05000366/LER-2004-001
| Edwin I. Hatch Nuclear Plant - Unit 2 | |
| Event date: | 2-18-2004 |
|---|---|
| Report date: | 04-13-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3662004001R00 - NRC Website | |
U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1)
DOCKET
05000-366 LER NUMBER (6) 2004 -- 001 -- 0
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes are identified in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
On 2/18/2004 at 1547 ET, Unit 2 was in the Run mode at a power level of approximately 2772 CMWT (98.8% rated thermal power). An 8-inch pipe cut on the Plant Service Water (PSW, EIIS Code BI) system was made during the implementation of Design Change Request (DCR) 03-026T. Piping downstream of the cut area was degraded. The DCR required removal of a section of pipe, capping the upstream side, and abandoning the degraded downstream piping. The cut area was located approximately 12 ft. above the floor and was directly over a cable tray in the 2G switchgear room.
In preparation for the pipe cut, a clearance boundary was established and protective measures were taken to prevent water damage to surrounding equipment. The cut was made by an air-driven cutting tool. As the cut was nearly completed, the pipe shifted. The volume of water release was more than anticipated and traveled beyond the area prepared to handle water.
Investigation revealed that the trapped water was not fully drained from the piping. Personnel failed to realize that a combination of sediment build-up and a piping section without a drain could trap a considerable volume of water in the pipe. As a precaution, pipefitters had drilled a hole in the top of the 8-inch pipe close to the cut location; however, because the hole was located in the portion of the pipe being discarded, the area available for inspection was downstream of the cut. Upstream of the inspection hole there was a sediment build-up resulting in trapped water. The pipe appeared dry when it was inspected through the drilled hole. When the cut was made, the pipe moved and the trapped water was released. Although the electrical equipment directly beneath the cut was covered and adequately protected from water, the adjacent electrical equipment was not protected because the amount of water anticipated was underestimated.
Water from the cut traveled along cable trays and scaffold boards and drained onto surrounding panels and junction boxes. Panel 2H21-P232 (the '2C' Emergency Diesel Generator Relay Panel), received enough water to cause an auto-start of the '2C' DG (EDG, EIIS Code EK). Additionally, a Generator or� FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) Field Ground and a Battery Malfunction alarm (caused by a DC distribution ground) were both received. The water flow stopped after an estimated 30 to 50 gallons had drained from the pipe cut.
The 2H21-P232 panel contains '2C' DG control logic. There are six contacts located in this panel that if shorted by water would start the DG. During this event the normal supply breaker to the bus did not trip and the bus remained energized. The '2C' DG did not tie to the bus. Licensed Operations personnel shut down the DG by 1604 ET, and the DG's mode switch was left in the test position.
Troubleshooting and repair activities were completed; and the Operability Surveillance (34SV-R43- 006-2S, DIESEL GENERATOR 2C SEMI-ANNUAL TEST) was completed on 2/20/2004 at 0505 ET.
It was concluded from the event that at least one of the start contacts for '2C' DG were shorted by the water intrusion causing an invalid start signal to be generated resulting in the '2C' DG starting.
Additionally, since the DG's control switch could be taken to and maintained in the test position, the LOCA relays were not initiating a start signal to the DG and no LOCA signal was received.
Recovery from the PSW intrusion into the '2C' DG control panel (21121-P232) involved drying out the panel, inspecting the HGA and HFA relays in the panel associated with the DG start logic and load shed logic. Relays were dried, calibrated, repaired, or replaced as required. No water was found during the inspection of the 6 HGA and 14 HFA relays. When relay 2R43-K770 was removed from its housing and the housing dried out the DC distribution ground and Field ground cleared.
After all recovery actions were completed, the '2C' DG was functionally tested by performing the DG quick start test. This test most closely approximates an automatic start of the DG.
CAUSE OF EVENT
Personnel failed to anticipate the water that could be released from the pipe cut because the combination of pipe configuration and sediment build-up was not considered. A contributing cause of the event was the failure to protect all electrical equipment from water damage. At the time the pipe was cut, water drained onto 21121-P232 (`2C' Relay Panel) from the 8-inch PSW pipe being cut shorting an undervoltage relay causing an invalid signal to start the '2C' DG.
