05000331/LER-2005-001

LER-2005-001,

Docket Number
Event date:	06-02-2005
Report date:	08-01-2005
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
Initial Reporting
ENS 41742	10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition
3312005001R00 - NRC Website

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) � )SEQUENTIAL REVISION Duane Arnold Energy Center 05000331 YEAR NUMBER� NUMBER

I. Description of Event:

On June 2, 2005, with the plant operating at 94% power in Run Mode, while reviewing an event at Monticello (LER 2005-001), it was determined that Duane Arnold Energy Center (DAEC) was vulnerable to a similar failure. Specifically, it was determined that the Remote Shutdown Panel (RSP) did not meet design criteria for Appendix R in that metering circuits in the control room could cause a lock out of an essential bus (1A4). The design criteria was not met because the metering circuits are not isolated by the operation of RSP transfer switches, and could have resulted in a fault after the RSP was activated, and therefore, could have delayed the restoration of reactor vessel level. The metering circuit in question was not independent of the area, room, or zone under consideration (the control room) and therefore the remote shutdown system design did not meet the Technical Specification bases requirements for the design of the remote shutdown system. As such, this event is reportable per 10CFR50.72(b)(3)(ii)(B), "Degraded or Unanalyzed Condition." As a result of this issue, a 30-day LCO (Technical Specification 3.3.3.2) for an inoperable RSP was entered on June 2, 2005.

The 30-day LCO was exited on June 18, 2005, after the installation of a temporary modification that corrected the condition.

II. Assessment of Safety Consequences:

A 10CFR50.72(b)(3)(ii)(B), "Degraded or Unanalyzed Condition" notification was made on June 2, 2005 and is listed as event number EN 41742. This report is being submitted pursuant to 10CFR50.73(a)(2)(ii)(B).

This event did not affect the availability of other systems needed to maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.

Therefore, there were no actual safety consequences associated with this event. There was no effect on public health and safety as a result of this event.

There were no Safety System Functional Failures as a result of this event.

III. Cause of Event:

The cause of this event was the failure to identify the potential vulnerability of the DAEC remote shutdown system design to a fault in the metering circuits, which could result in a lockout of Bus 1A4 power supply to the RSP.

IV. Corrective Actions:

On June 17, 2005, a temporary modification, TM-05-007 was implemented. This modification disconnected control room ampere meters cables in the 1A4 essential switchgear room removing the possibility of a "hot short" causing a lockout. Jumpers were installed in each 4160 Volt current transformer to keep the bus over-current protection in service.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Duane Arnold Energy Center 05000331 YEAR A permanent modification will be installed to permanently resolve the issue with the current monitoring circuit. This modification is due to be completed by January 30, 2006.

EIIS System and Component Codes:

N/A — no component failures occurred.

V. Additional Information:

Previous Similar Occurrences:

A review of LERs at the DAEC over the last 3 years identified no LERs with similar causes.