05000528/LER-2006-002
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. None 05000 | |
| Event date: | 03-21-2006 |
|---|---|
| Report date: | 05-18-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 5282006002R00 - NRC Website | |
All times in this report are approximate and Mountain Standard Time unless noted otherwise.
1. REPORTING REQUIREMENT(S):
This Licensee Event Report (LER) (50-528/2006-002-00) is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B), to report a condition prohibited by Technical Specifications.
Specifically, on March 21, 2006 at 0117, Control Room personnel (utility, licensed) completed a Mode change from Mode 4 (Hot Shutdown) to Mode 3 (Hot Standby) with only the "A" class pressurizer (Pzr) heaters (EIIS: AB) Operable. Technical Specification 3.4.9, Pressurizer, requirestwo groups of Pzr heaters be Operable in Mode 3. Contrary to Technical Specification 3.0.4, a Mode change was completed without meeting the Limiting Condition for Operation (LCO) for Technical Specification 3A.9. This event is a condition prohibited by Technical Specifications and reportable under 10 CFR 50.73(a)(2)(i)(B).
2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The Pzr provides a point in the Reactor Coolant System (RCS) (EIIS: AB) where liquid and vapor are maintained in equilibrium under saturated conditions for pressure control purposes to prevent bulk boiling in the remainder of the RCS. Key functions include maintaining required primary system pressure during steady state operation and limiting the pressure changes caused by reactor coolant thermal expansion and contraction during normal load transients. The Pzr pressure control elements addressed by Technical Specification 3.4.9 include the Pzr water level, the required heaters and their backup heater controls, and emergency power supplies. The Pzr heaters are single unit, direct immersion heaters that protrude vertically into the Pzr through sleeves welded in the lower head. There are 36 Pzr heaters in Unit 1.
A number of the heaters are connected to proportional controllers, which adjust the heat input to account for steady-state losses and to maintain the desired steam pressure in the Pzr. The remaining heaters are connected to on-off controllers. These heaters are normally de-energized but are automatically turned on by a low Pzr pressure signal or a high level error signal. This latter feature is provided since load increases result in an in-surge of relatively cold coolant into the Pzr, thereby decreasing the bulk water temperature. The Chemical and Volume Control System (EIIS: CA) acts to restore level, resulting in a transient pressure below normal operating pressure. To minimize the extent of this transient, the backup heaters are energized, contributing more heat to the water. Backup heaters are de-energized in the event of concurrent high-level error and high-Pzr pressure signals. A low-low Pzr water level signal de-energizes all heaters before they are uncovered to prevent heater damage.
3. INITIAL PLANT CONDITIONS:
On March 21, 2006 at 0117 Palo Verde Control Room personnel (utility, licensed) were preparing to return Unit 1 to power operation following a short notice outage (SNO) and changed Modes from Mode 4 to Mode 3. At the start of the event circuit breaker (EIIS:
ANSI — 52) PGBL32E3, which supplies power to the "B" class Pzr heaters, was in a tripped open condition because of a ground on the A05 Pzr heater. With PGBL32E3 tripped open, the "B" class Pzr heaters were inoperable. Control Room personnel were unaware that PGBL32E3 was open. No other major structures, systems, or components were inoperable that contributed to the event.
4. EVENT DESCRIPTIONtc Prior to the event, on Mardi' 2%200640230 Operations`and electrical maintenance personnel were conducting a retest on anon-class Pzr heater bank. The testing required jumpers to be applied and then removed to simulate the control signal.
Heaters energized when the jumper was landed and de-energized when the jumper was lifted as expected. The PZR Trouble Plant Annunciator System (RK) (EllS: ALM) alarm was locked in and placed in "fast flash" based on plant conditions at the time. At 0249 PGBL32E3 tripped open. The circuit breaker trip alarm was not announced due to the alarm being in fast flash and was not recognized by the night shift Control Room personnel (licensed, utility). Additionally, subsequent rounds performed by three different Area Operators (utility, non-licensed) and two routine shift alarm typer summary reviews performed by Control Room personnel (utility, licensed) failed to identify that PGBL32E3 was in a tripped open condition.
