05000528/LER-2011-002
| Palo Verde Nuclear Generating Station (Pvngs) Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| LER closed by | |
| IR 05000528/2013002 (14 May 2013) | |
| 5282011002R01 - NRC Website | |
All times are Mountain Standard Time and approximate unless otherwise indicated.
1. REPORTING REQUIREMENT(S):
This Licensee Event Report (LER) is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications (TS). Trains A and B of the Qualified Safety Parameter Display System (QSPDS)(EllS: IP) were inoperable for an amount of time greater than the 30 days allowed by TS Limiting Condition for Operation (LCO) 3.3.10, Post Accident Monitoring (PAM) Instrumentation.
2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The QSPDS analyzes and processes selected plant parameters and displays them to assist the operator (utility - licensed) in quickly assessing plant conditions during accident situations. Signals obtained from seismically qualified instrumentation are analyzed by class 1 E microprocessors. The output of these microprocessors is transmitted to the Control Room for continuous display and recording. These outputs are also transmitted to the non- class Emergency Response Facility Data Acquisition and Display System (ERFDADS)(EllS:
IP).
The QSPDS consists of two redundant class 1 E channels which are seismically qualified and electrically and physically independent for the display of safety parameters including inadequate core cooling (ICC) processing information. Indications provided include:
- Core exit temperature - signal processing and display
- Reactor Coolant System saturation (or subcooled) margin - computation and display
- Reactor vessel water level - signal processing and display The ICC detection parameters provide the operator with continuous indication of the thermal-hydraulic state within the reactor vessel during the progression of an event leading to and from ICC.
The QSPDS transmits data to the Control Room display units via fiber optic communication modems which are installed in control board B04. The fiber optic communication modems receive 120 VAC power independent of other QSPDS component power supplies. The QSPDS includes other independent data transmission interfaces to display equipment on control board B02 and ERFDADS.
3. INITIAL PLANT CONDITIONS:
On June 29, 2011, Palo Verde Unit 1 was in Operating MODE 1 (Power Operation) at 100 percent power at normal operating temperature and normal operating pressure. There were no other major structures, systems, or components that were inoperable at the start of the event that contributed to the event.
4. EVENT DESCRIPTION:
On June 29, 2011, in preparation for a modification to upgrade QSPDS, a walk down of the installed system in Unit 1 was performed. During the walk down, it was discovered that the 120 volt class power supply cables to the A and B train QSPDS display modems in control board B04 did not meet the minimum six inch physical separation criteria per Regulatory Guide 1.75 contained in the PVNGS Installation Specification for Cable Splicing and Terminations 13-EN-0306. On July 1, 2011, at 15:30, following further evaluation by Engineering and Operations, both trains of QSPDS were declared INOPERABLE and Conditions A and C of TS LCO 3.3.10, Post Accident Monitoring (PAM) Instrumentation, were entered. On July 3, 2011, at 16:05, both trains were declared OPERABLE and Conditions A and C of TS LCO 3.3.10 were exited after the power supply cables to the A and B train QSPDS display modems were rerouted per work order instructions to meet the physical separation criteria.
5. ASSESSMENT OF SAFETY CONSEQUENCES:
The inadequate separation between the power supply cables to the A and B train QSPDS display modems could potentially cause a loss of power, due to a single fault, to both of the display modems that feed the QSPDS displays located on the Unit 1 control board B04. In the event that the QSPDS displays become unavailable, the train A Post Accident Monitoring recorders on control board B02, fed directly from the A QSPDS instrument chassis, would still remain available to the operators. Additionally, the communication link between both trains of QSPDS and ERFDADS would remain available to permit full functionality of data retrieval via ERFDADS for the operators and the Emergency Response Organization.
This event did not result in any challenges to the fission product barriers or result in the release of radioactive materials. There were no actual safety consequences as a result of this event. This event did not prevent the fulfillment of a safety function and did not result in a safety system functional failure as described by 10 CFR 50.73 (a)(2)(v).
6. CAUSE OF THE EVENT:
The root cause of this event was inadequate adherence to cable separation criteria during modification and maintenance activities which led to the installation of power supply cables for the A and B train QSPDS display modems with less than six inches of physical separation. Contributing to the event was a lack of knowledge of the specification requirements by work planners and front line craftsmen.
7. CORRECTIVE ACTIONS:
As an immediate corrective action, the power supply cables to the A and B train QSPDS display modems were rerouted per work order instructions to meet the physical separation criteria and both trains of QSPDS were declared OPERABLE.
To prevent recurrence, the maintenance work order writer's guide was revised to require that cable separation criteria contained in the PVNGS Installation Specification for Cable Splicing and Terminations 13-EN-0306 be incorporated into Main Control Board work instructions.
The following corrective actions were completed:
- Maintenance personnel performed walkdowns of main control board cabinets in all three units to identify and correct non-conforming cable separation configurations.
- Training was provided to front line craftsmen and work planners on cable separation criteria contained in the PVNGS Installation Specification for Cable Splicing and Terminations 13-EN-0306.
- Work instructions for pending QSPDS upgrade modifications were revised to include cable separation criteria contained in the PVNGS Installation Specification for Cable Splicing and Terminations 13-EN-0306.
8. PREVIOUS SIMILAR EVENTS:
The station has not identified previous similar events in which the root cause was attributed to inadequate adherence to cable separation criteria.