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EVENT PROBABILITY NAME ZTDPHD 1.00E-01 PR6BWZ 9.66E-02 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.05E+OO 1.04E+OO Table F.S-1 DCPP Level 1 Importance List Review DESCRIPTION APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 POTENTIAL SAMAS . Failure to control SG 2/3 This SF represents failure to control S/G level in scenarios where the fire I Water Level: Partial has impacted the SG controls/instrumentation.
The fire procedure Instruments are available identifies the fire areas where these degradations may occur and provides viable manual mitigation actions. Most of the top sequences I containing this SF also include feed and bleed failures that occur in conjunction with loss of instrument air conditions that fail PORV 474. Providing PORV with an alternate air source that can support long term F&B function in these events would potentially improve the reliability of the F&B function (SAMA 5). Fire -456 available,. This SF is primarily associated with induced LOCAs for fires in fire area 8000C and 455C failed. 6-A-3. The boundary conditions are failure of the pressure relief top Overlaps with PR9. Water event given failure of PORV 455C and block valve 8000C and Challenge.
availability of PORV 456. These scenarios also generally include spurious operation of the pressurizer heaters, which can force a PORV I open and lead to a LOCA without the ability to close a block valve (failed by fire). The DCPP fire procedure already directs actions for the relevant fire area to de-energize the pressurizer heaters..
In many scenarios, an RHR pump is failed due to the failure to trip the "deadheaded" RHR pumps. A potential means of precluding the need to trip the RHR pumps would be to install a normally open CCW flow bypass line around the RHR Hx outlet valve. This would ensure that minimum cooling flow would be available to prevent damage to the RHR pumps when they are running with the RCS at high pressure (SAMA 1 ). In other cases, RHR B is failed because the pump, suction valve 87008 and FCV-641 B are failed. The cables for these components could be protected in fire areas 6-A-2 (RHR A) and 6-A-3 (RHR B) to address the scenarios for both the A and B RHR trains (SAMA 8). Page F-178 EVENT PROBABILITY NAME RF3Z 1.60E-01 PR6GWZ 9.66E-02 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.04E+OO 1.04E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS FIRE: SWITCHOVER TO Automating the swap to recirculation mode could improve the reliability CONTAINMENT SUMP of the function (SAMA 7). RECIRCULATION AFTER SLOCA DEGRADED INSTRUMENTATION Fire-456 and 80008 This SF is primarily associated with induced LOCAs for fires in fire area failed. 8000C and 455C 6-A-2. The boundary conditions are failure of the pressure relief top available.
Overlaps with event given failure of PORV 456 and block valve 80008 and availability PR 1 E. Water Challenge.
of 8000C and 455C. These scenarios also generally include spurious operation of the pressurizer heaters, which can force a PORV open and lead to a LOCA without the ability to close a block valve (failed by fire). The DCPP fire procedure already directs actions for the relevant fire area to de-energize the pressurizer heaters. In many scenarios, an RHR pump is failed due to the failure to trip the "deadheaded" RHR pumps. A potential means of precluding the need to trip the RHR pumps would be to install a normally open CCW flow bypass line around the RHR Hx outlet valve. This would ensure that minimum cooling flow would be available to prevent damage to the RHR pumps when they are running with the RCS at high pressure (SAMA 1 ). In other cases, RHR A is failed because the pump, suction valve 8700A, and FCV-641 A are failed. The cables for these components could be protected in fire areas 6-A-2 (RHR A) and 6-A-3 (RHR B) to address the scenarios for both the A and B RHR trains (SAMA 8). Page F-179 EVENT PROBABILITY NAME AW4 1.61 E-02 ZSVHES 5.80E-03 LA1 6.41 E-03 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.04E+OO 1.04E+OO 1.03E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.S-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS SUPPORT FOR BOTH Some of the larger contributors to failure of the AFW MOPs are related MOP'S UNAVAILABLE to spray damage from fire protection system flooding scenarios (fire areas 14A and 302). A potential means of addressing this failure mode would be to provide barriers to protect the TD AFW pump from spray damage. For the MD AFW pumps, ventilation ducts that must remain open for AFW room cooling are located in flood area and protecting the MD AFW pumps requires replacing the pump with one that that can function in the water (SAMA 9). An alternate approach to restoring SG makeup would be to provide an engine driven SG makeup pump that can be aligned in time to mitigate loss of SG makeup scenarios (SAMA 2). Smaller contributors include failures of DC Bus H. In these cases, a portable DC generator could be used to provide control power to a MDAFW pump if 4KV power is available or to support the TO AFW pump (SAMA 10). 480V Switchgear This is an operator action that is performed in a fire event to mitigate Ventilation
-Operator loss of normal 480V Switchgear cooling with degraded indication (to Action: No fire damage to support operator action). The existing fire procedures already identify flow switches that room cooling for the 480V switchgear may be impacted by fires in the relevant areas (primarily 140) and identify that manual action to open the doors/place portable fans for alternate cooling should be performed.
This is a relativley simple mitigation method and human dependence issues would limit credit requiring additional operator action. A redundant train of 480V switchgear room HVAC could be installed to reduce these contributors (SAMA 6). RHR PUMP TRAIN A This event represents the failure of RHR pump A to start and run for 24 STARTS AND RUNS hours. The top contributors are for small LOCAs combined with failure of FOR 24 HOURS: ALL the B RHR pump train to operate for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (ultimately, there is no SUPPORT AVAILABLE recirculation capability).
Installing a swing RHR pump that can be (SBLOCA) suppl i ed from any power division would provide the capability to pump water through an existing RHR Hx to provide a means of removing heat Page F-180 EVENT PROBABILITY NAME LP1 6.21 E-04 LB2 9.69E-02 OG1 9.27E-03 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.03E+OO 1.03E+OO 1.03E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.S-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS from containment (SAMA 11 ). Both RHR Trains: ALL LP1 is a conditional split fraction that equates to SF LB2, which is SUPPORT AVAILABLE explicitly addressed below. (SLOCA) RHR PUMP TRAIN B: This event represents the failure of RHR pump B to start and run for 24 ALL SUPPORT hours. The top contributors are for small LOCAs combined with failure of AVAILABLE (LA FAILED the A RHR pump train to operate for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (ultimately, there is no -SLOCA) recirculation capability).
Installing a swing RHR pump that can be supplied from any power division would provide the capability to pump water through an existing RHR Hx to provide a means of removing heat from containment (SAMA 11 ). 230kV Offsite Power: ALL This event is represents the availability of offsite power to the plant SUPPORT AVAILABLE (including parts of the DCPP switchyard).
While it is theoretically possible to improve the reliability of the switchyard equipment, it would be difficult to quantify the changes in reliability based on component changes. A more effective means of mitigation is considered to be providing the plant with the capability to survive a long term SBO. In this case, a 480V AC generator could be used to supply the battery chargers for long term AFW support in conjunction with a self cooled, 480V AC RCS high pressure injection pump that can be used to make up for normal seal leakage or boil off if SG makeup fails (SAMA 12). Page F-181 I EVENT PROBABILITY NAME AZAF3 2.70E-02 GXH 3.50E-02 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.03E+OO 1.03E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS UNIT 1 4.16 KV BUS F: This event represents the fire induced failure of the 4KV Bus F (but not HF13/HF14 impacted-due to operator error to manually swap from the Aux transformer to the Recovery successful Startup transformer). The top contributors are fires in the 12Kv cable spreading room (area 1 085) and safeguards room (area 8G), which are combined with other fire induced and random failures that lead to induced SBOs and cases where only 1 4KV division is available combined with other hardware failures that prevent RCS makeup. Charging remains available but Sl and feed and bleed fails due to lack of support. Or control room ventilation to SSPS is lost due to the fire with failure of operator actions for recovery resulting in failure of Sl. This split fraction often occurs with AWFZ and AZAH7 (ZAH7). For scenarios with charging available, providing an engine driven SG makeup pump could restore secondary side heat removal capability (SAMA 2). For the SBO scenarios, alternate, independent means of both primary and secondary side makeup would be required for long term success, which could be provided by portable, engine driven primary and secondary side makeup pumps (SAMA 18). 1/3 DIESELS GXH is an "Intermediate" SF used to calculate GH1 and other UNAVAILABLE (BUS H) conditional SFs associated with failure of DH 1-1. The top contributors including this event are flooding events in the AFW rooms that include random loss of offsite power. In these scenarios, the condensate feedwater system is unavailable and combined with F&B failure (2/3 PORVs failed: Bus 1 H fails PORV 456, and PORV 474 via FCV-584), there are no heat removal options. A potential approach to restoring SG makeup would be to provide an engine driven SG makeup pump that can be aligned in time to mitigate loss of SG makeup scenarios (SAMA 2). Another approach is to install independent swing diesel (SAMA 15). Page F-182 EVENT PROBABILITY NAME ZPRL3A 4.37E-02 AWFZ 5.24E-01 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.03E+OO 1.03E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS Normal letdown LOCA This event represents a letdown path LOCA with failure of the recovery due to fire action to isolate the LOCA pathway by opening the DC supply breakers induced/random failures:
for the valves. DCPP currently has fire procedures that direct this action All components impacted for fires in the relevant area and no additional changes to the procedures -Recovery of 8149A,B,C have been identified that would significantly improve action reliability.
