Semantic search
| Entered date | Event description | |
|---|---|---|
| ENS 49786 | 2 February 2014 18:16:00 | On February 2, 2014, at 11:29 PST, Diablo Canyon Power Plant Unit 2 500kV line differential relay actuated. This action tripped the turbine and opened the generator output breakers to isolate the generator. With the turbine tripped and Unit 2 operating above the P-9 50% power permissive, a reactor trip was initiated from the reactor protection system. All systems operated as designed with no problems observed. All three Unit 2 Auxiliary Feedwater pumps started, the Containment Fan Cooling units started and ran in slow speed, and the standby Auxiliary Saltwater train started, all as expected. Unit 2 is stable at normal operating temperature and pressure. All power transferred to the plant startup source without incident. Condenser vacuum was maintained. The preliminary cause of the differential relay actuation was a flashover of Phase B 500 kV to ground across the Phase B lightning arrestor during a rainstorm. Decay heat is being removed by steam dumps to the condenser. No relief valves lifted during the transient. The steam generators are being supplied by the auxiliary feedwater pumps. There were no injuries to personnel. Unit 1 was not affected. NRC Senior Resident Inspector and Region Branch Chief have been informed of this event. A press release is planned for local media. |
| ENS 47258 | 13 September 2011 01:57:00 | On September 12, 2011, at 1745 PDT operators declared the control room envelope (CRE) inoperable and entered Technical Specification (TS) 3.7.10 Action B. This was due to discovery of inadequately documented CRE in-leakage test data. On September 12, 2011, DCPP (Diablo Canyon Power Plant) personnel reviewing the CRE testing dated February 3, 2005 determined that the test report provided inadequate information to conclude that the most limiting alignment for control room pressurization would result in zero cubic feet per minute (CFM) in-leakage into the CRE, contrary to the Final Safety Analysis Report (FSAR) accident analysis for the most limiting design basis accident. Three of the four ventilation alignments tested had reported values of in-leakage greater than zero CFM. Plant staff implemented compensatory measures by placing the control room ventilation system into its pressurization accident alignment at 1828 PDT using the alignment from the test which had a reported value of zero CFM in-leakage. Additionally, administrative controls are being established to maintain post-Loss of Coolant Accident Emergency Core Cooling System leakage at a rate that would ensure operator doses are maintained less than the FSAR accident analysis results for the highest in-leakage rate reported by the test. Plant personnel notified the NRC Resident Inspector.
On 9/13/11 procedure revisions were approved with reduced limits for post-Loss of Coolant Accident Emergency Core Cooling System (ECCS) leakage. These reduced limits ensure operator doses are maintained less than the FSAR accident analysis results for the highest in-leakage rate reported by the CRE in-leakage test. Plant staff have since determined that the potential benefit of operating the control room ventilation system in its pressurization alignment was unnecessary with the ECCS leakage restriction and on 9/16/11 operators restored the control room ventilation system into its normal operating alignment. The licensee has notified the NRC Resident Inspector. Notified R4DO (Greg Pick)
This is an update to EN #47258 reported on 9/13/11 where it was reported that operators had declared the Control Room Envelope inoperable. (This report was subsequently) updated on 9/16/2011. On 10/18/11 at 16:45 PDT, plant staff determined that the CRE testing dated February 3, 2005 was not performed using a bounding configuration which would result in greatest consequence to the control room operators. The recorded in-leakage from the test was therefore considered to be non-bounding. (As a result of this determination, plant staff have) implemented additional compensatory measures by issuing a shift order requiring the use of self-contained breathing apparatus and potassium iodide tablets under certain accident conditions in accordance with Regulatory Guide 1.196 and NEI 99-03. Plant personnel notified the NRC Resident Inspector. Notified R4DO (Campbell). |