ML23212A918
| ML23212A918 | |
| Person / Time | |
|---|---|
| Site: | BWX Technologies |
| Issue date: | 04/04/2023 |
| From: | Freudenberger R BWXT |
| To: | Office of Nuclear Material Safety and Safeguards |
| References | |
| 23-019, 56336 | |
| Download: ML23212A918 (1) | |
Text
eW>l1 orr1e1~t Yet orJt't BVVX Technologies, Inc.
April 4, 2023 23-019 ATTN: Document Control Desk Director, Office of Nuclear Material Safety & Safeguards U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Reference:
License No. SNM-42, Docket 70-27
Subject:
60-Day Written Report for Event Notification Number EN-56336
Dear Sir or Madam,
Enclosed please find the BWXT Nuclear Operations Group, Inc. - Lynchburg (BWXT NOG-L) 60-Day Written Report for Event Notification (EN) 56336. The EN was reported under 1o CFR Part 70 Appendix A (b)(2).
On the evening of January 19, 2023, a spill occurred from overfilling the Annular Waste Organic Tank in BWXT NOG-L's Uranium Recovery Facility. On January 20, 2023, during the next periodic inspection of the ventilation duct drain, personnel noted the presence of organic solution, indicating some of the overflowed waste solution had been drawn into the ventilation ductwork.
The initial event assessment determined that the solution had flowed out of the waste tank's overflow line and vent onto the floor, with some solution being drawn into the ventilation system and later identified in the duct drain. The overflow line is one of three IROFS credited in the accident sequence for waste organic solution entering the ventilation ductwork. On February 3, 2023, it was discovered that the overflow line from the Annular Waste Organic Tank contained an intact rupture disc. Liquid could not flow freely through the overflow line due to the obstruction created by the rupture disc. Therefore, the IROFS function of the overflow could not be credited in the accident sequence as documented in the Integrated Safety Analysis. Subsequent to this discovery, BWXT NOG-L Safety and Licensing management determined the event to be reportable in accordance with Appendix A(b)(2) of 10 CFR Part 70. The event was reported on February 3, 2023 within twenty-four hours of determination as EN-56336. The enclosed report provides an event description, background information, assessment of safety significance, identified causes, and an extent of condition review summary.
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People Strong BWXT Nucle.::u Operations G roup, Inc.
P.O. Box 785 L.ynchburg , VA 2 4605 USA INNOVATION DRIVEN >
1* 1.434522.0000 www.bwxt.com QFFl&l#2k rJCi Otlkl(
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If you have questions or require additional information, please contact Daniel Ashworth, Manager of Licensing and Safety Analysis, at dlashworth@bwxt.com or 434-522-5472.
Sincerely, 7LL,~
Richard J. Freudenberger Manager, Environment, Safety, Health and Safeguards BWXT Nuclear Operations Group, Inc., Lynchburg Enclosure cc: NRC, Region II NRC, Resident Inspector NRC, James Downs, NMSS/DFM BWXT Nuclear Oper3.tions Group, Inc.
People Strong F'.O . Box 785 Lynchburg, VA 24505 USA
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If Pllli ti 1111111 I U.S. NRC 23-019 Enclosure 60-Day Written Report for Event Notification #56336 - February 3, 2023 Event Description A spill of approximately 20 liters of waste organic solution occurred on the evening of January 19, 2023 from an annular organic tank in BWXT Nuclear Operations Group-Lynchburg's (NOG-L) Uranium Recovery facility. The intended evolution was to transfer the waste solution from one bank of columns to another using the waste tank's pump. Instead, the waste solution was inadvertently transferred to the tank itself due to mispositioned valves, which caused the tank to overfill and spill onto the floor. The managers of Recovery Operations and NCS were promptly notified of the spill, which had a U-235 concentration of 1.6 g U-235/liter. The spill itself was not an NCS concern and was cleaned up according to area procedures. During the first shift's periodic inspection of the ventilation duct drain on the morning of January 20, 2023, personnel noted the presence of approximately 3 liters of organic solution.
The concentration of the organic solution in the ventilation duct drain was 3 g U-235/liter. No Nuclear Criticality Safety (NCS) limit was violated by the presence of the waste organic solution in the ventilation system. Although the as-found condition presented no safety concern because of the low uranium concentration of the solution involved, the presence of solution in the ventilation ductwork indicated the Annular Waste Organic Tank overflow and air gap to the ventilation system, which are credited as IROFS, did not function as designed. Based on the initial investigation of the event, it appeared that the tank overflow and air gap were degraded in some manner. Both seemed to have functioned, but did not preclude all of the waste solution from entering the ventilation system. The tank was removed from service and remains out of service.
