05000311/LER-2004-002
| Docket Number | |
| Event date: | 03-16-2004 |
|---|---|
| Report date: | 05-17-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3112004002R00 - NRC Website | |
U.S. NUCLEAR REGULATORY COMMISSION
DOCKET
PLANT AND SYSTEM IDENTIFICATION
Westinghouse — Pressurized Water Reactor Reactor Protection System {JC}* * Energy Industry Identification System {HS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: March 16, 2004 Discovery Date: March 17, 2004
CONDITIONS PRIOR TO OCCURRENCE
The plant was in MODE 1 (POWER OPERATION) at the time of the event. No other structures, systems or components were inoperable at the start of this event that contributed to the event.
DESCRIPTION OF OCCURRENCE
On March 16, 2004, at 0830 hours0.00961 days <br />0.231 hours <br />0.00137 weeks <br />3.15815e-4 months <br />, Loop 21 of OTDT (Over-Temperature Delta-Temperature) Tavg (T- average) calibration was completed. On March 17, 2004, while performing the channel calibration for Loop 22 OTDT, it was discovered that Loop 21 OTDT channel calibration, performed the previous day, did not include the performance of the OTDT Pressurizer Pressure calibration. Since needed, the Pressurizer Pressure channel calibration for the loop should have been done in conjunction with the OTDT channel calibration in order to maintain the accuracy and operability of each OTDT setpoint. Therefore, the OTDT 21 loop setpoint was non-conservative and the Loop 21 OTDT channel was inoperable. OTDT channel 22 calibration was completed satisfactorily on March 17, 2004, and returned to service. The 21 OTDT channel was then correctly calibrated and returned to service. During the period of time between the start of the channel calibration for Loop 21 OTDT and its satisfactory completion, Loop 21 was inoperable. Technical Specification 3.3.1.1, table 3.3-1, item 7, Action 6, requires the inoperable channel to be placed in the tripped condition within six hours.
This action was not complied with. When Loop 22 became inoperable, with Loop 21 still inoperable, Technical Specification 3.0.3 should have been entered. This was not complied with because it was not recognized that Loop 21 was inoperable. Both of these issues are Technical Specification prohibited conditions and are reportable under 10 CFR 50.73(a)(2)(i)(B).
FACILITY NAME (1)
DOCKET
ANALYSIS OF OCCURRENCE
A Design Change Package (DCP) to increase Tavg for Salem Unit #2 required channel calibrations for each of four OTDT loops of Reactor Protection. These revised 100% RTP (Rated Thermal Power) parameters calibrations were computed by Reactor Engineering and given to System Engineering to revise the calibration procedures. Immediately following the actual increase of Tavg temperature, a set of readings (State-Point Data) was taken by Reactor Engineering and this data was computed into Tavg and Delta-T values. These values were then programmed into a Computerized Scaling Manual (CSM) by System Engineering.
The CSM is software developed by Westinghouse to calculate the required calibration scaling for each OTDT loop procedure. It also calculates other scaling for procedures (i.e. Pressurizer Pressure), if required.
The scaling data from the CSM was then given to the Maintenance procedure writers to revise the calibration procedures so that Maintenance could calibrate each loop. All four loops were calibrated in a continuous series, one channel at a time, until all four loops were completed. The final effect from the State-Point data resulted in all four loops of OTDT required to be calibrated in addition to the 21 and 23 Pressurizer Pressure loops. Pressurizer Pressure represents Reactor Coolant Pressure, which is one of three inputs to the OTDT setpoint.
CAUSE OF OCCURRENCE
The cause of this event was attributed to the lack of adequate process controls for calibration of the OTDT instruments to assure that all inputs were properly calibrated before returning an instrument to service.
The DCP Project team and System Engineering were over-reliant on the work management process that implemented the OTDT setpoint changes. The work management process consisted of work order operations identified by the DCP that only listed OTDT procedures to be implemented instead of including work order operations to calibrate the Pressurizer Pressure channels in the correct sequence. Therefore, there was lack of adequate process controls for calibration of the OTDT instruments to assure that all inputs for a loop were properly calibrated before returning an instrument to service.
PREVIOUS OCCURRENCES
A review of reportable events for Salem and Hope Creek nature.
in the last two years did not identify events of a similar U.S. NUCLEAR REGULATORY COMMISSION LER NUMBER (6) FACILITY NAME (1)
DOCKET
SAFETY CONSEQUENCES AND IMPLICATIONS
The purpose of the OTDT and OPDT reactor trip functions is to protect the core thermal limits (OTDT covers DNB and vessel exit boiling, OPDT covers fuel center-line melting). The core thermal limits are a function of the fuel design and are determined over a range of reactor core thermal conditions, and vessel exit boiling limits ensure that vessel delta-T is representative indication of reactor power. For the allowed range of RCS pressure values, the OTDT reactor trip setpoints (vessel delta-T as a function of vessel average temperature) provide significant margin to the actual core thermal limits (the minimum margin of approximately 5% occurs at the point at which the OTDT and OPDT lines intersect). For the worst-case transient that relies on the OTDT (as credited in the accident analysis to prevent fuel damage), the analysis has demonstrated that the point the reactor trip occurs (in terms of temperature and pressure) is not at the point of the minimum margin noted above, but at conditions where the margin between the actual thermal limits and trip setpoint is on the order of 20%.
There were no safety consequences associated with this event since there was no loss of safety function.
Following the improper OTDT Loop 21 calibration the resultant trip logic was 2 out of 3 (without credit for OTDT Loop 21), which would accommodate a single failure and still cause a reactor trip when required. During the Loop 22 OTDT calibration the resultant trip logic (without credit for OTDT Loop 21) was 1 out of 2, which would also accommodate a single failure and still cause a reactor trip when required. The condition was corrected before additional OTDT calibrations were performed.
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CORRECTIVE ACTIONS
1. All OTDT calibration procedures for both Salem Units were placed on hold until appropriate corrective actions were in place.
2. Procedures steps will be implemented to ensure that the OTDT channel cannot be returned to service until both the Pressurizer Pressure channel and temperature inputs have been calibrated.
3. The process controls for calibration of the OTDT instruments for both Salem Units will be revised to assure that all inputs are properly calibrated before returning an instrument to service.
COMMITMENTS
The corrective actions cited in this LER are voluntary enhancements and do not constitute commitments.