|
---|
Category:SAFETY EVALUATION REPORT--LICENSING & RELATED ISSUES
MONTHYEARML20211G9631999-08-30030 August 1999 SER Accepting Licensee Response to GL 96-05, Periodic Verification of Design-Basis Capability of Safety-Related Motor-Operated Valves ML20196J2191999-06-30030 June 1999 SER Concluding That Licensee USI A-46 Implementation Program,In General,Met Purpose & Intent of Criteria in GIP-2 & Staff Sser 2 for Resolution of USI A-46 ML20207G6411999-06-0303 June 1999 Safety Evaluation Supporting Amends 105,235 & 171 to Licenses DPR-21,DPR-65 & NPF-49,respectively ML20206M4631999-05-11011 May 1999 Safety Evaluation Supporting Alternative Proposed by Licensee to Perform Ultrasonic Exam on Inner Surface of Nozzle to safe-end Weld ML20206G6221999-05-0404 May 1999 SER Accepting Util Request to Apply leak-before-break Status to Pressurizer Surge Line Piping for Millstone Nuclear Power Station,Unit 2 ML20204H7131999-03-17017 March 1999 Safety Evaluation Concluding That NNECO Provided Adequate Justification for Deviations from RG 1.97,Rev 2, Recommendations,For Instrumentation Monitoring CST Level & Containment Area Radiation at Mnps Unit 2 ML20204C9441999-03-10010 March 1999 Safety Evaluation Denying Licensee Request for License Amend to Revise Frequency of Certain SRs for Electrical Power Sys ML20207L2631999-03-0505 March 1999 Safety Evaluation Supporting Amend 104 to License DPR-21 ML20207L5961999-02-22022 February 1999 Safety Evaluation Concluding That Code Requirements,Which Require 100 Percent Volumetric Exam of RPV flange-to-shell, Impractical to Perform to Extent Required & That Alternative Provide Reasonable Assurance of Structural Integrity ML20203D7601999-02-11011 February 1999 Safety Evaluation Supporting Millstone 1 Certified Fuel Handler Training & Retraining Program ML20196B0501998-11-24024 November 1998 Safety Evaluation Re Licensee 960213 Submittal of 180-day Response to GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves, for Plant,Unit 2 ML20155K1981998-11-0909 November 1998 Safety Evaluation Re Application of leak-before-break Status to Portions of Safety Injection & Shutdown Cooling Sys ML20195B8711998-11-0909 November 1998 Safety Evaluation Approving Revised Evaluation of Primary Cold Leg Piping leak-before-break Analysis for Plant ML20155C3781998-10-30030 October 1998 SER Denying Amend to Allow Changes to Fsar.Nrc Found That NNECO Had Not Considered Diversity Provided by Switch in Control Room That Removes Power to 1 of 2 MOV in SDC Sys Flow Path in Evaluation of High Low Pressure Design ML20155C8441998-10-29029 October 1998 Safety Evaluation Accepting Licensee Proposal to Withdraw ATWS Test Commitment ML20238F2781998-08-27027 August 1998 SER Related to Proposed Rev 20 to Northeast Utilities Quality Assurance Program Topical Rept for Millstone Nuclear Power Station,Units 1,2 & 3 ML20237D5001998-08-20020 August 1998 SER Approving Code Case N-389-1, Alternative Rules for Repairs,Replacements,Or Mods,Section Xi,Div 1 ML20236U7051998-07-22022 July 1998 Safety Evaluation Granting All Requests for Relief W/Exception of Requests RR-89-17 (Authorized for Class 1 Sys Only) & RR-89-21.Requests RR-13 & RR-14 Will Be Addressed in Separate Evaluation ML20236K6971998-07-0101 July 1998 SER Accepting Third 10-year Interval Inservice Insp Program Plan,Rev 2 & Associated Request for Relief & Proposed