ML041890409
| ML041890409 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 07/06/2004 |
| From: | Indiana Michigan Power Co |
| To: | Robert Schaaf NRC/NRR/DRIP/RLEP |
| Schaaf R, NRR/DRIP/RLEP, 415-1312 | |
| Shared Package | |
| ML041890401 | List: |
| References | |
| TAC MC1221, TAC MC1222 | |
| Download: ML041890409 (7) | |
Text
Assumptions used in the Evaluation of Severe Accident Mitigation Alternatives Applicants Environmental Report - Operating License Renewal Stage Donald C. Cook Nuclear Plant SAMA Number Potential Improvement Assumptions 5
Provide hardware connections to allow ESW (SW) to cool charging pump seals.
Eliminated charging system CCW dependency. Eliminated RCP seal failures for all loss of ESW and loss of CCW accident sequences.
9 Increase charging pump lube oil capacity.
Eliminated charging system CCW dependency. Eliminated RCP seal failures for all loss of ESW and loss of CCW accident sequences.
10 Eliminate RCP thermal barrier dependence on CCW, such that loss of CCW does not result directly in core damage.
Eliminated RCP seal failures for SBO, loss of ESW, and loss of CCW accident sequences, however, assumed that leakage of 6 gpm per pump would occur. Reduced non-recovery probability for ESW and CCW events by a factor of ten for sequences with AFW success. Assumed that RCPs could continue to run without seal failure following loss of normal seal cooling events.
12 Create an independent RCP seal injection system, with dedicated diesel.
Assumed that the new system would be effective at mitigating SBO, loss of ESW, and loss of CCW events. Assumed that RCP seals would remain intact for a time period sufficient to allow operator action to initiate the new system. Assumed that no RCS inventory would be lost through seal leakage. Assumed a total failure probability for the new system of 0.1. That value bounds operator action failures as well as random hardware errors associated with the new system. Assumed that RCPs could continue to run without seal failure following loss of normal seal cooling events.
13 Create an independent RCP seal injection system, without dedicated diesel.
Assumed that the new system would be effective at mitigating loss of ESW and loss of CCW events. Eliminated RCP seal failures for all loss of ESW and loss of CCW accident sequences. Assumed that no RCS inventory would be lost through seal leakage.
Assumed that RCPs could continue to run without seal failure following loss of normal seal cooling events.
17 Add a third CCW pump.
Eliminated all failures of CCW pumps.
24 Improve ability to cool RHR heat exchangers.
All failures that result in loss of cooling to RHR or Containment Spray can be recovered by operator action. The failure probability of this operator action was assumed to be 1.0E-02.
25 Stage backup fans in switchgear rooms.
Eliminated all failures of 4kVAC room cooling.
26 Provide redundant train of ventilation to 480V board room.
Eliminated all failures of 4kVAC room cooling.
27 Implement procedures for temporary HVAC.
Eliminated all failures of 4kVAC room cooling.
Eliminated all EDG room ventilation failures 28 Provide backup ventilation for the diesel-generator rooms that could be used if the room normal HVAC supply fails.
Eliminated all EDG room ventilation failures 33 Install an independent method of suppression pool cooling.
All failures that result in loss of cooling to RHR or Containment Spray can be recovered by operator action. The failure probability of this operator action was assumed to be 1.0E-02.
Assumptions used in the Evaluation of Severe Accident Mitigation Alternatives Applicants Environmental Report - Operating License Renewal Stage Donald C. Cook Nuclear Plant SAMA Number Potential Improvement Assumptions 34 Develop an enhanced drywell spray system.
In the Level 2 PRA, model eliminated all failures of containment spray injection.
35 Provide a dedicated existing drywell spray system.
In the Level 2 PRA, model eliminated all failures of containment spray injection.
39 Create/enhance hydrogen igniters with independent power supply.
(GSI-189)
In the Level 2 PRA, model eliminated all failures of hydrogen igniters.
40 Create a passive hydrogen ignition system.
In the Level 2 PRA, model eliminated all failures of hydrogen igniters.
41 The action to turn on hydrogen igniters fails frequently due to the time needed to remotely turn off the ice condenser air handling units, as committed to during the original installation of the hydrogen igniter system. This commitment will be investigated and removed if justifiable.
Eliminated errors of execution for operation of hydrogen igniters. Note that hydrogen igniters would still be unavailable for SBO sequences prior to power recovery.
49 Create other options for reactor cavity flooding (Part b).
Assumed that all potentially dry cavity sequences were eliminated.
