ENS 46447
ENS Event | |
|---|---|
15:15 Dec 2, 2010 | |
| Title | Uranium Concentration Greater than Expected in Gas Stripper System Following an Acid Wash |
| Event Description | Background:
The purpose of the Ammonia Recovery Facility (ARF) facility is to recover ammonia from the ammonium diuranante (ADU) process effluent by use of a stripper column. The feed of effluent to ARF has a uranium concentration is typically less than 1 ppm. Two uranium analyzers provide assurance that the effluent uranium concentration is less than 100 ppm prior to discharge to the Ammonia Recovery process feed tank V-621. The ISA Summary for this process states that only minute quantities of radioactive material are present in the feed to the ARF and that there are no credible accident sequences that result in intermediate or high consequences. Event Description: On 12/02/2010 at 0715, a Process Engineer informed Nuclear Criticality Safety (NCS) that he had confirmed that an acid wash of ARF stripper column had recovered 8 kg of Uranium (U). The acid wash is expected to have removed all significant amounts of Uranium from the system. This resulted in a review of the adequacy of the ISA treatment for the ARF stripper column. Safety Significance of Event: The safety significance is low. The amount of Uranium recovered, approximately 8 kg, is less than 25% of a minimum critical mass in spherical geometry. The concentration of the liquid is about 1 g U/liter. The 8 kg constitutes an approximate ten year accumulation since the last column acid wash in 2001. Based on the accumulation rate over the past 10-years, another 40 years of accumulation would be required without any removal during maintenance before achieving a critical mass. The system was down for maintenance at the time of discovery. Maintenance activities were suspended and will remain suspended until an appropriate processing path is identified to process this material and appropriate controls are established. The system will not be restarted until the system has been reanalyzed and appropriate controls are verified to be in place to meet 10CFR70.62 performance criteria. Potential Criticality Pathways Involved (Brief Scenarios of how criticality could occur): Criticality is possible if material in the ARF equipment exceeds a minimum critical concentration and a minimum critical mass for a given geometry. Controlled Parameters: The controlled parameters are upstream of the ARF process and are based on concentration of the feed material. The uranium concentration in ARF feed is typically less than 1 ppm. Two uranium analyzers provide assurance that the ADU effluent uranium concentration is less than 100 ppm prior to discharge to the Ammonia Recovery process. Estimated Amount, Enrichment, Form of Licensed Material and % of worst case Critical Mass: The facility is only licensed to 5 wt.% U-235. The material present in the stripper column prior to being dissolved was likely ammonium diuranate. Once dissolved, the material is uranyl nitrate. The mass in the system is expected to have been less than 25% of a minimum critical mass in spherical geometry. When equipment geometry is taken into account, much higher masses are required to obtain a critical condition. For example, the ARF feed tank with a uniform slab of U02-H20 would require an areal density exceeding 10 kg U/ft2 (more than 500 kg U). Nuclear Criticality Controls) or Control System(s)) and Description of the Failure Deficiencies: The upstream controls on concentration performed as required. The material plate-out within the stripper column was greater than anticipated. Corrective Actions to Restore Safety Systems and When Each Was Implemented: The system was down for maintenance at the time of discovery. Maintenance activities were suspended and will remain suspended until an appropriate processing path is identified to process this material and appropriate controls are established. The system will not be restarted until the system has been reanalyzed and appropriate controls are verified to be in place. The licensee initiated the acid wash of the gas stripper as a result of concerns over the differences in the inlet and outlet pressures of the system, which indicated that the system was becoming less efficient. The licensee briefed Region 2 management and Region 2 fuel cycle facility inspectors about this event. |
| Where | |
|---|---|
| Areva Np Inc Richland Richland, Washington (NRC Region 2) | |
| License number: | SNM-1227 |
| Reporting | |
| Part 70 App A (B)(2) | |
| Time - Person (Reporting Time:+2.4 h0.1 days <br />0.0143 weeks <br />0.00329 months <br />) | |
| Opened: | Robert Link 17:39 Dec 2, 2010 |
| NRC Officer: | Joe O'Hara |
| Last Updated: | Dec 2, 2010 |
| 46447 - NRC Website | |
Areva Np Inc Richland with Part 70 App A (B)(2) | |
WEEKMONTHYEARENS 524332016-12-13T23:00:00013 December 2016 23:00:00
[Table view]Part 70 App A (B)(2) Non-Performance of Administrative Item Relied on for Safety ENS 464472010-12-02T15:15:0002 December 2010 15:15:00 Part 70 App A (B)(2) Uranium Concentration Greater than Expected in Gas Stripper System Following an Acid Wash ENS 445212008-09-25T14:20:00025 September 2008 14:20:00 Part 70 App A (B)(2) 24 Hour Notification of the Discovery That a Spark Arrestor for Hepa Filter Fire Control Was Not Installed 2016-12-13T23:00:00 | |