Alternatives for Plant,Unit 2 ML20236K3531998-07-0101 July 1998 Safety Evaluation Supporting Amend 218 to License DPR-65 ML20249C2541998-06-24024 June 1998 Safety Evaluation Accepting Proposed Rev 19 to NNECO QAP Topical Rept & Amended Through 980609.Informs That NNECO Exception to Provisions in Paragraph 10.3.5 of Constitutes Temporary & Acceptable Alternative ML20248J0031998-06-0404 June 1998 Safety Evaluation Accepting Millstone Nuclear Power Station Emergency Plan ML20248M2991998-06-0202 June 1998 Safety Evaluation Approving Application Re Restructuring of Central Maine Power Co by Establishment of Holding Company ML20248C4131998-05-26026 May 1998 SER of Individual Plant Exam of External Events Submittal on Millstone Nuclear Power Station,Unit 3 ML20217M4181998-04-30030 April 1998 Suppl Safety Evaluation Accepting Licensee RCS Pressure & Heat Removal by Containment Heat Removal Sys post-accident Monitoring Instrumentation ML20216G7921998-03-13013 March 1998 Safety Evaluation Authorizing Proposed Alternative to Check Valve Obturator Movement Requirements of OM-10 for SIL Accumulator Outlet for Listed Check Valves ML20203E8521998-02-17017 February 1998 SER Accepting Request for Relief from Requirements of 10CFR50.55a(f) for Performing Required Inservice Testing of Certain Class 2 Components IAW ASME Boiler & Pressure Vessel Code Section XI for Plant,Unit 3 ML20203E9341998-02-17017 February 1998 SER Accepting Request for Relief from Requirements of 10CFR50.55a(g) for Performing Required Exams for Certain Class 1 Components IAW ASME Boiler & Pressure Vessel Code Section XI for Plant,Unit 3 ML20203E2441998-02-0909 February 1998 Safety Evaluation Accepting Re Approval of Realistic,Median Centered Spectra Generated for Resolution of USI-A-46 ML20198R9941998-01-13013 January 1998 SER Accepting Licensee Response to GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves, for Millstone Nuclear Power Station,Unit 3 ML20202H7461997-12-10010 December 1997 Safety Evaluation Accepting Licensee Position That Correction of AC-11 Single Failure Vulnerability Unncessary ML20202J0911997-12-0202 December 1997 Safety Evaluation Accepting Proposed Exemption,Which Meets Special Circumstance Given in 10CFR50.12(a)(2)(ii) ML20198S2411997-10-31031 October 1997 SE Accepting Licensee Request for Deviations from Recommendations in Reg Guide 1.97,Rev 2 for Temp & Flow Monitoring Instrumentation for Cooling Water to ESF Sys Components & Containment Isolation Valve Position ML20212G5991997-10-27027 October 1997 Safety Evaluation Supporting Amend 103 to License DPR-21 ML20217K8801997-10-27027 October 1997 Correction to Safety Evaluation Supporting Amend 103 to License DPR-21.Phrase or Rod Block Protection Has Been Deleted from Listed Sentence in Staff Associated SE ML20212F1381997-10-22022 October 1997 Safety Evaluation Supporting Amend 102 to License DPR-21 ML20217M9301997-08-19019 August 1997 Safety Evaluation Accepting Continued Operation W/O High Startup Rate Trip by Nene for Millstone,Unit 2 ML20149J2661997-07-23023 July 1997 Safety Evaluation Accepting Changes & Reanalyses in ECCS Evaluation Models & Application of Models for Plant,Unit 2 ML20141L8821997-05-28028 May 1997 Safety Evaluation Supporting Amend 101 to License DPR-21 ML20138A0111997-04-23023 April 1997 Safety Evaluation Accepting Licensee Proposal,Not to Perform