ENS 51998
ENS Event | |
|---|---|
17:30 Jun 9, 2016 | |
| Title | Unanalyzed Condition Due to a Chemical Processing Malfunction |
| Event Description | I. EVENT DESCRIPTION: High enriched scrap fuel material is processed in BWXT NOG-Lynchburg's Uranium Recovery facility to reclaim as much of the uranium as possible. The material is dissolved in acid and transferred to a series of horizontal columns where the acid is neutralized. The solution may be transferred to a set of accountability weigh columns for measurement prior to entering the uranium extraction process. The solution is subsequently transferred to a series of horizontal feed columns. Process water is used to periodically flush the horizontal columns during cleanup for materials accountability.
On June 9, 2016, a BWXT Nuclear Criticality Safety (NCS) engineer was notified that a bluish tint had been observed in the favorable geometry process water connection to the horizontal columns. By procedure, a blue dye is added to the acid to aid in its identification in the event of a spill. Further evaluation determined that the favorable geometry process water line was directly connected to the horizontal column system and the presence of the blue dye indicated a potential backflow of uranium bearing solution into the water line. The favorable geometry water line is under constant water pressure. The valves controlling the water flow are normally closed. There is also a check valve in the line to prevent backflow. The line is supplied from a favorable geometry header on the mezzanine above. The header supplies water to other processes in Uranium Recovery, including an unfavorable geometry hot water heater. The Integrated Safety Analysis (ISA) was reviewed and an accident sequence for this potential backflow could not be identified. On June 9, 2016 at 1330 [EDT] it was the determined the accident sequence was unanalyzed and not properly documented in the ISA. Although IROFS [Items Relied on for Safety] listed for other accident sequences were applicable to the backflow scenario, the performance requirements of 10 CFR 70.61 were not maintained. As documented in the ISA, criticality was not 'highly unlikely.' II. EVALUATION OF THE EVENT: Backflow into the favorable geometry water line can only be achieved by a forced flow to overcome the water pressure in the line. The only source for this pressurized flow is during the transfer from the accountability weigh columns to the horizontal column system. The solution is transferred using an air diaphragm pump. A trained and qualified operator opens the valve to initiate the transfer of solution from the accountability weigh columns to the horizontal columns (an uncredited control). The transfer of solution to the horizontal columns is monitored by a trained and qualified operator (an uncredited control). The water heater is substantially upstream of the supply line to the horizontal columns. The direction of flow of the process water in the supply header is away from unfavorable geometry hot water heater. The process water header is a favorable geometry (a credited IROFS). An operator checks the process water pressure on a daily basis (a credited IROFS). If the above existing IROFS and uncredited controls were considered in an ISA accident sequence, the likelihood of a criticality could be demonstrated to be highly unlikely. However, these uncredited controls are not designated as IROFS. Although the as-found condition presented no safety concern, the scenarios as documented in the ISA did not demonstrate that the performance requirements of 10 CFR 70.61 were maintained. There was no immediate risk of a criticality or threat to the safety of workers or the public as a result of this event. Ill. NOTIFICATION REQUIREMENTS: BWXT is making this 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> report in accordance with 10 CFR 70, Appendix A, (b)(1), 'Any event or condition that results in the facility being in a state that was not analyzed, was improperly analyzed, or is different from that analyzed in the Integrated Safety Analysis, and which results in failure to meet the performance requirements of 70.61.' IV. STATUS OF CORRECTIVE ACTIONS: A section of the piping from the process water supply header was removed to physically isolate the process water supply from the horizontal columns. Criticality is no longer credible. The hot water heater is the only unfavorable geometry connected to the process water system in the Uranium Recovery facility. The hot water heater was assayed with a gamma survey instrument in several locations along the bottom and up the sides. No counts above background were detected. In addition, multiple liquid samples were taken from the bottom of the water heater and a cartridge filter housing prior to the hot water heater. All samples were well counted and determined to be below the Minimum Detectable Activity (MDA). An investigation of the root causes of this event is ongoing. Corrective actions will be determined as a result of the investigation. The licensee has notified the NRC Resident Inspector and Region II personnel.
