05000255/LER-2006-004

LER-2006-004,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
2552006004R00 - NRC Website

U.S. NUCLEAR REGULATORY COMMISSION Palisades Nuclear Plant 05000-255 2006 -- 004 -- 00

EVENT DESCRIPTION

On May 4, 2006, with the plant in Mode 5, an actuation of the reactor protection system (RPS) [JC] occurred during performance of startup testing activities. The RPS actuation signal was generated from activation of the 'A' steam generator [SG;AB] low level trip circuitry.

At the time of occurrence, the RPS was reset and a single control rod was fully withdrawn for testing.

As a result of the RPS actuation, the withdrawn control rod inserted into the core as expected.

This actuation is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A).

CAUSE OF THE EVENT

At the time of occurrence, a slight nitrogen overpressure of approximately 1.3 psi was being maintained on the secondary side of 'A' steam generator for chemistry control, as is typical for idle steam generators when in Mode 5.

Subsequently, when the main steam isolation valves (MSIVs) [ISV;SB] were opened to support a planned test activity, a sudden release of the nitrogen overpressure in 'A' steam generator occurred.

This resulted in a momentary level oscillation within 'A' steam generator between the tube bundle region and the downcomer region where steam generator level is measured.

While there was no loss of water inventory from 'A' steam generator, level in the downcomer region oscillated approximately 15% above and below the initial indicated level of approximately 40%.

Since the RPS trip setpoint for low steam generator level is approximately 28%, the magnitude of the level oscillation was sufficient to exceed the RPS trip setpoint.

CORRECTIVE ACTIONS

Procedures will be revised to appropriately address the potential consequences of opening MSIVs when the reactor is reset as observed in this occurrence.

SAFETY SIGNIFICANCE

The safety significance of this occurrence is considered minimal since the reactor was already in a shutdown condition. There was no adverse safety impact on any equipment or the plant.

PREVIOUS SIMILAR EVENTS

None