Type C Leakage Rate Testing on 14 Subject CIVs ML20137V5931997-04-15015 April 1997 Safety Evaluation Supporting Amend 100 to License DPR-21 ML20137U3121997-04-10010 April 1997 Safety Evaluation Supporting Amends 99,206 & 135 to Licenses DPR-21,DPR-65 & NPF-49,respectively ML20134A0331997-01-23023 January 1997 Safety Evaluation Accepting Util Proposed Alternatives to ASME Code Requirements ML20133N3401997-01-14014 January 1997 Safety Evaluation Supporting Amend 98 to License DPR-21 ML20135C4221996-12-0202 December 1996 Safety Evaluation Accepting Proposed Alternative Described in Relief Request R-1 Re Valve Inservice Testing Program at Facility ML20128P4381996-10-0909 October 1996 Safety Evaluation Accepting Review of Cracked Weld Operability Calculations & Staff Response to NRC Task Interference Agreement ML20128L7541996-10-0404 October 1996 Safety Evaluation Supporting Amend 97 to License DPR-21 ML20248C5451995-05-0202 May 1995 SER on Millstone Unit 3 Individual Plant Exam of External Events to Identify plant-specific Vulnerabilities,If Any,To Severe Accidents & Rept Results Together W/Any licensee-determined Improvements & C/A to Commission ML20248C5731994-07-19019 July 1994 SER Step 1 Review of Individual Plant Exam of External Fire Events for Millstone Unit 3 ML20059H4991994-01-24024 January 1994 Safety Evaluation Accepting Revised Responses to IEB-80-04 Re MSLB Reanalysis 1999-08-30
[Table view] Category:TEXT-SAFETY REPORT
MONTHYEARML20217P5391999-10-25025 October 1999 Rev 0,Change 1 to Millstone Unit 1 Northeast Utils QA Program ML20217C8721999-10-0606 October 1999 Rev 21,change 3 to MP-02-OST-BAP01, Nuqap Topical Rept, App F & G Only B17896, Monthly Operating Rept for Sept 1999 for Millstone Nuclear Power Station,Unit 1.With1999-09-30030 September 1999 Monthly Operating Rept for Sept 1999 for Millstone Nuclear Power Station,Unit 1.With B17894, Monthly Operating Rept for Sept 1999 for Millstone Nuclear Power Station,Unit 2.With1999-09-30030 September 1999 Monthly Operating Rept for Sept 1999 for Millstone Nuclear Power Station,Unit 2.With B17898, Monthly Operating Rept for Sept 1999 for Millstone Nuclear Power Station,Unit 3.With1999-09-30030 September 1999 Monthly Operating Rept for Sept 1999 for Millstone Nuclear Power Station,Unit 3.With ML20216J4341999-09-24024 September 1999 Mnps Unit 3 ISI Summary Rept,Cycle 6 ML20211N8401999-09-0202 September 1999 Rev 21,change 1 to Northeast Utils QA TR, Including Changes Incorporated Into Rev 20,changes 9 & 10 B17878, Monthly Operating Rept for Aug 1999 for Mnps,Unit 1.With1999-08-31031 August 1999 Monthly Operating Rept for Aug 1999 for Mnps,Unit 1.With B17874, Monthly Operating Rept for Aug 1999 for Millstone Nuclear Power Station,Unit 3.With1999-08-31031 August 1999 Monthly Operating Rept for Aug 1999 for Millstone Nuclear Power Station,Unit 3.With ML20216F5141999-08-31031 August 1999 Rept on Status of Public Petitions Under 10CFR2.206 B17879, Monthly Operating Rept for Aug 1999 for Millstone Nuclear Power Station,Unit 2.With1999-08-31031 August 1999 Monthly Operating Rept for Aug 1999 for Millstone Nuclear Power Station,Unit 2.With ML20211G9631999-08-30030 August 1999 SER Accepting Licensee Response to GL 96-05, Periodic Verification of Design-Basis Capability of Safety-Related Motor-Operated Valves ML20211A6561999-07-31031 July 1999 Monthly Operating