The Defense Nuclear Facilities Safety Board (DNFSB) said in a new report the Energy Department Office of Environmental Management has more work to do to resolve safety issues connected with criticality and flammable gas at the Waste Treatment Plant’s Pretreatment Facility at the Hanford Site in Washington state.
The 100-page-plus technical report centers on four areas of concern: hydrogen in process vessels, criticality in process vessels, standard high-solids vessel design, and hydrogen in piping and ancillary vessels.
The board forwarded a copy of the document to acting DOE Assistant Secretary for Environmental Management Jim Owendoff on Oct. 12.
Among other things, the board said nuclear modeling calculations used at the Pretreatment Facility don’t meet proper industry standards; certain key assumptions on criticality in process vessels don’t have necessary “technical rigor”; and there are many uncertainties surrounding “location, quantity and properties” of plutonium particulate in the Hanford Tank Farms.
The Hanford Site in southeast Washington was used during the Manhattan Project and Cold War to produce plutonium for the U.S. nuclear arsenal, leaving behind plutonium particles. Nuclear criticality safety is meant to prevent an inadvertent nuclear chain reaction.
There has already been a significant amount of back-and-forth between DOE and the DNFSB on the Pretreatment Facility when it comes to potentially explosive gases and criticality hazards.
In 2009, the board reported that stagnant waste in pipes could lead to hydrogen buildup and the risk of a potential explosion. Also, fissile material accumulation at the bottom of process vessels could create the potential for inadvertent criticality, the DNFSB has said in the past.
In January, DOE sent a letter to the DNFSB outlining progress in addressing areas such as criticality in process vessels and hydrogen in piping and ancillary vessels (HPAV). DOE cited strides on areas including hydrogen buildup in process vessels; heat transfer analysis; and the threat of unintended criticality.
While DOE considers the progress sufficient to allay safety concerns, DNFSB isn’t so sure.
The Pretreatment Facility is one of four primary sections of the WTP, which will convert up to 56 million gallons of chemical and radioactive waste at Hanford into a glass form for permanent storage. It will receive Hanford tank waste and divide it into separate streams for the Low-Activity Waste and High-Level Waste Facilities.
Under a federal court order, full operations of the WTP must begin by the end of 2036. The plant must legally begin treating Hanford’s less-radioactive low-level waste by 2023, though WTP prime Bechtel would miss out on major fees if processing does not begin in 2022.
“The Department of Energy appreciates the analysis of its work regarding proposed control strategies to address the technical issues associated with the Waste Treatment and Immobilization Plant’s Pretreatment Facility,” said a DOE spokesperson. “The report provided by the Defense Nuclear Facilities Safety Board will be reviewed, and its analysis will be taken into consideration as design proceeds at an appropriate time.”