A impacted. (HEP=1) potential enhancement would be to provide fire barriers to protect the cables related to the valves in the letdown path associated with LOCA (valves 8149A,B,C valves and LCV-459 and LCV-460).
Ensuring that either LCV-459 or 460 is protected in area SA 1 could prevent or mitigate the fire induced LOCA (SAMA 14). No support for AFWP2, This event_ represents the failure of AFW given than the fire has AFWP3 and fire impacts impacted TO AFW pump 1-1 and the unavailability of MD Pumps 1-2 on AFWP1. and 1-3 due to support system failure. Since there is a loss of all secondary heat removal the only cooling function that remains is feed and bleed. The top sequences containing this SF are for fire initiators in the Electrical area (6-A-5) and the Safeguards Room (8G). For fire in area 6A5 CCW and Sl is lost due to the fire. Since CCW is lost, all charging is lost and feed and bleed is unavailable.
In order to mitigate these scenarios, alternate, independent means of both primary and secondary side makeup would be required for long term success, which could be provided by portable, engine driven primary and secondary side makeup pumps (SAMA 18). For area 8G see AFAZ3. Page F-183 EVENT PROBABILITY NAME GF1 3.50E-02 PRC1A 1.73E-01 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.02E+OO 1.02E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.S-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS DG 1-3 (BUS F) STARTS This SF represents the failure of DG 1-3 to start and run for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. & RUNS FOR 6 HR Cross-tie from the opposite unit is available, but common cause failures would likely limit the credit associated with including the capability in the model. Installation of a self-contained, independent swing diesel, not dependent on external support systems, would provide increased defense in depth and should be considered for loss of onsite emergency AC power sources (SAMA 15). A potential alternate solution is to use a 480V AC generator to supply the battery chargers for long term AFW support in conjunction with a self cooled, 480V AC RCS high pressure injection pump that can be used to make up for normal seal leakage or boil off if SG makeup fails (SAMA 12). PR Failed due to PORV This SF represents the failure of PORV 456 and block valve 8000C in an 456C 8000C Failure-manner that leads to a PORV LOCA. The SF is highly coupled with the FOR FIRE AREA 1A and SF ZHTRP2, which leads to failure of the remaining RHR pump that 9A could otherwise be used to mitigate the LOCA. In these cases, operating RHR pumps are "deadheaded" and will eventually fail unless the operator trips the pump(s) or initiates flow to the associated RHR heat exchanger from CCW. The procedures are currently set up to direct the operators to trip the pumps at some point after they have initiated if they are not required.
A potential means of precluding the need to trip the RHR pumps would be to install a normally open CCW flow bypass line around the RHR Hx outlet valve. This would ensure that minimum cooling flow would be available to prevent damage to the RHR pumps when they are running with the RCS at high pressure (SAMA 1). Page F-184 EVENT PROBABILITY NAME SIZCR6 8.41 E-01 HRF23A 6.00E-01 ZPRSI2 2.80E-01 Diablo Canyon Power Plant License Renewal Application
-RISK REDUCTION WORTH 1.02E+OO 1.02E+OO 1.02E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS 897 4A, and All This event is primarily linked to fire area 5-A-1 and represents the failure ZSI1 componnts impacted of the safety injection function when Sl to RWST recirculation valve MOV 8974A transfers closed. In all top contributors, Sl is required to mitigate a letdown line LOCA. DCPP currently has fire procedures that direct this action for fires in the relevant area and no additional changes to the procedures have been identified that would significantly improve action reliability.
A potential enhancement would be to provide fire barriers to protect the cables related to the valves in the letdown path associated with LOCA (valves 8149A,B,C valves and LCV-459 and LCV-460). Ensuring that either LCV-459 or 460 is protected in area 5A 1 could prevent or mitigate the fire induced LOCA (SAMA 14). Fire-HR Fails due to This event is primarily linked to fire area 5-A-1 and represents the failure ZHR23A fails: NO FLOW of the safety injection function when either MOV 8923A or B fail closed. PATH FROM RHR TO In all top contributors, Sl is required to mitigate a letdown line LOCA. HIGH PRESSURE DCPP currently has fire procedures that direct this action for fires in the PUMPS: relevant area and no additional changes to the procedures have been identified that would significantly improve action reliability.
A potential enhancement would be to provide fire barriers to protect the cables related to the valves in the letdown path associated with LOCA (valves 8149A,B,C valves and LCV-459 and LCV-460).
Ensuring that either LCV-459 or 460 is protected in area 5A 1 could prevent or mitigate the fire induced LOCA (SAMA 14). Operator action to This SF represents the failure to terminate a fire induced spurious Sl terminate spurious Sl: signal. In this case, the fire has degraded the instrumentation used to Degraded instrumentation diagnose the Sl termination action. The DCPP fire procedure already includes guidance on addressing spurious actuation of Sl and it is directed to be used for any fire scenario.
A potential enhancement to consider would be to include a note identifying the spurious signal actuations that may occur in each fire area with a reference to the attachment that governs the mitigating steps for the associated spurious Page F-185
-EVENT PROBABILITY NAME OB1Z2 1.34E-01 RF1Z 8.68E-03 ZTDPHS 5.00E-02 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.02E+OO 1.02E+OO 1.02E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.S-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS actuation (SAMA 16). -Failure of the Feed and The event represents the failure of the feed and bleed function in cases Bleed function due to where there is successful operator action (even with degraded Loss of Instrument Air instrumentation), but failure due to hardware based reasons. Providing (Guranteed failure in all a backup air supply to PORV PCV 474 could reduce the feed and bleed fire scenarios) and failures associated with loss of instrument air (SAMA 5). Instrumentation Degraded FIRE: SWITCHOVER TO This SF is related to operator error to perform swap to recirculation CONTAINMENT SUMP mode in fire scenarios.
The sequences including the SF typically include RECIRC AFTER SLOCA induced LOCAs via spurious pressurizer heater actuation or PORV OR B/F WITH CS pathways that force bleed and feed operation.
Automating the swap to FAILED recirculation mode could improve the reliability of the function (SAMA 7). Failure to control SG 2/3 This SF is related to operator failure to control SG level, which leads to Water Level: All the need for Feed and Bleed cooling. In the top contributors, the Instruments are available transition to F&B is failed due to hardware issues. Providing a backup air supply to PORV PCV 474 could reduce the feed and bleed failures associated with loss of instrument air (SAMA 5). In other scenarios, the swap to recirculation mode fails. Automating the swap to recirculation mode could improve the reliability of the function (SAMA 7). Page F-186 EVENT PROBABILITY NAME SACSS4 3.91 E-02 SACSS5 1.49E-01 Diablo Canyon Power Plant License Renewal Application RISK. REDUCTION WORTH 1.02E+OO 1.02E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS SEISMIC FAILURE OF This SF represents the failure of all vital 4KV AC power given that the AC TB STRUCT turbine building does not fail due to the seismic event. In most cases, the SUCCESSFULE:
SEIS4, 230kV offsite supply is also failed and power is not available to the site Hazard Levels: 2.00E+OO at all. Given that this SF is associated with a large scale seismic event to 2.500E+OO (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above the top of active fuel (TAF), a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). SEISMIC FAILURE OF This SF represents the failure of all vital 4KV AC power given that the AC TB STRUCT turbine building does not fail due to the seismic event. In most cases, the SUCCESSFULE:
SEIS5, 230kV offsite supply is also failed and power is not available to the site Hazard Levels: at all. Given that this SF is associated with a large scale seismic event 2.500E+OO to 3.00E+OO (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified pressure operated relief valve (PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). Page F-187 EVENT PROBABILITY NAME WFL02N 2.20E-03 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.02E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review -----DESCRIPTION POTENTIAL SAMAS Operator Fails to Isolate This SF is associated with a number of different fire protection flooding Raw Water Reservoir for scenarios that result in flood damage to the charging and CCW pumps, 6 inch Firewater Flood as well as the RHR pumps. Lack of RCP seal cooling results in an RCP seal LOCA without high pressure injection capability.
