05000265/LER-2004-001, Re Drywell High Radiation Monitor Failure Due to Unsoldered Wiring Connection
| ML040970465 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 03/29/2004 |
| From: | Tulon T Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVP-04-033 LER 04-001-00 | |
| Download: ML040970465 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2652004001R00 - NRC Website | |
text
Exeln.
Exelon Generation Company, LLC www.exeloncorp.com Nuclear Quad Cities Nuclear Power Station 22710 206" Avenue North Cordova, IL 61242-9740 March 29, 2004 SVP-04-033 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Quad Cities Nuclear Power Station, Unit 2 Facility Operating License No. DPR-30 NRC Docket No. 50-265
Subject:
Licensee Event Report 265/04-001, "Drywell High Radiation Monitor Failure due to Unsoldered Wiring Connection" Enclosed is Licensee Event Report (LER) 265/04:001, "Drywell High Radiation Monitor Failure due to Unsoldered Wiring Connection," for Quad Cities Nuclear Power Station, Unit 2.
This report is submitted in accordance with the requirements of the Code of Federal Regulations, Title 10, Part 50.73(a)(2)(v)(C), which requires reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.
Should you have any questions concerning this report, please contact Mr. W. J. Beck at (309) 227-2800.
Respectfully, Ti thy J. Tulon Site Vice President Quad Cities Nuclear Power Station cc:
Regional Administrator - NRC Region IlIl NRC Senior Resident Inspector - Quad Cities Nuclear Power Station
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Abstract
On January 28, 2004, it was determined during troubleshooting that a wire on the selector switch for the Unit 2 "Al drywell (DW) radiation monitor was crimped back on itself at a connection point but was not soldered.
This instrument provides post-accident indication as well as an isolation of Primary Containment (Group II isolation) in response to high radiation levels in the drywell.
The troubleshooting was being performed in response to a drop in the indicated value on January 18, 2004, from 3R/hr to 1R/hr.
It was determined that the chassis was manufactured with an unsoldered switch connection, and that this connection made intermittent contact.
In the event of a gross failure of the fuel cladding, the discontinuity may have prevented a containment isolation initiation during a DW high radiation condition.
- However, high DW pressure and low reactor water level instrumentation would have initiated a Group II isolation in the event of a break in the reactor coolant pressure boundary inside containment.
The DW radiation monitors on Unit 1 and Unit 2 were checked and no additional loose or unsoldered connections were identified.U.S. NUCLEAR REGULATORY COMMISSION (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME 1 DOCKETNUMBER(2 LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL I REVISION Quad Cities Nuclear Power Station Unit 2 05000265 NUMBER NUMBER 2004 001 00 2 of 3 (If more space Is required, use additional copies of NRC Form 366A)(17)
PLANT AND SYSTEM IDENTIFICATION
Boiling Water Reactor, 2957 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
EVENT IDENTIFICATION Drywell High Radiation Monitor Failure due to Unsoldered Wiring Connection A.
CONDITION PRIOR TO EVENT
Unit: 2 Event Date: January 18, 2004 Event Time: 1527 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.810235e-4 months <br /> Reactor Mode: 1 Mode Name: Power Operation Power Level: 096%
Power Operation (1) - Mode switch in the RUN position with average reactor coolant temperature at any temperature.
B.
DESCRIPTION OF EVENT
On January 28, 2004, during troubleshooting activities on the Unit 2 "Al Drywell (DW) radiation monitor [RI] chassis, it was determined that tapping on the chassis would change the reading from lR/hr to 3R/hr. This instrument provides post-accident indication [IP] as well as an isolation of Primary Containment (Group II isolation)
[JMI in response to high radiation levels in the drywell.
The faulted chassis was replaced with a bench-tested spare.
Further investigation revealed that a wire on the failed chassis's selector switch was crimped back on itself at a connection point but not soldered.
The troubleshooting was being performed because on January 18, 2004, at 1527 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.810235e-4 months <br />, the Unit 2 'Al DW radiation monitor indication dropped from 3R/hr to lR/hr.
Because the green "Operate' light remained lit and the reading remained on scale, it was determined that the instrument was operable. On January 19, 2004, following discussions concerning the instrument trend, a work request was written to examine the chassis in the Control Room.
Because both the "Al and the AB' DW radiation monitors need to trip for the Group II isolation signal to be initiated, the unsoldered connection is reportable as a condition that could have prevented the fulfillment of the safety function of a system that is needed to control the release of radioactive material.
A review of maintenance history identified that no maintenance had been performed on this switch.
Therefore, it is assumed that this condition has existed since the time of purchase in 1991, and any monitor in which the chassis was installed was inoperable while the chassis was installed.
C.
CAUSE OF EVENT
The chassis was manufactured with an unsoldered switch connection that had intermittent contact.U.S. NUCLEAR REGULATORY COMMISSION (7.2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6.
PAGE (3)
YEAR SEQUENTIAL REVISION Quad Cities Nuclear Power Station Unit 2 05000265 NUMBER NUMBER 2004 001 00 3 of 3 (If more space is required, use additional copies of NRC Form 366A)(17)
D.
SAFETY ANALYSIS
The safety significance of this event was minimal.
Although a Group II isolation from high DW radiation requires both the "Al and 'BO DW radiation monitors to trip, the Group II isolation also occurs in response to high DW pressure and low reactor water level for a break in the primary coolant pressure boundary inside containment.
The UFSAR describes the high DW radiation trip, but credit is not taken for the trip in the design basis accident analyses.
Also, although the switch connection was not soldered, the intermittent connection provided by the crimped connection may have been adequate to provide a trip if one were required.
E.
CORRECTIVE ACTIONS
Immediate Actions Immediate Corrective Actions included inspections of two other spare modules that were on site, with no solder issues identified.
Corrective Actions Completed The switches installed in the Unit 2 monitors were inspected, and no additional loose or unsoldered connections associated with the switches were identified.
Other solder connections in the chassis not associated with the switch were identified as substandard, but their condition was not such that the functionality was affected. The solders were brought up to standard.
The switches installed in the Unit 1 monitors were inspected, and no loose or unsoldered connections were identified.
F.
PREVIOUS OCCURRENCES
A review for extent of condition did not identify any other similar failures.
Reviews of work orders and condition reports over the last 12 years identified no other similar failures of DW radiation monitors.
A review for previous events did not identify a like failure at the Station or in the industry. Therefore it is concluded that this missing solder connection is an example of a single manufacturing defect.
There have been four previous instances of degradation of the DW radiation monitors in the last two years. Two of these involved cable splice issues, one involved a mispositioned detector, and one involved both a mispositioned detector and a degraded cable.
These events did not render the monitors incapable of providing the safety function.
The corrective actions for these events addressed the root causes involved in each event.
G.
COMPONENT FAILURE DATA
The monitor is a Sorrento RP-2CM model radiation monitor.