ENS 40749
ENS Event | |
|---|---|
13:17 May 14, 2004 | |
| Title | Change in the Methodology Used by Ge/Gnf to Demonstrate Compliance with Eccs Performance Requirements |
| Event Description | Nine Mile Point 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 during five reactor recirculation loop operation, with containment inerted. The increased oxidation results in the analysis of record being non-conservative to the 17% limit as specified in 10CFR50.46(b)(2). Maximum Average Planar-Linear Heat Generation Rate (MAPLHGR) limit adjustments will be applied to bring the oxidation limits below the 17% limit.
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. 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. The change in the allowable MAPLGHR limit for five loop operation with the containment inerted results in the offsite dose for this scenario being 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): Reactor Engineering has implemented the 2% MAPLHGR Limit reduction through imposition of a .98 MAPRAT to restore compliance to the 10CFR50.46 limits. Operations will place administrative controls/ procedure changes to preclude operating without containment inerted at or above 25% power to limit oxygen available for this postulated phenomenon. In accordance with 10CFR50.73, a LER will be submitted 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 notified the NRC Resident Inspector. |
| Where | |
|---|---|
Nine Mile Point  New York (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Other Unspec Reqmnt | |
| Time - Person (Reporting Time:+2.47 h0.103 days <br />0.0147 weeks <br />0.00338 months <br />) | |
| Opened: | Quentin Hicks 15:45 May 14, 2004 |
| NRC Officer: | Bill Gott |
| Last Updated: | May 14, 2004 |
| 40749 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 500982014-05-08T20:45:0008 May 2014 20:45:00
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