Rept for July 1999 for Millstone Nuclear Power Station,Unit 2 B17858, Monthly Operating Rept for July 1999 for Millstone Nuclear Power Station,Unit 3.With1999-07-31031 July 1999 Monthly Operating Rept for July 1999 for Millstone Nuclear Power Station,Unit 3.With B17856, Monthly Operating Rept for July 1999 for Millstone Nuclear Power Station,Unit 1.With1999-07-31031 July 1999 Monthly Operating Rept for July 1999 for Millstone Nuclear Power Station,Unit 1.With ML20210J0311999-07-21021 July 1999 Rev 20,Change 10 to QAP 1.0, Organization ML20210E5931999-07-19019 July 1999 Revised Page 16 of 21,to App F of Northeast Util QA Program Plan ML20210C5911999-07-15015 July 1999 Revised Rev 20,change 10 to Northeast Util QA Program TR, Replacing Summary of Changes ML20210A0411999-07-15015 July 1999 Rev 20,change 10 to Northeast Util QA Program Tr B17814, Special Rept:On 990612 B Train EDG Failed to Restart within 5 Minutes Following Completion of 18 Month 24 H Endurance Run Required by TS 4.8.1.1.2.g.7.Caused by Procedural inadequacy.Re-performed Hot Restart Via Manual Start1999-07-12012 July 1999 Special Rept:On 990612 B Train EDG Failed to Restart within 5 Minutes Following Completion of 18 Month 24 H Endurance Run Required by TS 4.8.1.1.2.g.7.Caused by Procedural inadequacy.Re-performed Hot Restart Via Manual Start ML20209D1881999-07-0101 July 1999 Rev 20,change 9 to Northeast Util QA Program Tr ML20196J2191999-06-30030 June 1999 SER Concluding That Licensee USI A-46 Implementation Program,In General,Met Purpose & Intent of Criteria in GIP-2 & Staff Sser 2 for Resolution of USI A-46 ML20211A6751999-06-30030 June 1999 Revised Monthly Operating Rept for June 1999 for Millstone Nuclear Power Station,Unit 2,providing Revised Average Daily Unit Power Level & Operating Data Rept ML20196A8451999-06-30030 June 1999 Post Shutdown Decommissioning Activities Rept ML20209J0541999-06-30030 June 1999 Monthly Operating Rept for June 1999 for Millstone Unit 2 B17830, Monthly Operating Rept for June 1999 for Millstone Nuclear Power Station,Unit 3.With1999-06-30030 June 1999 Monthly Operating Rept for June 1999 for Millstone Nuclear Power Station,Unit 3.With ML20196K1791999-06-30030 June 1999 Addendum 6 to Millstone Unit 2 Annual Rept, ML20196J1821999-06-30030 June 1999 Rev 21,Change 0 to Northeast Utilities QAP (Nuqap) Tr B17833, Monthly Operating Rept for June 1999 for Millstone Power Station,Unit 1.With1999-06-30030 June 1999 Monthly Operating Rept for June 1999 for Millstone Power Station,Unit 1.With ML20195H1011999-06-11011 June 1999 Rev 20,change 8 to Northeast Utilities QAP (Nuqap) TR ML20207G6411999-06-0303 June 1999 Safety Evaluation Supporting Amends 105,235 & 171 to Licenses DPR-21,DPR-65 & NPF-49,respectively ML20211A6631999-05-31031 May 1999 Revised Monthly Operating Rept for May 1999 for Millstone Nuclear Power Station,Unit 2,providing Revised Average Daily Unit Power Level,Operating Data Rept & Unit Shutdowns & Power Reductions B17808, Monthly Operating Rept for May 1999 for Millstone Nuclear Power Station,Unit 3.With1999-05-31031 May 1999 Monthly Operating Rept for May 1999 for Millstone Nuclear Power Station,Unit 3.With ML20211B7351999-05-31031 May 1999 Cycle 7 Colr B17804, Monthly Operating Rept for May 1999 for Mnps,Unit 2.With1999-05-31031 May 1999 Monthly Operating Rept for May 1999 for Mnps,Unit 2.With