05000275/LER-2010-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. Diablo Canyon Unit 2 05000323 | |
| Event date: | 10-13-2009 |
|---|---|
| Report date: | 08-27-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vi) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2752010001R01 - NRC Website | |
I. Plant Conditions
The event date and times are identified below. For the discovery date, December 24, 2009, Unit 1 was in Mode 1 (Power Operation) at approximately 100 percent reactor power with normal operating reactor coolant temperature and pressure; Unit 2 was in Mode 1 (Power Operation) at approximately 100 percent reactor power with normal operating reactor coolant temperature and pressure.
II. Description of Problem
A. Background
The CRVS [VI] has four distinct modes of operation: mode 1: normal operation mode, mode 2: fire mode, mode 3: recirculation mode, and mode 4: pressurization mode. For the mode 4 - pressurization mode, the Control Room is pressurized with a remote source of air, to a minimum positive pressure, relative to all surrounding air spaces, to prevent the in-leakage of radioactive gases and particulates. CRVS mode 4 operations can occur from manual operation or automatic initiation on high radiation signal or engineered safety feature Phase 'A' Isolation.
Control room air supplies for both Units are monitored by four radiation monitors, 1-RM-25, 1-RM-26, 2-RM-25, and 2-RM-26. The safety function of these radiation monitors is to shift the CRVS to mode 4 on a high radiation alarm from any one of these detectors.
B. Event Description
On October 13, 2009, 11:57 PDT, the combined DCPP CRVS transferred to its pressurization mode of operation (mode 4) due to a high radiation signal from a system radiation monitor, 1-RM-25.
On October 13, 2009, 12:26 PDT, radiation monitor 1-RM-25 was found to be trending up and indicating 3 R/hr. Plant technicians removed this monitor from service upon verification of an invalid signal from the monitor.
On October 13, 2009, 14:42 PDT, radiation monitor 1-RM-26 was found to be trending up. Plant technicians removed this monitor from service upon verification of an invalid signal from the monitor.
�LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) 7 OFDiablo Canyon Unit 1 0 5 0 0 0 2 5 2010 0 0 1 0 1 3 5 On October 14, 2009, 0300 PDT, radiation monitor 2-RM-25 was found to be trending up. Plant technicians removed this monitor from service upon verification of an invalid signal from the monitor.
On October 15, 2009, plant technicians determined the cause of the 1-RM-25 failure to be water intrusion.
On October 24, 2009, plant technicians completed the repairs of 1-RM-25, returning the Unit 1 train back to service.
On December 24, 2009, plant technicians determined the cause of the 1-RM-26 failure to be water intrusion, confirming a common mode failure, and also completed the repairs of 1-RM-26.
On January 2, 2010, plant technicians completed the repairs of 2-RM-25.
C.�Status of Inoperable Structures, Systems, or Components that Contributed to the Event None.
D. Other Systems or Secondary Functions Affected No additional safety systems were adversely affected by this event.
E. Method of Discovery Plant Technicians assigned to repair 1-RM-25 and 1-RM-26 replaced the affected components and determined the cause of the component failures to be water intrusion.
F�Operator Actions None.
G.�Safety System Responses On October 13, 2009, 11:57 PDT, the combined DCPP CRVS transferred automatically to its pressurization mode of operation (mode 4) due to an invalid high radiation signal from a system radiation monitor 1-RM-25.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) HI.�Cause of the Problem
A. Immediate Cause
None
B. Cause
The cause of the failures was determined to be wind-driven water intrusion through barriers (o-rings) due to manufacturer workmanship flaws.
IV.�Assessment of Safety Consequences This event was reviewed against the reporting criteria of 10 CFR 50.73(a)(2)(vii) and found to be applicable. Under this regulation, "Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system designed to:
(A)Shut down the reactor and maintain it in a safe shutdown condition; (B)Remove residual heat; (C)Control the release of radioactive material; or (D)Mitigate the consequences of an accident.
There were no safety consequences as a result of this event. The failure mode of the radiation detector placed the CRVS in a safe mode by activating the pressurization portion of the system and isolating the DCPP control room from external elements.
This event was reviewed to determine if it meets the criteria for a safety system functional failure. 10 CFR 50.73(a)(2)(vi) provides that "Events covered in paragraph (a)(2)(v) of this section may include one or more procedural personnel errors, equipment failures, and/or discovery of design, analysis, fabrication, construction, and/or procedural inadequacies. However, individual component failures need not be reported pursuant to paragraph (a)(2)(v) of this section if redundant equipment in the same system was operable and available to perform the required safety function.
Although 3 of the 4 CRVS radiation detectors failed, radiation detector 2-RE-26, which is in the same system, was operable and available to perform its required safety function. The failures are not deemed to be a safety system functional failure.
Based on the foregoing, this event is not considered risk significant and did not adversely affect the health and safety of the public.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) 1 OFDiablo Canyon Unit 1 0 5 0 0 0 2 7 5 2010 0 0 1 0 5 5 V.�Corrective Actions A.�Immediate Corrective Actions 1. Plant technicians verified the absence of a high radiation condition.
2. Plant technicians removed the affected radiation monitors from service.
B.�Corrective Actions to Prevent Recurrence 1. The failed radiation detectors were replaced with vendor-verified, defect-free components, 1-RE-25, 1-RE-26, and 2-RE-25.
2. Plant technicians will replace radiation detector 2-RE-26.
3. For future component procurement, a purchasing requirement will be added to ensure that the manufacturer inspect the o-ring sealing components of all replacement detectors to ensure that the component is defect free prior to final assembly. PG&E will formally notify the Vendor of this event and request Vendor to prevent recurrence.
C.�Prudent Measure 1. A protective weather coating was applied to the radiation monitors.
VI.�Additional Information
A. Failed Components
1-RE-25, Nuclear Measurements Corporation, Model No. GA-2TMO 1-RE-26, Nuclear Measurements Corporation, Model No. GA-2TMO 2-RE-25, Nuclear Measurements Corporation, Model No. GA-2TMO
B. Previous Similar Events
None.
C. Industry Reports None.