In some cases, AFW and Condensate/FW makeup capability to the SGs is also failed. A potential means of mitigating the event would be to provide water level sensors in critical areas, such as those housing the charging pumps, AFW pumps, CCW pumps, and RHR pumps that could actuate on high level to shut down the fire protection pumps when there is not a coincident fire alarm (SAMA 17). These types of events could also potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). Page F-188
! ---EVENT PROBABILITY NAME SDS1 2.17E-02 BB1G 1.97E-02 OR1 2.30E-02 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.02E+OO 1.02E+OO 1.02E+OO APPENDIX E REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS RCP Shutdown seals Fail This SF represents failure of the shutdown seals to actuate and is to Actuate primarily important in fire related events. The fires occur in several different areas and result in the loss of seal cooling for a range of different reasons, which makes it impractical to protect component cables to prevent the loss of the seal cooling function.
The DCPP fire procedures already identify components that may be impacted on an area by area basis and provide mitigating actions to recover from the failures.
The scenarios including this SF also generally include fire induced LOCAs from pressurizer heater actuation or charging flow imbalance.
Multiple other functions/components are also failed, such as the CCW heat exchangers and SG steam relief capability. The wide range of failures essentially requires a fire-safe train of equipment for success. SAMA 18 represents an independent primary and seconday side makeup capability, but for all but very small LOCAs, successful mitigation would require a permanently installed system with higher makeup flow capacity than the portable pumps envisioned for SAMA 18. This type of system would be more expensive than SAMA 18. For this analysis, SAMA 18 is assigned as a bounding case for these contributors. UNIT 2 VITAL AC/DC This SF is an intermediate SF for Unit 2 power failures.
These failures SYSTEM: Train 2G fails show up in the importance list, but are non-minimal failures that do not with Recovery -TS=S directly impact the sequence of events. No SAMAs are required. OPERATOR This top contributors associated with this SF are non-isolated SGTR COOLDOWN AND initiating events, which are often combined with failures to isolate the DEPRESSURIZE RCS ruptured SG. While the importance of this event may be overestimated due to conservative HRA techniques, some changes could be made to reduce the frequency of the sequences containing this action. Primary side isolation valves would simplify both the action to isolate a ruptured SG, the action to cool down/depressurize the RCS after isolation, and help prevent induced SGTR events (SAMA 19). *Page F-189 EVENT PROBABILITY NAME ZAH7 5.00E-01 AZAG7 5.00E-01 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.02E+OO 1.01 E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS 4.16 kV Bus H fails due to This is an intermediate SF for AZAH7, which represents the fire induced fire: HH14 affected-failure of 4KV bus H with conditional failure to locally close the 4KV Conditional recovery -breaker on Bus H to provide power to the bus from the startup Local action transformer.
This generally occurs in conjunction with the SF for failure of the F (AZAF3) bus given the condition that the action to swap to the startup source was not a cause of failure (which also leaves bus F unavailable) and AWFZ. The top contributors are fires in the safeguards room (area 8G), which are combined with cases where lack of power combined with other failures prevent RCS makeup for mitigation of induced LOCAs from pressurizer heater actuation.
For these scenarios, alternate, independent means of both primary and secondary side makeup would be required for long term success, which could be provided by portable, engine driven primary and secondary side makeup pumps (SAMA 18). H G 14 affected -This event represents the fire induced failure of 4KV bus G with Conditional recovery-conditional failure to locally close the 4KV breaker on Bus G to provide Local action power to the bus from the startup transformer. This generally occurs in conjunction with fires in the 12KV cable spreading room (area 1 085) that result in SBO conditions due to fire induced failures that also leave the F and H buses unavailable.
A potential solution is to use a 480V AC generator to supply the battery chargers for long term AFW support in conjunction with a self cooled, 480V AC RCS high pressure injection pump that can be used to make up for normal seal leakage or boil off if SG makeup fails (SAMA 12). Page F-190 I I EVENT PROBABILITY NAME SVZ3R1 2.73E-02 AZAH7 5.00E-01 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.01 E+OO 1.01 E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS 480V SWITCHGEAR This SF represents the failure of the 480V switchgear ventilation function VENTILATION:
E-43, S-given that a fire has failed one of the two redundant trains. The SF is 43 and HD43-SO generally paired with failure of the operator action to open the doors for impacted -run failure alternate ventilation, which is an action that is clearly directed in the current DCPP fire procedure for the relevant fire area (instrumentation is available to support the action). Failure of 480V switchgear ventilation eventually results in loss of all 3 divisions of safety related 480V AC power and all three safety related DC divisions after battery depletion.
Because the 480V switchgear and battery chargers are failed, mitigating equipment will be required to operate without 480V AC and 125/250V DC support. A redundant train of 480V switchgear room HVAC could be installed to reduce these contributors (SAMA 6). Alternatively, these types of events could potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). H H 14 affected -This SF represents the fire induced failure of 4KV bus H with conditional Conditional Recovery-failure to locally close the 4KV breaker on Bus H to provide power to the Local action bus from the startup transformer.
This generally occurs in conjunction with the SF for failure of the F (AZAF3) bus given the condition that the action to swap to the startup source was not a cause of failure (which also leaves bus F unavailable) and AWFZ. The top contributors are fires in the safeguards room (area 8G), which are combined with cases where lack of power combined with other failures prevent RCS makeup for mitigation of induced LOCAs from pressurizer heater actuation.
For these scenarios, alternate, independent means of both primary and secondary side makeup would be required for long term success, which could be provided by portable, engine driven primary and secondary side makeup pumps (SAMA 18). Page F-191 EVENT PROBABILITY NAME ZPRIS2 1.50E-01 GXF 3.50E-02 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.01 E+OO 1.01 E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review --DESCRIPTION POTENTIAL SAMAS Instrumentation degraded This SF represents the failure to isolate a spuriously opened PORV with degraded instrumentation.
There are several contributing fire areas and different combinations of injection/heat removal failure that lead to core damage; however, one of the larger contributors is the loss of RHR due to the failure to trip "deadheaded" RHR pumps. A potential means of precluding the need to trip the RHR pumps would be to install a normally open CCW flow bypass line around the RHR Hx outlet valve. This would ensure that minimum cooling flow would be available to prevent damage to the RHR pumps when they are running with the RCS at high pressure (SAMA 1 ). The current DCPP fire procedure already identifies actions to close spuriously operating PORVs from the hot shutdown panel and to trip the pressurizer heaters in the scenarios where they can be impacted, which would prevent the induced PORV LOCAs. 1/3 DIESELS This is an intermediate SF for GF1 related to the failure of DG 1-3 to UNAVAILABLE (BUS F) start and run for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. Cross-tie from the opposite unit is available, but common cause failures would likely limit the credit associated with including the capability in the model. Installation of a self-contained, independent swing diesel, not dependent on external support systems, would provide increased defense in depth and should be considered for loss of onsite emergency AC power sources (SAMA 15). A potential alternate solution is to use a 480V AC generator to supply the battery chargers for long term AFW support in conjunction with a self cooled, 480V AC RCS high pressure injection pump that can be used to make up for normal seal leakage or boil off if SG makeup fails (SAMA 12). Page F-192 EVENT PROBABILITY NAME ZHTRP3 6.50E-03 PR6AW1 9.66E-02 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.01 E+OO 1.01 E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS Operator Action -This event represents the failure to trip the RHR pumps before failure Instrumentation OK when they have been "deadheaded" without CCW flow to the RHR heat exchangers.