B17807, Monthly Operating Rept for May 1999 for Mnps,Unit 1.With1999-05-31031 May 1999 Monthly Operating Rept for May 1999 for Mnps,Unit 1.With ML20209J0661999-05-31031 May 1999 Revised Monthly Operating Rept for May 1999 for Millstone Unit 2 ML20206M4631999-05-11011 May 1999 Safety Evaluation Supporting Alternative Proposed by Licensee to Perform Ultrasonic Exam on Inner Surface of Nozzle to safe-end Weld ML20206J8351999-05-0707 May 1999 Rev 20,Change 7 to QAP-1.0, Northeast Utls QA Program (Nuqap) Tr ML20206G6221999-05-0404 May 1999 SER Accepting Util Request to Apply leak-before-break Status to Pressurizer Surge Line Piping for Millstone Nuclear Power Station,Unit 2 B17782, Monthly Operating Rept for Apr 1999 for Millstone Nuclear Power Station,Unit 1.With1999-04-30030 April 1999 Monthly Operating Rept for Apr 1999 for Millstone Nuclear Power Station,Unit 1.With ML20205R3531999-04-30030 April 1999 Addendum 4 to Annual Rept, B17775, Monthly Operating Rept for Apr 1999 for Millstone Nuclear Power Station Unit 3.With1999-04-30030 April 1999 Monthly Operating Rept for Apr 1999 for Millstone Nuclear Power Station Unit 3.With ML20205K6141999-04-30030 April 1999 Non-proprietary Version of Rev 2 to Holtec Rept HI-971843, Licensing Rept for Reclassification of Discharge in Millstone Unit 3 Spent Fuel Pool ML20206E2971999-04-30030 April 1999 Rev 1 to Millstone Nuclear Power Station,Unit 2 COLR - Cycle 13 B17777, Monthly Operating Rept for Apr 1999 for Millstone Unit 2. with1999-04-30030 April 1999 Monthly Operating Rept for Apr 1999 for Millstone Unit 2. with ML20205Q5891999-04-0909 April 1999 Rev 20,change 6 to QAP-1.0,Northeast Utils QA Program TR ML20205R8751999-04-0909 April 1999 Provides Commission with Staff Assessment of Issues Related to Restart of Millstone Unit 2 & Staff Recommendations Re Restart Authorization for Millstone Unit 2 ML20206T3991999-03-31031 March 1999 First Quarter 1999 Performance Rept, Dtd May 1999 B17747, Monthly Operating Rept for Mar 1999 for Millstone Nuclear Power Station,Unit 1.With1999-03-31031 March 1999 Monthly Operating Rept for Mar 1999 for Millstone Nuclear Power Station,Unit 1.With 1999-09-30
[Table view] |
Text
-._. . _ ._ _ . . _ _ _ _ . __ _ . . _ _. _ ._ _._ _ _ _.__.,
i am p UNITED STATES 3
- NUCLEAR REGULATORY COMMISSION -
WASHINGTON, D.C. 30006 4001 SAFE TY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST TO WITHDRAW AN ANTICIPATED TRANSIENT WITHOUT SCRAM TEST COMMITMENT NORTHEAST N1 CLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT NO. 2 DOCKET NO. 50-336 l
1.0 INTRODUCTION
I By letter dated September 5,1997, Northeast Nuclear Energy Company (NNECO, licensee) requested NRC staff approval to withdraw a commitment made on July 25,1988, as part of its anticipated transient without scram (ATWS) modifications for the Millstone Nuclear Power Plant, Unit 2 (Millstone Unit 2). A request for additional Information (RAI) related to this topic was sent to the licensee on January 23,1998, and a response to the RAI was provided on May 6,1998. In addition, conference calls took place on June 22 and July 10,1998, between the staff and NNECO to discuss the failure modes of the shared power sources between the Reactor Protection System (RPS) and the Diverse Scram System (DSS), Based on these conversations, NNECO submitted additional information on September 14,1998.
