United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9810290034


LICENSEE EVENT REPORT (LER)

FACILITY NAME: Dresden Nuclear Power Station, Unit 2 PAGE: 1 OF 3
DOCKET NUMBER: 05000237
TITLE: Supplement to High Pressure Coolant Injection System Inoperable Due to Gland Seal Leak Off Condenser Hotwell Level Control Malfunction From A Drain Pump Start Level Switch Failure Caused by Manufacturer Design Deficiency.
EVENT DATE: 05/04/98 LER #: 98-009-01 REPORT DATE: 10/26/98
OTHER FACILITIES INVOLVED: DOCKET NO: 05000
OPERATING MODE: 1 POWER LEVEL: 099
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR SECTION:
50.73(a)(2)(v) & OTHER: Part 21
LICENSEE CONTACT FOR THIS LER:
NAME: K. Yates, System Engineer TELEPHONE: (815) 942-2920 ext 2715
COMPONENT FAILURE DESCRIPTION:
CAUSE: B SYSTEM: BJ COMPONENT: LS MANUFACTURER: M040
REPORTABLE TO NPRDS: Y
SUPPLEMENTAL REPORT EXPECTED: NO

ABSTRACT:

On May 4, 1998, at 0433 hours, while performing Dresden Operating Surveillance (DOS) 2300-09. High Pressure Coolant Injection (HPCI) Gland Seal Leak Off (GSLO) Drain Pump and Condenser Hotwell Level Control Functional Test. the hotwell drain pump exhibited erratic operation and resulted in a hotwell low level. The "HPCI Gland Seal Condr Hotwell Lvl Hi/Lo" alarm was received and the low level in the hotwell confirmed. The HPCI system was declared inoperable and the action statement for the Limiting Condition For Operation (LCO) was entered. An ENS notification was performed at 0524 hours, Though not operable, the system remained available while troubleshooting work packages were prepared. The symptoms and troubleshooting results indicated that the GSLO drain pump start float switch (2-2300-LCS-2) had failed in the closed position. The root cause, based on the Original Equipment Manufacturer (OEM) failure analysis, was inadequate magnetic force to consistently actuate the microswitch resulting from a manufacturer design deficiency. The OEM modified their design specification based on the OEM's failure analysis. Corrective actions from this event include replacement of both the Unit 2 and Unit 3 GSLO drain pump control level switches with the OEM modified switches. Functional testing, DIS 2300-15. High Pressure Coolant Injection Gland Seal Condenser Level Control/Alarm Switch Functional Test, and DOS 2300-09 was completed satisfactorily on the Unit 2 HPCI GSLO pump/level control and the LCO was exited at 1500 hours on May 12, 1998. The overall safety significance of this event was minimal because all other Emergency Core Cooling Systems (ECCS) were operable while HPCI was inoperable. This failure is considered to be 10 CFR Part 21 reportable.

END OF ABSTRACT

TEXT PAGE 2 OF 3

PLANT AND SYSTEM IDENTIFICATION:

General Electric - Boiling Water Reactor - 2527 MWt rated core thermal power

Energy Industry Identification System (EIIS) Codes are identified in the text as [XX] and are obtained from IEEE Standard 805-1984, IEEE Recommended Practice for System Identification in Nuclear Power Plants and Related Facilities.

EVENT IDENTIFICATION:

High Pressure Coolant Injection System Inoperable due to Gland Seal Leak Off Condenser Hotwell Level Control Malfunction from a Drain Pump Start Level Switch Failure Caused by Manufacturer Design Deficiency.

A. PLANT CONDITIONS PRIOR TO EVENT:

Unit: 2 Event Date: 5/4198 Event Time 0433 COT
Reactor Made: 1 Mode Name: Run Power Level: 099
Reactor Coolant System Pressure: 1003 psig

No systems or components were inoperable or out of service at the start of this event which contributed to the event.

B. DESCRIPTION OF EVENT:

This report is being submitted pursuant to 10 CFR 50.73(a)(2)(v)(D), which requires the reporting of any event or condition that alone could have prevented the fulfillment of the safety function of a system required to mitigate the consequence of an accident.

On May 4, 1998, at 0433 hours, while performing Dresden Operating Surveillance (DOS) 2300-09, High Pressure Coolant Injection (HPCI)[BJ] Gland Seal Leak Off (GSLO) Drain Pump and Condenser Hotwell Level Control Functional Test, the hotwell drain pump exhibited erratic operation and resulted in a hotwell low level. The "HPCI Gland Seal Condr Hotwell Lvl Hi/Lo" alarm was received and the low level in the hotwell confirmed. The HPCI system was declared inoperable and the action statement for the Limiting Condition For Operation (LCO) was entered. An ENS notification was performed at 0542 hours. Though not operable, the system remained available while troubleshooting work packages were prepared,

The subject level switch assembly used in the GSLO level control system application is of a new style and manufacturer, first installed in April 1998.

The symptoms and troubleshooting results indicated that the GSLO drain pump start float switch (2-2300-LCS-2) had failed closed, The switch was replaced with an identical new switch. During switch replacement, the new switch was observed to fail in the same manner, Both failed switches were then shipped to the Original Equipment Manufacturer (OEM) on May 7, 1998, for analysis. The OEM analysis indicated that the switches failed due to insufficient magnetic strength and too much travel in the float mechanism to consistently actuate the float switch microswitch. Based on their analysis the OEM modified the switch design.