A potential means of precluding the need to trip the RHR pumps would be to install a normally open CCW flow bypass line around the RHR Hx outlet valve. This would ensure that minimum cooling flow would be available to prevent damage to the RHR pumps when they are running with the RCS at high pressure (SAMA 1 ). PRESSURE RELIEF: This SF is primarily associated with induced LOCAs for fires in fire area Fire-8000C, 456 6-A-1. The SF boundary conditions indicate that block valve 8000C and available, 455C failed. PORV-456 are available while PORV-455C is failed. The fire procedure This will overlap with indicates that for fires in this area, block valve 8000A and the PZR PRM. Water Challenge.
heaters may be impacted.
These scenarios generally include spurious Block valve closure fails. operation of the pressurizer heaters and induced LOCAs. Core damage results either because the action to swap to recirculation fails, or because an otherwise RHR pump has been damaged due to the failure to trip after prolonged "deadheaded" operation.
A potential means of precluding the need to trip the RHR pumps would be to install a normally open CCW flow bypass line around the RHR Hx outlet valve. This would ensure that minimum cooling flow would be available to prevent damage to the RHR pumps when they are running with the RCS at high pressure (SAMA 1 ). To reduce the frequency of failures related to the action to transition to recirculation mode, the process could be automated (SAMA 7). Page F-193 EVENT PROBABILITY NAME GG2 2.90E-02 BB1H 1.42E-02 SACSS6 3.30E-01 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.01 E+OO 1.01 E+OO 1.01 E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS DG 1-2 (BUS G) : GF-F Cross-tie from the opposite unit is available, but common cause failures would likely limit the credit associated with including the capability in the model. Installation of a self-contained, independent swing diesel, not dependent on external support systems, would provide increased defense in depth and should be considered for loss of onsite emergency AC power sources (SAMA 15). Alternatively, a smaller sized EDG could be used to power the AFW battery chargers for long term SBO operation and a new, self cooled, 480V AC PDP could be used for primary side makeup (SAMA 12). Train 2H fails with This SF is an intermediate SF for Unit 2 power failures.
These failures Recovery -TH=S show up in the importance list, but are non-minimal failures that do not directly impact the sequence of events. No SAMAs are required.
SEISMIC FAILURE OF This SF represents the failure of all vital 4KV AC power given that the AC TB STRUCT turbine building does not fail due to the seismic event. In most cases, SUCCESSFULE:
SEIS6, the 230KV offsite supply is also failed and power is not available to the Hazard Levels: 3.00E+OO site at all. Given that this SF is associated with a large scale seismic to 3.99E+OO events (>1.75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). Page F-194
EVENT PROBABILITY NAME GX 1.90E-04 CD1FL 4.55E-02 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.01 E+OO 1.01 E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review --------*------DESCRIPTION POTENTIAL SAMAS 3/3 DIESELS This is an intermediate SF for failure of all three DGs. Cross-tie from the UNAVAILABLE opposite unit is available, but common cause failures would likely limit the credit associated with including the capability in the model. Installation of a self-contained, independent swing diesel, not dependent on external support systems, would provide increased defense in depth and should be considered for loss of onsite emergency AC power sources (SAMA 15). A potential alternate solution is to use a 480V AC generator to supply the battery chargers for long term AFW support in conjunction with a self cooled, 480V AC RCS high pressure injection pump that can be used to make up for normal seal leakage or boil off if SG makeup fails (SAMA 12). FLOOD-ALL SUPPRT This SF represents the failure of the Condensate system in flooding AVAILABLE-MFW events when all support systems and MFW pumps are available.
The PUMPS AVAILABLE top contributor is from a flood sequence in which a pipe from the RWST breaks in the fuel handling building.
All AFW pumps and the RWST are lost, as well as RHR due to lack of inventory.
Failure of condensate results in loss of all heat removal capability.
In other cases, fire protection system breaks in the AFW pump rooms result in failure of AFW, which in combination with Feed and Bleed and Condensate system failure lead to core damage. For fire protection system ruptures, a potential means of mitigating the event would be to provide water level sensors in critical areas, such as those housing the charging pumps, AFW pumps, CCW pumps, and RHR pumps that could actuate on high level to shut down the fire protection pumps when there is not a coincident fire alarm (SAMA 17). These types of events could also potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). Page F-195 EVENT PROBABILITY NAME GH3 1.87E-01 ZPRSI1 2.80E-01 ZSGALL 9.97E-01 Diablo Canyon Power Plant License Renewal Application RISK REDUCTION WORTH 1.01 E+OO 1.01 E+OO 1.01 E+OO APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Table F.5-1 DCPP Level 1 Importance List Review DESCRIPTION POTENTIAL SAMAS DG 1-1 (BUS H) : GF-This SF represents the failure of DG H given failure of the F and G DGs. F,GG-F Cross-tie from the opposite unit is available, but common cause failures would likely limit the credit associated with including the capability in the model. Installation of a self-contained, independent swing diesel, not dependent on external support systems, would provide increased defense in depth and should be considered for loss of onsite emergency AC power sources (SAMA 15). A potential alternate solution is to use a 480V AC generator to supply the battery chargers for long term AFW support in conjunction with a self cooled, 480V AC RCS high pressure injection pump that can be used to make up for normal seal leakage or boil off if SG makeup fails (SAMA 12). Operator action to This SF represents the failure to terminate a fire induced spurious Sl terminate spurious Sl -signal. In this case, the fire has not degraded the instrumentation used Instrumentation OK to perform the Sl termination action. The DCPP fire procedure already includes guidance on addressing spurious actuation of Sl and it is directed to be used for any fire scenario.
A potential enhancement to consider would be to include a note identifying the spurious signal actuations that may occur in each fire area with a reference to the attachment that governs the mitigating steps for the associated spurious actuation (SAMA 16). PCV-19, -20, -21, and -22 This SF represents the fire induced opening of PCVs-19, -20, -21, and -spuriously open due to 22 given that all of the AFW ADVs are impacted by the fire. This, fire-fire impact PCV-19, combined with other failures (generally fire induced), leads to loss of SG PCV-20, PCV-21 and makeup capability.
The top contributors also all include fire induced PCV-22 small LOCAs such that SG makeup alone cannot mitigate the accident.
For the diverse set of fire initiators that include this event, a comprehensive mitigation strategy is considered to be required.
These types of events could also potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). Page F-196 !
EVENT PROBABILITY NAME CPFIRE 1.00E-01 SPCET3 7.67E-01 ISCET3 7.10E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1 I ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.16E+OO Failure of Isolating the This SF represents the failure to manually isolate the RCP seal water Containment Pen of return lines given a fire induced failure of the valves, which leads to an greater than 2": Failure of open pathway from containment that exists prior to core damage. A Pen 45 valves due to fire potential means of improving reliability of the isolation action would be to provide fire area specific guidance that addresses containment isolation valves. In some cases, reference to the SAMGs or additional guidance may be appropriate when isolation will result in the loss of a function that is required to prevent core damage (SAMA 21) 1.15E+OO RCP SEAL COOLING There are numerous path that lead to core damage that include the UNAVAILABLE unavailability of RCP seal cooling, but all of the top LERF contributors are the result of induced steam generator tube ruptures.
