05000327/LER-2004-002
| Sequoyah Nuclear Plant (Sqn) Unit 1 | |
| Event date: | 10-28-2004 |
|---|---|
| Report date: | 12-27-2004 |
| 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 |
| 3272004002R00 - NRC Website | |
I. PLANT CONDITION(S)
Unit 1 was in Mode 6 preparing for the initiation of core alterations.
II. DESCRIPTION OF EVENT
A. Event:
On October 28, 2004, at approximately 0418 Eastern daylight time (EDT), Chemistry personnel notified Operation's personnel in the main control room (MCR) that at 0410 Unit 1 reactor coolant system (RCS) [EllS Code AB] boron concentration was 1999 parts per million (ppm). Operation's personnel entered Technical Specification (TS) Limiting Condition for Operation (LCO) 3.9.1 action because the RCS boron concentration was below the TS limit of 2000 ppm. Operations personnel immediately initiated boration of Unit 1 RCS at 35 gallons per minute (gpm). Chemistry personnel reported that samples at 0010, 0110, and 0310 were also 1999 ppm. The 0210 RSC sample had a boron concentration of 2002 ppm. This event is being reported as an operation prohibited by TS since the TS requires immediately suspending all operations involving core alterations or positive reactivity changes and initiate and continue boration at greater than or equal to 35 gpm. Operations did not initiate boration of the RCS earlier because Chemistry personnel did not inform Operations of the out-of-limits condition. Chemistry personnel were unaware that Unit 1 had entered Mode 6, thus requiring a minimum RCS boron concentration of 2000 ppm.
On November 11, 2004, it was determined that there was a failure to comply with TS 3.9.1. TS 3.9.1 requires immediately initiating boration of the RCS after it is determined that the RCS boron concentration is below TS limits. WA personnel reviewed Operations logs and determined that compliance with TS had not been performed as required.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C. Dates and Approximate Times of Major Occurrences:
October 27, 2004� Operations signed off Mode 6 prerequisites using boron dayshift� sample from previous mid-shift of 2007 ppm. No action was initiated to raise boron concentration.
October 27, 2004� Chemistry Manager signs off Mode 5 to Mode 6 Checklist based on previous sample.
OR NUMBER! (6) October 27, 2004, at 2023 EDT October 27, 2004, at 2115 EDT October 27, 2004, at 2310 EDT October 27, 2004, at 2357 EDT October 28, 2004, at 0010 EDT October 28, 2004, at 0418 EDT October 28, 2004, at 0504 EDT November 10, 2004 Operations requested Chemistry personnel sample RCS boron concentration every hour to ensure boron concentration is stable while lowering RCS level.
Hydrogen peroxide was added to the RCS. Boron concentration after the peroxide addition was 2000 ppm.
RCS boron concentration is 2000 ppm boron.
Unit 1 entered Mode 6.
Chemistry sampled RCS and determined the boron concentration was 1999 ppm. The results were not communicated to the MCR because Chemistry personnel were unaware that Unit 1 had entered Mode 6.
Chemistry personnel notified MCR personnel that at 0410 Unit 1 RCS boron concentration was 1999 ppm. Operations entered LCO 3.9.1 action. Operations personnel immediately initiating boration of Unit 1 RCS at 35 gpm.
Chemistry personnel reported that samples at 0010, 0110, and 0310 were also 1999 ppm. The 0210 RSC sample had a boron concentration of 2002 ppm.
Operations secured boration after adding 1840 gallons. The RCS boron concentration from the 0510 sample was 2159 ppm. Operations personnel exited LCO 3.9.1.
On November 11, 2004, it was determined that there was a failure to comply with TS 3.9.1. TS 3.9.1 requires immediately initiating boration of the RCS after it is determined that the RCS boron concentration was below TS limits. WA personnel reviewed Operations logs and determined that compliance with TS had not been performed as required.
D. Other Systems or Secondary Functions Affected:
None.
E. Method of Discovery:
The event was discovered when WA personnel reviewed Operations logs and determined that the compliance with TS had not been performed as required.
