WorldWide Drilling Resource

34 AUGUST 2022 WorldWide Drilling Resource® Researchers Dig for Answers about Salt and Radioactive Waste Adapted from Information by Sandia National Laboratories Scientists from Sandia, Los Alamos, and Lawrence Berkeley national laboratories began the third phase of a years-long experiment to understand how salt and very salty water behave near hot nuclear waste containers in a salt-bed repository. Salt’s unique physical properties can be used to provide safe disposal of radioactive waste, said Kristopher Kuhlman, a Sandia geoscientist and technical lead for the project. Salt beds remain stable for hundreds of millions of years. Salt heals its own cracks and any openings will slowly creep shut. For example, salt at the Waste Isolation Pilot Plant (WIPP) outside Carlsbad, New Mexico - where some of the nation’s Cold War-era nuclear waste is interred - closes on the storage rooms at a rate of a few inches a year, protecting the environment from the waste. However, unlike spent nuclear fuel, the waste interred at WIPP does not produce heat. To understand the behavior of excavated salt when heated, scientists have been conducting experiments 2150 feet underground at WIPP in an experimental area more than 3200 feet away from ongoing disposal activity. They also monitor distribution and behavior of brine, or saltwater, found within the salt bed left over from an evaporated 250-million-year-old sea. The small amount of brine found in WIPP is ten times saltier than sea water. The third phase of the project began in late 2021. The team is drilling a new array of nine heated boreholes, building on what they learned in prior phases of the experiments. “The first two phases involved a lot of equipment testing; some [have] failed, and some [were] sent back to the manufacturer,” said Melissa Mills, a Sandia geochemist. “We’ve also learned to keep back-up equipment on hand because salt dust and brine destroys equipment. We need to doubleseal things because the brine can seep down insulated wire, and then equipment dies. It’s been a process to learn how to work in the salt environment.” Kuhlman agreed. “Many things can go wrong when you take sensitive lab equipment and put it in a salt mine. We went back and read the reports from the WIPP experiments in the 80s. We want to learn from the past, but sometimes we have had to make our own mistakes.” Researchers are collaborating with international partners to use data from this project to improve computer models of the complex chemical, temperature, waterbased, and physical interactions taking place underground. This will improve future modeling of nuclear waste repositories globally. Ultimately, the team would like to scale up to larger and longer experiments to obtain data relevant to future salt repositories. This data, supplementing already collected data, would inform repository designers and policymakers about the safety of permanently disposing heat-generating nuclear waste in salt repositories. Researchers Melissa Mills and Kristopher Kuhlman peer through a salt sample from the Waste Isolation Pilot Plant experimental site. ENV