ML16160A094
| ML16160A094 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 06/08/2016 |
| From: | David Aird NRC/RES/DRA/PRB |
| To: | Niagara Mohawk Power Corp |
| David Aird 301-415-0634 | |
| References | |
| IR 2015003, LER 220-2015-004 | |
| Download: ML16160A094 (8) | |
Text
Final ASP Program Analysis - Reject Accident Sequence Precursor Program - Office of Nuclear Regulatory Research Nine Mile Point, Unit 1 Automatic Reactor Scram Due to Main Steam Isolation Valve Closure Event Date: 9/4/2015 LER: 220-2015-004 IR: 50-220/2015-003 CCDP= 6.7x10-8 Plant Type: General Electric BWR-2 with a Wet Mark I Containment Plant Operating Mode (Reactor Power Level): Mode 1 (100 Percent Reactor Power)
Analyst:
David Aird Reviewer:
Keith Tetter Contributors:
N/A BC Approved Date:
6/7/2016 EVENT DETAILS Event Description. On September 4, 2015, Unit 1 at Nine Mile Point automatically scrammed due to an inadvertent Main Steam Isolation Valve (MSIV) isolation. At the time, the reactor was operating at 100% rated power. During the event, the feed and condensate pumps operated as designed and restored reactor water level to the normal level set point. The Emergency Condensers were initially utilized to maintain reactor pressure due to the MSIV isolation. Later, the Turbine Bypass Valves were utilized for pressure control following the restoration of Main Steam Line 12. Additional information is provided in LER 220-2015-004 (Ref. 1).
During the initial transient, one Solenoid-Actuated Relief Valve (ERV), ERV-122, lifted in response to the reactor pressure increase, as designed. A rapid isolation due to MSIV closure or turbine trip without bypass will open the ERVs for a short time (10-15 seconds) to reverse the pressure transient. After the scram, ERV-122 failed to fully reseat after pressure lowered below its lift setpoint. Proceduralized operator action was required to manually close ERV-122 due to lowering reactor pressure and increasing torus temperature. Nine Mile Point has six total ERVs
- three per main steam line downstream of the flow restrictor and upstream of the MSIV.
Cause. While testing the second of two MSIVs, MSIV-112 failed to stop its close stroke and reopen automatically per design. The full closure of MSIV-112 caused steam flow in the opposite main steam line to rise to the high steam flow setpoint and caused a Reactor Protection System Main Steam Line Isolation signal. The closure of the remaining MSIVs caused an automatic reactor scram.
MODELING Basis for ASP Analysis/SDP Results. The ASP Program uses Significance Determination Process (SDP) results for degraded conditions when available and applicable. The ASP Program performs independent analyses for initiating events. ASP analyses of initiating events account for all failures/degraded conditions and unavailabilities (e.g., equipment out for test/maintenance) that occurred during the event, regardless of licensee performance.1 1 ASP analyses also account for any degraded condition(s) that were identified after the initiating event occurred if the failure/degradation exposure period(s) overlapped the initiating event date.
LER 220-2015-004 2
In Inspection Report (IR) 05000220/2015003 (Ref. 2), Section 4OA3, the inspectors reviewed the event and follow-up actions by the licensee. No findings were identified at the time. This LER is not yet closed.
An independent ASP analysis is required because this was an initiating event (reactor scram due to MSIV closure) with the failure of an additional component (ERV-122).
Analysis Type. An initiating event analysis was performed using the Nine Mile Point Unit 1 Standardized Plant Analysis Risk (SPAR) model Revision 8.21, created in May 2014.
SPAR Model Modifications. No SPAR model modifications were needed to perform this analysis.
Key Modeling Assumptions. The following assumptions were determined to be significant to the modeling of this event:
The probability of IE-TRANS (General Transient Initiating Event) was set to 1.0; all other initiating event probabilities were set to zero.
Basic event MSS-MSV-OC-STEAM (Steam Loop Valves Fail to Remain Open) was set to TRUE because the MSIVs closed. Main Steam Line 12 was restored later in the event to enable utilization of the Turbine Bypass Valves to the condenser. This action was not modeled in this bounding analysis.
