A study prepared for the CB&I AREVA MOX Services Board of Governors states that switching from the MOX method of plutonium disposition to a downblending approach could result in a nuclear chain reaction. But the National Nuclear Security Administration (NNSA) said a criticality incident cannot result from storing downblended plutonium, and that the study isn’t credible. The feds are sticking to their belief that downblending excess U.S. plutonium, the preferred option outlined in President Barack Obama’s fiscal 2017 budget request, is the best path forward to carry out a deal in which the United States and Russia must each dispose of 34 metric tons of weapon-usable plutonium.
Energy Secretary Ernest Moniz said last year that funding the MOX method, which includes the unfinished Mixed Oxide Fuel Fabrication Facility (MFFF) being constructed at the Savannah River Site in South Carolina, is unsustainable due to its exploding costs – which he forecast at $1 billion annually to adequately fund the entire project. The DOE-led Red Team of experts backed Moniz’s assertions last summer by reporting that MOX would cost upward of $800 million annually and that downblending would cost just $400 million a year. Instead of MOX-ing the plutonium by converting it into commercial nuclear fuel, downblending would use inhibitor materials to dilute the plutonium at SRS. Then, the plutonium would be sent to a federal repository, most likely the Waste Isolation Pilot Plant (WIPP) near Carlsbad, N.M. The study and several others provided support for Obama’s backing of the downblending method in his DOE budget request.
High Bridge Associates earlier this month released a report for CB&I AREVA MOX Services, which is building the plutonium conversion plant at Savannah River. The project management specialist found that the plutonium packing in the downblending method would be crushed over time at WIPP due to the salt formation. The WIPP design allows for bedded salt to serve as a protective layer to seal off waste from the environment. The NNSA has acknowledged that, over time, this salt formation would squeeze the disposal rooms and waste. High Bridge believes the squeezing would result, at a minimum, in the release of large amounts of energy and radioactive products into the environment. “The extremely high pressures created as the salt cavern closes in on the storage drums will force the plutonium closer together, creating the geometry of crushed storage drums which facilitates a critical chain reaction,” High Bridge wrote.
But NNSA spokeswoman Francie Israeli said the Sandia National Laboratories in New Mexico, at the request of the Energy Department, reviewed the assertions of the High Bridge report and concluded that the risk of criticality issues at WIPP are unfounded. Moniz used the Sandia findings to defend downblending during a Feb. 29 U.S. House hearing, though the full study was not available until March 2. An executive summary of the study surfaced last month. Israeli said on Wednesday that even though the full study was released two days after the hearing, “Sandia’s review addresses the criticality issue that is the basis for the High Bridge report’s assertions.”
While burial at WIPP would add to the 4.8 metric tons of diluted plutonium already on site, and increase the average density of the plutonium by adding more diluted material to that stockpile, criticality of diluted and packaged Pu-239 cannot result, Israeli said. “In the presence of salt, whether as solid or brine, criticality would be virtually impossible since chlorine in natural salt is an excellent neutron absorber,” Israeli said by email. “The High Bridge Criticality Control Overpacks scenario is simplistic and not credible.”
Charles Hess, High Bridge vice president and chief nuclear officer, disputed that finding. While the NNSA argues that diluted plutonium cannot cause a criticality incident, Hess said the plutonium does not need to be separated from its inhibitor materials to cause an incident. Criticality can result from increasing the density by adding more plutonium or water, he said. “The geologic action of the WIPP salt dome will accomplish both,” Hess added.
In a separate 2015 report also commissioned by the CB&I AREVA MOX Services Board of Governors, High Bridge denounced a report from Aerospace Corp. that found the MOX method will cost $51 billion over its lifetime, compared to $17 billion for downblending. High Bridge concluded that MOX would cost only $19 billion, including the $5 billion already spent, and downblending would cost $20 billion. High Bridge argued in the report that the downblending option comes with several programmatic and security uncertainties that will drive up the cost and result in delays. The group also accused Aerospace of purposefully inflating the projected MOX cost in its assessment.