I. EVENT DESCRIPTION: On June 10th, 2016 BWXT NOG-Lynchburg notified the NRC of an improperly analyzed condition involving the potential backflow of uranium bearing solution from a fissile solution processing system into the Uranium Recovery process water system. This notification was recorded as Event Notification 51998. One of the corrective actions in response to Apparent Violation 70-27/2016-004-01 was to conduct an Extent of Cause review of 'tasks involving ancillary systems (e.g., process water, nitric acid, HF acid, compressed air, steam, etc.) in our Uranium Recovery and Specialty Fuel Facility to verify these systems have documented accident scenarios as needed to meet the requirements of 10 CFR 70.' During the review of a waste processing system in the Specialty Fuel Facility (SFF), an additional potential backflow scenario was identified for a waste processing system. The system consists of a series of four favorable geometry columns. Waste solution is transferred to the columns using a less than or equal to 2.5 liter pump. The transfer of solution to the columns is monitored by a trained and qualified operator. Waste solution transferred to the columns is limited to a concentration of 5 grams 235U/liter as a Routine Operating Limit. A process water line is directly connected to the column system. The water is used to further dilute the concentration of the waste solution to a level that is acceptable for discharge into the hot waste drain (less than 0.04 grams 235U/liter). The column system is equipped with vent lines that overflow to the floor. The pump is capable of over-pressurizing the columns and possibly forcing waste solution into the favorable geometry process water system if the overflow vent lines were to fail. An unfavorable geometry hot water heater is located a significant distance downstream of the connection to the process water system. The Integrated Safety Analysis (ISA) was reviewed and an accident sequence for potential backflow of solution from the waste columns into the process water system could not be identified. II. EVALUATION OF THE EVENT: Administrative IROFS were identified in other accident sequences of the ISA that are applicable to the waste column backflow scenario. These IROFS include the operator control of solution concentration initially transferred to the waste processing system, and the daily check of the process water pressure which limits backflow into the system. Although these IROFS were available and reliable, additional IROFS are needed to meet the performance requirements of 10 CFR 70.61. Neither the operator's monitoring of the solution transfer or the overflow through the column vent lines are credited as IROFS in the ISA. They are considered uncredited safety controls. If either of the uncredited safety controls and the currently existing IROFS could be considered in an accident sequence, the likelihood of a criticality could be demonstrated to be highly unlikely. However, only IROFS documented in the ISA can be credited as preventing a criticality accident. Although the as-found condition presented no safety concern, the scenarios as documented in the ISA did not demonstrate the performance requirements of 10 CFR 70.61 were maintained. On June 8, 2017 at 10:00 am it was the determined the potential backflow of solution from the waste processing system was improperly analyzed and not documented in the ISA. As documented in the ISA, criticality was not highly unlikely. The SFF waste processing system was not in operation at the time of discovery. There was no immediate risk of a criticality or threat to the safety of workers or the public as a result of this event. Ill. NOTIFICATION REQUIREMENT: BWXT is making this 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> report to update Event Notification 51998 in accordance with 10 CFR 70, Appendix A, (b)(1) - Any event or condition that results in the facility being in a state that was not analyzed, was improperly analyzed, or is different from that analyzed in the Integrated Safety Analysis, and which results in failure to meet the performance requirements of 70.61. IV. STATUS OF CORRECTIVE ACTIONS: The process water line connected to the SFF waste processing system was locked out and posted as 'Out of Service.' Additional corrective actions are to be determined. The Extent of Cause review for AV 70-27/2016-004-01 is complete and the results are being finalized. The licensee informed the NRC Resident Inspector. Notified R2DO (Suggs), NMSS Events Notification, and Fuels Group by email. |
| Where | |
|---|---|
| B&W Nuclear Operating Group, Inc. Lynchburg, Virginia (NRC Region 2) | |
| License number: | SNM-42 |
| Reporting | |
| Part 70 App A (B)(1) | |
| Time - Person (Reporting Time:+18.53 h0.772 days <br />0.11 weeks <br />0.0254 months <br />) | |
| Opened: | David Spangler 12:02 Jun 10, 2016 |
| NRC Officer: | Richard Smith |
| Last Updated: | Jun 9, 2017 |
| 51998 - NRC Website | |
B&W Nuclear Operating Group, Inc. with Part 70 App A (B)(1) | |
WEEKMONTHYEARENS 519982016-06-09T17:30:0009 June 2016 17:30:00
[Table view]Part 70 App A (B)(1) Unanalyzed Condition Due to a Chemical Processing Malfunction ENS 507762015-01-09T21:00:0009 January 2015 21:00:00 Part 70 App A (B)(1) Unanalyzed Condition While Cleaning the Catch Tray ENS 504252014-09-04T15:00:0004 September 2014 15:00:00 Part 70 App A (B)(1) Unanalyzed Condition Related to Potential Material Transfer Cart Tipping ENS 492582013-08-09T17:00:0009 August 2013 17:00:00 Part 70 App A (B)(1) Storage Racks Determined to Be in an Unanalyzed Condition ENS 480912012-07-10T16:30:00010 July 2012 16:30:00 Part 70 App A (B)(1) Metallurgical Sample Pans Exceeded Volume Limit ENS 460012010-06-11T13:45:00011 June 2010 13:45:00 Part 70 App A (B)(1) Unanalyzed Accumulation of Material in the Uranium Recovery Area 2016-06-09T17:30:00 | |