2.0 BACKGROUND
The ATWS Rule (10 CFR 50.62) requires that the equipment / systems installed to prevent and/or mitigate the consequences of ATWS events be electrically independent of the existing RPS to
. minimize the potential for common mode failures (CMFs) that could affect both RPS and ATWS circuits. The Millstone Unit 2 DSS is part of the ATWS mitigation system. Electrical independence of the DSS from the existing RPS should be provided from the sensor outputs up to and including the final actuation device. The ATWS design at Millstone Unit 2 shares a common power supply between the RPS and DSS that deviates from the staff guidance provided in the supplemental information concerning electrical independence that was published with the ATWS Rule.
l The staff has allowed exceptions to the electricalindependence guidance for the DSS and RPS power supply circuits where these systems are designed, procured, installed, and maintained as fully redundant safety-related (Class 1E) circuits. NNECO was also required to demonstrate that CMFs of the shared power sources would not result in loss of both RPS and ATWS prevention / mitigation functions as discussed in item 2.a.2 of the staff's RAI dated June 8,1988.
The staff asked NNECO to explain why a CMF affecting the RPS power distribution system, including degraded voltage and frequency conditions, that would compromise both the RPS and the ATWS prevention / mitigation functions, cannot go undetected. The staff further indicated that, if alarms were relied on to provide early detection of degraded voltage and/or frequency conditions, NNECO was requested to identify the specific alarms provided along with a discussion of the periodic surveillance testing performed to verify alarm operability.
9811030024 981029 PDR ADOCK 05000336 P PDR Ehclosure
2-NNECO responded by stating that vital aternating current (ac) power to the four-channel RPS and the four-channel DSS is supplied from four vital (Class 1E safety related) inverters. These inverters are equipped with the following local and control room alarms and indications;
- a. Input Breaker Trip l b. AC Voltage Output Low (Setpoint of 108 VAC)
! c. AC Ground Fault
- d. High Temperature (Setpoint of 175 deg. F)
The inverters are powered by a station 125 VDC system, which consists of two batteries, three l battery chargers, and two battery busses. Each bus powers two inverters which, in tum, provide the four separate channels of vital 120-volt ac for the four-channel RPS and DSS. The battery bus and battery charger systems are monitored and alarmed for various conditions including:
- a. Charger Trouble:
- 1. High Voltage at 150 VDC
- 2. Low Voltage at 120 VDC
- b. DC Bus Undervoltage at 126 VDC
- c. Ground Alarms
- d. Indications are provided for battery current and voltage and direct current (dc) bus current and voltage.
NNECO also stated that the Millstone Unit 2 procedures call for testing of de bus undervoltage alarms at every other outage. However, NNECO indicated that revised procedures, which would be implemented at the next planned refueling outage, include testing one set of ac voltage output low alarms, charger trouble alarms, and de bus undervoltage alarms at alternate refueling outages. The revised procedures would ensure that one set of these alarms are tested during each outage. By letter dated September 5,1997, the staff was informed that provisions to test the above alarms were not implemented and that NNECO was requesting withdrawal of the testing commitment it made on July 25,1988, as part of its ATWS modifications.
3.0 EVALUATION As previously noted, an RAI was issued on January 23,1998, requesting clarification on the testing of the power supply circuit alarms. NNECO was asked if it had the capability to detect degraded conditions on the power distribution system without reliance on or credit for the alarms in question (ac voltage output low alarms, charger trouble alarms, and de bus undervoltage alarms). By response dated May 5,1998, as clarified on September 14,1998, NNECO indicated that, during normal plant operation, the power distribution system is subject to constant l
monitoring of instruments located on the main control board in the control room. Routine rounds are also conducted by the operators to verify main control board indications and to confirm local indications and satisfactory operation of equipment in the field. The periodicity of these routine rounds is commensurate with the surveillance requirements of the technics! specifications for the electrical distribution system. The combination of the observation of control board indications
, and routine rounds provides detection of abnormal or degraded conditions. Any indications of a l deviation from normal conditions would be identified in the observation of control board I
indications and the performance of the routine rounds. With the exception of the charger trouble l alarms, one train of the de bus undervoltage alarms is tested each refueling cycle on an attemating basis. All the ac vcitage output alarms are tested once per refueling cycle.
