ENS 42585
ENS Event | |
|---|---|
19:30 May 17, 2006 | |
| Title | Postulated Criticality Due to Backflow to an Unfavorable Geometry Vessel |
| Event Description | During a regularly scheduled review of the ISA for a process system in the ELO building, the ISA team postulated where fissile solution could backflow into an unfavorable geometry vessel (55-gallon drum). This system configuration did not have sufficient IROFS designated to ensure that the performance criteria of 10 CFR 70.61 were met. The process system was immediately shut down, the potential for back flow to the unfavorable geometry vessel was removed, and the potential for similar accident sequences in this and related process systems was evaluated. This evaluation found one additional system configuration in the same process system where fissile solution could backflow into an unfavorable geometry vessel. The details of this condition are still undergoing internal investigation. This configuration does not have sufficient IROFS designated to ensure that the performance criteria of 10 CFR 70.61 are met. The process equipment associated with this scenario is also shut down and will remain shut down pending establishment of sufficient IROFS to meet the performance criteria of 10 CFR 70.61
The material in the identified system sources that is normally in the tanks that could back flow to the unfavorable geometry vessel is uranyl nitrate solution with a range of [deleted] g U/liter. However on certain rare occasions, there is the potential for uranyl nitrate solution with up to [deleted] U/liter to be present in these tanks. This is the highest concentration observed by veteran system operators. The 95/95 upper limit of keff for a single 55 gallon drum containing uranyl nitrate solution with [deleted] U/liter, sitting on a 30 cm thick concrete slab and with [deleted] cm of water tight fitted water reflector is approximately [deleted]. At [deleted] U/liter the 95/95 upper limit of keff is approximately [deleted]. The allowed 95/95 upper limit on keff for normal conditions is [deleted] and [deleted] for abnormal conditions. SAFETY SIGNIFICANCE Safety significance is low. The potential of accidental nuclear criticality in the as found condition remained unlikely. POTENTIAL CRITICALITY PATHWAYS INVOLVED: The potential criticality pathway involves having more than [deleted] U/liter uranyl nitrate solution in the system tanks, an improper valve line up and then pumping the solution back through an air powered double diaphragm pump into the 55-gallon drum. CONTROLLED PARAMETERS (Mass, Moderation, Geometry Concentration etc.): The controlled parameter on the 55 gallon drum of feed material was concentration. The maximum allowed concentration is [deleted] U/1 UNH solution. ESTIMATED AMOUNT, ENRICHMENT, FORM OF LICENSED MATERIAL (Include process limit and % worst case critical mass: The facility is limited by NRC license to an enrichment of [deleted] wt.% U-235. The maximum amount of material that could potentially back flow into the 55-gallon drum is approximately [deleted] liters and the maximum expected concentration would be [deleted] U The normally expected concentration is less than [deleted] U/liter. According to ARH-600 page III.B6-3, the minimum critical spherical mass of UN solution is in excess of [deleted] kg. CORRECTIVE ACTIONS TO RESTORE SAFETY SYSTEMS AND WHEN EACH WAS IMPLEMENTED: The back flow potential was eliminated and the system tagged out of service pending a complete re-analysis of the process system and the establishment of sufficient IROFS to meet the performance requirements of 10 CFR 70.61. Related process systems that might have a similar potential were also shut down pending completion of an evaluation to ensure that the same potential does not exist in these areas. |
| Where | |
|---|---|
| Framatome Anp Richland Richland, Washington (NRC Region 2) | |
| License number: | SNM-1227 |
| Reporting | |
| Part 70 App A (B)(2) | |
| Time - Person (Reporting Time:+19.93 h0.83 days <br />0.119 weeks <br />0.0273 months <br />) | |
| Opened: | Robert Link 15:26 May 18, 2006 |
| NRC Officer: | John Mackinnon |
| Last Updated: | May 18, 2006 |
| 42585 - NRC Website | |
Framatome ANP Richland with Part 70 App A (B)(2) | |
WEEKMONTHYEARENS 558972022-05-13T02:10:00013 May 2022 02:10:00
[Table view]Part 70 App A (B)(2) Gamma Monitors NON-FUNCTIONAL ENS 425852006-05-17T19:30:00017 May 2006 19:30:00 Part 70 App A (B)(2) Postulated Criticality Due to Backflow to an Unfavorable Geometry Vessel ENS 421192005-11-03T22:00:0003 November 2005 22:00:00 Part 70 App A (B)(2) Deficiency Found in Integrated Safety Analysis Program 2022-05-13T02:10:00 | |