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| Entered date | Event description | |
|---|---|---|
| ENS 41503 | 18 March 2005 19:37:00 | The following information was obtained from the licensee via facsimile (licensee text in quotes): Report of a violation of the Technical Requirements contained in section 2C of the operating license, which requires initial notification within 24 hours to the NRC via the ENS with written follow-up within 30 days. A recent failure of the 'A' CRD pump to start required maintenance on an associated local shutdown panel. Troubleshooting indicated that a relay associated with the panel was the cause of the breaker for the pump to not be set up for a remote start from the control room. The relay in question malfunctioned on Feb. 17th so the 'A' CRD pump was not available since that time. The failure of this pump requires entry into a 7-day shutdown LCO. Troubleshooting, indicated there is firm evidence that this condition, which is prohibited by technical specifications, existed before the discovery on 3/16/5. A 7-day LCO was entered upon discovery and repairs have been completed and the LCO exited. The licensee has notified the NRC Resident Inspector. |
| ENS 41039 | 14 September 2004 16:44:00 | The following information was received from the licensee via facsimile: Notified New Jersey Department of Environmental Protection of a planned shutdown of OCNGS (Oyster Creek Nuclear Generating Station) scheduled to commence at 2000 hrs. (EDT) on 9-14-04. The licensee has notified the NRC Resident Inspector. |
| ENS 40748 | 14 May 2004 10:50:00 | Oyster Creek has been informed of a change in its vendor's calculation of Peak Cladding Temperature (PCT) and local cladding oxidation that is based on a reanalysis of the oxygen available for injection into the reactor vessel that would then recombine with hydrogen produced during the postulated zinc-water reaction. Based on 10CFR50 Appendix K inputs and assumptions the additional heat released from this increased reaction rate would result in an estimated increase of 25 degrees F in PCT and 1.73% in maximum local oxidation. Using these results, the increased oxidation results in the analysis of record being non-conservative to the 17% limit as specified in 10CFR50.46(b)(2) by 1.23%. Maximum Average Planar-Linear Heat Generation Rate (MAPLHGR) limit adjustments will be applied to bring the oxidation limits below the 17% limit. However, sufficient margin exists under current operation to ensure the maximum local oxidation limit would not be exceeded. All other 10CFR50.46 ECCS criteria are not impacted. Additionally, based on a conservative evaluation using nominal inputs and assumptions significant margin to 10CFR50.48 ECCS criteria exists even under unlimited oxygen conditions. This voluntary notification is being made as a result of the 10CFR50.46(a)(3)(ii) requirement to report this issue in accordance with 10CFR50.72 and 10CFR50.73. Background During a Loss of Coolant Accident (LOCA), oxygen is available in the fuel bundles due to evaporation of the Emergency Core Cooling System (ECCS) water and release of the dissolved oxygen. In addition, oxygen can also be drawn into the reactor vessel later in the LOCA when the vessel pressure has dropped to the Primary Containment (Drywell) pressure. Condensation of the steam in the reactor vessel upper plenum due to the injection of sub-cooled ECCS water causes a reduction in pressure that will result in drawing the non-condensable gases (including oxygen) from the Drywell. Hydrogen is generated, within the fuel bundles during a LOCA due to Zirconium metal - water reaction caused by high cladding temperatures. It has been postulated that, at the pressure and temperature conditions in the reactor core during a LOCA, free hydrogen and oxygen could combine and release heat that will increase the steam temperature. Since steam is the heat sink when the core is uncovered, an increase in the steam temperature can result in an increase in the PCT for non-jet pump plants including Oyster Creek (BWR/2). The LOCA scenario for a BWR/2 designed plant is different since the core remains uncovered and there is no period of reflooding for large breaks. The cladding will still be heating up when the oxygen from the containment gets into the vessel. This phenomenon also results in an increase in local oxidation. Based on current core thermal power level and existing margin to limits on power operation there is sufficient margin for analyzed accident scenarios requiring ECCS operation including appropriate compensation to restore the analytical oxidation within 10CFR50.46 criteria and there is no impact on safe operation. This is further supported by the results of conservative evaluation using nominal inputs. As a result of this change in the ECCS model and the consequential adjustment to the allowable MAPLGHR limit, the offsite dose for this scenario is still bounded by our current safety analysis. Therefore, this event is not significant with respect to the health and safety of the public. Corrective Action(s): An administrative adjustment to our allowable MAPLHGR limits will be imposed to compensate for the estimated change in cladding oxidation and thereby restore the previously analyzed margin on core thermal power limits to within the new ECCS model prediction. Additionally deinerting of the Primary Containment will be constrained to less than 25% rated power-level until more specific analyses are complete. In accordance with 10CFR50.73, a voluntary LER will be submitted within 60 days with a more detailed discussion of the nature of this change in the ECCS evaluation model, its estimated effect of the limiting ECCS analysis, and a proposed schedule for providing a reanalysis or taking other action as may be needed to comply with this regulation. The licensee will notify the NRC Resident Inspector. |