Basic event PPR-SRV-OO-1VLV (One SRV Sticks Open) was set to TRUE because ERV-122 failed to reseat after pressure lowered below its lift setpoint. Operators, following procedure, manually closed ERV-122 fifteen minutes after the scram to stabilize reactor pressure and torus temperature. This recovery action was not modeled in this bounding analysis. The effect of one SRV sticking open is minimal in all cases except for station blackout.
All other safety systems responded as designed.
ANALYSIS RESULTS CCDP/Rejection Basis. The conditional core damage probability (CCDP) for this analysis is 6.7x10-8. The ASP Program threshold is a CCDP of 1x10-6. Therefore, this event is not a precursor and is screened out of the ASP Program.
Dominant Sequence. The dominant accident sequence is Transient (TRANS) Sequence 56-11 (CCDP = 4.1x10-8) that contributes approximately 61% of the total internal events CCDP.
This is an Anticipated Transient without Scram (ATWS) scenario. Figure 1 in Appendix B illustrates this sequence showing the ATWS event tree. The cut sets/sequences that contribute to the top 95% and/or at least 1% of the total internal events CCDP are provided in Appendix A.
The events and important component/system failures in TRANS Sequence 56-11 are:
A plant transient occurs, Reactor protection system fails, Safety relief valve(s) fail to open.
LER 220-2015-004 3
REFERENCES
- 1. Nine Mile Point Nuclear Station, "LER 220-2015-004 - Automatic Reactor Scram Due to Main Steam Isolation Valve Closure, dated November 3, 2015 (ML15331A038).
- 2. U.S. Nuclear Regulatory Commission, Nine Mile Point Nuclear Station, LLC - NRC Integrated Inspection Report 05000220/2015003, dated November 9, 2015 (ML15314A506).
LER 220-2015-004 A-1 Appendix A: SAPHIRE 8 Worksheet Summary of Conditional Event Changes Event Description Cond Value Nominal Value IE-TRANS GENERAL PLANT TRANSIENT 1.00E+0a 7.62E-1 MSS-MSV-OC-STEAM STEAM LOOP VALVES FAIL TO REMAIN OPEN True 9.22E-6 PPR-SRV-OO-1VLV ONE SRV STICKS OPEN True 8.56E-4
- a.
All other initiating event probabilities were set to zero.
Dominant Sequence Results Only items contributing at least 1.0% to the total CCDP are displayed.
E V E N T T R E E S E Q U E N C E CCDP
% C O N T R I B U T I O N D E S C R I P T I O N TRANS 56-11 4.05E-8 60.6%
RPS, PPR TRANS 56-07 9.76E-9 14.6%
RPS, /PPR, /RRS, PC1, /SLC, /NX, TAF TRANS 56-09 5.12E-9 7.6%
RPS, /PPR, /RRS, PC1, SLC TRANS 53 3.20E-9 4.8%
