Like other specialists studying the root causes of corrosion and degradation in nuclear waste storage materials, Frankel isn’t content to kick the can down the road. Instead of waiting for the leaks to get worse or for governments to finally decide to permanently store the waste, these scientists are investigating how to recognize and predict damage to nuclear waste storage containers and how to control it to safeguard people and the environment. In Hanford alone, more than 200 million L of this waste still sits after many decades in underground tanks waiting to be processed, according to Thomas M. Brouns, who leads the environmental management sector at nearby Pacific Northwest National Laboratory (PNNL). About one-third of the nearly 180 storage tanks, many of which long ago outlived their design lives, are known to be leaking, contaminating the subsurface and threatening the nearby Columbia River. Another 136 million L of the stuff awaits processing at the Savannah River Site. “Vitrification of nuclear waste seems to be well established by now, but actually it still faces complex problems,” says Ashutosh Goel, a materials scientist at Rutgers University. The plan at Hanford, for example, calls for entombing nuclear waste in borosilicate glass and encasing the glass in stainless-steel canisters. Yet the exact formulation of the glass, or glasses, is still under investigation. Open questions include the following: What glass compositions will lead to the highest uptake of nuclear waste? How suited are those glasses to vitrification? And how well will they resist corrosion after being interned for eons in a repository environment? After 1,000 years or so, Goel says, the steel canister surrounding the glass will likely corrode, and groundwater may seep in and interact directly with the glass, degrading it. “The stability of the glass in the presence of groundwater represents the last line of defense against release of radionuclides” into our environment, he adds. So scientists would like to better understand how and if glass might leach any radioactive materials locked inside. Whether groundwater degrades the glass enough to cause it to release its radioactive cargo depends on several processes, experiments have shown. For alkali-borosilicate glasses, a well-studied family, the degradation steps would include ion exchange between ionic species in the water and alkali ions in the glass; hydrolysis of silica, boria, and other chemical groups that compose the glass network; and dissolution and release of glass components into solution or onto the surface of the reacting glass.
Chemical & Engineering News 30th March 2020 read more »