ML121800319
| ML121800319 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 06/28/2012 |
| From: | David Bice Entergy Operations |
| To: | Kalyanam N Plant Licensing Branch IV |
| Kalyanam N, NRR/DLPM, 415-1480 | |
| Shared Package | |
| ML121800304 | List: |
| References | |
| TAC ME8282 | |
| Download: ML121800319 (5) | |
Text
Response to Item #3 Delta Risk value of Zero The 0.0 for delta CDF and LERF will be removed from Attachment W and replaced with actual change in risk values PRA Modeling of Recoveries and Modifications ANO-2 does not have a single location for remotely controlling the plant should a Control Room abandonment be required. The Alternate Shutdown procedure provides guidelines that are necessary to assure a safe shutdown of the unit in the event of a significant fire in which both trains of safe shutdown equipment could be rendered inoperable from the Control Room.
Safe shutdown, as defined by 10 CFR 50, Appendix R, applies to both hot and cold shutdown functions. Initial actions taken in the Control Room and verified with follow-up actions taken outside the Control Room ensure the fuel in the reactor vessel is maintained in a safe and stable condition (i.e., hot standby, Mode 3, as defined by NFPA 805).
Additional defense-in-depth (DID) actions are taken by Operations personnel to maintain the unit in Hot Standby and if necessary, place the unit in Cold Shutdown. Therefore, RAs as identified from the fire risk evaluations (FREs) and additional DID actions have been identified for ensuring that the plant is maintained in a safe and stable condition. Key plant parameters to accomplish a safe shutdown are monitored from the Technical Support Center (TSC) using the Safety Parameters Display System (SPDS).
Two analyses were developed to assist in calculating the delta risk for the ANO-2 Control Room: a compliant case and a post transition case. The following describes how the RAs and planned modifications were modeled in each case.
Compliant Case Analysis In order to calculate the delta risk as part of the FRE, a compliant case was first developed.
Because the primary safety functions are challenged for a fire in the Control Room followed by abandonment, the compliant case assumes that a single success train for plant control and mitigation is available to protect the primary safety functions. This approach is based upon Note 2 of Regulatory Guide (RG) 1.205, Revision 2, which states:
The deterministically compliant plant has been referred to as an ideal plant that may not exist or be feasible in practice. Based on experience with the two NFPA 805 pilot plants, the risk of most variances from the deterministic requirements can readily be evaluated by postulating modifications, such as moving or protecting cables, which would meet the deterministic requirements. This provides the base case against which the added risk of the proposed alternative is evaluated. Because of the great similarity between the deterministic criteria of NFPA 805 and the requirements in Appendix R to 10 CFR Part 50, it should be clear, in most cases, what the compliant configuration would be. An exception might occur for fire scenarios where evacuation of the main control room is necessary. This has been addressed in the regulatory guide by defining the term primary control station, which is used in the NFPA 805 definition of recovery action; see Regulatory Position 2.4.
For the ANO-2 Control Room compliant case, a successful train is assumed to be available for accident mitigation (i.e., Emergency Feedwater (EFW) Train A supplying inventory to Steam Generator (SG) B). In addition to the success path for ensuring that primary to secondary heat removal is available, the Reactor Coolant System (RCS) is assumed to remain intact by ensuring that fire failures will not impact RCS integrity. These assumptions ensure a conservative single success path is available with operator failures associated with a primary control station effectively set to zero. Only random failures of equipment associated with the single train success path are considered in the compliant case analysis; all other systems are considered failed due to the fire.
The compliant case does not include all plant modifications, nor does the compliant case consider fire related recoveries.
Post Transition Analysis The Post Transition case (assuming the failures due to a fire in the Control Room) was also analyzed to determine the CDF. With the exception of credited recoveries and modifications identified as necessary to protect the plant from core damage, this analysis assumes all affected equipment in the Control Room fails due to the fire.
Table 1 provides a list of the recoveries that were modeled and credited to reduce risk in the PRA. These recoveries focus on the systems modeled in the Fire PRA and were deemed necessary to ensure that RCS integrity is maintained, SG pressure is maintained, and a source of SG inventory for primary-to-secondary heat removal is provided.
Table 1 Recoveries Credited in FRE Component Event Description Component ID Notes Description (Operator Action)
SG-A Blowdown Operator Action to Isolate Eliminate loss of SG 2CV-1016-1 Isolation Motor Operated blowdown with fire damage inventory and limit RCS Valve (MOV) to valves cooldown Operator Action to Isolate Eliminate loss of SG SG-B Blowdown 2CV-1066-1 blowdown with fire damage inventory and limit RCS Isolation MOV to valves cooldown Chemical & Volume Operators Isolates Control System Letdown Eliminate potential loss of 2CV-4816 Letdown Flow Outside the (CVCS LD) Throttle RCS inventory Main Control Room Control Valve (CV)
Operators Isolates Eliminate potential loss of 2CV-4817 CVCS LD Throttle CV Letdown Flow Outside the RCS inventory Main Control Room Minimize potential for loss of 2P-32A/2P-32B/ Reactor Coolant Pumps Operators trips RCPs at RCS inventory via RCP 2P32C/2P32D (RCPs) the switchgear controlled bleed-off (CBO)
New Auxiliary Feedwater Operator Starts and Aligns Establish Primary to TBD (AFW) Pump AFW pump Secondary Heat Removal
In addition to the recoveries identified in Table 1, additional recovery actions have been identified to provide defense-in-depth (DID). These additional recovery actions support the safety functions listed for Table 2, as well as protect equipment necessary for additional mitigating actions. The main focus of these DID actions is to ensure that a single train of components is available for plant control. The operator manual actions (OMAs) that are transitioning as RAs are listed in Table 2.