/RPS, /SRV, ISO, MFW, DEP, CRD TRANS 56-06-15 2.47E-9 3.7%
RPS, /PPR, /RRS, PC1, /SLC, /NX, /TAF, DE1 TRANS 56-06-07 2.44E-9 3.6%
RPS, /PPR, /RRS, PC1, /SLC, /NX, /TAF,
/DE1, /LCS, LVL TRANS 56-08 2.44E-9 3.6%
RPS, /PPR, /RRS, PC1, /SLC, NX TRANS 56-10 9.42E-10 1.4%
RPS, /PPR, RRS Total 6.69E-8 100.0%
Referenced Fault Trees Fault Tree Description CRD CRD INJECTION (2 PUMP)
DE1 MANUAL REACTOR DEPRESS DEP MANUAL REACTOR DEPRESS ISO ISOLATION CONDENSER LVL RESTORE LEVEL AND PREVENT OVERFILL MFW FEEDWATER NX INHIBIT ADS PC1 POWER CONVERSION SYSTEM PPR SRV'S OPEN RPS REACTOR PROTECTION SYSTEM RRS RECIRC PUMP TRIP SLC STANDBY LIQUID CONTROL TAF TRANSFER BRANCH ATWS-1 Cut Set Report - TRANS 56-11 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L %
C U T S E T 4.06E-8 100 Displaying 24 Cut Sets. (24 Original) 1 4.71E-9 11.61 IE-TRANS,PPR-SRV-CC-SRV5,RPS-SYS-FC-PSOVS 2
4.71E-9 11.61 IE-TRANS,PPR-SRV-CC-SRV6,RPS-SYS-FC-PSOVS 3
4.71E-9 11.61 IE-TRANS,PPR-SRV-CC-SRV3,RPS-SYS-FC-PSOVS 4
4.71E-9 11.61 IE-TRANS,PPR-SRV-CC-SRV1,RPS-SYS-FC-PSOVS 5
4.71E-9 11.61 IE-TRANS,PPR-SRV-CC-SRV2,RPS-SYS-FC-PSOVS 6
4.71E-9 11.61 IE-TRANS,PPR-SRV-CC-SRV4,RPS-SYS-FC-PSOVS 7
1.05E-9 2.60 IE-TRANS,PPR-SRV-CC-SRV5,RPS-SYS-FC-RELAY 8
1.05E-9 2.60 IE-TRANS,PPR-SRV-CC-SRV6,RPS-SYS-FC-RELAY 9
1.05E-9 2.60 IE-TRANS,PPR-SRV-CC-SRV3,RPS-SYS-FC-RELAY
LER 220-2015-004 A-2 CCDP T O T A L %
C U T S E T 10 1.05E-9 2.60 IE-TRANS,PPR-SRV-CC-SRV1,RPS-SYS-FC-RELAY 11 1.05E-9 2.60 IE-TRANS,PPR-SRV-CC-SRV2,RPS-SYS-FC-RELAY 12 1.05E-9 2.60 IE-TRANS,PPR-SRV-CC-SRV4,RPS-SYS-FC-RELAY 13 6.93E-10 1.71 IE-TRANS,PPR-SRV-CC-SRV5,RPS-SYS-FC-CRD 14 6.93E-10 1.71 IE-TRANS,PPR-SRV-CC-SRV6,RPS-SYS-FC-CRD 15 6.93E-10 1.71 IE-TRANS,PPR-SRV-CC-SRV3,RPS-SYS-FC-CRD 16 6.93E-10 1.71 IE-TRANS,PPR-SRV-CC-SRV1,RPS-SYS-FC-CRD 17 6.93E-10 1.71 IE-TRANS,PPR-SRV-CC-SRV2,RPS-SYS-FC-CRD 18 6.93E-10 1.71 IE-TRANS,PPR-SRV-CC-SRV4,RPS-SYS-FC-CRD Cut Set Report - TRANS 56-07 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L %
C U T S E T Total 9.76E-9 100 Displaying 4 Cut Sets. (4 Original) 1 6.80E-9 69.67 IE-TRANS,OPR-XHE-CTRL-TAF,RPS-SYS-FC-PSOVS 2
1.52E-9 15.57 IE-TRANS,OPR-XHE-CTRL-TAF,RPS-SYS-FC-RELAY 3
1.00E-9 10.25 IE-TRANS,OPR-XHE-CTRL-TAF,RPS-SYS-FC-CRD 4
4.40E-10 4.51 IE-TRANS,OPR-XHE-CTRL-TAF,RPS-SYS-FC-HCU Cut Set Report - TRANS 56-09 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L %
