Board Warns Unresolved Safety Issues Still Exist
Mike Nartker
WC Monitor
1/31/2014
The Defense Nuclear Facilities Safety Board this week officially closed a formal recommendation from 2010 concerning the pulse jet mixing systems to be used at the Hanford Waste Treatment Plant, but also warned that there are still related safety issues that need to be resolved. In an Jan. 28 letter to Secretary of Energy Ernest Moniz, DNFSB Chairman Peter Winokur said the Board was closing Recommendation 2010-2 due to DOE’s change in approach for resolving the WTP’s pulse jet mixing issues, which rendered the recommendation’s individual sub-recommendations “no longer relevant.” Winokur also wrote, though, that the “underlying safety-related pulse jet mixing issues remain unresolved,” such as accumulation of fissile materials at the bottom of plant vessels; hydrogen generation resultant from the accumulation of solids; solids accumulation that could interfere with control systems; and the ability to obtain representative waste samples. “The Board will continue to review and monitor the design and construction of WTP and will advise as necessary to ensure the adequate protection of the public health and safety,” Winokur wrote in the one-page letter.
Change In Testing Approach
The pulse jet mixers, located in vessels in the WTP’s Pretreatment and High-Level Waste facilities, are intended to ensure that the waste taken from Hanford’s underground tanks remains in solution as it moves through the plant. The mixers’ operation has been described as working akin to a turkey baster, with the waste repeatedly pumped up and shot back down to prevent solids from settling at the bottom of the vessels. Such settling could pose criticality and hydrogen generation concerns—an issue previously raised by the DNFSB. In its 2010 recommendation, the Board said that the testing performedup to that point on the WTP mixers “has been insufficient to establish, with confidence, that the pulse jet mixing and transfer systems will perform adequately at full scale” (WC Monitor, Vol. 21 No. 55).
To help fully resolve the pulse jet mixing issues, DOE had previously planned to conduct a large-scale testing program. In late 2012, though, the Department announced it was changing its approach to instead perform “full-scale testing” of the vessels of concern and their associated pulse jet mixing systems. “This change in strategy is being done to provide a higher level of assurance that the vessels will meet their mixing functions compared to the current plan which uses computational fluid dynamic modeling or testing at smaller scales,” then-Secretary of Energy Steven Chu said in a message to DOE employees (WC Monitor, Vol. 23 Nos. 49&50). In a letter sent last fall to the Board, Deputy Energy Secretary Daniel Poneman wrote, “Pursuant to the revised technical approach, nuclear safety issues (i.e. criticality and flammable gas release) will be resolved by analysis and testing, if needed, and P JM control issues will be addressed by testing. These concerns are projected to be resolved during Fiscal Years 2014 and 2015.”
In a written response late this week, DOE Office of Environmental Management spokeswoman Candice Trummell said the Department is working to further refine its testing plans. “The Department appreciates the continued technical insight and support of the Defense Nuclear Facility Safety Board (DNFSB) in resolving the remaining technical issues associated with the Hanford Waste Treatment and Immobilization Plant (WTP). The Department is working closely with its contractor to identify methods to streamline and optimize the testing of the pulse jet mixed vessels. We will continue to work with the DNFSB to identify the path forward, and resolve the technical issues associated with the WTP in preparation for safe and effective tank waste treatment operations,” Trummell said.