These types of events can be prevented by maintaining level in the SGs after core damage to prevent overheating of the SG tubes. A portable, high pressure engine driven SG makeup source with diverse suction supplies can provide this capability (SAMA 2). 1.15E+OO INDUCED-SGTR:
Loss This SF represents the probability that an induced steam generator tube of seal cooling, smallest rupture occurs. While SG makeup alone cannot necessarily prevent leak size, no CST core damage for cases in which primary side inventory has been lost, resupply providing the capability to inject water into the SGs will prevent tube failure. A portable, high pressure engine driven SG makeup source with diverse suction supplies can provide this capability (SAMA 2). Page F-197 EVENT PROBABILITY NAME OSZ1 5.30E-02 ISCET1 5.80E-02 OR1 2.30E-02 OX1 1.60E-02 RECSR 6.50E-02 SA1 3.26E-03 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.15E+OO MANUAL ACTUATION IN Addressed in the Level 1 importance list. EVENT SSPS FAILS: Instrumentation degraded 1.11 E+OO INDUCED-SGTR:
Loss of This SF represents the probability that an induced steam generator tube SG cooling at setpoint rupture occurs. While SG makeup alone cannot necessarily prevent pressure core damage for cases in which primary side inventory has been lost, providing the capability to inject water into the SGs will prevent tube failure. A portable, high pressure engine driven SG makeup source with diverse suction supplies can provide this capability (SAMA 2). 1.09E+OO OPERATOR Addressed in the Level 1 importance list. COOLDOWN AND DEPRESSURIZE RCS 1.07E+OO OPERATOR DECIDES This SF represents the probability that the operators will fail to isolate a TO ISOLATE ruptured SG in a tube rupture scenario.
It is generally coupled with the RUPTURED SG failure to cool down the RCS as part of the mitigation process. In these cases, the types of strategies that are available to reduce the LERF are limited, but providing primary side SG isolation valves is a potential means of simplifying the mitigation strategy and terminating the scenario (SAMA 19). 1.06E+OO Recovery actions for CSR Addressed in the Level 1 importance list. Scenarios from HSP 1.06E+OO SSPS TRAIN A: This SF, which is a failure of the 11 A 11 train of the solid state protection GENERAL TRANSIENT system , is often paired with operator failure to trip the reactor that result in A TWS events, which are assumed to result in core damage for Seismic initiators.
A potential means of reducing the contribution of this SF is to use an alternate signal, such as AMSAC , to automate the de-energization of the 480V buses feeding the rod drive motor generator sets (SAMA 20). Page F-198 EVENT PROBABILITY NAME S12 4.82E-05 SB2 1.48E-02 WLFO 1.00E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.06E+OO SSPS TRAIN A&B FAIL This is an intermediate SF for SB2, which represents failure of the 11 8 11 (GENERAL TRANSIENT)
SSPS channel given failure of the 11 A channel. There are limited options available to address the sequences where operators fail to manually actuate the safety systems after automatic actuation has failed. This SF is often paired with operator failure to trip the reactor that result in A TWS events, which are assumed to result in core damage for Seismic initiators.
A potential means of reducing the contribution of this SF is to use an alternate signal, such as AMSAC, to automate the de-energization of the 480V buses feeding the rod drive motor generator sets (SAMA 20). 1.06E+OO SA-F (GENERAL This is an intermediate SF for SB2, which represents failure of the 11 8 11 TRANSIENT)
SSPS channel given failure of the 11 A 11 channel. The SB2 SF is often paired with operator failure to trip the reactor that result in A TWS events, which are assumed to result in core damage for Seismic initiators.
A potential means of reducing the contribution of this SF is to use an alternate signal, such as AM SAC, to automate the de-energization of the 480V buses feeding the rod drive motor generator sets (SAMA 20). 1.06E+OO Both SSPS Trains Not This SF, which is a failure of the 11 8 11 train of the solid state protection available, no fire system, is often paired with operator failure to trip the reactor that result in A TWS events, which are assumed to result in core damage for Seismic initiators.
A potential means of reducing the contribution of this SF is to use an alternate signal, such as AMSAC, to automate the de-energization of the 480V buses feeding the rod drive motor generator sets (SAMA 20). Page F-199 EVENT PROBABILITY NAME SDC6 1.26E-01 PRB1A 1.76E-01 ZHTRP2 1.60E-01 ZSVHES 5.80E-03 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.04E+OO SEISMIC FAILURE OF This SF represents the seismic failure of 125V DC power. This SF is DC DUE TO FRAGILITY:
typically combined with LOOP events, which result in SBO scenarios SEIS6 , Hazard Levels: given that DC power is required for on-site power alignment.
Given that 3.00E+OO to 3.99E+OO this SF is associated with a large scale seismic events (>1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.04E+OO PR Failed due to PORV Addressed in the Level 1 importance list. 455C 80008 Failure-FOR Fl RE AREA 1 A and 9A 1.04E+OO Operator Action -Addressed in the Level 1 importance list. Degraded Instrumentation 1.04E+OO 480V Switchgear Addressed in the Level 1 importance list. Ventilation
-Operator Action: No fire damage to flow switches Page F-200 EVENT PROBABILITY NAME SDC5 3.82E-02 PR6BWZ 9.66E-02 SDC4 8.45E-03 AZAF3 2.70E-02 AF1SB 1.38E-04 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1 I ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS -REDUCTION WORTH 1.04E+OO SEIS5, Hazard Levels: This SF represents the seismic failure of 125V DC power. This SF is 2.500E+OO to 3.00E+OO typically combined with LOOP events, which result in SBO scenarios given that DC power is required for on-site power alignment.
Given that this SF is associated with a large scale seismic events (>1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.04E+OO Fire -456 available, Addressed in the Level 1 importance list. 8000C and 455C failed. Overlaps with PR9. Water Challenge.
1.03E+OO SEISMIC FAILURE OF Addressed in the Level 1 importance list. DC DUE TO FRAGILITY:
SEIS4, Hazard Levels: 2.00E+OO to 2.500E+OO 1.03E+OO UNIT 1 4.16 KV BUS F: Addressed in the Level 1 importance list. HF13/HF14 impacted-Recovery successful 1.03E+OO UNIT 1 4.16 KV BUS F: This SF represents the probability that 4KV bus F fails in a lower All support available (with magnitude seismic event. It is typically combined with other failures of recovery-Seismic Group buses G and H along with a failure to trip the reactor due to B) unavailability of DC power to the shunt trip coils for manual trip (local breaker action not credited). This results in an A TWS. A potential means of reducing the contribution of this SF is to use an alternate signal, such as AM SAC, to automate the de-energization of the 480V Page F-201 EVENT PROBABILITY NAME AY3FGH 2.26E-05 AH3SB 4.67E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH buses feeding the rod drive motor generator sets (SAMA 20). 1.03E+OO VITAL AC TRAINS This is an intermediate SF for AH3SB, which represents the failure of 4 F&G&H FAIL (SEISMISC KV BusH given failure of buses F and Gin seismic events. The GROUP B) contributors that include this SF are generally combined with the failure to trip the reactor when DC power is not available to the shut trip coils to support a manual trip (local breaker action not credited).
This results in an A TWS. A potential means of reducing the contribution of this SF is to use an alternate signal, such as AMSAC, to automate the de-energization of the 480V buses feeding the rod drive motor generator sets (SAMA 20). 1.03E+OO UNIT 1 4.16 KV BUS H: This SF represents the failure of 4 KV Bus H given failure of buses F DF-S, DG-S, AF-F,AG-F and G in seismic events. The contributors that include this SF are (with recovery) -Seismic generally combined with the failure to trip the reactor when DC power is Group B not available to the shut trip coils to support a manual trip (local breaker action not credited).
This results in an A TWS. A potential means of reducing the contribution of this SF is to use an alternate signal, such as AM SAC, to automate the de-energization of the 480V buses feeding the rod drive motor generator sets (SAMA 20). Page F-202 EVENT PROBABILITY NAME AG2SB 3.50E-01 ZSGALL 9.97E-01 AZAG7 5.00E-01 WLF1 1.00E-01 AWR1 2.93E-04 ZPRSI2 2.80E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.03E+OO UNIT 1 4.16 KV BUS G: This SF represents the failure of 4 KV Bus G given failure of bus F in DF-S, AF-F, with seismic events. The contributors that include this SF are generally recovery (Seismic Group combined with the failure to trip the reactor when DC power is not B) available to the shut trip coils to support a manual trip (local breaker action not credited).