C U T S E T 5.12E-9 100 Displaying 12 Cut Sets. (12 Original) 1 3.40E-9 66.42 IE-TRANS,RPS-SYS-FC-PSOVS,SLC-XHE-XM-ERROR 2
7.60E-10 14.85 IE-TRANS,RPS-SYS-FC-RELAY,SLC-XHE-XM-ERROR 3
5.00E-10 9.77 IE-TRANS,RPS-SYS-FC-CRD,SLC-XHE-XM-ERROR 4
2.20E-10 4.30 IE-TRANS,RPS-SYS-FC-HCU,SLC-XHE-XM-ERROR 5
1.09E-10 2.13 IE-TRANS,RPS-SYS-FC-PSOVS,SLC-EPV-CF-VALVS Cut Set Report - TRANS 53 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L %
C U T S E T 3.20E-9 100 Displaying 18 Cut Sets. (18 Original) 1 1.00E-9 31.25 IE-TRANS,ADS-XHE-XM-MDEPR,ISO-XHE-XM-ERROR,MFW-XHE-XO-ERROR 2
9.51E-10 29.72 IE-TRANS,ADS-XHE-XM-MDEPR,CDS-AOV-CC-MKUP2,ISO-XHE-XM-ERROR 3
9.51E-10 29.72 IE-TRANS,ADS-XHE-XM-MDEPR,CDS-AOV-CC-MKUP1,ISO-XHE-XM-ERROR Cut Set Report - TRANS 56-06-15 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L %
C U T S E T Total 2.47E-9 100 Displaying 5 Cut Sets. (5 Original) 1 1.70E-9 68.96 IE-TRANS,ADS-XHE-XM-MDEP1,RPS-SYS-FC-PSOVS 2
3.80E-10 15.41 IE-TRANS,ADS-XHE-XM-MDEP1,RPS-SYS-FC-RELAY 3
2.50E-10 10.14 IE-TRANS,ADS-XHE-XM-MDEP1,RPS-SYS-FC-CRD 4
1.10E-10 4.46 IE-TRANS,ADS-XHE-XM-MDEP1,RPS-SYS-FC-HCU 5
2.53E-11 1.03 IE-TRANS,ADS-SRV-CF-VALV1,RPS-SYS-FC-PSOVS
LER 220-2015-004 A-3 Cut Set Report - TRANS 56-06-07 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L %
C U T S E T Total 2.44E-9 100 Displaying 4 Cut Sets. (4 Original) 1 1.70E-9 69.67 IE-TRANS,OPR-XHE-NOOVRFIL,RPS-SYS-FC-PSOVS 2
3.80E-10 15.57 IE-TRANS,OPR-XHE-NOOVRFIL,RPS-SYS-FC-RELAY 3
2.50E-10 10.25 IE-TRANS,OPR-XHE-NOOVRFIL,RPS-SYS-FC-CRD 4
1.10E-10 4.51 IE-TRANS,OPR-XHE-NOOVRFIL,RPS-SYS-FC-HCU Cut Set Report - TRANS 56-08 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L %
C U T S E T Total 2.44E-9 100 Displaying 4 Cut Sets. (4 Original) 1 1.70E-9 69.67 IE-TRANS,OPR-XHE-ADSINHIB,RPS-SYS-FC-PSOVS 2
3.80E-10 15.57 IE-TRANS,OPR-XHE-ADSINHIB,RPS-SYS-FC-RELAY 3
2.50E-10 10.25 IE-TRANS,OPR-XHE-ADSINHIB,RPS-SYS-FC-CRD 4
1.10E-10 4.51 IE-TRANS,OPR-XHE-ADSINHIB,RPS-SYS-FC-HCU Cut Set Report - TRANS 56-10 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L %
C U T S E T Total 9.42E-10 100 Displaying 15 Cut Sets. (15 Original) 1 1.37E-10 14.59 IE-TRANS,RPS-SYS-FC-PSOVS,RRS-CRB-CF-PUMP1 2
1.37E-10 14.59 IE-TRANS,RPS-SYS-FC-PSOVS,RRS-CRB-CF-PUMP2 3
1.37E-10 14.59 IE-TRANS,RPS-SYS-FC-PSOVS,RRS-CRB-CF-PUMP3 4
1.37E-10 14.59 IE-TRANS,RPS-SYS-FC-PSOVS,RRS-CRB-CF-PUMP4 5
1.37E-10 14.59 IE-TRANS,RPS-SYS-FC-PSOVS,RRS-CRB-CF-PUMP5 6
3.07E-11 3.26 IE-TRANS,RPS-SYS-FC-RELAY,RRS-CRB-CF-PUMP1 7