53 Use firewater spray pump for CTS.
In the Level 2 PRA mode, eliminated all failures of containment spray injection.
67 Improve bus cross-tie ability between a units emergency buses.
Failure of power to any single bus can be recovered by operator action to align power from another bus. Assumed a failure probability of 0.1 for the operator action.
68 Provide alternate battery charging capability.
Eliminated all failure of battery chargers and room cooling fans from DC power systems.
72 Create a cross-unit tie for EDG fuel oil.
Evaluated diesel-generator failure data to estimate potential improvement to diesel-generator failure data.
73 Develop procedures to repair or change out failed 4KV breakers.
Assigned zero to values for offsite power non-recovery probability for time periods shorter than six hours. Assigned zero to values for the probability of uncovering the core prior to power recovery for time periods shorter than six hours.
79 Create a lake water backup for EDG cooling.
Eliminated all cooling water failures from diesel-generator models.
80 Use firewater as a backup for EDG cooling.
Eliminated all cooling water failures from diesel-generator models.
Assumptions used in the Evaluation of Severe Accident Mitigation Alternatives Applicants Environmental Report - Operating License Renewal Stage Donald C. Cook Nuclear Plant SAMA Number Potential Improvement Assumptions 84 Develop procedures for use of pressurizer vent valves during SGTR sequences.
Eliminated all pressurizer PORV failures from SGTR accident sequences.
85 Install a redundant spray system to depressurize the primary system during a SGTR.
Eliminated all pressurizer PORV failures from SGTR accident sequences.
94 Install self-actuating CIVs.
Guaranteed success of containment isolation in the Level 2 PRA model.
95 Install additional instrumentation for ISLOCA sequences.
Eliminated all ISLOCA initiating events.
96 Increase frequency of valve leak testing.
Eliminated all ISLOCA initiating events.
100 Revise EOPs to improve ISLOCA identification.
Set cognitive failure to recognize ISLOCA events to zero failure probability.
101 Revise ISLOCA procedure to specifically address the ISLOCA sequence with the frequency that was dominant in Rev. 1 of the PRA.
Eliminated operator failure associated with detection and mitigation of ISLOCA events.
103 Add redundant and diverse limit switch to each CIV.
Guaranteed success of containment isolation in the Level 2 PRA model.
108 Implement a digital FW upgrade.
Reduced frequency of transient events with feedwater available from 1.3 per year to 0.85 per year. Eliminated all loss of main feedwater events.
115 Provide portable generators to be hooked in to the turbine-driven AFW, after battery depletion.
Eliminated all failure of battery chargers and room cooling fans from DC power systems.
117 Create ability for emergency connections of existing or alternate coolant inventory.
All failures that result in loss of cooling to RHR or Containment Spray can be recovered by operator action. The failure probability of this operator action was assumed to be 1.0E-02.
All hardware failures of RHR pump train components were eliminated.
123 Provide capability for diesel-driven, low pressure vessel makeup.
All hardware failures of RHR pump train components were eliminated.
124 Provide an additional HPSI pump with independent diesel.
Assumed a new system would be equivalent to existing high-pressure ECCS (charging pump) trains. The new system would have a total system failure probability, including human errors, of 0.1. The new system would preclude uncovering the core for eight hours during SBO events.
Assumptions used in the Evaluation of Severe Accident Mitigation Alternatives Applicants Environmental Report - Operating License Renewal Stage Donald C. Cook Nuclear Plant SAMA Number Potential Improvement Assumptions 125 Install independent AC HPSI system.
Assumed a new system would be equivalent to existing high-pressure ECCS (charging pump) trains. The new system would have a total system failure probability, including human errors, of 0.1. The new system would preclude uncovering the core for eight hours during SBO events.
126 Prevent overpressurization of RHR piping by SI system.
Analyzed the failure mode modeled and determined that less conservative modeling of success criteria would eliminate this failure mode as a significant contributor to CDF.
127 Create the ability to manually align ECCS recirculation.
Set the failure probability of valves used to align to ECCS recirculation to zero. Assumed human errors associated with manual alignment would be no higher that for remote alignment.
134 Replace two of the four safety injection pumps with diesel-driven pumps.
Assumed a new system would be equivalent to existing high-pressure ECCS (charging pump) trains. The new system would have a total system failure probability, including human errors, of 0.1. The new system would preclude uncovering the core for eight hours during SBO events.
139 Create automatic swapover to implement low pressure pump to HPSI pump piggyback operation during recirculation following RWST depletion.
Set the failure probability for all operator actions that model the switchover to recirculation to zero. Assumed that the failure probability for the signal that actuates any automatic switchover would be zero.