This results in an A TWS. A potential means of reducing the contribution of this SF is to use an alternate signal, such as AM SAC, to automate the de-energization of the 480V buses feeding the rod drive motor generator sets (SAMA 20). 1.03E+OO fire impact PCV-19, PCV-Addressed in the Level 1 importance list. 20, PCV-21 and PCV-22 1.03E+OO HG14 affected-Addressed in the Level 1 importance list. Conditional recovery-Local action 1.02E+OO WATER LEVEL FOR This SF represents the failure to close the containment sump discharge SUMP valves given the unavailability of both SSPS trains in fire events. A RECIRCULATION
- Both potential improvement would be to include explicit guidance in the fire SSPS Trains Not procedure to manually close either FCV-500 or FCV-501 for fires in available, fire with zones that could fail SSPS (SAMA 21). Recovery 1.02E+OO Failure to supply water Addressed in the Level 1 importance list. from FWST or RWR (non seismic) 1.02E+OO Operator action to Addressed in the Level 1 importance list. terminate spurious Sl: Degraded instrumentation Page F-203 EVENT PROBABILITY NAME ZSETB7 9.87E-01 SVI6 3.57E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.02E+OO Fire induced loss of This SF represents the fire induced loss of thermal barrier cooling. The thermal barrier cooling: sequences including these events lead to LERF primarily due to 355, 356, 357, 750 hydrogen burns that fail containment and induced SGTR events. While impacted -355 not SG makeup alone cannot necessarily prevent core damage for cases in recoverable which primary side inventory has been lost, providing the capability to inject water into the SGs will prevent tube failure. The scenarios including this SF also generally include fire induced LOCAs from pressurizer heater actuation or charging flow imbalance.
Multiple other functions/components are also failed, such as the CCW heat exchangers and SG steam relief capability. The wide range of failures essentially requires a fire-safe train of equipment for success. SAMA 18 represents an independent primary and seconday side makeup capability, but for all but very small LOCAs, successful mitigation would require a permanently installed system with higher makeup flow capacity than the portable pumps envisioned for SAMA 18. This type of system would be more expensive than SAMA 18. For this analysis, SAMA 18 is assigned as a bounding case for these contributors.
The frequency of containment failure due to hydrogen burns could be reduced by providing a means of eliminating hydrogen buildup in a diverse range of scenarios, such as with a hydrogen igniter system (SAMA 22). 1.02E+OO ALL FOUR VITAL This SF represents the failure of all four vital instrument channels in INSTRUMENT large magnitude seismic events. Given that this SF is associated with a CHANNELS:
SEIS6, large scale seismic event (greater than 1.75g), a new mitigating system Hazard Levels: 3.00E+OO capable of responding after seismic events (potentially up to 4g) is to 3.99E+OO considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). Page F-204 I I EVENT PROBABILITY NAME SVZ3R1 2.73E-02 SACSS4 3.91 E-02 SSG6 3.19E-02 ZPRL3C 4.37E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.02E+OO 480V SWITCHGEAR Addressed in the Level 1 importance list. VENTILATION:
E-43, S-43 and HD43-SO impacted -run failure 1.02E+OO SEISMIC FAILURE OF Addressed in the Level 1 importance list. AC TB STRUCT SUCCESSFULE:
SEIS4, Hazard Levels: 2.00E+OO to 2.500E+OO 1.01 E+OO SEIS6, Hazard Levels: This top event represents the seismic failure of the steam generator 3.00E+OO to 3.99E+OO supports and postulated failure of the reactor coolant system and steam connecting piping. Failure of this top event is modeled as leading to core damage. The top event failure also is modeled as failing containment because it results in high containment internal pressure.
Given that this SF is associated with a large scale seismic event (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.01 E+OO Normal letdown LOCA Th.is event represents a letdown path LOCA w i th failure of the recovery due to fire action to isolate the LOCA pathway by opening the DC supply breakers induced/random failures:
for the valves. DCPP currently has fire procedures that direct this action All components impacted for fires in the relevant area arid no additional changes to the -Recovery of 8149A , B,C procedures have been identified that would significantly improve action impacted. (HEP=0.1) reliability. A potential enhancement would be to provide fire barriers to protect the cables related to the valves in the letdown path associated with LOCA (valves 8149A,B,C valves and LCV-459 and LCV-460).
Page F-205 EVENT PROBABILITY NAME SEL6 2.99E-02 ZPRS2F 9.98E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH Ensuring that either LCV-459 or 460 is protected in area 5A 1 could prevent or mitigate the fire induced LOCA (SAMA 14). 1.01 E+OO EXCESSIVE LOCA: This top event represents a seismically induced excessive LOCA. Given SEIS6, Hazard Levels: that this SF is associated with a large scale seismic event (greater than 3.00E+OO to 3.99E+OO 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.01 E+OO Inadvertent pressurizer This SF represents the failure to terminate a fire induced spurious Sl spray through aux or signal. In this case, the fire has failed the instrumentation used to normal path: All diagnose the Sl termination action. The DCPP fire procedure already components impacted includes guidance on addressing spurious actuation of Sl and it is directed to be used for any fire scenario.
A potential enhancement to consider would be to include a note identifying the spurious signal actuations that may occur in each fire area with a reference to the attachment that governs the mitigating steps for the associated spurious actuation (SAMA 16). Page F-206 EVENT PROBABILITY NAME SPR6 8.42E-02 RF3Z 1.60E-01 C2CT3 1.80E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.01 E+OO SEIS6, Hazard Levels: This top event represents a seismically induced pressure relief/small 3.00E+OO to 3.99E+OO LOCA. Given that this SF is associated with a large scale seismic event (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qual i fied PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.01 E+OO FIRE: SWITCHOVER TO Addressed in the Level 1 importance list. CONTAINMENT SUMP RECIRCULATION AFTER SLOCA DEGRADED INSTRUMENTATION 1.01 E+OO CONTAINMENT This SF is assoicated with top event CSCET, which considers FAILURE AT VESSEL containment failure due to RCS blowdown or combustible gas BREACH: No HPME detonation. The scenarios including this SF are all large magnitude caused DCH (low seismic events. Given that this SF is associated with a large scale pressure, or HPME seismic event (greater than 1.75g), a new mitigating system capable of doesn't occur at higher responding after seismic events (potentially up to 4g) is considered to be pressure) without spray required.
Such a system would include a 4KV power source, a core or CFCUs spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). Page F-207 EVENT PROBABILITY NAME L2CT3 3.30E-01 D2F1 2.48E-04 SSG5 1.12E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS
- REDUCTION WORTH 1.01 E+OO LARGE CONTAINMENT This SF is assoicated with top event L2CET, which considers large FAILURE AT VESSEL containment failure due to RCS blowdown or combustible gas BREACH: No HPME detonation.
The scenarios including this SF are all large magnitude caused DCH (low seismic events. Given that this SF is associated with a large scale pressure, or HPME seismic event (greater than 1. 75g), a new mitigating system capable of doesn't occur at higher responding after seismic events (potentially up to 4g) is considered to be pressure) without spray, required. Such a system would include a 4KV power source, a core with CFCUs spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.01 E+OO 125V DC BUS F This SF represents the unavailability of the bus F 125 V battery.
In most (BATTERY)
-ALL cases, it occurs in scenarios in which all 3 DC divisions have failed. An SUPPORT AVAILABLE alternate DC generator could be used to either power critical DC buses or to directly power critical DC equipment (SAMA 1 0). The generator would have to be stored in a seismically qualified area. 1.01 E+OO SEIS5, Hazard Levels: This top event represents the seismic failure of the steam generator 2.500E+OO to 3.00E+OO supports and postulated failure of the reactor coolant system and steam connecting piping. Failure of this top event is modeled as leading to core damage. The top event failure also is modeled as failing containment because it results in high containment internal pressure.
Given that this SF is associated with a large scale seismic event (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). Page F-208 EVENT PROBABILITY NAME PR6GWZ 9.66E-02 ZTDPHD 1.00E-01 SVI5 1.08E-02 SSG4 3.00E-03 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.01 E+OO Fire-456 and 80008 Addressed in the Level 1 importance list. failed. 8000C and 455C available. Overlaps with PR 1 E. Water Challenge.
1.01 E+OO Failure to control SG 2/3 Addressed in the Level 1 importance list. Water Level: Partial Instruments are available 1.01 E+OO SEIS5, Hazard Levels: This SF represents the failure of all four vital instrument channels in 2.500E+OO to 3.00E+OO large magnitude seismic events. Given that this SF is associated with a large scale seismic event (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.01 E+OO SEIS4, Hazard Levels: This top event represents the seismic failure of the steam generator 2.00E+OO to 2.500E+OO supports and postulated failure of the reactor coolant system and steam connecting piping. Failure of this top event is modeled as leading to core damage. The top event failure also is modeled as failing containment because it results in high containment internal pressure.
