ENS 45446
ENS Event | |
|---|---|
04:00 Oct 13, 2009 | |
| Title | Nitrous Oxide (Nox) Generation Rate Higher than Expected After Aluminum Fines Were Introduced |
| Event Description | Bldg 333's U-Aluminum Bowl Cleaning system is designed to remove uranium from centrifuge bowls by circulating nitric acid through the bowls. The system has historically produced NOx (nitrous oxide, etc) during the nitric acid dissolution process. Safety controls designated as Items Relied On For Safety (IROFS) include a NOx detection system (IROFS BPF-43) with sensors located at the nitric acid knockout column's siphon break potential NOx release point if process ventilation fails and at employee working level.
On October 13, 2009, NFS began using the Bowl Cleaning system to dissolve U-Al fines (very small particles of U-AI) rather than adding them to the normal dissolver column. The fines were loaded into strainers and placed directly into the bowls to be dissolved with nitric acid. After the dissolution process began, the Operator noticed that the temperature of the system was increasing and that NOx (in the form of a brown cloud) was beginning to form inside the Bowl Cleaning station containment vessels. The system was shutdown. The Nox detector designated as an IROFS alarmed and the facility was evacuated. Immediate corrective actions included building, and health and safety personnel re-entry in SCBA to validate shutdown conditions and remote monitoring of Nox levels in Bldg 333. Based on re-entry data and remote Nox detector readings, Nox levels inside the building (outside of containment) were not significant. Laboratory analysis of similar U-AI fines material was conducted October 14-October 16. It behaved in the laboratory in the same manner as what was observed during the operational event. Based on the lab testing, a Nox generation rate specific for the fines material was estimated. Based on engineering calculations, it was determined that the Nox generation for the fines was significantly higher than the previously analyzed Nox generation for the U-AI ingots. The previous Nox evaluation for the U-Al Bowl Cleaning station resulted in an intermediate occupational consequence. Using the generation rate specific for the fines results in high occupational consequences. On October 19, 2009, based on the revised Nox generation rate, it was determined that insufficient lROFS were in place and that the performance criteria of 10 CFR 70.61 were not met. a) Radiological Hazards involved including: High- enrichment Uranium: quantity Approx 1,000 g; Isotope: U-235 quantity Approx 710 g b) Chemical Hazards involved including: Chemical: Nox gas; Quantity: Approx. 1.85 lbs. c) Discuss the actual or potential health and safety consequences to the workers, the public, and the environment, including relevant chemical and radiation data for actual personnel exposures to radiation or radioactive materials or hazardous chemicals produced from licensed materials. Include in the discussion below the concentration of chemicals and duration of exposure, if any: Potential worker and public exposure to Nox. Process ventilation and Nox detection worked as designed. No actual exposure to workers or the public were recorded. d) Discuss the sequence of occurrences leading to the event, including degradation or failure of structures, systems, equipment, components and activities of personnel relied on to prevent potential accidents or mitigate their consequences: See above. e) Discuss whether the remaining structures, systems, equipment components, and activities of personnel relied on to prevent potential accidents or mitigate their consequences are available and reliable to perform their function: IROFS BPF-43 is in place and functioned correctly during the event. Operating personnel responded to the alarm as specified in the operating procedure and evacuated the facility. External conditions affecting the event: None. Additional actions taken in response to the event: Discussed situation with Operations, Safety management and with the NRC Resident Inspector. The U-Al Bowl Cleaning system is currently not operating.
The "(nitrous oxide, etc)" in the first paragraph of the original report is updated to state "(NO, NO2, etc)." The licensee has notified the NRC Resident Inspector. Notified the R2DO (Henson) and NMSS EO (Rubenstone) via email. |
| Where | |
|---|---|
| Nuclear Fuel Services Inc. Erwin, Tennessee (NRC Region 2) | |
| License number: | SNM-124 |
| Reporting | |
| Part 70 App A (B)(1) | |
| Time - Person (Reporting Time:+157 h6.542 days <br />0.935 weeks <br />0.215 months <br />) | |
| Opened: | Jennifer Wheeler 17:00 Oct 19, 2009 |
| NRC Officer: | Pete Snyder |
| Last Updated: | Oct 22, 2009 |
| 45446 - NRC Website | |
Nuclear Fuel Services Inc. with Part 70 App A (B)(1) | |
WEEKMONTHYEARENS 505772014-10-29T07:00:00029 October 2014 07:00:00
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2014-10-29T07:00:00 | |