141 Replace old air compressors with more reliable ones.
Set the failure probability and maintenance unavailability for all air compressors to zero.
144 Install MG set trip breakers in control room.
Set to zero the failure probability for operator action to manually insert control rods and provide long-term shutdown of the reactor.
145 Add capability to remove power from the bus powering the control rods.
Set to zero the failure probability for operator action to manually insert control rods and provide long-term shutdown of the reactor.
149 Install a system of relief valves that prevents any equipment damage from a pressure spike during an ATWS.
Eliminated all failures of pressurizer PORVs.
153 Create/enhance RCS depressurization ability.
Eliminated all failures of pressurizer PORVs.
154 Make procedural changes only for the RCS depressurization option.
Eliminated all failures of pressurizer PORVs.
157 Install secondary side guard pipes up to the MSIVs.
Set the frequency of steamline break initiating events to zero.
160 Provide self-cooled ECCS seals.
Eliminated charging system and safety injection CCW dependency. Eliminated RCP seal failures for all loss of ESW and loss of CCW accident sequences.
Assumptions used in the Evaluation of Severe Accident Mitigation Alternatives Applicants Environmental Report - Operating License Renewal Stage Donald C. Cook Nuclear Plant SAMA Number Potential Improvement Assumptions 162 Make CCW trains separate.
Set logical events to model CCW train cross-tie valves closed.
163 Make ICW trains separate.
Set logical events to model ESW train cross-tie valves closed.
166 Provide containment isolation design per GDC and SRP.
Guaranteed success of containment isolation in the Level 2 PRA model.
167 Improve RHR sump reliability.
Set the failure probability of recirculation sump to zero.
168 Provide auxiliary building vent/seal structure.
Eliminated all ISLOCA initiating events.
169 Add charcoal filters on auxiliary building exhaust.
Eliminated all ISLOCA initiating events.
170 Add penetration valve leakage control system.
Guaranteed success of containment isolation in the Level 2 PRA model.
171 Enhance screen wash.
Eliminated the possibility of plugging any system cooled by raw water systems. Set the frequency of loss of main feedwater events to zero.
172 Enhance training for important operator actions.
- 1)
HI1-FAILURE-HE, Reduction in failure probability for this event is not possible without physical plant changes such as those evaluated in Item 39. No further evaluation performed.
- 2)
OLI---13B-EHHE, Use of less conservative success criteria would eliminate this event from the importance analysis. No further evaluation performed.
- 3)
RRI---CCW-EHHE, Reduced the value of this event and six other related events by a factor of 3.333 based on lessening dependence on prior actions.
- 4)
CCW-CVCSMHHE, Reduced the value of this event and three other related basic events that represent cognitive errors by a factor of 3.333 based on lessening dependence on prior actions. Reduced the value of two related events that represent execution failures by a factor of two based on lessening stress level.
- 5)
CSR-HIGHDEP-HE, Assumed that the benefit of reducing this and eight other related events would be one-fourth the benefits of completely automating the switchover to recirculation evaluated under Item 139.
- 6)
RCC---EXE-EHHE, Reduced failure probability by a factor of 2.5 based on lowering stress level.
- 7)
OA2----E3-MHHE-L, Reduced the stress level used to evaluate three other related events thereby reducing their failure probability by a factor of two. Maintained the low dependence of this event on other events.
- 8)
OA1--E3CD-MHHE-M, Reduced the failure probability of this and two other related events by a factor of two.Errors of execution cause failure to cooldown and depressurize to prevent overfill of ruptured steam generator.
- 9)
RRI---AFW-EHHE, Reduced the value of this event and six other related events by a factor of 3.333 based on lessening dependence on prior actions.
- 10) EPORVMANOPENHE, Determined that more detailed modeling would eliminate this event from cutsets. No further evaluation performed.
- 11) BAMV-ESWWESTHE, Standard HRA analysis methods would not allow a reduction in the calculated failure probability for this event. Any reduction in importance would require that automatic systems be installed.
Assumptions used in the Evaluation of Severe Accident Mitigation Alternatives Applicants Environmental Report - Operating License Renewal Stage Donald C. Cook Nuclear Plant SAMA Number Potential Improvement Assumptions
- 12) BAMV-ESWEASTHE, Standard HRA analysis methods would not allow a reduction in the calculated failure probability for this event. Any reduction in importance would require that automatic systems be installed.
- 13) CCW-----COG-HE, Reduced the value of this event and one other related basic event that represents cognitive errors by a factor of 3.333, based on lessening dependence on prior actions. Reduced the value of four related events that represent execution errors by a factor of two, based on lowering stress level.
