ENS 47911

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v t e ENS Event
21:16 May 8, 2012
Title	Autoclave High Pressure Isolation System Failure
Event Description	At 1616 CDT, on 05-08-12 the Plant Shift Superintendent (PSS) was notified that C-360 (Toll Transfer & Sampling Building) Autoclave #2 had a failure in the Autoclave High Pressure Isolation System [AHPIS]. [AHPIS] is designed to: 1) prevent a cylinder failure inside the autoclave as a result of overheating; and 2) mitigate releases to the atmosphere from releases inside the autoclave. Autoclave containment is required to be operable per TSR 2.1.3.1 while the autoclave is in TSR modes 3 (containment), 4 (autoclave closed), and 5 (autoclave heating). On 5/08/12 at 1610 CDT an operator noticed water flowing from the autoclave head to shell sealing surface on the #2 autoclave in C-360 while a cylinder was being heated (TSR mode 5 - autoclave heating). The PSS was notified of the loss of containment at 1616 CDT and the [AHPIS] was declared inoperable. The steam cycle was interrupted and the autoclave was placed in a non-applicable TSR mode at 1657 CDT. No release of UF6 occurred due to the failure of the [AHPIS]. This event is reportable as a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> event in accordance with 10CFR 76.120(c)(2)(i). This is an event in which equipment is disabled or fails to function as designed when: a.) the equipment is required by a TSR to prevent releases, prevent exposures to radiation and radioactive materials exceeding specified limits, mitigate the consequences of an accident, or restore this facility to a pre-established safe condition after an accident; b.) the equipment is required by a TSR to be available and operable and either should have been operating or should have operated on demand; and c.) no redundant equipment is available and operable to perform the required safety function. The NRC Senior Resident Inspector has been notified of this event. PGDP Assessment and Tracking Report No. ATRC-12-1195; PGDP Event Report No. PAD-2012-02; Responsible Division: Operations * * UPDATE FROM BILLY WALLACE TO DONALD NORWOOD AT 1640 EDT ON 5/9/2012 * * * After further review the licensee determined that additional reportability criteria were met as described below: At 1616 on 05/08/2012, the PSS was notified that C-360 Autoclave #2 had water flowing from the autoclave head to shell sealing surface indicating a potential failure in the Autoclave High Pressure Isolation System (AHPIS) containment, which is relied on as an engineered control in NCSE 042 (SRI 5.5.3). The AHPIS is designed to minimize leaks to atmosphere from the autoclave under maximum pressures resulting from a UF6 release from the cylinder, valve or pigtail in the autoclave. The maximum acceptable leak rate for the autoclaves is 12 SCFM at a minimum test pressure of 90 psig or a 10 psi pressure drop in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. In order to determine if the AHPIS would have met its safety function, a pressure decay test will be performed. However, the pressure decay test will not be performed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of discovery. Therefore, it is conservatively assumed that the leak discovered is greater than 12 SCFM or greater than 10 psi pressure drop in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />; resulting in a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> NCS reportable event. When the leak was noticed, the heat cycle was interrupted and the autoclave placed in a safe configuration. No release of UF6 had occurred in the autoclave when the leak out the autoclave was found. This event is reportable as a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> event in accordance with 24-Hr. NRC BL 91-01 Supp. 1. This is a criticality safety event in which violations involving operations that comply with the double contingency principle and do not meet the criteria for a 4-hr report, but still result in a violation of the double contingency principle, such as, events where the double contingency principle is violated but control is immediately reestablished. Safety Significance of Events: --While an NCSA control was not maintained resulting in the potential autoclave leak rate being exceeded, a release of fissile material from a cylinder in the autoclave did not occur and therefore a criticality was not possible. Potential Criticality Pathways Involved: --In order for a criticality to be possible, a cylinder, valve, or pigtail of a fissile cylinder would have to fail and release greater than a safe mass of fissile material into the autoclave and the autoclave containment would have to fail allowing a