Removing obstructions in the tanks that would interfere with retrieval operations, such as old thermocouples, presents several hazards that can be mitigated with specialized tools, techniques, and training and the use of mock-ups.
Thermocouples are temperature-sensing devices that help Hanford technicians monitor conditions inside tanks. In addition to the radiological and industrial hazards involved in removing contaminated equipment from tanks, corrosion of the 50-foot-long thermocouples creates a risk they could break apart during removal.
Earlier this spring, workers removed damaged thermocouples used to measure waste temperatures in Tanks A-101 and A-103. In these tanks, the lower sections of the thermocouples were damaged, requiring the use of cutting and clamping techniques to safely remove them.
“Various shield designs and clamping techniques were tested during planning mock-ups, which significantly mitigated the radiation hazards,” said Christine Lobos, EM tank farm facility representative. “Our overall site cleanup strategy is to focus consistently on safety of the workforce, the public, and the environment while progressing our cleanup mission.”
To protect workers, many weeks of planning and training in mock-up conditions helped before crews retrieve the contaminated equipment from the underground tanks.
“Each tank presents its own set of challenges,” said Diego Arteaga, contractor fieldwork supervisor. “The removal of the first thermocouple at Tank A-103 required a complete design of clamps due to the deterioration. Because of the training, we knew what to do and how to do it safely.”
The workers used high-pressure spray washes on the thermocouples at Tanks A-101 and A-103 to reduce some of the radiation levels. The team then cut the thermocouples into segments and lowered the corroded lower segments to the tank floor. The remaining sections were removed from the tanks, placed in shielded containers, and shipped to Hanford’s Environmental Restoration Disposal Facility for disposal.
“Multiple layers of safety were integrated into the retrieval work on the tanks,” said Arteaga. “The team showed the value of preparation when doing dangerous work and our work paid off.”