During the night shift to day shift turn over on March 22, following a detailed alarm typer summary review, the "PZR BACKUP HTRS 5 ELEC PROT TRIP" (PT ID RCYS1005) was recognized as being in alarm. Control Room personnel initiated the applicable alarm response actions. A local inspection of PGBL32E3 revealed that the circuit breaker had a tripped "86" lockout relay. On March 22 at 0645, Control Room personnel declared the "B" class Pzr heaters inoperable and entered Technical Specification LCOs 3.4.9 (B), 3.3.11 (B), Remote Shutdown System, and Technical Requirements Manual LCO 3.8.101 (A), Containment Penetration Conductor Overcurrent Protection Devices. Based on further review of the alarm typer summaries, the alarm condition was determined to have occurred on March 20, 2006 at 0249.
Control Room logs indicated that Unit 1 changed Modes from Mode 4 to Mode 3 on March 21, 2006 at 0117 with only the "A" class Pzr heaters Operable. This Mode change was a violation of Technical Specification 3.0.4 (completion of a Mode change without meeting the LCO for Technical Specification 3.4.9.) Troubleshooting efforts for the tripped "86" lockout relay on PGBL32E3 revealed a ground on Pzr backup heater A05. A temporary modification (T-Mod 2878166) was installed to isolate backup heater A05 and connect in its place backup heater B04. On March 24, 2006 at 1731, after a satisfactory retest of temporary modification 2878166, Control Room personnel declared the "B" class Pzr heaters Operable and exited Technical Specification LCOs 3.4.9 (B), 3.3.11 (B) and Technical Requirements Manual LCO 3.8.101 (A).
On March 22, 2006 a corrective action document was initiated to identify and investigate the violation of Technical Specification 3.0.4 that occurred on March 21, 2006 at 0117 (completion of a Mode change without meeting the LCO for Technical Specification 3.4.9.)
ASSESSMENT OF SAFETY CONSEQUENCES:
The condition did not result in any challenges to the fission product barriers or result in the release of radioactive materials. Therefore, there were no adverse safety consequences or implications as a result of this condition and the condition did not adversely affect the safe operation of the plant or health and safety of the public.
The "A" class heaters were available throughout the event and capable of performing the same functions. The condition would not have prevented the fulfillment of the safety function and did not result in a safety system functional failure as defined by 10CFR50.73(a)(2)(v).
The condition did not result in a transient more severe than those analyzed in the Updated Final Safety Evaluation Report Chapters 6 and 15. The condition did not have any nuclear safety consequences, or personnel safety impact.
6. CAUSE OF THE EVENT:
The root cause of the event was attributed to human error in that operational fundamentals were not consistently applied for controlling and monitoring plant parameters to ensure compliance with license conditions.
A contributing cause was identified in that the class backup Pzr heater hand switch green light intensity was not distinguishable when in "86" lockout. When equipment experiences an "86" lockout, the indicator light will burn more brilliantly (higher intensity) that alerts the operator of an electrical fault.
7. CORRECTIVE ACTIONS:
A significant investigation was conducted and resulted in the following actions.
Operation's personnel involved in this event were coached.
Work Order 2879002 was initiated on 03/27/06 to address the green light intensity on back up PZR Heater hand switch. The intensity was adjusted to maximum to be distinguishable for "86" lockout and the green lens replaced.
Operations Management will reinforce Operations Fundamentals as described in Institute of Nuclear Power Operations Significant Event Report 3-05, Weaknesses in Operator Fundamentals. Actions will include both individual task and crew performance observations while on shift and in training settings. The intent of this action is to improve individual and team performance in the monitoring and control of the power plant
8. PREVIOUS SIMILAR EVENTS:
In the past three years, four LERs were submitted to report violations of Technical Specifications 3.0.4.
one Auxiliary Feed Water pump inoperable. The cause of this event was attributed to an inadequate understanding of surveillance testing requirements by Engineering and Operations personnel.
percent with axial shape index outside TS limits. The cause of this event was attributed to an inadequate understanding of TS 3.2.5 by the involved Operations personnel.
two required Low Pressure Safety Injection (LPSI) trains being inoperable due to a degraded mechanical pump seal. The cause of this event was attributed to an equipment problem.
injection valve out of position. The cause of the event was attributed to cognitive personnel error.
The causes for these previously reported events were different than the root cause of the event discussed in this LER. As such, the corrective actions taken as a result of these previously reported events would not have prevented the event discussed in this LER.
This LER (50-528/2006-002-00) is related to the violation of Technical Specification 3.0.4 reported in LER 50-528/2006-001-00 in that the events described in both LERs had the same root cause and occurred during the same Unit 1 start up.