Lesson Learned Statement:Differences between field conditions and laboratory simulation of field conditions when mixing reactive wastes must be minimized and thoroughly understood.Discussion:On 12/01/98 acid and base solutions stored as fissile materials were being bulked into a 55-gallon drum of uranyl nitrate solution, an apparent chemical reaction occurred in the drum and caused a spill of approximately 2-3 liters of material on the floor.Analysis:The scope of work being performed when the event occurred, was the bulking of fissile acid and base solutions with depleted uranyl nitrate solution. Work Instruction SO-WI-061, “Bulking Fissile Acid and Base Solutions in Vault 2A with Uranyl Nitrate Solution, Drums 58-67” was the work controlling document for this activity. Those performing this activity adhered to Work instruction requirements. Compatibility testing according to an established bulking plan using small amounts of solutions in appropriate proportions was performed prior to initiation of the scope of work. Results of these tests revealed off-gassing and foaming when some solutions were added to uranyl nitrate solutions. In cases where off gassing produced trace amounts of cyanide and/or chlorine gas (below limits), chemical treatment of the solutions was performed as an added precaution to eliminate cyanide and chlorine gas. This chemical treatment was performed prior to bulking activities per Work Instruction SO-WI-060, “Pretreating Liquid Fissile Wastes to Inhibit Cyanide and Chlorine Off-Gassing During Downblending”. The approach was to eliminate cyanide first, allow residual hydrogen peroxide to decompose, and then add sodium thiosulfate to destroy residual hydrogen peroxide and to convert free chlorine when it forms during downblending into salt. The scope of work was for 10 drums of uranyl nitrate solution to be bulked with fissile acid and base solutions per the bulking plan. The 10 drums were segregated from an original population of 67 drums because laboratory compatibility tests for these 10 drums demonstrated off-gassing and foaming, whereas the other 57 drums did not. The bulking of one drum involves the pumping of fissile acid and base solutions from carboys into a 55-gallon drum of uranyl nitrate solution. For the 10 drums, the least amount of carboys to be transferred to a single drum is 6, with the most being 14 carboys. When the spill occurred, eight of eight carboys of fissile solution planned for transfer had been transferred to the 55-gallon drum of uranyl nitrate solution. This was the second of ten drums covered by this scope of work. The third, fourth, and fifth carboy emptied into the 55-gallon drum demonstrated chemical reactions in the lab tests. The spill occurred after the eighth carboy was added to the drum. The eighth carboy demonstrated no chemical reaction during lab testing. Before and after each carboy transfer to the drum, the solution in the drum is agitated with an electric agitator. Two chemical operators were performing the bulking activities when the spill occurred. Contents of eight carboys to be transferred had been transferred and agitation had been initiated for approximately 2 seconds when the chemical reaction expelling material from the drum occurred. Operators noted, after addition of the third carboy, a fog in the drum and a color change of the solution in the drum. Bubbles the size of match heads were also noted after addition of the third carboy. The operators described the reaction as that of a balloon bursting underwater. Approximately 2-3 liters of material was expelled from the drum. Initially, in the first few seconds the material expelled approximately 3” above the drum top and it briefly spurted from one bung hole, hit the bottom of the agitator approximately 6” to 8” above the lid. The spray deflected downwards and onto the drum top and onto the floor. The flow quickly subsided and ceased to overflow the drum after approximately 20 seconds. There were 3 to 3 1/2” of freeboard in the drum after the eight carboys had been added. The operators left the transfer station immediately when the spill occurred. The agitator was turned off as soon as the reaction was realized. The responsible supervisor immediately notified the plant shift superintendent (PSS), Criticality Safety, and the DOE Facility Representative. Access to the area was controlled until Industrial Hygiene (IH) determined it was safe to reenter the area. Health Physics surveyed the operators and found one anti-contamination (anti-C) booty to be contaminated. There was no skin or work clothing contamination. This event occurred in a High Contamination Area. Operators performing the transfer chose to wear air-supplied respirators with egress cylinder during the transfer of all eight carboys for this drum. Wearing of supplied-air respirators was mandatory for carboys three, four, and five. Operators wore long-sleeve neoprene gloves, chemical apron, anti-C coveralls and booties. An eyewash/safety shower was located in the work area. All personal protection equipment (PPE) was in place per the work instruction and the radiation work permit (RWP). The bulking worksheet for this transfer incorrectly listed the third, fourth, and seventh carboys as demonstrating observable chemical reactions in the laboratory. The bulking worksheet should have listed the third, fourth, and fifth carboy as potentially reactive. This error was not related to the event. Temperature was monitored during the transfer. Temperature of the drum during the transfer of the eight carboys ranged from 500F to 520F. The temperature of the drum 10 minutes after the reaction was 580F. Ambient temperature in the area was about 560F. Operator cited that holding a chemical resistant diaper over one of the bungholes of the receiving drum provided protection from material expelled from the drum. It was speculated that the combination of lower temperatures, lack of constant agitation, a lack of sweep gas, short waits between addition of material, and the presence of carbonates from bases may have caused a build up of carbon dioxide in the material that caused the spill when the build-up of the gas was released from the solution by agitation. Criticality safety provided steps for cleanup of the spilled material. Cleanup was to be performed the day after the critique. It was decided this event would be documented and issued as a lessons learned. A meeting was scheduled for the following day to initiate an action plan to minimize recurrence of this type of an event when work restarts.Recommended Actions:Differences between field conditions and laboratory simulation of field conditions when mixing reactive wastes must be minimized and thoroughly understood. The preliminary compatibility testing in the lab should emulate as close as possible actual conditions to be encountered in the field (i.e., ambient temperature, agitation, etc.) and vise versa. Take steps to provide continuous agitation during bulking and ensure sufficient freeboard is maintained in the bulking container to contain material during off-gassing events. Upgrade PPE for potential exposure to drum liquids.Originator:Bechtel Jacobs Company, LLC E. J. Lavender, (423) 576-4620 Performance/Quality AssuranceValidator:Brad A. McKeehan, (423) 241-5077Contact:Joanne E. Schutt, (423) 574-1248Name Of Authorized Derivative Classifier:Name Of Reviewing Official:Priority Descriptor:Blue / InformationKeywords:CHEMICAL REACTION, BULKING, DOWNBLENDING, SPILL, LIQUID FISSILEReferences:Critique Summary CR-98-032 "Liquid Fissile Bulking Operation Spill in Vault 2A"Information in this report is accurate to the best of our knowledge. As means of measuring the effectiveness of this report please use the "Comment" link at the bottom of this page to notify the Lessons Learned Web Site Administrator of any action taken as a result of this report or of any technical inaccuracies you find. Your feedback is important and appreciated. DOE Function / Work Categories:Environmental RestorationISM Category:Hazard:Personal Injury / Exposure - Airborne MaterialsPersonal Injury / Exposure - Hazardous Material (General)
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