large release to atmosphere of uranium and settle out in an unfavorable geometry with sufficient moderator present. Controlled Parameters: --The first leg of double contingency is based on mass. --The first leg of double contingency is based on administrative and design controls to ensure that it is unlikely to have a large release of UF6 from the cylinder, valve or pigtail in the autoclave while healing the cylinder. --The second leg of double contingency is based on geometry moderation. Estimated Amount, Enrichment, Form of Licensed Material: --No leakage of UF6 occurred. Nuclear Criticality Safety Control(s) or Control System(s) and Description of the Failures or Deficiencies: --The first leg of double contingency is based on mass. --The first leg of double contingency is based on administrative and design controls to ensure that it is unlikely to have a large release of UF6 from the cylinder, valve or pigtail in the autoclave while heating the cylinder. This control was maintained. --The second leg of double contingency is based on geometry / moderation. --Small leaks out of the autoclave to atmosphere are considered normal case and the Autoclave High Pressure Isolation System ensures containment to minimize a significant release to atmosphere if a release occurs in the autoclave during heating. The AHPIS ensures that the maximum leak rate from the autoclave will not exceed 12 SCFM or a maximum acceptable pressure drop of 10 psi in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. If the containment leak rate is maintained, only a small amount of uranium could leak to atmosphere and the uranium would form in thin layers on surfaces in a geometrically safe configuration. Also there would be insufficient uranium to leak outside of the building; therefore there would not be a sufficient source of moderation. Since this control is assumed to have failed, uranium could leak out of the autoclave to atmosphere if a large release of UF6 occurred in the autoclave and potentially deposit in geometrically unfavorable configurations in areas where sufficient moderators exist. Since the leak rate cannot be confirmed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, it is conservatively assumed that the geometry moderation parameter was lost and double contingency was not maintained. Corrective Actions To Restore Safety Systems and When Each Was Implemented: --Perform a pressure decay test on Autoclave #2 according to procedures and if the leak rate is determined to be greater than 12 SCFM or 10 psi in one hour, repair AHPIS prior to heating another cylinder containing uranium. The NRC Resident Inspector has been notified of this event. PGDP Assessment and Tracking Report No. ATRC-12-1195; PGDP Event Report No. PAD-2012-03; Responsible Division: Operations. Notified R2DO (Freeman) and NMSS EO (Campbell). * * RETRACTION FROM DAVID PETTY TO DONG PARK AT 1403 EDT ON 5/15/2012 * * * Subsequent to the above notifications on May 10, 2012, autoclave no. 2 was subjected to a pressure decay test in the as-found condition. The test indicated that the High Pressure Isolation Safety System would have been capable of performing its intended safety function if called upon on May 8, 2012, during the heat cycle subject of the event reports. Thus, the event was not required to be reported under 10CFR 76.120(c)(2)(i) and the notifications may be retracted. Subsequent to the above notifications on May 10, 2012, autoclave no. 2 was subjected to a pressure decay test in the as-found condition. The test indicated that the High Pressure Isolation Safety System would have been capable of performing its intended safety function if called upon on May 8, 2012, during the heat cycle subject of the event reports. The pressure drop from the as-found test was less than the maximum allowable pressure drop for the system required for criticality safety. Thus, the event did not meet the criteria to be reported under 24-Hr. NRC BL 91-01 Supp. 1. The NRC Senior Resident Inspector has been notified of this event. Notified R2DO (Shaeffer) and NMSS EO (Guttmann).

ENS 47911 +/- *RETRACTED*
Where
Paducah Gaseous Diffusion Plant Paducah, Kentucky (NRC Region 2)
License number:	GDP-1
Reporting

10 CFR 76.120(c)(2) Response
Time - Person (Reporting Time:+11.43 h0.476 days <br />0.068 weeks <br />0.0157 months <br />)
Opened:	Rod Cook 08:42 May 9, 2012
NRC Officer:	Howie Crouch
Last Updated:	May 15, 2012
47911 - NRC Website
v • d • e

v t e Emergency Notification System
Paducah Gaseous Diffusion Plant with 10 CFR 76.120(c)(2), Response
WEEKMONTHYEAR2014-05-08T15:24:00 [Table view]
[ENS list for Paducah Gaseous Diffusion Plant]

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