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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 55897 | 13 May 2022 02:10:00 | Part 70 App A (B)(2) | Gamma Monitors NON-FUNCTIONAL | The following information was provided by the licensee via fax or email: Two gamma monitors on filters associated with the waste water treatment system were discovered to be non-functional during their monthly calibration check. These gamma monitors are designated as an Item Relied on for Safety (IROFS) and are used to prevent gradual long term accumulations of uranium from exceeding a safe mass. The system has been shut down and will remain down until the required safety function is restored. This condition is being conservatively reported under the requirements of 10CFR70 Appendix A b(2) due to two Failed IROFS although Framatome believes that the performance requirements of 10CFR70.61 are still met. | ||
| ENS 42585 | 17 May 2006 19:30:00 | Part 70 App A (B)(2) | Postulated Criticality Due to Backflow to an Unfavorable Geometry Vessel | 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. | ||
| ENS 42119 | 3 November 2005 22:00:00 | Part 70 App A (B)(2) | Deficiency Found in Integrated Safety Analysis Program | BACKGROUND: Framatome ANP routinely vacuum transfers LEU powder into 55-gallon drums for storage in the BLEU facility 55-gallon drum warehouse. A change was implemented recently to also vacuum transfer LEU powder from 45-gallon drums into 55-gallon drums, also for storage in the BLEU facility 55-gallon drum warehouse. EVENT DESCRIPTION: On day shift November 3, 2005 at approximate 2:00 PST, a process operator vacuum transferred LEU powder enriched to (deleted) wt% 235U from a 45-gallon to a 55-gallon drum in the BLEU facility at the Richland site. This transfer was performed according to an approved standard operating procedure (SOP). This was the first such transfer under a recently approved nuclear criticality safety analysis (NCSA) part of the Integrated Safety Analysis (ISA) When the operator was preparing the newly filled 55-gallon drum for transfer to and storage in the warehouse, the Nuclear Inventory Management System (NIMS) would not print a label for the drum. Operations personnel contacted an NCS specialist about this issue. While troubleshooting this problem, the NCS specialist discovered that the LEU powder contained hydrogenous additives. He recognized that the Richland site ISA did not implement IROFS to prevent transfer of powder containing hydrogenous additives from 45-gallon to 55-gallon drums. At this point, the drum was sampled and locked in place pending further evaluation. The 45-gallon to 55-gallon transfer process was also placed out of service pending further evaluation. SAFETY SIGNIFICANCE OF EVENT: The safety significance of this event is very low. In accordance with the NCSA a 55-gallon drum filled with LEU powder, enriched to (deleted ) 235U with a bulk density of (deleted ) and containing (deleted ) wt% moisture, that is fully reflected by water has a keff of (deleted). A moisture value of (deleted) wt% is required in such a drum to reach a keff of 1.0. The drum involved in this event actually contained 115.4 kg of LEU powder enriched to (deleted) wt% 235U with a bulk density of (deleted) and containing (deleted) total moisture equivalence (moisture and moisture equivalent approved additives determined by follow up laboratory analysis). Based on total moisture equivalent content alone, the material in the drum would have to have more than (deleted) times the limit (deleted) and more than (deleted) times the actual amount (deleted) before criticality could occur in the drum. The actual enrichment and bulk density of the material involved in this event provide additional margin compared to the values required for criticality discussed in the previous paragraph. POTENTIAL CRITICALITY PATHWAYS INVOLVED (BRIEF SCENARIO(S) OF HOW CRITICALITY COULD OCCUR): Criticality could only occur if moderation control on the material placed in the drum is lost. This could hypothetically occur if powder containing over (deleted) times the allowed limit (deleted) were placed into the drum. CONTROLLED PARAMETERS (MASS, MODERATION, GEOMETRY, CONCENTRATION, ETC.): The process parameter controlled in this portion of the process is moderation. NUCLEAR CRITICALITY SAFETY CONTROL(S) OR CONTROL SYSTEM(S) AND DESCRIPTION OF THE FAILURES OR DEFICIENCIES: Within the 1SA the NCSA, E04-NCSA-323 version 3.0 accident sequence 1.4.1 description bounds this event. It states, "UO, powder containing greater than (deleted) wt% H2O equivalent is transferred to a 55-gallon drum from the BLEU powder preparation south addback station. Defense 1 for this accident sequence states, 'Moderation control: Any 45-gallon drum of UOX powder that does not have at least two independent determinations that it has (deleted) wt% or less moisture must be stored in a specially designated, locked storage grid to prevent accidental drum movement.' This is IROFS 1105 and was maintained throughout this event. At HRR, per SOP, if a drum contains greater than (deleted) wt% moisture and/or > (greater) wt% moisture equivalent additives, it is locked in a storage location. Only trained key custodians may unlock these storage locations for further processing or handling of the drum, Based on the moisture and moisture equivalent approved additive content of the powder, the drum involved in this event was not such a drum. Defense 2 for this accident sequence states, 'Moderation control: The programmable controller interfaces with NIMS to verify acceptable moisture content before it permits transfer valve to open.' This is IROFS 6002 and was maintained throughout this event for moisture content of the powder. As implemented, this IROFS does not verify that the powder to be transferred contains no hydrogenous additives. However, as an uncredited defense, before permitting the transfer valve to open, NIMS does verify that the powder contains s (deleted) wt% AZS and (deleted) wt% ALS, which is (deleted) wt% moisture equivalent approved additives. Therefore, on a total moisture and moisture equivalent basis, NIMS does verify that the powder contains less than (deleted) wt% total moisture equivalence. This is approximately (deleted) times less than the (deleted) wt% total moisture equivalence required to approach a keff value of (deleted). Defense 3 for this accident sequence states, Moderation control provided by an AEC (active engineered control). An in-line moisture monitor is interlocked to shut off the vacuum blower and stop the rotary valve to prevent a significant amount of Uox powder containing greater than (deleted) wt% H2O from being transferred to the drum. This is IROFS 4704 and was maintained throughout this event for moisture content of the powder. This IROFS, however, will not detect dry hydrogenous additives. CORRECTIVE ACTIONS TO RESTORE SAFETY SYSTEMS AND WHEN EACH WAS IMPLEMENTED: After discovery of the deficiency, the drum was sampled and locked in place pending further evaluation. The 45-gallon to 55-gallon transfer process was also placed out of service pending further evaluation. |