05000528/LER-2004-002
| Palo Verde Nuclear Generating Station Unit 1 | |
| Event date: | 02-08-2004 |
|---|---|
| Report date: | 04-02-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 5282004002R00 - NRC Website | |
1. REPORTING REQUIREMENT(S):
APS is reporting this condition pursuant to 10 CFR 50.73(a)(2)(i)(B) as a violation of Technical Specification 3.0.4.
Technical Specification 3.0.4 states:
When an LCO is not met, entry into a MODE or other specified condition in the Applicability shall not be made except when the associated ACTIONS to be entered permit continued operation in the MODE or other specified condition in the Applicability for an unlimited period of time.
This Specification shall not prevent changes in MODES or other specified conditions in the Applicability that are required to comply with ACTIONS or that are part of a shutdown of the unit.
Exceptions to this Specification are stated in the individual Specifications.
LCO 3.0.4 is only applicable for entry into a MODE or other specified condition in the Applicability in MODES 1, 2, 3, and 4.
The "Applicability" for the LCO 3.2.5 is Mode 1 with thermal power >20 percent rated thermal power. The associated actions to be entered if the LCO is not met do not permit continued operation in the specified condition for an unlimited period of time. Contrary to the requirements of TS 3.0.4, rated thermal power was raised above 20 percent without meeting the LCO 3.2.5 for Axial Shape Index (ASI).
2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The core operating limit supervisory system (COLSS) (EllS Code: JC, ID) is a digital computer based on-line monitoring program used to provide information to aid the operator in complying with the technical specification operating limits on rated thermal power (total core power), linear heat rate, departure from nucleate boiling ratio (DNBR), axial shape index (ASI), and azimuthal power tilt. To do so, COLSS uses measurements of incore detector signals, control element assembly positions and plant thermal/hydraulic properties to determine the core power distribution and thermal performance. The COLSS program runs independently in the plant monitoring and core monitoring computers.
Axial Shape Index LCO The LCO on ASI ensures that the actual value of core average axial shape index is maintained within the range of values used in the safety analyses. The core average ASI is maintained within the limits listed below.
COLSS Operable:
-0.18 -0.28
3. INITIAL PLANT CONDITIONS:
On February 08, 2004, at approximately 11:45 Mountain Standard Time (MST), Palo Verde Unit 1 was in Mode 1 at 20 percent power.
There were no other major structures, systems, or components that were inoperable at the start of the event that contributed to the event. There were no failures that rendered a train of a safety system inoperable and no failures of components with multiple functions were involved.
4. EVENT DESCRIPTION:
On February 7, 2004, at approximately 15:03 (MST), while returning to service following a forced outage, Unit 1 entered Mode 1 (>5 percent rated thermal power). Surveillance Test (ST) 40ST-9ZZM1 was in progress and in accordance with procedure 400P- 9ZZ11, Appendix H, a Technical Specification Component Condition Record (TSCCR) #2681943 was opened to track surveillance requirements required by the ST that were not yet accomplished, including SR 3.2.5.1 for the ASI requirement.
At approximately 02:01 (MST), on February 8, 2004, Unit 1 synchronized its main generator to the grid and continued to increase power. By 05:15 (MST), Unit 1 had reached 18 percent power and completed feedwater control system swap over successfully. While at 18 percent power, ASI was outside the limits (-0.28 for power Operators did not take action to return ASI within limits prior to exceeding 20 percent.
Control Room staff based their decision on a note in 40ST-9ZZM1, step 8.1.17, that states the surveillance requirement is only applicable when power is > 20 percent and the surveillance should be performed within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> thereafter and SR 3.2.5.1 which states in part "...that the SR is not required to be performed until 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after Mode 1 with THERMAL POWER > 20%...". This was incorrectly taken to mean that compliance with the LCO was not required for up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
At approximately 11:38 (MST), Unit 1 raised power to > 20 percent, with ASI still outside the requirements of the COLR. Exceeding 20 percent power when the LCO is not met is a TS 3.0.4 violation. TS 3.0.4 does not allow entry into the specified condition when the LCO is not met. ASI was brought within limits at 12:21 (MST).
This condition has been documented in the corrective action program. There were no other major structures, systems, or components that were inoperable at the start of the event that contributed to the event. There was no actual loss of safety function that rendered a train of a safety system inoperable, and no failures of components with multiple functions were involved. The event did not result in the release of radioactivity to the environment and did not adversely affect the safe operation of the plant or health and safety of the public.
5. ASSESSMENT OF SAFETY CONSEQUENCES:
An ASI value of -0.338 with power level greater than 20 percent, exceeded the Core Operating Limits Report (COLR) limit of -0.28 and, therefore, the LCO. TS 3.2.5 actions require the ASI be restored within COLR limits in 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. The ASI was returned within COLR limits in 43 minutes after exceeding 20 percent power. While the TS limit for ASI was exceeded, the Analysis of Record (AOR) bounded the event in that enough conservatism exists in the AOR to bound the ASI for the duration it was outside the TS limits. The safety function to protect fuel design limits remained fulfilled.
There are no actual safety consequences as a result of this condition, the condition would not have prevented the fulfillment of the safety function, and the condition did not result in a safety system functional failure as defined by 10 CFR50.73 (a) (2) (v).
6. CAUSE OF THE EVENT:
Notes in procedures 400P-9ZZ11, Appendix H, and 40ST-9ZZM1, step 8.1.17, misled the Control Room staff to believe the applicability of LCO 3.2.5 was only required within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after the plant was > 20 percent power. This led the Control Room staff to incorrectly interpret a provisional note in SR 3.2.5.1 which states in part "...that the SR is not required to be performed until 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after Mode 1 with THERMAL POWER > 20% RIP." The basis for this note is to allow the plant to maneuver through feedwater swap over (usually occurring between 15% — 18% power) which may result in the plant going temporarily above 20 percent power. In that situation, ASI does not need to be surveilled for up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. However, Feedwater swap over did not result in plant power exceeding 20 percent. TS 3.0.4 does not allow entry into the specified condition in the Applicability when LCO 3.2.5 is not met. Therefore, exceeding 20 percent power when ASI was still outside the COLR limits was a TS 3.0.4 violation.
No unusual characteristics of the work location (e.g., noise, heat, poor lighting) directly contributed to this event.
7. CORRECTIVE ACTIONS:
An independent investigation of this event is being conducted in accordance with Palo Verde's corrective action program. Based on the preliminary results from the investigation the following corrective actions have been taken or are planned to prevent recurrence:
- A Temporarily Approved Procedure Action was written to remove the option to take up to two hours after 20 percent power to complete SR 3.2.5.1 from the applicable procedures.
- The applicable procedures will be updated and revised as necessary.
- Operations Support and Training will perform a needs analysis and implement training as appropriate.
- A self-assessment for Technical Specification usage, adherence and training will be conducted.
Any additional corrective actions taken as a result of the investigation of this event will be implemented in accordance with the APS corrective action program. If information is subsequently developed that would significantly affect a reader's understanding or perception of this event, a supplement to this LER will be submitted.
8. PREVIOUS SIMILAR EVENTS:
In the past three years, a similar condition prohibited by TS 3.0.4 was reported in LER 2001- 002-00 when Unit 3 entered Mode 3 with one Auxiliary Feedwater pump inoperable.
9. ADDITIONAL INFORMATION:
None.