ENS 40748

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v t e ENS Event
12:13 May 14, 2004
Title	Change in the Methodology Used by Ge/Gnf to Demonstrate Compliance with Eccs Performance Requirements
Event Description	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.

ENS 40748 +/-
Where
Oyster Creek New Jersey (NRC Region 1)
Reporting

Other Unspec Reqmnt
Time - Person (Reporting Time:+-1.38 h-0.0575 days <br />-0.00821 weeks <br />-0.00189 months <br />)
Opened:	Frank Ciganik 10:50 May 14, 2004
NRC Officer:	Chauncey Gould
Last Updated:	May 14, 2004
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v • d • e

v t e Emergency Notification System
Oyster Creek with Other Unspec Reqmnt
WEEKMONTHYEAR2005-03-18T19:00:00 [Table view]
[ENS list for Oyster Creek]

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