3-Failure of Common Power Suoolv The staff also requested confirmation that a failure of a power supply (degraded conditions on a 125 VDC or 120 vital ac inverter No. 2 -Vital Bus VA20) and, Channel'A' High Pressurizer Pressure of the RPS in bypass, will not prevent the ATWS mitigating system (which includes the DSS) and the RPS from performing their intended functions, it should be noted that NNECO has submitted a proposed license amendment to the Millstone Unit 2 Technical Specifications to limit the RPS bypass, including high pressurizer pressure, to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> from the current requirement that allows indefinite bypass. This change will decrease the time that Chanael 'A' High Pressurizer Pressure of the RPS can be in bypass.
For this postulated situation, the following conditions apply:
- 1. With Channel'A' High Pressurizer Pressure of the RPS in bypass, ATWS Channel'A'is also bypassed as a precautionary measure to preclude a reduction in availability of the ATWS trip logic to one-out-of-three.
l
- 2. When both RPS and ATWS Channel'A' are bypassed, Channel'A'is precluded from l providing a trip input. The combinations affected are 'AB,' 'AC,' and 'AD' logic matrices.
- 3. A degraded Vital Bus VA20 will affect the Channel'B' sensors, which are used for both the ATWS mitigating system and the RPS. The combinations affected are 'AB,BC,' and 'BD' l
logic matrices.
- 4. A degraded Vital Bus VA20 may also affect RPS logic matrix 'CD,' because the power supply design for this RPS logic matrix includes both Vital Bus VA20 and Vital Bus VA40.
The concem would be the possibility of a single failure within the common bus system propagating through the logic matrix power supplies into the matrix circuitry.
ATWS Evaluation For the ATWS mitigating system, based on the preceeding common power supplies, [..SS log c matrices 'AB,AC,AD,BC,' and 'BD' could be lost by a single failure. However, DGE MW matrix 'CD' would not be affected and would remain available to process the ATWS trip. Tr:is 1:
because the ATWS circuitry employs an auctioneered power supply design that supplies both the six combinational trip logic matrices and the associated actuation relays. One power apply is fed from Vital Bus VA10 and the other is fed from Vital Bus VA20. Therefore, a!thou;;h the matrix power supply fed from Vital Bus VA20 may be affected, the auctioneered power supply fed
! from Vital Bus VA10 would be available and the ATWS mit; gating system (which includes the DSS) will not be prevented from performing its intended function.
RPS Evaluation l
The RPS logic matrices could be vulnerable to a degraded Vital Bus VA20. This vulnerability results from a modification to the original RPS design to prevent spurious trips. In analyzing a potential logic matrix circuitry failure, due to a vital bus single failure, NNECO determined that only a failure that resulted in the welding closed of the logic matrix relay contacts would prevent j performance of the required protective function. Since the contacts are normally closed (Iow resistance), insignificant self heating of the contacts could occur. In event heat levels in the relay l
e 4
. 4 coils would rise, however, one or both relay coils could fail. Such relay coil failures are not of concem since failure of one or both of these coils will deenergize the respective trip circuit breaker control relay resulting in a half trip condition. Thus, no RPS power supply single failure resulting in loss of RPS function is credible.
NNECO also found no failures that would cause a high-voltage condition at the output terminals of a power supply. NNECO's evaluation documented the following conditions with no effect on the RPS logic matrices.
- s. single phase to ground faults and su'rges applied to a vital ac source,
- b. continuous phase-to-phase short-circuit of the vital ac input to one matrix power supply, and
- c. transverse mode surges or a continuous high voltage were applied to a matrix power supply.
Based on the proceeding discussion, for the postulated scenario, the RPS will not be prevented from performing its intended function.
4.0 .QQNCLUSION Based on the proceeding evaluation, the staff has concluded that NNECO's attemate proposal
] (one train of the de bus undervoltage alarms is tested each refueling cycle on an attemating basis, and all the ac voltage output alarms tested once per refueling cycle) is acceptable for ensuring power availability to the RPS and ATWS systems. The staff has further concluded that NNECO has provided adequate justification that the ATWS mitigating system and the RPS will continue to perform their intended functions when subject to a failure of a common power supply and the bypass of Channel'A' high pressurizer pressure.
