One of the Defense Nuclear Facilities Safety Board’s top concerns in the Department of Energy nuclear weapons complex is the potential for a thermal runaway incident in Area G, the hazardous waste storage area at the Los Alamos National Laboratory (LANL) in New Mexico. Although the risk may be somewhat mitigated by recent measures taken or planned, DNFSB in its latest annual report to Congress lists among its “highest priorities” several significant safety issues in Area G.
LANL’s Area G was cited by the DOE Accident Investigation Board for multiple safety deficiencies in the wake of the 2014 thermal event at the Waste Isolation Pilot Plant, which was linked to a waste container that originated at the laboratory. The transuranic waste storage facility has been closed for more than two years, and is due to reopen in December. Not least among the failures, according to DOE’s Phase II accident report, was that waste handlers “did not identify the increased likelihood of previously analyzed accident scenarios for drums containing treated nitrate salts and that adequate controls may not be in place.”
“Since 2014, the Los Alamos contractor has declared four Potential Inadequacies of the Safety Analysis (PISA) at Area G, all of which remained unresolved at year’s end,” according to the DNFSB report on March 30. “These unresolved PISAs included the potential for a release event similar to the one that occurred at the Waste Isolation Pilot Plant (WIPP) on February 14, 2014.”
On March 21, LANL published a scientific evaluation of the “Likelihood of a Thermal Runaway for Nitrate Salt Containers in Storage” at Area G. Of roughly 3,500 transuranic waste containers stored above ground in Area G, these are 60 isolated and closely monitored containers, the remainder of the improperly treated drums of nuclear waste products from the same batch as the one that spewed open at WIPP. Transuranic waste includes plutonium-contaminated objects and radioactive materials produced in plutonium recovery operations for the nuclear weapons program.
To know how best to treat and handle the potentially vulnerable containers, the LANL investigators set out to quantify the risks of another violent breach. “One of the most obvious dangers is a repeat of the original violent reaction, which would endanger nearby workers, not only with radioactive contamination, but also with large amounts of heat, dangerous gases and the physical dangers associated with a bursting drum,” they wrote. “If there still existed a high probability of violent reaction, then these drums should only be accessed remotely.”
In order to quantify the risk, the investigators made a number of assumptions, including that the chemical contents of the container were relatively evenly mixed, that the chemical reaction would obey a proportional rule of thumb related to energy and temperature, and that the container would not be subjected to additional spikes of heat.
These caveats were considered necessary to narrow the parameters of the study and because they addressed elements of uncertainty that could not be taken for granted. The consistent mixture of the contents, for example, could not be ascertained in the sealed containers. Similarly, the “rule of thumb” might not apply under exceptional circumstances, including a container of uneven mixtures. A spike in heat, although definitely an issue in the larger picture that includes the threat of wildland fire at Area G, would nevertheless be extrinsic to the chemical energy inside the container that causes the eruption.
According to the monograph’s conclusion, a computational model of the drum was programmed and tested for a range of parameters that included the caveats, leading to a “beyond extremely unlikely” probability for an uncontrollable reaction. Nevertheless, the study makes two suggestions with added emphasis: “that the current LANL nitrate drums be protected from any additional increases in temperature,” as well as a very strong recommendation “that any processing of the LANL nitrate drums take place with the drums cooled to at least 10 degrees C,” or 50 degrees Fahrenheit.
Monitoring for the presence of specific gases that could be detected in advance of an exothermic reaction should also provide an advance warning, the authors advised.
The DOE’s LANL Environmental Management Field Office said in a statement that the canisters of nitrate salt waste at issue are stored at “less than 75 degrees F to ensure that there is no possibility of a heat buildup within any drum.” Asked if it was crucial to keep the waste at a temperature of 10 degrees Celsius during processing, the office replied, “We are studying a range of different treatment options, including dropping the temperature of the waste during processing. Keeping the waste cool adds a measure of safety, since any chemical reactivity would be slowed due to cooling.”
The danger of a thermal reaction ties into another question the DNFSB addressed during March 22 public hearings in Santa Fe regarding the risk of wildfire at the lab. All the hazards related to the safety deficiencies reported at LANL “are magnified in the event of a wildfire of the type to which Los Alamos has been historical susceptible,” the safety board reported to Congress. Under the circumstances, a spontaneous eruption could both cause or be caused by a wildfire.
Meanwhile, in a package of recently released site reports, DNFSB has reported a bustle of safety activity at Area G, focused on Dome 375, a modular structure built by Permacon, in which the 60 isolated containers are stored in a monitored, environmentally controlled environment. Deadlines have been set for venting the remediated nitrate salt drums, another way to reduce chemical pressures that could cause a runaway event. A supplemental chiller has been commissioned for the dome, with operating procedures due this month. These improvements, which include significantly increasing fire breaks and decreasing a zone of shrubbery near the dome, come at a time when fire hazard warnings have heightened.
On March 31, LANL officials notified the New Mexico Environment Department that high winds had damaged a power pole in Area G two days earlier. While power distribution to parts of Area G was interrupted, power to Dome 375 was not affected when the pole was taken out of service, but the next day an outage to the entire area occurred while repairs were made. Before that interruption, controlled entry to Area G was allowed and temperature, visual, and routine sampling measurements were accomplished.
Another problem is the remaining 3,500 canisters of waste at Area G, some 2,000 of which will have to be remediated prior to shipment to WIPP. This stockpile was of concern to safety experts and regulators even before the latest signs of risk magnification. According to another new report, an annual performance review for Area G, current plans call for disposal operations at Area G to cease by October 2017. “It is assumed that the closure of MDA G will mark the end of pit disposal at Area G,” the report says, referring to the practice of disposing of low-level wastes and hazardous wastes in trenches to be covered over. Processing of future wastes will take place in the new TransuranicWaste Facility, which is currently under construction about a mile northwest of Technical Area 54 in which Area G is located.
In February, DNFSB field representatives passed along a few glimpses of LANL’s Enduring Mission Waste Plan, which was prepared for the NNSA Field Office. The volume of TRU waste at that time was approximately 17,900 55-gallon drums, estimated to require 270 above-ground and 730 below-ground shipments to WIPP. The plan also forecasts an additional 6,950 drum equivalents of new waste during fiscal years 2015 through 2021, which could be transported in 315 shipments to WIPP.
With no place to permanently dispose of the transuranic waste and an accumulating backlog until WIPP reopens, the area might not meet the 2017 deadline for closure, which would impact other areas of the laboratory where wastes are being created or temporarily stored. As unanticipated wastes mount, waste must either be shipped off-site or become an additional burden on current temporary storage areas.
The EM Field Office at LANL was asked for information on how shipments to WIPP would be prioritized in relation to the inventories from DOE sites around the country, if the depository opens later this year as planned. “The Department of Energy is in the process of working with impacted TRU waste generator sites to develop a plan for prioritizing waste shipments to WIPP,” DOE said.