The accident sequence for waste organic solution entering the ductwork relies on: 1) the control of the solution concentration in the waste tank, 2) an overflow line on the tank, and 3) an air gap between the tank vent and the ventilation system. The initial event assessment determined that the solution had flowed out of the overflow and vent line to the floor, with some solution being drawn into the ventilation system and identified in the duct drain. Upon further investigation on February 3, 2023, at approximately 3:30 pm EST, it was discovered that the overflow line from the annular organic tank contained an intact rupture disc - the overflow did not allow for free flowing liquid. Therefore, the IROFS function of the overflow could not be credited in the accident sequence as documented in the Integrated Safety Analysis (ISA). The event was reported to the NRC Operations Center in accordance with 10 CFR 70, Appendix A (b) (2) - Loss or degradation of items relied on for safety that results in failure to meet the performance requirement of§ 70.61.
There was no risk of a criticality or impact to the safety of workers and/or the public as a result of this event.
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OFFIOl I k r r&& OtlkM U.S. NRC 23-019 Enclosure Background Information The Annular Waste Organic Tank was one of a number of tanks originally installed in the late 1990s as part of BWXT NOG-L's Downblending program. The program involved the dissolution and blending of foreign owned High Enriched Uranium (HEU) materials with natural uranium blendstock to produce Low Enriched Uranium (LEU) for use in the production of commercial nuclear fuel. The annular tanks were designed to contain almost 400 liters of fissile solution. The tanks are a toroidal design, approximately 13 feet in height with an outside diameter of 72 inches and inside diameter of 70 inches, which provides a favorable geometry annulus with a nominal thickness of 1.3 inches. The tanks' safe slab design was essential to ensuring the criticality safety of the Downblending process. An overpressure mechanism was required to be installed on the HEU tanks to prevent bulging of the favorable geometry annulus due to overpressurization. The HEU tanks were vented to the ventilation ductwork via an air gap to prevent the transfer of fissile solution to the ventilation system.
The Downblend program concluded in 2006. Several annular tanks were physically removed and one was removed from service and retained as a spare. Two other tanks continued to be used to accumulate low level (<0.04 g U-235/liter) liquid waste for discharge to Waste Treatment. The fifth was repurposed for interim storage of waste organic solution prior to disposal.
Safety Significance There was no actual or potential safety significance as a result of this event. The overflow and air gap are credited as IROFS to maintain the limit of "no mass (beyond contamination) flowing into ventilation duct from organic tank". The solution that accumulated in the duct drain was very low concentration and well below the U-235 mass limit for accumulations in the ventilation system . A survey of the ductwork upstream of the duct drain was performed to confirm there were no accumulations of uranium bearing materials. None of the survey points indicated a material accumulation concern. The ventilation system exhausts through the Recovery scrubber. The concentration of the scrubber discharge solution is sampled once per shift relative to a limit of 0.04 g U-235/liter. No elevated readings were reported.
The Annular Waste Organic Tank is limited to a concentration of 10 g U-235/liter, which is below the subcritical limit of 11.6 g U-235/liter, per ANSI/ANS-8.1-2014. A criticality is not possible with solution concentrations below this value.
Immediate Actions The following immediate actions were taken in response to this event:
- The Annular Waste Organic Tank was placed out of service per BWXT NOG-L's Conduct of Operations procedure on January 19, 2023 and remains out of service.
- The solution in the ventilation duct drain was sampled . The drain contained approximately 3 liters of solution with a concentration of 3.15 g U-235/liter.
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U.S.NRC 23-019 Enclosure
- The rupture disc was removed as part of the investigative process to confirm its presence in the overflow line.
- The ventilation system ductwork between the air gap and the duct drain was surveyed with a gamma survey instrument. The survey did not indicate any count rates close to an action level.
None of the survey points were elevated to a point to indicate a concern relative to the 3-gram U-235 standard.
- An initial Extent of Condition Review was conducted for the two other annular waste tanks in the Uranium Recovery area. Similar conditions were not identified. These tanks are configured differently than the Annular Waste Organic Tank. Any overflow from the other annular waste tanks is collected in columns in Uranium Recovery.
- BWXT NOG-L Management chartered an investigation team led by a trained TapRoot investigator and representatives from Uranium Recovery Operations and NCS.