Principal Contributor. J. Joyce Date:- October 29, 1998 i
9
l C
Millst:na Nucirr Power Station Unit 2 cc:
Lillian M. Cuoco, Esquire Mr. F. C. Rothen Senior Nuclear Counsel Vice President - Work Services Northeast Utilities Service Company Northeast Utilities Service Company P. O. Box 270 P. O. Box 128 Hartford, CT 06141-0270 Waterford, CT 06385 Mr. John Buckingham Emest C. Hadley, Esquire Department of Public Utility Control 1040 B Main Street Electric Unit P.O. Box 549 10 Liberty Square West Wareham, MA 02576 l New Britain, CT 06051 Mr. John F. Streeter Edward L. Wilds, Jr., Ph.D. Recovery Officer- Nuclear Oversight Director, Division of Radiation Northeast Utilities Service Company Department of Environmental Protection P. O. Box 128 79 Elm Street Waterford, CT 06385 l Hartford, CT 06106-5127 Mr. John Carlin Regional Administrator, Region i Vice President- Human Services U.S. Nuclear Regulatory Commission Northeast Utilities Service Company l 475 Allendale Road P. O. Box 128 King of Prussia, PA 19406 Waterford, CT 06385 First Selectmen Mr. Allan Johanson, Assistant Director Town of Waterford Office of Policy and Management l 15 Rope Ferry Road Policy Development and Planning Waterford, CT 06385 Division 450 Capitol Avenue - MS# 52ERN Mr. Wayne D. Lanning, Director P. O. Box 341441 Millstone inspections Hartford, CT 06134-1441 Office of the Regional Administrator 475 Allendale Road Mr. M. H. Brothers i
King of Prussia, PA 19406-1415 Vice President - Operations Northeast Nuclear Energy Company Charles Brinkman, Manager P.O. Box 128 l Washington Nuclear Operations Waterford, CT 06385 i ABB Combustion Engineering l 12300 Twinbrook Pkwy, Suite 330 Mr. J. A. Price Rockville, MD 20852 Director- Unit 2 Northeast Nuclear Energy Company Senior Resident inspector P.O. Box 128 l Millstone Nuclear Power Station Waterford, CT 06385 l
clo U.S. Nuclear Regulatory Commission P.O. Box 513 ,
i Niantic, CT 06357 l
l 1
- - - - . . - . . . . - - . _ . _ - . . . - .- - . - . _.. -.- - . . _ . . - ._ -. - . -_~. -
l Millstona Nucle r Power Station Unit 2 I
cc:
Mr. Leon J. Olivier Attomey Nicholas J. Scobbo, Jr.
Chief Nucler Officer- Millstone Ferriter, Scobbo, Caruso, Rodophele, PC Northeast Nuclear Energy Company 1 Beacon Street,11th Floor P.O. Box 128 Boston, MA 02108 Waterford, CT 06385 Mr. J. P. McElwain Citizens Regulatory Commission Recovery Officer- Millstone Unit 2 ATTN: Ms. Susan Pony Luxton Northeast Nuclear Energy Company i 180 Great Neck Road P. O. Box 128 Waterford,CT 06385 Waterford, Connecticut 06385 Deborah Katz, President Citizens Awareness Network P. O. Box 83 Shelbume Falls, MA 03170 The Honorable Terry Concannon Co-Chair i Nuclear Energy Advisory Council Room 4035 Legislative Office Building Capitol Avenue Hartford, CT 06106 Mr. Evan W. Woollacott Co-Chair Nuclear Energy Advisory Council 128 Terry's Plain Road Simsbury, CT 06070 Little Harbor Consultants, Inc.
Millstone -ITPOP Project Office P. O. Box 0630 Niantic, CT 06357-0630 l
Mr. Daniel L. Curry Project Director Parsons Power Group Inc.
2675 Morgantown Road Reading, PA 19607
-. - . . _ _ _ .