- 14) CCWXTIE-MHHE, Reduced the value of this event and three other related basic events that represent execution errors by a factor of two, based on lowering stress level. Reduced the value of two related events that represent cognitive failures by a factor of 3.333, based on lessening dependence on prior actions.
- 15) CCW-REPAIR--HE, Reduced the value of this event and three other related basic events that represent execution errors by a factor of two, based on lowering stress level. Reduced the value of two related events that represent cognitive failures by a factor of 3.333, based on lessening dependence on prior actions.
- 16) AFW-OPENDOORHE, Recent room heatup calculations show that this failure mode is no longer applicable.
- 17) HPRC-LPR-EXEME, Assumed that the benefit of reducing this and eight other related events would be one-fourth the benefits of completely automating the switchover to recirculation evaluated under Item 139.
- 18) AFW-CROSSTIEHE, Event appears because a simplified analysis of the HEP. More detailed modeling would likely eliminate this event from the importance results. No further evaluation performed.
- 19) AABS-MS-T11DHE, Reduction in failure probability for this event is not possible without major physical plant changes.
- 20) ABBS-MS-T11AHE, Reduction in failure probability for this event is not possible without major physical plant changes.
- 21) RRIA-CSI-PBBHE, Reduced the value of this event and six other related events by a factor of 3.333, based on lessening dependence on prior actions.
- 22) LTS----S1-EHHE, Assumed that the benefit of reducing this and one other related event would be one-fourth the benefits of completely eliminating the failure mode as evaluated under item 144.
- 23) HPRA-LPR-CSRME, Assumed that the benefit of reducing this and eight other related events would be one-fourth the benefits of completely automating the switchover to recirculation evaluated under Item 139.
- 24) CCW-RCP---MHHE, Reduced the value of this event and three other related basic events that represent execution errors by a factor of two, based on lowering stress level. Reduced the value of two related events that represent cognitive failures by a factor of 3.333, based on lessening dependence on prior actions.
- 25) BBXV-1ESW130HE, Eliminated the failure mode of this and three other related events.
- 26) BAXV-1ESW131HE, Eliminated the failure mode of this and three other related events.
- 27) OIB-DYNAM-EHHE, Eliminated this failure mode.
177 Add protection to prevent tornado damage to RWST and penetration rooms.
IPEEE shows that tornados are insignificant contributors to core damage. Therefore, eliminating all tornado-related accident sequences would have an insignificant reduction in risk.
179 Add protection to prevent tornado damage causing failure of power and upper surge tanks.
IPEEE shows that tornados are insignificant contributors to core damage. Therefore, eliminating all tornado-related accident sequences would have an insignificant reduction in risk.
Assumptions used in the Evaluation of Severe Accident Mitigation Alternatives Applicants Environmental Report - Operating License Renewal Stage Donald C. Cook Nuclear Plant SAMA Number Potential Improvement Assumptions 184 Provide a means to ensure RCP seal cooling so that RCP seal LOCAs are precluded for station blackout events.
This item is evaluated in conjunction with items 5, 9, 10, 12, 13, 17, and 160.
185 Improve diesel-generator reliability.
Reduced start and run failure probability and maintenance unavailability of diesel generators by a factor of two.
186 Improve Circulating Water Screens and Debris Removal Eliminated the possibility of plugging any system cooled by raw water systems. Set the frequency of loss of main feedwater events to zero.
187 Improve reliability of power supplies Reduced frequency of transient events with feedwater available from 1.3 per year to 0.85 per year. Eliminated all loss of main feedwater events.
188 Improve switchyard and transformer reliability Reduced frequency of transient events with feedwater available from 1.3 per year to 0.85 per year. Eliminated all loss of main feedwater events.
189 Reduce bio-fouling of raw water systems Eliminated the possibility of plugging any system cooled by raw water systems. Set the frequency of loss of main feedwater events to zero.
190 Improve reliability of main feedwater pumps Reduced frequency of transient events with feedwater available from 1.3 per year to 0.85 per year. Eliminated all loss of main feedwater events.
191 Establish a preventive maintenance program for expansion joints, bellows, and boots.
IPE shows that flooding events are insignificant contributors to core damage. Therefore, reducing flooding initiating event frequency would have an insignificant reduction in risk.
192 Improve reliability of AFW pumps and valves.
A review of importance analysis shows that AFW pump failures are not important to overall risk.
193 MSIV Vulnerability The failure mode addressed by this item is not included in the PRA.