Investigation Summary An investigation team was immediately established to review the event to determine the root causes and recommend corrective actions to prevent recurrence. The team researched the history of the Annular Waste Organic Tank by reviewing previous safety basis documentation, system drawings, operating procedures, Safety Evaluation Requests, NCS evaluations, and Nuclear Safety releases and conducting personnel interviews. The tank was first installed in 1999 as part of NOG-L's Downblending program. The tank was one of several originally designed to process HEU solutions. The associated SER package contained adequate drawings and process information for the Downblending application. An overpressure relief line, which included a rupture disc, was installed to prevent bulging of the tank's favorable geometry annulus. Plastic wrap was installed around the overpressure line for ALARA purposes. The tank was vented to the ventilation system using a different air gap than the one currently installed. The design relied on a "pipe-in-pipe" configuration with a catch tray to collect condensation.
The tank operated without incident until the Down blend program concluded in 2006 at which point the tank was taken out of service.
In 2011, an SER was submitted to repurpose the tank to collect waste organic solution from Uranium Recovery. The SER did not contain adequate process information, including drawings of the tank. The NCS engineer who completed the SER evaluation had no prior Downblend experience and no knowledge of the rupture disc. As a result, the NCS evaluation and safety release did not identify the existence of the rupture disc. The overflow line was observed to be present, but the presence of the rupture disc was not easily discerned.
The NCS evaluation of the Waste Organic Tank required " ... an air gap to prevent liquid backflow into the ventilation ductwork". A physical air gap between the tank vent and the ventilation line was observed to be present. The previous air gap and drip pan were replaced during the transition from the Downblend scrubber to the Uranium Recovery scrubber. The previous configuration was likely considered unnecessary since the Downblending program, which entailed the processing of high U-235 concentration solutions, had ended. The required as-built P&ID drawing of the tank did not adequately ass:c: o: ::es au: x
8FFl81slzb. W81i 8Ub.Y U.S. NRC 23-019 Enclosure capture the location of the rupture disc, but did depict the new air gap design. The tank was released and operated without incident until January of 2023.
Root Causes The investigation team identified the following primary Root Causes using the TapRoot causal analysis methodology:
- 1. Design Specifications for Ventilation System Air Gaps Need Improvement: The original air gap design relied on a "pipe-in-pipe" configuration. The design was sufficient to prevent the transfer of HEU solutions to the ventilation ductwork. The previous air gap was replaced during the transition from the Downblend scrubber to the Uranium Recovery scrubber. Due to the inadequacy of the new air gap, a small portion of the waste solution discharged from the tank was transferred into the ventilation system.
- 2. Work Package Needs Improvement: The SER for repurposing of the former Downblend Tank to the Waste Organic Tank was missing the P&ID drawing which identified the presence of the rupture disc.
The drawing was included in the 1999 Downblend SER package. Had the drawing been included with the SER, it is likely the presence of the rupture disc in the overflow line would have been identified. Adequate Process Safety Information is critical to the ability of the safety evaluators to accurately identify the process hazards and perform the hazards analysis and discipline specific safety evaluations.
- 3. Procedure Not Available or Inconvenient/or Use: An as-built P&ID drawing of the Annular Waste Organic Tank was .created following release of the tank for operation. The drawing was created without utilizing a standard for font size, symbology, etc., which led to the rupture disc being missed during the review of as-built drawing. The P&ID did not adequately capture the location of the rupture disc. Its presence was easily missed due to the small font used on the drawing.
Corrective Actions for the Root Causes are under development and, once approved by management, will be implemented prior to the restart of waste organic tank operations in accordance with NOG-L's Conduct of Operations procedure.
Extent of Condition Extent of Condition Low concentration waste organic solution was discharged into the ventilation system because of a failed IROFS (the overflow) and a degraded IROFS (the ventilation system air gap). The overflow was obstructed by an intact rupture disc and was not available. The ventilation system air gap was functional, but allowed a small portion of the waste solution to enter the ductwork. An initial Extent of Condition Review was conducted for the two other annular waste tanks in the Recovery area. Similar conditions were not identified. These tanks are configured differently than the annular waste organic tank. Any overflow from the other annular waste tanks is collected in columns in Uranium Recovery.
9PPlllsctt IJII 9ULY U.S. NRC 23-019 Enclosure The initial Extent of Condition review was followed by a broader review of other air gaps and overflows credited as IROFS for the ventilation system. No similar conditions were identified for other ventilation system air gaps and overflows credited as IROFS for the ventilation system.
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