3.07E-11 3.26 IE-TRANS,RPS-SYS-FC-RELAY,RRS-CRB-CF-PUMP2 8
3.07E-11 3.26 IE-TRANS,RPS-SYS-FC-RELAY,RRS-CRB-CF-PUMP3 9
3.07E-11 3.26 IE-TRANS,RPS-SYS-FC-RELAY,RRS-CRB-CF-PUMP4 10 3.07E-11 3.26 IE-TRANS,RPS-SYS-FC-RELAY,RRS-CRB-CF-PUMP5 11 2.02E-11 2.15 IE-TRANS,RPS-SYS-FC-CRD,RRS-CRB-CF-PUMP1 12 2.02E-11 2.15 IE-TRANS,RPS-SYS-FC-CRD,RRS-CRB-CF-PUMP2 13 2.02E-11 2.15 IE-TRANS,RPS-SYS-FC-CRD,RRS-CRB-CF-PUMP3 14 2.02E-11 2.15 IE-TRANS,RPS-SYS-FC-CRD,RRS-CRB-CF-PUMP4 15 2.02E-11 2.15 IE-TRANS,RPS-SYS-FC-CRD,RRS-CRB-CF-PUMP5 Referenced Events Event Description Probability ADS-SRV-CF-VALV1 ADS VALVES FAIL FROM COMMON CAUSE 1.49E-5 ADS-XHE-XM-MDEP1 OPERATOR FAILS TO DEPRESSURIZE THE REACTOR 1.00E-3 ADS-XHE-XM-MDEPR OPERATOR FAILS TO DEPRESSURIZE THE REACTOR 1.00E-3 CDS-AOV-CC-MKUP1 HOTWELL LEVEL CONTROL VALVE 1 FAILS 9.51E-4 CDS-AOV-CC-MKUP2 HOTWELL LEVEL CONTROL VALVE 2 FAILS 9.51E-4 IE-TRANS GENERAL PLANT TRANSIENT 1.00E+0 ISO-XHE-XM-ERROR OPERATOR FAILS TO CONTROL ISOLATION CONDENSER COOLING 1.00E-3 MFW-XHE-XO-ERROR OPERATOR FAILS TO START/CONTROL FEEDWATER INJECTION 1.00E-3 OPR-XHE-ADSINHIB OPERATOR FAILS TO INHIBIT ADS 1.00E-3 OPR-XHE-CTRL-TAF OPERATOR FAILS TO CONTROL LEVEL TO TAF 4.00E-3 OPR-XHE-NOOVRFIL OPERATOR FAILS TO CONTROL LEVEL 1.00E-3 PPR-SRV-CC-SRV1 SAFETY RELIEF VALVE FAILS TO OPEN 2.77E-3 PPR-SRV-CC-SRV2 SAFETY RELIEF VALVE FAILS TO OPEN 2.77E-3
LER 220-2015-004 A-4 PPR-SRV-CC-SRV3 SAFETY RELIEF VALVE FAILS TO OPEN 2.77E-3 PPR-SRV-CC-SRV4 SAFETY RELIEF VALVE FAILS TO OPEN 2.77E-3 PPR-SRV-CC-SRV5 SAFETY RELIEF VALVE FAILS TO OPEN 2.77E-3 PPR-SRV-CC-SRV6 SAFETY RELIEF VALVE FAILS TO OPEN 2.77E-3 RPS-SYS-FC-CRD CONTROL ROD DRIVE MECHANICAL FAILURE 2.50E-7 RPS-SYS-FC-HCU HCU COMPONENTS FAIL 1.10E-7 RPS-SYS-FC-PSOVS HCU SCRAM PILOT SOVS FAIL 1.70E-6 RPS-SYS-FC-RELAY TRIP SYSTEM RELAYS FAIL 3.80E-7 RRS-CRB-CF-PUMP1 RECIRC PUMP 1 BREAKERS FAIL FROM COMMON CAUSE 8.09E-5 RRS-CRB-CF-PUMP2 RECIRC PUMP 2 BREAKERS FAIL FROM COMMON CAUSE 8.09E-5 RRS-CRB-CF-PUMP3 RECIRC PUMP 3 BREAKERS FAIL FROM COMMON CAUSE 8.09E-5 RRS-CRB-CF-PUMP4 RECIRC PUMP 4 BREAKERS FAIL FROM COMMON CAUSE 8.09E-5 RRS-CRB-CF-PUMP5 RECIRC PUMP 5 BREAKERS FAIL FROM COMMON CAUSE 8.09E-5 SLC-EPV-CF-VALVS SLC SQUIB VALVES FAIL BY COMMON CAUSE 6.42E-5 SLC-XHE-XM-ERROR OPERATOR FAILS START/CONTROL SLC 2.00E-3
LER 220-2015-004 B-1 Appendix B: Key Event Tree Figure 1: Nine Mile Point General Plant Transient Event Tree (Sequence 56-11 Bolded)