Liquid level measurement in high-level nuclear waste slurries

The U.S. Department of Energy has built and will operate a facility to vitrify high-level nuclear waste (HLW) at the Savannah River Site (SRS). Much of the HLW at SRS is in the form of a sludge slurry. The Defense Waste Processing Facility (DWPF) will solidify nuclear wastes by immobilizing the wastes in durable borosilicate glass. Early in the development of the DWPF, dip tube bubblers were used to measure liquid level in the sludge processing vessels; however, these bubblers plugged while performing this service. Level probes must be made of special material to survive the corrosive, erosive, and highly radioactive nature of the slurry. An extensive search was conducted to locate a liquid level measurement technology that would meet the demanding accuracy requirements and survive the harsh operating environment. The results of this search yielded a pneumatic 1:1 pressure repeater as the alternative. Statistical analysis has shown the accuracy of the liquid level measurement system after correction to be within ±0.3% of full scale in water. Extensive research has shown that the response of these sensors does not change significantly over time in this application. Tests were done with pressure cycling, radiation exposure, and simulated use. This liquid level technology has been in service for more than a year in a one-tenth scale pilot vessel with no serious problems