05000387/LER-2004-001
| Susquehanna Steam Electric Station - Unit 1 L | |
| Event date: | 03-07-2004 |
|---|---|
| Report date: | 05-04-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3872004001R00 - NRC Website | |
EVENT DESCRIPTION
At 02:01 on March 7, 2004 with Unit 1 in Mode 5 at 0% power and Unit 2 in Mode 1 at 100% power, the 'A' Diesel Generator (DG; EIIS Code: EK) started due to a detected under-voltage condition on the 1A201 4.16kV Engineered Safeguard System (ESS; EIIS Code EK) bus. The bus under-voltage condition was created when an in-plant operator (non-licensed, utility) removed fuses from an incorrect 4.16 kV bus breaker cubicle during equipment alignment activities for a planned load center / 4.16 kV bus maintenance outage. Prior to the event, bus 1A201 was unloaded in accordance with TP-105-006 to support a planned 1B210 load center maintenance outage. The in-plant operator had successfully performed the required alignments for breaker cubicles 1A20106, 1A20102, 1A20108, and 1A20103.
TP-105-006, Attachment T, then required removal of fuses FU5 and FU6 in breaker cubicle 1A20101 to prevent an inadvertent automatic start of the 'A' DG. Instead, the operator removed fuses FU5 and FU6 in breaker cubicle 1A20104 which prevented the off-site power sources from providing power to bus 1A201. The 1A201bus under-voltage relays sensed the under-voltage condition and the 'A' DG started as designed. Power for the 'A' Emergency Service Water (ESW; HS Code: BI) pump was not available as a result of the TP-105-006 alignment. Since the 'A' ESW pump was not available to automatically supply cooling to the 'A' DG, control room operators (licensed, utility) manually started the 'B' and 'C' ESW pumps to provide cooling to the 'A' DG within two minutes of the 'A' DG start. All plant equipment operated as designed. The 'A' DG was returned to standby status at 16:44 on March 7, 2004.
CAUSE OF EVENT
Two root causes were found. The in-plant operator removing the fuses and the in-plant operator providing a peer-check did not use adequate self-check / peer-check techniques to identify the location of the breaker cubicle for fuses FU5 and FU6 and TP-105-006 was not written in accordance with human performance standards.
Less than adequate self-check / peer-check techniques were used by both the in-plant operator removing the fuses and the in-plant operator providing the peer check. Both operators had a mind-set that all the actions in the procedure subsection were in cubicle 1A20204 and misread 1A20101 as 1A20104.
In addition to the human performance error, TP-105-006 was not written in accordance with human performance standards. TP-105-006, Attachment T, Section 1 is written with sub-sections "a" through "d" identifying a specific breaker cubicle in the heading. Those sub-sections are further divided into steps that list actions to be taken at the cubicle listed at the beginning of the sub-section. Sub-section `e' of Attachment T contained a human performance trap. It was not written in accordance with station human performance standards for procedure writing. Sub-section 'e' of Attachment T was titled, "Cubicle 1A20104, A DG". The first step of sub-section 'e' required action in cubicle 1A20104. The next step removed fuses FU5 and FU6 in cubicle 1A20101 instead of 1A20104. Remaining steps then required actions in cubicle 1A20104.
ANALYSIS / SAFETY SIGNIFICANCE
This event is reportable as an event that resulted in an unplanned automatic actuation of an emergency diesel generator per 10 CFR 50.73(a)(2)(iv)(A). The fuse removal error that caused Unit 1 ESS bus 1A201to de-energize had no nuclear safety consequences. The `A' DG started as designed. No actual design basis events occurred that required plant equipment to perform its required design function. Additionally, there was no loss of safety function of equipment required to respond to a potential design basis event for either Unit 1 or Unit 2. Since Unit 1 was in Mode 5, the number of required ESS buses is less than during power operation and the required number of buses remained operable. All required Diesel Generators remained operable for both Units 1 and 2. Although the 'A' ESW pump did not have power from 1A201, the remaining ESW pumps were adequate to fulfill the required safety functions for Units 1 and 2.
In accordance with guidance in NUREG-1022, Revision 2, Section 5.1.1, the due date for this report is May 6, 2004.
CORRECTIVE ACTIONS
Corrective actions that have been completed:
- Human performance training was conducted at the plant's performance simulator between March 14, 2004 and March 16, 2004 which all available operators and supervisors attended. The activity focused on four error prevention tools: self-checking, peer checking, three-way communication, and pre-job briefs. The objective was to perform an assessment of the utilization and application of error prevention techniques and provide behavioral reinforcement of human performance tools and techniques.
Corrective actions to be completed:
- Provide a peer-to-peer observation program to evaluate use of human performance tools for field operational activities.
- Incorporate human performance standards into Unit 1 and Unit 2 load center/ 4.16kV bus procedures.
IN