ULNRC-05977, Enclosure 1 to ULNRC-05977, License Renewal Application, Clarification of Responses to SAMA RAIs to the Callaway LRA
| ML13094A020 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 04/02/2013 |
| From: | Ameren Missouri |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML130940060 | List: |
| References | |
| ULNRC-05977 | |
| Download: ML13094A020 (4) | |
Text
ULNRC-05977 April 2, 2013 Page 1 of 4 CALLAWAY PLANT UNIT 1 LICENSE RENEWAL APPLICATION Clarification of Responses to SAMA RAIs to the Callaway LRA
ULNRC-05977 April 2, 2013 Page 2 of 4 Clarification 3 - RAI 5.a The response indicates that planned installation of the no leakage reactor cooling pump (RCP) seals will mitigate a large fraction of the fire and internal flood risk, which addresses the scenarios where seal loss-of-coolant accidents (LOCAs) are dominant contributors. The response does not address fire and internal flood scenarios that are not mitigated by the new RCP seals. The NRC staff's review of these scenarios concludes that each has a maximum estimated benefit, including consideration of uncertainty, of less than $100K. However, Scenarios 4501-2B and 4501-1B are very similar and involve loss of AFW (auxiliary feedwater) due to empting the CST (condensate storage tank). Mitigating both of these scenarios amounts to a maximum potential benefit, including uncertainty, of approximately $100K. Clarify if Callaway has existing procedures for providing an alternate source of water for AFW and, if not, identify/assess a SAMA candidate to address these scenarios.
Callaway Response Callaway has existing procedures for refill of the CST under the Emergency Coordinator Supplemental Guidelines as provided in the disposition to SAMAs 66 and 67. Additionally, the Essential Service Water (ESW) system is the Safety Related water supply to the AFW system.
AFW system supply automatically swaps over to ESW on low suction pressure from the CST. If the normal makeup system to the CST and both trains of ESW are unavailable, then the Emergency Coordinator Supplemental Guidelines may be used to refill the CST using fire water.
Corresponding Amendment Changes No changes to the License Renewal Application (LRA) are needed as a result of this response.
ULNRC-05977 April 2, 2013 Page 3 of 4 Clarification 4 - RAI 5.b It is noted that the top 6 internal flood scenarios do not involve RCP seal LOCAs. The largest, Zone 1 Scenario F1A has a potential maximum benefit for a SAMA that might eliminate this scenario of approximately $130K. The other scenarios have potential maximum benefits considerably lower. The clarification response to RAI 5.b indicates that Ameren is undertaking a study of the potential for strengthening plant doors (new SAMA 189) that might reduce the risk due to internal flooding. Clarify if damage due to Zone 1 Scenario F1A is mitigated by strengthening plant doors and is therefore addressed by SAMA 189 and, if not, identify/assess a SAMA candidate to address this scenario.
Callaway Response Flood scenario F1A in Zone 1 is not mitigated by strengthening doors under SAMA 189. This flood scenario is a result of water accumulation in flood Zone 1, as well as propagation to additional Zones. Strengthening of Zone 1 doors would increase the flood height in Zone 1 and only slightly delay propagation of the flood to the remaining flood Zones in the scenario. The current flooding analysis for this area is conservative in that there are doors and hatches that would likely fail, relieving the accumulation of water in Zone 1. However, the analysis does not credit failures to benefit mitigation of flooding events. Review of this scenario did not identify cost beneficial ( $130K) hardware or procedural modifications that would reduce the risk of flood scenario F1A.
Corresponding Amendment Changes No changes to the License Renewal Application (LRA) are needed as a result of this response.
ULNRC-05977 April 2, 2013 Page 4 of 4 Clarification 6 - RAI 7.b The response states that SAMA 186 was intended to evaluate providing backup cooling to only the CCW (component cooling water) heat exchanger loads. This SAMA was originally added by Ameren in response to RAI 7.b where it is stated: "SAMA 186 was added to evaluate procedures to provide fire water to the ESW (essential service water) system." The latest response indicates that since a procedure already exists for supplying fire water to the EDGs (emergency diesel generators) the only additional load to be supplied is the CCW system. This would appear to be similar to SAMA 64. The revised SAMA 168 [sic] has a benefit of $1K while SAMA 64 has a benefit of $59K (no failure of CCW pumps) or $104K (fire water to the RHR (residual heat removal) heat exchanger) depending on how evaluated. These are both much less than the benefit for original SAMA 186 (supply fire water to replace the entire ESW) of
$636K (Case SW02). This implies that the benefit of supplying fire water to the EDGs (presumably not credited in the current PRA (probabilistic risk assessment)) is very large.
Clarify that essentially all ESW loads are accounted for by SAMA 64 and the existing procedure to supply fire water to the EDGs. If not, provide a revised assessment of original SAMA 186 to supply fire water to the ESW system (to supply all ESW system loads except the EDGs).
Callaway Response All important ESW loads have procedures in place to provide backup cooling except the CCW heat exchanger. All important CCW system loads have procedures in place to provide backup cooling on loss of CCW except the RHR heat exchanger. Providing fire water as a backup means of cooling the CCW system is not considered to be cost beneficial. The current flow rate of the ESW is much greater than that available from the fire water system. Given the differences in pump flow rate and pipe sizes, considerable cost would be involved in a modification that would allow fire water to serve as a backup either to the entire ESW system or for ESW to the CCW heat exchanger. No cost beneficial options to provide backup cooling to the CCW heat exchanger were identified.
The benefit differential between the original SAMA 186 evaluation and the revised evaluation is based on a revised approach. The original SAMA 186 to supply fire water to the ESW system (SW02) was modeled as fire water essentially replacing the ESW pumps and allowed fire water to supply all ESW loads and included both trains. The revised case of supplying fire water to cool the CCW heat exchanger only modeled fire water to a single CCW heat exchanger, not both trains. Therefore, this case credits fire water as backup cooling to less equipment than the original case (SW02). The revised approach evaluated a less costly modification in an attempt to identify a potentially cost beneficial modification; however, the benefit remained well below the cost.
Corresponding Amendment Changes No changes to the License Renewal Application (LRA) are needed as a result of this response.