ENS 52217
ENS Event | |
|---|---|
15:25 Sep 1, 2016 | |
| Title | Unanalyzed Condition on Turbine Driven Auxiliary Feedwater Pump |
| Event Description | During a review of ongoing analyses related to postulated tornado missiles, a question was raised about the sentinel valve on the turbine driven auxiliary feedwater pump (TDAFW). The sentinel valve is designed as a warning system on steam equipment to warn personnel of increased back pressure. The valve is not an ASME component and its operation is not required to support TDAFW operation.
The draft analysis predicts the TDAFW exhaust stack could be partially crimped by a tornado missile and the resultant back pressure on the turbine would increase to approximately 40 psi. This is higher than the set point for the sentinel valve (nominally 27 and 29 psi for Units 1 and 2, respectively). Therefore, in a design basis tornado with a design basis tornado missile striking the TDAFW exhaust stack, and in a condition where the TDAFW is demanded to run, the sentinel valve is expected to lift and allow steam to flow into the room. Vendor correspondence indicates that at approximately 40 psi the sentinel valve will conservatively pass 600 lbm/hr. Thus, it is conservatively considered operation of the TDAFW under such conditions would create an adverse steam environment which would be beyond that which the TDAFW pump has been analyzed to operate. Actions planned to alleviate the above condition would eliminate the potential for adverse environmental conditions. The steam supplies to the TDAFW have been isolated to affect repairs, which are expected to be limited to removal of the sentinel valve from each Unit and installation of a plug. Said activities are expected to be completed within the Allowed Out-of-Service Time (AOT) of the TDAFW of seventy-two hours per Technical Specification 3.7.5. NRC Resident Inspector has been informed.
On 09/01/2016 Comanche Peak reported an ENS Report (no. 52217) related to unanalyzed conditions related to the sentinel valve on the turbine driven auxiliary feedwater pump (TDAFW) during postulated tornado-based scenarios and non-tornado based scenarios. The technical concern was the potential for the sentinel valve to release steam into the TDAFW room and result in adverse environmental conditions within the room and potentially external to the TDAFW room for both tornado-based and non-tornado based scenarios. Subsequent investigations by Engineering have determined the sentinel valve would not be demanded to open during tornado based scenarios and would not result in adverse environmental conditions internal or external to the TDAFW room in any design bases scenario. The licensee has notified the NRC Resident Inspector. Notified the R4DO (Farnholtz). |
| Where | |
|---|---|
Comanche Peak  Texas (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+3.23 h0.135 days <br />0.0192 weeks <br />0.00442 months <br />) | |
| Opened: | John Alexander 18:39 Sep 1, 2016 |
| NRC Officer: | Steven Vitto |
| Last Updated: | Oct 27, 2016 |
| 52217 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 528172017-06-21T15:00:00021 June 2017 15:00:00
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