L-MT-05-116, Day Special Report: Failure of Wide Range Radiation Monitor Electronic Process Flow Probe

From kanterella
Jump to navigation Jump to search
Day Special Report: Failure of Wide Range Radiation Monitor Electronic Process Flow Probe
ML053410376
Person / Time
Site: Monticello Xcel Energy icon.png
Issue date: 11/30/2005
From: Conway J
Nuclear Management Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
L-MT-05-116
Download: ML053410376 (3)


Text

Monticello Nuclear Generating Plant Committed to Nuclear Operated by Nuclear Management Company, LLC November 30, 2005 L-MT-05-116 Technical Specification 3.14.1 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Monticello Nuclear Generating Plant Docket No. 50-263 License No. DPR-22 30-Day Special Report: Failure of Wide Ranae Radiation Monitor Electronic Process Flow Probe Nuclear Management Company, LLC is submitting this report based on the potential that the Channel "A" Reactor Building Vent Wide Range Radiation Monitor (WRGM) may have been inoperable for greater than the seven days in accordance with the Monticello Nuclear Generating Plant Technical Specification Table 3.14.1. This report is being submitted for an inoperable Reactor Building Vent WRGM flow probe. provides the results of our review of the event. Appropriate entries were made into the Corrective Action Program in response to this event.

This letter contains no new commitments and no revisions to existing commitments.

ohn . a f Site Vice President, Monticel uclear Generating Plant Nuclear Management Company, LLC Enclosure cc: Administrator, Region Ill, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC 2807 West County Road 75

  • Monticello, Minnesota 55362-9637 Telephone: 763-295-5151 a Fax: 763-295-1454

ENCLOSURE I BACKGROUND AND ACTION TAKEN Monticello Nuclear Generating Plant (MNGP) Technical Specification (TS) Table 3.14.1, "Instrumentation for Accident Monitoring," includes the Reactor Building Vent Wide Range Radiation Monitors (also known as Wide Range Gas Monitors or WRGMs). This TS Table requires two instrument channels to be operable, or one channel may be inoperable for no longer than seven days. Since the "A"channel of the Reactor Building Vent WRGM may have been inoperable for longer than seven days, a 30-day special report is being voluntarily submitted.

On September 19, 2005, in response to recommendations from the original equipment manufacturer, the process flow board and flow probe for the "A"channel of the Reactor Building Vent WRGM were replaced. On September 22, 2005, a control room operator observed indications indicative of a change in total process flow between the two Reactor Building Vent WRGM channels. Trending plots confirmed the differences and a work order was written to investigate the condition. During performance of the work order between November 1 - 4, 2005, it was determined that electrolytic capacitors on the "A" Channel Reactor Building Vent WRGM process flow board had failed. The "A" Channel Reactor Building Vent process flow probe board was refurbished with new capacitors, reinstalled, and tested under the seven day allowed outage time permitted by TS Table 3.14.1.

CAUSE OF INOPERABILTY After replacement of the "A"Channel Reactor Building Vent WRGM flow probe and process board, the WRGM channels exhibited indications of a change in system conditions. The total process flow trend increased over the course of several days and then decreased back to within its expected range. Some variation between units is not unusual due to the location of the probes in the vent ducts and flow patterns. A work order was written to investigate the condition. The work order subsequently determined that electrolytic capacitors on the "A" Channel Reactor Building Vent WRGM process flow board had failed.

Based on the channel's performance between the first sign of variation, it is not possible to determine the exact time of failure. However, since there were indications that the problem began as early as September 22, 2005, it is being conservatively reported as an inoperable condition which lasted longer than the TS permitted allowed outage time.

PLANS AND SCHEDULE FOR RESTORING THE SYSTEM TO OPERABLE STATUS The "A"Channel Reactor Building Vent WRGM flow probe board was refurbished with new capacitors, reinstalled, tested and returned to service on November 4, 2005. The Page 1 of 2

ENCLOSURE I WRGM is currently operating as designed. Work orders have been created to refurbish the Reactor Building Vent WRGM "B"channel.

SAFETY SIGNIFICANCE The Reactor Building Vent WRGMs are not safety related nor are they included in the Maintenance Rule. They are Category 2, Regulatory Guide 1.97 accident monitoring systems. The Channel "B"Reactor Building Vent WRGM was fully capable of performing its design function during the entire period in which the Channel "A' Reactor Building Vent WRGM process flow probe was acting abnormally.

Page 2 of 2