Given that this SF is associated with a large scale seismic event (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat Page F-209 EVENT PROBABILITY NAME BB1G 1.97E-02 D2G2 1.94E-02 DA3FGH 2.33E-06 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH exchanger system (SAMA 4). 1.01 E+OO UN IT 2 VITAL AC/DC Addressed in the Level 1 importance list. SYSTEM: Train 2G fails with Recovery -TS=S 1.01 E+OO 125V DC BUS G This SF represents the unavailability of the bus G 125 V battery given (BATTERY) -GIVEN failure of the bus F battery.
In most cases, it occurs in scenarios in D2F=F which all 3 DC divisions have failed. An alternate DC generator could be used to either power critical DC buses or to directly power critical DC equipment (SAMA 1 0). The generator would have to be stored in a seismically qualified area. 1.01 E+OO VITAL DC TRAINS F, G This SF represents the unavailability of all 3 125V DC divisions.
An AND H (2 HOUR) alternate DC generator could be used to either power critical DC buses UNAVAILABLE or to directly power critical DC equipment (SAMA 1 0). The generator would have to be stored in a seismically qualified area. Page F-210 EVENT PROBABILITY NAME SDC3 2.23E-03 D2H3 4.87E-01 ZPRL3A 4.37E-02 Table Note: TABLE F.5-2A APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST1/ ST5)1 IE IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.01 E+OO SEIS3, Hazard Levels: This SF represents the seismic failure of 125V DC power. This SF is 1.75E+OO to 2.00E+OO typically combined with LOOP events, which result in SBO scenarios given that DC power is required for on-site power alignment.
An alternate DC generator could be used to either power critical DC buses or to directly power critical DC equipment (SAMA 1 0). The generator would have to be stored in a seismically qualified area. 1.01 E+OO D2F-F, D2G-F The probability of this event reflects the failure of multiple DC buses given the availability of 480V AC buses. As such, a backup independent DC power supply system capable of being connected to the affected bus in a timely manner may lower the importance of this event (SAMA 1 0). 1.01 E+OO All components impacted Addressed in the Level 1 importance list. -Recovery of 8149A,B,C impacted. (HEP=1) 1. ST1 and STS refer to release categories Large Early and ISLOCA , respectively Diablo Canyon Power Plant License Renewal Application Page F-211 Diablo Canyon Power Plant License Renewal Application APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 Page F-212 EVENT PROBABILITY NAME CIA 1.03E-01 ZOI5 1.90E-01 ZHTRP2 1.60E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2B APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.86E+OO FAILURE OF CONTAINMENT This SF rerpresents the failure of containment isolation in ISOLATION:
Fire with Recovery fire events. Because there are multiple valves associated with this function, there are a large set of fire initiating events and accident evolutions associated with this SF. These types of events could also potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). The existing DCPP fire procedures already include fire area specific actions to mitigate fire induced damage; however, the actions to address the containment isolation function are general. Another potential enhancement would be to explicitly identify the containment isolation valves that may be impacted for each fire area (SAMA 21 ). 1.28E+OO Manual containment Isolation:
This SF is associated with the operator action to manually INST. FOR OPERATOR CUE perform containment isolation when the instrumentation ARE PARTIALLY FAILED DUE used for diagnosis is partially degraded.
The existing TO FIRE DCPP fire procedures already include firea area specific actions to mitigate fire induced damage; however, the actions to address the containment isolation function are general. Another potential enhancement would be to explicitly identify the containment isolation valves that may be impacted for each fire area (SAMA 21 ). 1.21 E+OO Operator Action-Degraded Addressed in the Level 1 importance list. Instrumentation Page F-213 EVENT PROBABILITY NAME ZOI6 4.50E-02 PR6BWZ 9.66E-02 RF3Z 1.60E-01 PR6GWZ 9.66E-02 PRB1A 1.76E-01 ZTDPHD 1.00E-01 RECSR 6.50E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.S-28 APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.17E+OO Manual containment Isolation:
This SF is associated with the operator action to manually INSTRUMENTS FOR perform containment isolation when the instrumentation OPERATOR CUE ARE OK used for diagnosis is not impacted.
Because there are FROM FIRE multiple valves associated with this function, there are a large set of fire initiating events and accident evolutions associated with this SF. These types of events could also potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). 1.11 E+OO Fire -456 available , 8000C and Addressed in the Level 1 importance list. 455C failed. Overlaps with PR9. Water Challenge.
1.10E+OO FIRE: SWITCHOVER TO Addressed in the Level 1 importance list. RECIRCULATION AFTER SLOCA DEGRADED INSTRUMENTATION 1.09E+OO Fire-456 and 80008 failed. Addressed in the Level 1 importance list. 8000C and 455C available.
Overlaps with PR 1 E. Water Challenge.
1.08E+OO PR Failed due to PORV 455C Addressed in the Level 1 importance list. 80008 Failure-FOR FIRE AREA 1 A and 9A 1.08E+OO Failure to control SG 2/3 Water Addressed in the Level 1 importance list. Level: Partial Instruments are available 1.07E+OO Recovery actions for CSR Addressed in the Level 1 importance list. Scenarios from HSP Page F-214 EVENT PROBABILITY NAME OSZ1 5.30E-02 ZPRSI2 2.80E-01 AW4 1.61 E-02 P2CET3 2.82E-01 GXH 3.50E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.S-28 APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW --------------RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.07E+OO MANUAL ACTUATION IN Addressed in the Level 1 importance list. EVENT SSPS FAILS: Instrumentation degraded 1.05E+OO Operator action to terminate Addressed in the Level 1 importance list. spurious Sl: Degraded instrumentation 1.04E+OO SUPPORT FOR BOTH MOP'S Addressed in the Level 1 importance list. UNAVAILABLE 1.04E+OO RCS PRESSURE AT VESSEL This SF is linked to scenarios for which the RCS is at BREACH EXCEEDS 650 PSIA intermediate pressure at the time of vessel breach. They include primarily large magnitude seismic events and fire events in which 480V switchgear room cooling fails. Given that this SF is associated with a large scale seismic event (greater than 1.75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). For the fire events, containment failure is linked to hydrogen burns. The frequency of containment failure due to hydrogen burns could be reduced by providing a means of eliminating hydrogen buildup in a diverse range of scenarios, such as with a hydrogen igniter system (SAMA 22). 1.04E+OO 1/3 DIESELS UNAVAILABLE Addressed in the Level 1 importance list. Page F-215 EVENT PROBABILITY NAME AWFZ 5.24E-01 ZSGALL 9.97E-01 ZPRL3A 4.37E-02 AZAF3 2.70E-02 ZTDPHS 5.00E-02 PRC1A 1.73E-01 RF1Z 8.68E-03 HRF23A 6.00E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.S-28 APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH (BUS H) 1.04E+OO No support for AFWP2, AFWP3 Addressed in the Level 1 importance list. and fire impacts on AFWP1. 1.04E+OO fire impact PCV-19, PCV-20, Addressed in the Level 1 importance list. PCV-21 and PCV-22 1.04E+OO Normal letdown LOCA due to Addressed in the Level 1 importance list. fire induced/random failures:
All components impacted -Recovery of 8149A,B,C impacted. (HEP=1) 1.04E+OO UNIT 1 4.16 KV BUS F: Addressed in the Level 1 importance list. HF13/HF14 impacted-Recovery successful 1.03E+OO Failure to control SG 2/3 Water Addressed in the Level 1 importance list. Level: All Instruments are available 1.03E+OO PR Failed due to PORV 456C Addressed in the Level 1 importance list. 8000C Failure-FOR FIRE AREA 1 A and 9A 1.03E+OO FIRE: SWITCHOVER AFTER Addressed in the Level 1 importance list. SLOCA OR B/F WITH CS FAILED 1.03E+OO Fire-HR Fails due to ZHR23A Addressed in the Level 1 importance list. fails: NO FLOW PATH FROM RHR TO HIGH PRESSURE PUMPS: Page F-216 EVENT PROBABILITY NAME PR6AW1 9.66E-02 081Z2 1.34E-01 SIZCR6 8.41 E-01 ZPRIS2 1.50E-01 LSCET1 5.00E-01 ZSETB7 9.87E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.S-28 APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.03E+OO PRESSURE RELIEF: Fire-Addressed in the Level 1 importance list. 8000C, 456 available, 455C failed. This will overlap with PRM. Water Challenge.