FACILITY NAME (1)
DOCKET
05000-366 LER NUMBER (6) 2004 -- 001 -- 0
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT
This event is reportable per 10 CFR 50.73 (a)(2)(iv) because an automatic actuation of a system listed in paragraph (a)(2)(iv)(B)(8) occurred. Specifically, the '2C' DG automatically started from an invalid signal when water drained onto the 2H21-P232 relay panel.
The Unit 2 Class 1E AC Electrical Power Distribution System AC sources consist of the offsite power sources (preferred power sources, normal and alternate), and the onsite standby power sources (DGs `2A', '2C', and `1B'). As required by 10 CFR 50, Appendix A, GDC 17, the design of the AC electrical power system provides independence and redundancy to ensure an available source of power to the Engineered Safety Feature (ESF) systems. The Class 1E AC distribution system is divided into redundant load groups, so loss of any one group does not prevent the minimum safety functions from being performed. Each load group has connections to two preferred offsite power supplies and a single DG. Offsite power is supplied to the 230 kV and 500 kV switchyards from the transmission network by eight transmission lines. From the 230 kV switchyards, two electrically and physically separated circuits provide AC power, through startup auxiliary transformers 2C and 2D, to 4.16 kV ESF buses 2E, 2F, and 2G.
Startup auxiliary transformer (SAT) 2D provides the normal source of power to the ESF buses 2E, 2F, and 2G. If any 4.16 kV ESF bus loses power, an automatic transfer from SAT 2D to SAT 2C occurs.
The onsite standby power source for 4.16 kV ESF buses 2E, 2F, and 2G consists of three DGs. DGs `2A' and '2C' are dedicated to ESF buses 2E and 2G, respectively. DG `1B' (the swing DG) is a shared power source and can supply either Unit 1 ESF bus 1F or Unit 2 ESF bus 2F. A DG starts automatically on a loss of coolant accident (LOCA) signal (i.e., low reactor water level signal or high drywell pressure signal) or on an ESF bus degraded voltage or undervoltage signal. After the DG has started, it automatically ties to its respective bus after offsite power is tripped as a consequence of ESF bus undervoltage or degraded voltage, independent of or coincident with a LOCA signal.
In this event, it was concluded that at least one of the start contacts for '2C' DG was shorted by the water intrusion causing an invalid start signal to be generated resulting in the '2C' DG starting. The DG did not tie to the bus and was not required to. The bus remained energized throughout the event.
There were no other equipment actuations associated with this event. The DG performed as designed given the invalid start signal introduced by the water intrusion into the relay panel.
During this event the '2A' and `1B' DGs were available for Unit 2. With the '2C' DG inoperable, the plant entered Technical Specifications LCO 3.8.1, Condition B. Required Action B.4 requires, in part, the DG be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The TS Bases for this Required Action states that Regulatory Guide 1.93 provides guidance that operation in Condition B. may continue for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. .
Based on this analysis, it is concluded that this event did not adversely affect nuclear safety.
CORRECTIVE ACTIONS
Troubleshooting and repair activities were completed; and the Operability Surveillance (34SV-R43- 006-2S, DIESEL GENERATOR 2C SEMI-ANNUAL TEST) was completed on 2/20/2004 at 0505 ET.
The personnel involved in determining that the PSW line was isolated and free from water were made aware of their error and the consequences of it.
Additional procedural guidance is being incorporated into the appropriate plant procedures to ensure that electrical equipment is protected when breaching nearby systems. These procedure revisions will be completed by June 2004.
ADDITIONAL INFORMATION
No systems other than those previously described in this report were affected by this event.
This LER does not contain any permanent licensing commitments.
There were no previous similar events reported in the past two years in which an automatic actuation of a system listed in paragraph (a)(2)(iv)(B)(8) occurred because of inadequate equipment protection when breaching a system.
Cause Code: A