ENS 41939
ENS Event | |
|---|---|
23:05 Aug 22, 2005 | |
| Title | Technical Specification Shutdown Due to Core Protection Calculator System (Cpcs) Software Not Consistent with System Design Requirements. |
| Event Description | The following event description is based on information currently available. If through subsequent reviews of this event, additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73.
On August 22, 2005, at approximately 1605 hours0.0186 days <br />0.446 hours <br />0.00265 weeks <br />6.107025e-4 months <br /> Mountain Standard Time (MST), Palo Verde Nuclear Generating Station (PVNGS) Unit 2 commenced a reactor shutdown required by Technical Specification 3.0.3. Westinghouse notified Palo Verde that the current version of the Common Q based Core Protection Calculator System (CPCS) software is not consistent with the system design requirements and Technical Specification Bases regarding the system response to analog input module errors. In that a failed sensor input or failure of the two analog input modules in a given CPCS channel (four total channels) would not result in a CPCS channel trip. At Palo Verde, the CPCS provides the reactor trip functions for Low Departure from Nucleate Boiling Ratio (DNBR) and High Local Power Density (LPD). A failed input sensor would be the most likely cause for both of the redundant input modules to indicate errors simultaneously because the two redundant input modules within a safety channel are connected to a single sensor. A similar scenario would occur if both analog input modules simultaneously failed. In both cases the result would be a failure of the channel without initiating a trip signal. Operations evaluated the non-conforming condition and declared all four channels of the CPCS inoperable. Limiting Condition for Operability (LCO) 3.3.1 only addresses up to two automatic RPS trip channels inoperable, therefore Operations entered LCO 3.0.3 at approximately 13:26 MST. 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. The required offsite power sources are operable and the electrical grid is stable. The Common Q based CPCS is installed at the following nuclear power plant site in the United States: Palo Verde Unit 2. At this time, this condition is not transportable to Palo Verde Units 1 and 3. All Emergency Core Cooling systems and their Emergency Diesel Generators are fully operable if needed. The NRC Resident Inspector was notified of this event by the licensee. |
| Where | |
|---|---|
Palo Verde  Arizona (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | |
| LER: | 05000529/LER-2005-004 |
| Time - Person (Reporting Time:+-2.92 h-0.122 days <br />-0.0174 weeks <br />-0.004 months <br />) | |
| Opened: | Steve Banks 20:10 Aug 22, 2005 |
| NRC Officer: | John Mackinnon |
| Last Updated: | Aug 22, 2005 |
| 41939 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (55 %) |
WEEKMONTHYEARENS 506002014-11-06T18:16:0006 November 2014 18:16:00
[Table view]10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Technical Specification Required Shutdown Due to Dropped Control Element Assembly ENS 496012013-12-03T06:24:0003 December 2013 06:24:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Tech Spec Required Shutdown Due to Dropped Control Element Assembly ENS 442742008-06-06T06:56:0006 June 2008 06:56:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Tech Spec Required Shutdown Due to Leak in Safety Injection Tank Vent Line ENS 438042007-11-24T05:26:00024 November 2007 05:26:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Technical Specification Required Plant Shutdown Due to Inoperable Load Sequencer ENS 437362007-10-22T10:11:00022 October 2007 10:11:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Shutdown Due to Inoperable Steam Driven Auxiliary Feedwater Pump ENS 431732007-02-19T21:57:00019 February 2007 21:57:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Unit 2 Performed a Ts Required Shutdown ENS 428472006-09-19T08:05:00019 September 2006 08:05:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition, 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Pressurizer Heater Capacity Less than Tech Spec Limit ENS 424872006-04-10T19:33:00010 April 2006 19:33:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Unit 2 Entered a Ts Required Shutdown Due to Inoperable Auxiliary Feedwater Pumps ENS 420502005-10-11T23:02:00011 October 2005 23:02:00 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition, 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Tech Spec Required Shutdown of Both Unit 2 and 3 ENS 419392005-08-22T23:05:00022 August 2005 23:05:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Technical Specification Shutdown Due to Core Protection Calculator System (Cpcs) Software Not Consistent with System Design Requirements. ENS 419132005-08-12T07:19:00012 August 2005 07:19:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Plant Entered Lco Action Statement 3.8.1 to Be in Mode 5 Due to Unit 1 "B" Diesel Gen. Being Declared Inoperable ENS 415022005-03-18T22:00:00018 March 2005 22:00:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Technical Specification Required Shutdown Due to Inoperable Diesel Generator ENS 413892005-02-09T08:04:0009 February 2005 08:04:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown Technical Specifications Required Shutdown Due to Loss of Normal and Alternate Power to Safety Bus ENS 405032004-02-03T22:35:0003 February 2004 22:35:00 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown, 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Technical Specification Required Shutdown Due to Rcs Pressure Boundary Leakage 2014-11-06T18:16:00 | |