Each of Sites & Challenges & Issues Needed to Be Addressed 1999-09-01
[Table view] |
Text
_ _ _ _ _ - _ _ _
, h 'ghan
- 'o
~g UNITED STATES
- ! "' o NUCLEAR REGULATORY COMMISSION
- h. $ WASHINGTON, D. C. 20555
%.,,,# JAN 151985 l MEMORANDUM FOR: Hugh L. Thompson, Jr., Director Division of PWR Licensing-A, NRR FROM: Themis P. Speis, Director Division of Safety Review and Oversight
SUBJECT:
SAFETY EVALUATION REPORT RELATED TO THE LC0 RELAXATION '
PROGRAM FOR THE BYF,0N GENERATING STATION (TAC NO. M57242)
We have completed our review of the probabilistic risk analysis
. (WCAP-10526) submitted by Commonwealth Edison in support of their proposal
- to increase the Allowed Outage Times (A0Ts) from 3 days to 7 days for nine safety related systems in the Byron plant. This Safety Evaluation Report provides our risk perspective of the proposal, and is submitted as supporting y information for decision making by NRC. In brief, the results of our review
! are:
I Flagged a significant plant vulnerability in connection
! with Byron Unit 1 operating with its two pump essential i
service water (ESW) system without established cross-tie 4
capability for ESW backup from Unit 2; interim resolution 1 of this problem, pending completion of Unit 2, was obtained j by Commonwealth Edison's commitment of December 6, 1986 to j make at least one ESW pump from Unit 2 available for Unit 1 i prior to the operational restart of Unit 1; and i Support a decision to permit the proposed increase in A0T for six safety related systems in the Byron plant.
! Support denial of the proposed increase in A0T for the essential service water system, diesel generators, and the auxiliary
, feedwater system.
The Applicant's submittal was reviewed by the Reliability and Risk Assessment Branch with technical assistance by the Brookhaven National Laboratory (BNL). The Applicant's risk analysis utilized various PRA l! models and data developed for the Zion Probabilistic Safety Study, the j, rationale for this being the general similarity in the design and operation of the Zion and Byron plants.
l,
Contact:
A. Spano, RSIB Ext. 28302
- a. . r, , i JM 151986. i I
]
i e
Our review approach involved the following considerations:
(a) _ Single Unit Operation: The review was performed in the context of the existing operational status at Byron, i.e., operation of Unit ;
1 only, with no established capability for inter-unit sharing of i the essential water system. This is of consequence in regard to the l assessment of risk posed by the Byron 1 two pump ESWS, which, in. '
the absence of the potential backup capability that could be pro-vided by the Unit 2 ESW pumps, can fail with a frequency of'about 9x10 4 per year. Failure of this vital support system fails important safety functions, including the cooling of the reactor coolant pump (RCP) seals, which can lead (with an assumed probability of 0.5) to a non recoverable seal LOCA. Thus, the Loss-of-ESW initiating event by itself is estimated to-provide a direct contri-bution to core melt frequency of about 5x10 4/ year. In this connection, i the large difference in Byron 1 core melt frequency results obtained . ,
between BNL and the Applicant's study is principally due to the fact j i
that this accident initiator was not considered in WCAP-10526. I Estimates of the core melt frequency when a Unit 2 ESW pump is avail-able to Unit 1 are presented later.
(b) Risk Index The Applicant's study presented the impact of the proposed change in A0Ts in terms of changes in offsite health risks.
/
The staff analysis used core melt frequency as a risk measure, be- '
cause it is more directly related to changes in A0T, and because, in general, the core melt frequency is the limiting constraint to the proposed numerical guidelines of the NRC safety goal.
(c) System-Specific A0T Risk Impact: The Applicant's results apply to the case where the A0T change is applied to all nine proposed systems at the same time. This does not yield information on the relative risk impact posed by each of the various systems. The BNL analysis examined the effect of an A0T change on individual systems as well as on the proposed group of nine systems.
(d) Sensitivity Approach: The Applicant's A0T analysis was based on !