The boron out-of-limits condition was discovered when Chemistry personnel were informed that the unit was in Mode 6. When the Chemistry technician entered the data into the computer, the computer would not accept the data for Mode 6.
F. Operator Actions:
MCR operators responded to the event in accordance with plant procedures. After notification from Chemistry personnel of the out-of-limit condition, Operations entered LCO 3.9.1 action and immediately initiated boration of Unit 1 RCS at 35 gpm.
G. Safety System Responses:
No plant safety systems were required to respond to the identified condition.
Ill.� CAUSE OF THE EVENT
A. Immediate Cause:
The immediate cause of the event was failure of Chemistry personnel to notify Operations that the RCS boron concentration was below the limit of 2000 ppm.
Chemistry personnel were unaware that Unit 1 was in Mode 6. Therefore, it was not recognized that the boron concentration of 1999 was below the TS limit for Mode 6.
B. Root Cause:
The root cause of the event was failure to establish adequate margin to the RCS boron concentration limit prior to entering Mode 6. Both Operations and Chemistry management were cognizant of how close to the limit the boron concentration was, but failed to recognize the risk and take action to increase the margin.
C. Contributing Factor:
Contributing to the event were latent organization weaknesses such that there was no procedural guidance for achieving and maintaining a margin to the boron concentration limit. The Operations and Chemistry procedures only required that the minimum concentration requirements be met. The Chemistry Manager had failed to communicate to the Chemistry technicians that the department had authorized transition to Mode 6 and that chemistry parameters for Mode 6 must be maintained.
IV. ANALYSIS OF THE EVENT
Although the RCS boron concentration was below the technical specification limit of 2000 ppm, the shutdown margin (SDM) was always maintained. The minimum boron concentration required to maintain the keff less than or equal to 0.95 was 1263 ppm. With the RCS boron concentration at 1999 ppm, the plant condition was bounded as described in the SQN Final Safety Analysis Report.
V. ASSESSMENT OF SAFETY CONSEQUENCES
Based on the above Analysis of The Event, this event did not adversely affect the health and safety of plant personnel or the general public.
VI. CORRECTIVE ACTIONS
A. Immediate Corrective Actions:
Immediate actions taken were to 1) restore the RCS boron concentration to above 2000 ppm; 2) the Chemistry Manager, Operations Shift Managers and Unit Supervisors involved in the transition to Mode 6 were counseled on establishing adequate margins, anticipating changes in plant conditions and adequately communicating within and between departments; 3) appropriate Operations procedures were revised to provide provisions for requiring a margin to the 2000 ppm limit, documenting when prerequisites (that are subject to change) are signed off and to conduct a reverification of these parameters just prior to the Mode change; and 4) standdowns were held with Operations and Chemistry Department personnel discussing the event, the missed barriers and the lessons learned.
B. Corrective Actions to Prevent Recurrence:
Appropriate Operations procedures are being revised to ensure there are no other prerequisites that could be signed off early without validation prior to the mode change and revising the Chemistry procedure to build in a margin to SDM concentration.
A Training Bulletin was issued to Operations personnel, on the event emphasizing reactivity changes when shutdown, establishing adequate margins to requirements and maintaining a questioning attitude on plant conditions and procedure steps. This bulletin included the impact on reactivity on chemical additions (especially at reduced inventory) and other evolutions that may introduce different flow paths with different boron concentrations into the core. Discussion on the time to reach boron concentration equilibrium following boration was also discussed.
VII. ADDITIONAL INFORMATION
A. Failed Components:
None B. Previous LERs on Similar Events:
A review of previous reportable events for the past three years did not identify any previous similar events.
C. Additional Information:
None.
D. Safety System Functional Failure:
This event did not result in a safety system functional failure in accordance with 10 CFR 50.73(a)(2)(v).
E. Loss of Normal Heat Removal Consideration This event did not result in a loss of normal heat sink because the plant was in Mode 6.
VIII. COMMITMENTS
None.