ENS 48819
ENS Event | |
|---|---|
00:06 Mar 13, 2013 | |
| Title | Unit 2 Loss of Shutdown Monitoring Instrumentation System |
| Event Description | On March 12, 2013, at 1706 PDT, with the reactor coolant system not intact, plant operators identified [an] unexpected increase in nuclear reactivity count rate as indicated by source range instrumentation channel N-32. This increase was NOT indicated on redundant wide range instrumentation channels N-51 and N-52. Operators identified that technicians working in the area of the N-32 cable routing had bumped the cabling, resulting in the false increase in the count rate. The source range channel N-32 was subsequently declared inoperable. Prior to this event the other source range channel N-31 had been declared inoperable.
The above event resulted in loss of control room audible indication required by DCPP [Diablo Canyon Power Plant] technical specification to monitor the core reactivity condition and consequently caused loss of the monitoring system. Operators retained capability of monitoring core reactivity conditions through use of the two wide range nuclear instrumentation channels N-51 and N-52. In response to this concern, plant operators verified all core alterations were suspended, verified boron concentration was within acceptable limits for current conditions, suspended operations that could dilute the boron concentration, verified reactor trip breakers were open and control rods incapable of withdrawal, and initiated actions to restore to service one of the source range instrumentation channels with its associated control room audible count rate indication. NRC Resident Inspectors have been notified.
This is an update to EN#48819 reported on March 12, 2013 at 2158 PDT. This update informs the NRC that PG&E, in accordance with provisions of TS 3.0.4b, will be restoring the source range instrumentation channel N-32 to service in Mode 5, maintaining the availability and monitoring of the wide range instrumentation channels while in Mode 5 until the source range channel is returned to service. The licensee has notified the NRC Resident Inspector. Notified R4DO (Powers). |
| Where | |
|---|---|
Diablo Canyon  California (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor | |
| LER: | 05000323/LER-2013-002 |
| Time - Person (Reporting Time:+0.87 h0.0363 days <br />0.00518 weeks <br />0.00119 months <br />) | |
| Opened: | Michael Quitter 00:58 Mar 13, 2013 |
| NRC Officer: | Steve Sandin |
| Last Updated: | Mar 13, 2013 |
| 48819 - NRC Website
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