The OEM supplied new float switches that were assembled and tested in accordance with the OEM's modified design. The pump start (LCS-2) and pump stop (LCS-1) switches on both Unit 2 and Unit 3 were replaced with the OEM modified design switches. The new switches were satisfactorily tested by performance of DIS 2300-15, High Pressure Coolant injection Gland Seal Condenser Level Control/Alarm Switch Functional Test, and DOS 2300-09. Following replacement and testing of the new switches, the Unit 2 HPCI LCO actions were exited at 1500 hours on May 12, 1998, There have not been any further instances of HPCI GSLO, level switch failures since replacement with the OEM modified design. The parts requisition system (SI system) was revised to specify the modified OEM switch design.

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TEXT PAGE 3 OF 3

C. EVENT:

The root cause of this event was a manufacturer design deficiency of the installed HPCI GSLO condenser hotwell level control switches (NRC Cause Code B). The switches failed due to a combination of insufficient magnet strength and too much travel in the float mechanism to consistently actuate the float switch microswitch.

D. SAFETY ANALYSIS

The HPCI system is designed to provide make up coolant to the reactor in the event of a small-break LOSS Of Coolant Accident. When the HPCI System initiates, leakoff collected by the HPCI turbine gland seal leak off system is drawn to the GSLO condenser. The condensate is then returned to the HPCI pump suction via the GSLO condenser drain pump. If the GSLO condenser hotwell level control System fails to maintain a normal level in the hotwell, then the GSLO condenser can flood and steam will no longer be drawn off of the turbine shaft glands, stop valve stem, or control valve stems, This can happen due to an abnormally high or low level in the hotwell. For the event described in this report a low level in the GSLO condenser hotwell, the GSLO drain pump can become air bound. Once the pump is airbound, the pump no longer maintains normal level in the condenser. Thus, even though the pump is running, no condensate is removed from the condenser hotwell, resulting in condenser flooding (high level), Continued steam leakage into the HPCI room could result in a HPCI system isolation (Group IV) due to high room temperature. rendering the system inoperable. This condition alone would not have prevented the HPCI system from initiating during a design basis accident. The safety Significance of this event was minimal since all other emergency core cooling systems were available during the time that the HPCI system was inoperable.



E. CORRECTIVE ACTIONS:

The Unit 2 HPCI GSLO hotwell pump start/stop level switches were replaced with the OEM modified design switches, and satisfactorily tested. (Complete)
The Unit 3 HPCI GSLO hotwell pump start/stop level switches were replaced with the OEM modified design switches, and satisfactorily tested. (Complete)
The parts requisition system (SI system) was updated to specify the modified OEM switches enhanced with stronger magnets and float stops. (Complete)

F. PREVIOUS OCCURRENCES:

None.

G. COMPONENT FAILURE DATA:

      Manufacturer Nomenclature Model/ Part Number
Magnetrol Tuffy Level Switch 039-5000-400

(dedicated by ComEd)

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ATTACHMENT TO 9810290034 PAGE 1 OF 1
 
10/27/1998 Page 1


U.S. Nuclear Regulatory Commission Operations Center Event Report

Power Reactor Event# 34963
Site: DRESDEN Notification Date / Time: 10/27/199 14:45 (EST)
Unit: 2 Region: 3 Event Date / Time: 10/27/199 13:45 (CST)
Reactor Type: [1] GE-1, [2], GE-3, [3] State: IL Last Modification: 10/27/199
Containment Type:
NRC Notified by: K YATES Notifications: CREED, JAMES R3
HQ Ops Officer: JOHN MacKINNON HODGE, VERN NRR
Emergency Class: Non Emergency
10 CFR Section: 21.21 UNSPECIFIED PARAGRAPH
Unit Scram Code RX Crit Init Power Initial RX Mode Curr Power Current RX Mode
2 N Yes 99 Power Operation 99 Power Operation

HIGH PRESSURE COOLANT INJECTION (HPCI) GLAND SEAL LEAK OFF (GSLO) LEVEL SWITCHES FAILURE.

THIS PART 21 WAS FACSIMILE TO THE NRC HEADQUARTERS OPERATION CENTER

"ON MAY 4, 1998, AT 0433 HOURS, WHILE PERFORMING DRESDEN OPERATING SURVEILLANCE (DOS) 2300-09, HPCI GSLO DRAIN PUMP AND CONDENSER HOTWELL LEVEL CONTROL FUNCTIONAL TEST, THE HOTWELL DRAIN PUMP EXHIBITED ERRATIC OPERATION AND RESULTED IN A HOTWELL LOW LEVEL.

CAUSE OF THE EVENT

"THE ROOT CAUSE OF THIS EVENT WAS A MANUFACTURER DESIGN DEFICIENCY OF THE INSTALLED HPCI GSLO CONDENSER HOTWELL LEVEL CONTROL SWITCHES (NRC CAUSE CODE B). THE SWITCHES FAILED DUE TO A COMBINATION OF INSUFFICIENT MAGNET STRENGTH AND TOO MUCH TRAVEL IN THE FLOAT MECHANISM TO CONSISTENTLY ACTUATE THE FLOAT MICORSWITCH."

CORRECTIVE ACTIONS:

"THE UNIT 2 HPCI GSLO HOTWELL PUMP START/STOP LEVEL SWITCHES WERE REPLACED WITH OEM MODIFIED DESIGN SWITCHES, AND SATISFACTORILY TESTED.
"THE UNIT 3 HPCI GSLO HOTWELL PUMP START/STOP LEVEL SWITCHES WERE REPLACED WITH OEM MODIFIED DESIGN SWITCHES, AND SATISFACTORILY TESTED.
"THE PARTS REQUISITION SYSTEM (SI SYSTEM) WAS UPDATED TO SPECIFY THE MODIFIED OEM SWITCHES ENHANCED WITH STRONGER MAGNETS AND FLOAT STOPS."


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