Morning Report for January 28, 2005
Headquarters Daily Report
Part 21 2005-0004 - Potential Turbine Overspeed Due to Load Rejection and Failure of the Turbine Bypass Valves to Open
| Licensee/Facility: |
| Notification: |
MR Number: H-2005-0003
Source Document: Fax
Part 21 2005-0004 - - Potential Turbine Overspeed Due to Load Rejection and Failure of the Turbine Bypass Valves to Open
The turbine generator load rejection with failure of the turbine bypass valves to open event (LRNB) is a potentially limiting anticipated operational occurrence (AOO) that is considered in establishing the Minimum Critical Power Ratio (MCPR) operating limit, and confirming that the linear heat generation rate (LHGR) limits are adequate. Framatome ANP analyses for the LRNB event assume that the load rejection will initiate a fast closure of the turbine control valves (TCV) at all power levels. Some plants have indicated that the fast closure of the TCV is not initiated below a plant specific power level. The fast closure of the TCV initiates a scram and minimizes turbine over speed. If a fast closure of the TCV does not occur, the TCV will close at a slower rate, scram will be delayed, and the turbine will overspeed. This may increase the severity of the event. The turbine overspeed may result in an increase in recirculation pump speed that will also increase the severity of the event.
Framatome ANP has notified the affected plants, LaSalle Unit 2 and Browns Ferry Unit 3, and provided a set of revised operating limits, which are appropriate for the conditions when a fast closure of the TCV does not occur.
On 11/12/2004, General Electric Nuclear Energy (GENE) reported (ADAMS accession number ML043230568) a concern to NRC that the TCV closure, and scram, may not occur for all power levels above P-bypass for an LRNB event. P-bypass is a Technical Specification value at which the scram is enabled for TCV fast closure and is typically 25 to 40% of rated power.
|Accession No ||Accession Date |
|ML050190256 ||01/14/2005 |
|ML043230568 ||11/12/2004 |
|Name ||Office Abbrev ||Phone No ||E-Mail |
|TABATABAI, OMID ||NRR ||(301) 415-6616 ||OTY@nrc.gov |
Page Last Reviewed/Updated Thursday, March 25, 2021