Block valve closure fails. 1.03E+OO Fire-Loss of Instrument Air Addressed in the Level 1 importance list. (HEP successful) and Instrumentation Degraded 1.03E+OO 8974A, and All ZSI1componnts Addressed in the Level 1 importance list. impacted 1.03E+OO Instrumentation degraded Addressed in the Level 1 importance list. 1.03E+OO INDUCED PORV (OR This SF represents the probability that a PORV has failed PRESSURIZER SAFETY) in the open position after repeated cycling at elevated FAILURE temperatures , which leads to a low pressure RCS at vessel breach and containment typically fails due to long term overpressurization.
The sequences that include PORV failures are diverse and include internal events initiators , fire scenarios, and seismic events. These types of events could also potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). 1.03E+OO 355, 356, 357, 750 impacted -This SF represents the fire induced loss of t_Qermal barrier 355 not recoverable cooling. The sequences including these events are represented by a wide range of fire events that lead to long term containment overpressurization failures.
The scenarios including this SF also generally include fire induced LOCAs from pressurizer heater actuation or charging flow imbalance.
Multiple other Page F-217 EVENT PROBABILITY NAME ZAH7 S.OOE-01 SDS1 2.17E-02 ZHTRP3 6.50E-03 C2CT3 1.80E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2B APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2
- DCPP LI;VEL 2 (ST2)1 IMPORTANCE LIST REVIEW ---RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH functions/components are also failed, such as the CCW heat exchangers and SG steam relief capability.
The wide range of failures essentially requires a fire-safe train of equipment for success. SAMA 18 represents an independent primary and seconday side makeup capability, but for all but very small LOCAs, successful mitigation would require a permanently installed system with higher makeup flow capacity than the portable pumps envisioned for SAMA 18. This type of system would be more expensive than SAMA 18. For this analysis, SAMA 18 is assigned as a bounding case for these contributors.
1.02E+OO 4.16 kV Bus H fails due to fire: Addressed in the Level 1 importance list. HH14 affected-Conditional recovery -Local action 1.02E+OO RCP Shutdown seals Fail to Addressed in the Level 1 importance list. Actuate 1.02E+OO Operator Action -Addressed in the Level 1 importance list. Instrumentation OK 1.02E+OO CONTAINMENT FAILURE AT This SF is assoicated with top event CSCET, which VESSEL BREACH: No HPME considers containment failure due to RCS blowdown or caused DCH (low pressure, or combustible gas detonation.
The scenarios including this HPME doesn't occur at higher SF are all large magnitude seismic events. Given that this pressure) without spray or SF is associated with a large scale seismic event (greater CFCUs than 1.75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for Page F-218 EVENT PROBABILITY NAME AZAH7 5.00E-01 OG2305 6.04E-01 AWR1 2.93E-04 GF1 3.50E-02 AZAG7 5.00E-01 BB1G 1.97E-02 Diablo Canyon Power Plant License Renewal Application TABLE F.5-28 APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.02E+OO HH14 affected-Conditional Addressed in the Level 1 importance list. Recovery -Local action 1.02E+OO AVAILABILITY OF POWER The offsite power failures are generally combined with a FROM 230 KV OFFSITE GRID: failure of an EDG, a 4 KV Bus/supply failure, and a 480V 52HG15 impacted AC bus/supply failure, or some combination of similar events. Typically, the G 480V AC bus is not available to support TO AFW and an alternate means of SG makeup is required.
Because there are often induced LOCAs, primary side makeup is also necessary.
These types of events could also potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). 1.02E+OO Failure to supply water from Addressed in the Level 1 importance list. FWST or RWR (non seismic) 1.02E+OO DG 1-3 (BUS F) STARTS & Addressed in the Level 1 importance list. RUNS FOR 6 HR 1.02E+OO HG14 affected-Conditional Addressed in the Level 1 importance list. recovery -Local action 1.02E+OO UNIT 2 VITAL AC/DC SYSTEM: Addressed in the Level 1 importance list. Page F-219 EVENT PROBABILITY NAME GH4G 3.52E-02 GXF 3.50E-02 SCT6 4.51 E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.5-2B AP.PENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH Train 2G fails with Recovery -TS=S 1.02E+OO UNIT 1 BUS H DIESEL This SF is associated with a failure of DG 1-1, primarily GENERATOR:
DG 1-1 (BUS H) for fires in the 4-A-1 area (Chemical Lab Area, G Bus : GF-S, GG-B Compartment).
The scenario including this SF are typically associated with fires in the 4-A-1 area (Chemical Lab Area, G Bus Compartment).
In these cases, the fire impacts RHR pump 1-1 and 480V bus Gin combination with the random failue of DG 1-1 and fire induced failue of 4KV bus G. The result is a failure of power to the DG fuel . oil system, which leads to an SBO as it is also combined with a failure to align the backup power supply to the fuel oil system. DCPP has a viable recovery option for this typs of event, but the action to perform the task is impacted by degraded instrumentation and it has failed. These types of events could also potentially be mitigated through the use of portable, engine driven, high pressure RCS and SG injection pumps (SAMA 18). 1.02E+OO 1/3 DIESELS UNAVAILABLE Addressed in the Level 1 importance list. (BUS F) 1.02E+OO RELAY CHATTER: SEIS6, This SF represents the failure of the emergency AC Hazard Levels: 3.00E+OO to power system due to seismically induced relay chatter. 3.99E+OO Without relay reset, onsite AC sources cannot be aligned to required loads. Given that this SF is associated with a large scale seismic event (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor Page F-220 EVENT PROBABILITY NAME SCT5 2.72E-01 Diablo Canyon Power Plant License Renewal Application TABLE F.5-28 APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). 1.02E+OO RELAY CHATTER: SEIS5, This SF represents the failure of the emergency AC Hazard Levels: 2.500E+OO to power system due to seismically induced relay chatter. 3.00E+OO Without relay reset, onsite AC sources cannot be aligned to required loads. Given that this SF is associated with a large scale seismic event (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4). Page F-221 EVENT PROBABILITY NAME ZF032 1.90E-01 C2CT11 7.20E-03 Diablo Canyon Power Plant License Renewal Application TABLE F.S-28 APPENDIX E ENVIRONMENTAL REPORT AMENDMENT 2 DCPP LEVEL 2 (ST2)1 IMPORTANCE LIST REVIEW RISK DESCRIPTION POTENTIAL SAMAS REDUCTION WORTH 1.01 E+OO Failure to Align Backup Power This SF represents the failure to align a diesel fuel oil Supply: Partial Instruments are pump to its backup power supply when the available instrumentation required for diagnosis of the action has been degraded by a fire event. The scenarios including this SF are typically associated with fires in the 4-A-1 area (Chemical Lab Area, G Bus Compartment).
DCPP already has a portable diesel fuel oil transfer pump. If the model accounted for the use of this pump, the importance of this split fraction would fall below the review threshold. No SAMAs are required to address this contributor.
1.01 E+OO CONTAINMENT FAILURE AT This SF is related to the failure of containment at the time VESSEL BREACH: High or of vessel breach. The contributors including this SF are setpoint pressure, w/o sprays or primarily large magnitude seismic events. Given that this CFCUs, HPME cause DCH SF is associated with a large scale seismic event (greater than 1. 75g), a new mitigating system capable of responding after seismic events (potentially up to 4g) is considered to be required.
Such a system would include a 4KV power source, a core spray type injection system (with a qualified PORV) capable of spraying the core for cooling until the reactor cavity is flooded to a level above TAF, a connection to a large seismically qualified source of water (wells or seawater), and a heat exchanger system (SAMA 4).
F-222