Table 2 DID Actions Component Event Description Component ID Notes Description (Operator Action)
High Pressure Safety Locally open breakers for 2P-89B Pump protection Injection (HPSI) Pump HPSI pump Low Pressure Safety Locally open breakers for 2P-60B Pump protection Injection (LPSI) Pump LPSI pump Containment Spray Locally open breakers for 2P-35B Pump protection Pump Containment Spray pump 2CV-5630-1/ Refueling Water Tank Close both RWT Outlet Prevent inventory transfer to 2CV-5631-2 (RWT) Outlet Valves valves locally Containment Sump Boric Acid Makeup Tank 2CV-4920-1/ Open both BAMT Gravity Ensure borated water (BAMT) Gravity Feed 2CV-4921-1 Feed valves locally source to Charging Pumps Valves CVCS Volume Control Close VCT outlet valve Remove potential for loss of 2CV-4873-1 Tank (VCT) Outlet Valve locally Charging Turn OFF and operate 2T-1 Pressurizer Heaters pressurizer heaters as RCS pressure control necessary Operator action to prevent Stop and operate Charging 2P-36A/B/C Charging Pumps RCS overfill and control pumps locally, as needed Pressurizer level
- 2 Emergency Diesel Place #2 EDG in 2K-4B Protect EDG Generator (EDG) LOCKOUT locally Establish manual control 2A-4 4160V Vital Power De-energize/energize 2A-4 over power supplies Establish manual control 2B-6 480V Vital Power De-energize 2B6 locally over power supplies Open breakers to remove 2D24-2,4,6,8,9, DC Power to various Establish manual control DC power to various and 10 equipment over power supplies equipment Charging Header Verify open charging Ensure availability of 2CV-4840-2 Isolation header isolation Charging
- 2 EDG Service Water Verify open #2 EDG SW 2CV-1504-2 Protect EDG (SW) Outlet Outlet
Component Event Description Component ID Notes Description (Operator Action)
Verify RWT suction valve Backup borated water 2CV-4950-2 RWT Suction Valve open for charging source to Charging Pumps capability if necessary Ensure cooling source to Align Loop 2 SW header Emergency Core Cooling 2P-4C SW Pump locally System (ECCS) components Verify open 2P-7A EFW pump 2P-7A Ensure EFW availability for 2CV-0795-2 Condensate suction MOV suction MOV RCS Heat Removal (2CV-0795-2) locally In addition to the recoveries identified in Tables 1 and 2, modifications have been identified in the FREs that ensure the safety functions necessary to maintain the plant in a safe and stable condition will be protected. The modifications listed in Table 3 were credited in the PRA.
Table 3 Proposed Modifications Credited in FRE Comp ID Component Description Notes Credit modification to eliminate potential spurious operation.
2CV-1002 Upstream Only one cable in the Control Room can result in spurious Atmospheric Dump Valve opening of the valve. Therefore, a modification is proposed 2CV-1002 (ADV) Isolation MOV to prevent spurious opening from a fire in the Control Room TRANSFERS OPEN by installing flexible metallic conduit on conductor 1F of cable G2 (see Table S-1, Item S1-9 ).
Credit modification to eliminate potential spurious operation.
Only one cable in the Control Room can result in spurious 2CV-1052 Upstream ADV opening of the valve. Therefore, a modification is proposed 2CV-1052 Isolation to prevent spurious opening from a fire in the Control Room TRANSFERS OPEN by installing flexible metallic conduit on conductor 1F of cable R2 (see Table S-1, Item S1-9).
RCS Pressurizer Emergency Core Cooling 2CV-4698-1 Credit modification to eliminate potential spurious operation.
Vent TRANSFERS OPEN AFW Pump Provides independent source of SG inventory (see Table S-1, TBD MODIFICATION Item S1-11).
The following table provides the results of the quantification of the compliant and post transition base case, along with the delta CDF for the control room analysis.
Table 4 Fire Area G CDF and LERF Evaluation Summary Scenario IGF2 CDF LERF Zone NSP SF CCDP CLERP Description
(/rx-yr) (/rx-yr) (/rx-yr)
Deterministically 2199-G 3.79E-05 1.00E+00 1.00E+00 1.40E-01 5.29E-06 3.50E-03 1.33E-07 Compliant Case Post Transition 2199-G 3.79E-05 1.00E+00 1.00E+00 6.97E-02 2.64E-06 9.29E-04 3.52E-08 Baseline Case Results delta CDF -2.65E-06 delta LERF -9.78E-08