Bayesian estimated values of the frequency and duration of maintenance events. The relevant data base, both generic and
- plant specific, is of meager proportions. In the BNL analysis, uncertainties related to frequency and duration were addressed using a sensitivity approach in which the core melt frequency was linearly related to the mean maintenance duration time (Tm) for the systems of interest. The analysis covered the Tm range from 19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> (estimated to be the mean maintenance duration time for {
the current 3-day A0T technical specification) to the full 7-day {
period of 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />.
i i
ZrrI7 ~ ' ~ ~ ~ ~ ~ ~ ~
l ;, , w;
% ! 5 49 l 4-l The interim BNL results indicated the Byron 1 baseline core melt frequency for the existing 3-day A0T condition to be about 1x10 3/ year, the main con-tribution to this arising from the vulnerability posed by the Byron two pump ,
ESWS with no backup. Discussion of these results in meetings with the l
4 Applicant at NRC on December 3 and 6, 1985 focused on the question of the i expected reduction in core melt frequency that could be obtained if:
1 (a) revisions were made in three calculational factors affecting the i i
calculated annual frequency for loss of the Unit 1 ESW system and (b) one of l 1
the two Unit-2 ESW pumps were to be made available as additional emergency i l- backup to the two pump system in Unit 1.
- j. The net result of revising the three factors under (a) above, was an P approximate one-third reduction in the initiating event frequency for loss '
of ESW in Byron 1 (from about 1.5x10 3/ year to about 9.5x10 4/ year; see Appendix 1, Enclosure), with the net overall core melt frequency for Byron 1 j with 2 ESW pumps reduced from about 1x10 3/ year to about 7x10 4/ year. (These -
l estimates do not include a possible contribution due to common cause failures l between the ESW pumps). ,
t 1 This estimated core melt frequency of 7x10 4/ year for the Byron 1 two pump ESW is high. However, with the availability of a Unit-2 ESW pump (as committed to
.l by Commonwealth Ejison on December 6,1985) the initiating event frequency for loss of ESW is reduced by a factor of about 25, while the Byron core melt frequency point-estimate is reduced to nearly 2x10 4/ year.
1 As discussed more fully in the Enclosure, th9 core melt frequency results obtained with the mean maintenance duration time increased to a full 7 days
- indicate the Byron 1 risk impact for the two-ESW pump configuration to be j unacceptably high for the A0T increase applied to the ESWS, appreciably high for the DG and AFW system, and of little significance for the other six proposed ;
systems. While this conclusion clearly holds for Tm=168 hours, we believe 1);
the conclusion also holds for reduced values of Tm comparable with Zion plant experience.
1 j For the 3 pump ESW configuration, we believe the risk impact associated with increasing the A0T for the ESWS would still be too high. As indicated in the Enclosure, the primary reason for this is attributed to the sensitivity
- of the loss of ESW initiating event frequency to maintenance. Accordingly, a ,l
- relatively high rate of increase in core melt frequency is estimated to be !
obtained for the 3 pump case, amounting to approximately 1x10 6/ year for each l
additional hour of maintenance.
)' In conclusion, the results of the staff's probabilistic risk evaluation of
, the Byron A0T proposal would (a) support relaxation of the 3-day A0T for the t1 following systems: chargingpumps,safetyinjectionpumps,RHRpumps, fan !
coolers, containment spray pumps, and component cooling water pumps; (b) not
! support relaxation of the 3-day A0T for the following systems: essential l water system, diesel generators, and auxiliary feedwater pumps.
i l
i
4-Finally, it is important to point out that the risk perspective obtained in our evaluation is dependent, in particular, on the assumptions of-frequency and maintenance outage times provided in the Applicant's submittal. The technical specifications. set forth for Byron 1 provide, in general, no control on the. frequency of maintenance events, and, therefore, on the cum'lative u outage' times for the various systems. At the least, reasonable prudency would appear to warrant self-monitoring' actions by the utility to obtain trending.information on the frequency of maintenance' events, especially for the risk important ESW and DG support' systems, and the two pump AFW system.
~
no . _ _ ,
.hemis P. Spels, Director t .
Division of Safety Review and Oversight ,
Enclosure:
As stated cc: H. Denton R. Bernero
. .F. Miraglia j J. Knight .
V. Noonan j C t01shan % j E. Butcher'
- H 1
j
. _ . - - - - _ _ _ _ _