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 ID Component Description Event Description (Operator Action) Notes 2CV-1016-1 SG-A Blowdown Isolation Motor Operated Valve (MOV) Operator Action to Isolate blowdown with fire damage to valves Eliminate loss of SG inventory and limit RCS cooldown 2CV-1066-1 SG-B Blowdown Isolation MOV Operator Action to Isolate blowdown with fire damage to valves Eliminate loss of SG inventory and limit RCS cooldown 2CV-4816 Chemical & Volume Control System Letdown (CVCS LD) Throttle Control Valve (CV) Operators Isolates Letdown Flow Outside the Main Control Room Eliminate potential loss of RCS inventory 2CV-4817 CVCS LD Throttle CV Operators Isolates Letdown Flow Outside the Main Control Room Eliminate potential loss of RCS inventory 2P-32A/2P-32B/ 2P32C/2P32D Reactor Coolant Pumps (RCPs) Operators trips RCPs at the switchgear Minimize potential for loss of RCS inventory via RCP controlled bleed-off (CBO) TBD New Auxiliary Feedwater (AFW) Pump Operator Starts and Aligns AFW pump Establish Primary to 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 ID Component Description Event Description (Operator Action) Notes 2P-89B High Pressure Safety Injection (HPSI) Pump Locally open breakers for HPSI pump Pump protection 2P-60B Low Pressure Safety Injection (LPSI) Pump Locally open breakers for LPSI pump Pump protection 2P-35B Containment Spray Pump Locally open breakers for Containment Spray pump Pump protection 2CV-5630-1/ 2CV-5631-2 Refueling Water Tank (RWT) Outlet Valves Close both RWT Outlet valves locally Prevent inventory transfer to Containment Sump 2CV-4920-1/ 2CV-4921-1 Boric Acid Makeup Tank (BAMT) Gravity Feed Valves Open both BAMT Gravity Feed valves locally Ensure borated water source to Charging Pumps 2CV-4873-1 CVCS Volume Control Tank (VCT) Outlet Valve Close VCT outlet valve locally Remove potential for loss of Charging 2T-1 Pressurizer Heaters Turn OFF and operate pressurizer heaters as necessary RCS pressure control 2P-36A/B/C Charging Pumps Stop and operate Charging pumps locally, as needed Operator action to prevent RCS overfill and control Pressurizer level 2K-4B #2 Emergency Diesel Generator (EDG) Place #2 EDG in LOCKOUT locally Protect EDG 2A-4 4160V Vital Power De-energize/energize 2A-4 Establish manual control over power supplies 2B-6 480V Vital Power De-energize 2B6 locally Establish manual control over power supplies 2D24-2,4,6,8,9, and 10 DC Power to various equipment Open breakers to remove DC power to various equipment Establish manual control over power supplies 2CV-4840-2 Charging Header Isolation Verify open charging header isolation Ensure availability of Charging 2CV-1504-2 #2 EDG Service Water (SW) Outlet Verify open #2 EDG SW Outlet Protect EDG Component ID Component Description Event Description (Operator Action) Notes 2CV-4950-2 RWT Suction Valve Verify RWT suction valve open for charging capability if necessary Backup borated water source to Charging Pumps 2P-4C SW Pump Align Loop 2 SW header locally Ensure cooling source to Emergency Core Cooling System (ECCS) components 2CV-0795-2 EFW pump 2P-7A suction MOV Verify open 2P-7A Condensate suction MOV (2CV-0795-2) locally Ensure EFW availability for RCS Heat Removal 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 2CV-1002 2CV-1002 Upstream Atmospheric Dump Valve (ADV) Isolation MOV TRANSFERS OPEN Credit modification to eliminate potential spurious operation. Only one cable in the Control Room can result in spurious opening of the valve. Therefore, a modification is proposed to prevent spurious opening from a fire in the Control Room by installing flexible metallic conduit on conductor 1F of cable G2 (see Table S-1, Item S1-9 ). 2CV-1052 2CV-1052 Upstream ADV Isolation TRANSFERS OPEN Credit modification to eliminate potential spurious operation. Only one cable in the Control Room can result in spurious opening of the valve. Therefore, a modification is proposed to prevent spurious opening from a fire in the Control Room by installing flexible metallic conduit on conductor 1F of cable R2 (see Table S-1, Item S1-9). 2CV-4698-1 RCS Pressurizer Emergency Core Cooling Vent TRANSFERS OPEN Credit modification to eliminate potential spurious operation. TBD AFW Pump MODIFICATION Provides independent source of SG inventory (see Table S-1, 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 IGF2 CDF LERF Zone Scenario Description (/rx-yr) NSP SF CCDP (/rx-yr) CLERP (/rx-yr) 2199-G Deterministically Compliant Case 3.79E-05 1.00E+00 1.00E+00 1.40E-01 5.29E-06 3.50E-03 1.33E-07 2199-G Post Transition Baseline Case 3.79E-05 1.00E+00 1.00E+00 6.97E-02 2.64E-06 9.29E-04 3.52E-08 Results delta CDF -2.65E-06 delta LERF -9.78E-08