ENS 43503
ENS Event | |
|---|---|
16:20 Jul 18, 2007 | |
| Title | Unanalyzed Condition - Vent Space Less than Design Basis |
| Event Description | During an inspection of the Unit 2 Reactor Building Steam Chase as a result of a similar situation being previously discovered on Unit 1, a storage gangbox was noted to be resting on one of the two hinged blowoff panels in the floor of the Steam Chase (elevation 130') and the hinged blowoff panels were determined to be restrained which would prevent their opening. The blowoff panels are designed to open to provide pressure and temperature relief between the torus room and 130 ft elevation of the reactor building for high energy steam line breaks. The 'as found' configuration of the blowoff panels hinder their capability to open, which constitutes a non-conforming and unanalyzed condition in that the vent area between the torus room and main steam chase in the reactor building is less than the area assumed in the analysis for a HPCI steam line break.
As such, for a HPCl steam line break in the torus room, the short term pressure across the torus room ceiling would likely be greater than 2.3 psid, which is the maximum differential pressure stated in Chapter 15A of the Unit 2 FSAR. There is no known analyzed limit for the differential pressure between the torus room and the 130 ft elevation of the reactor building. The actual differential pressure given the 'as found' condition is not known at this time. Corrective actions have been taken to restore the assumed vent area between the torus room and the reactor building 130ft elevation. The gang box has been removed and both blow off panels no longer have restricted movement. The remaining 3' x 3' floor plug has also been removed, completely restoring the assumed vent area into compliance. Based on this information there is reasonable assurance that an adequate vent path currently exists such that the plant is no longer considered to be in a condition that significantly degrades plant safety. However, since the actual differential pressure given the 'as found' condition is not known at this time, the 'as found' condition as previously discussed is assumed to be an unanalyzed condition that represents a condition that significantly degraded plant safety; however, additional information is needed in order to more conclusively determine this. If more conclusive information is provided that indicates otherwise an update notification will follow. This was also reported under 10CFR50.72(b)(3)(v)(D). The licensee notified the NRC Resident Inspector.
A review of the 'as found' configuration of the plant was performed to determine if this configuration would still be bounded by the calculations that support the HELB analysis in the Unit 2 FSAR. The 'as found' configuration consisted of having one torus plug in place rather than open and the two hinged torus ceiling blow-off panels bolted shut instead of being free to open. This engineering review concluded that if the torus ceiling blow-off panels do not open and with only one torus plug open, the torus pressures will not exceed the current FSAR pressures. Additionally, the torus pressures were found to be acceptable as a result of the modeling of friction in the HPCI pipe break mass and energy releases. This being the case, for a HPCI steam line break in the torus room, the short term pressure across the torus room ceiling would be 1.93 psid for the 'as found' condition which is less than the maximum differential pressure of 2.27 psid as stated in Chapter 15A of the Unit 2 FSAR. It should be noted that corrective actions were taken upon discovery and that the assumed vent area between the torus room and the reactor building 130 ft elevation was restored shortly following discovery. The gang box was removed, the restraint on the blow-off panels removed and both blow-off panels were confirmed to have full range of motion to open if the conditions were present that would warrant that movement. Based on this review of the design calculations while taking the 'as found' conditions into consideration, the conclusion reached is that the nonconforming 'as found' conditions did not represent a condition that significantly degraded plant safety. For this reason this condition that was initially reported under 10CFR50.72(b)(3)(ii)(B) is being retracted. The licensee will notify the NRC Resident Inspector. R2DO(Shaeffer) notified. |
| Where | |
|---|---|
Hatch  Georgia (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | |
| Time - Person (Reporting Time:+2.38 h0.0992 days <br />0.0142 weeks <br />0.00326 months <br />) | |
| Opened: | Steve Brunson 18:43 Jul 18, 2007 |
| NRC Officer: | Mark Abramovitz |
| Last Updated: | Aug 30, 2007 |
| 43503 - NRC Website | |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Hatch with 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor, 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition, 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | |
WEEKMONTHYEARENS 526502017-03-30T13:22:00030 March 2017 13:22:00
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