Nuclear waste storage in salt: Explosion danger

Nuclear Monitor Issue: 

(April 9, 1999) New evidence has been found that salt, if irradiated by nuclear waste, may become a high explosive. Professor H.W. den Hartog from Groningen University, the Netherlands, has studied the behavior of irradiated salt for 15 years. "If irradiated, salt is heated, explosive reactions occur," he said.

(508.4997) Herman Damveld - One of the scientific controversies concerning storage of nuclear waste in underground salt formations is the damage done by irradiation. If salt is irradiated by nuclear waste, it is partly converted into its elements: chlorine and sodium.
Den Hartog wanted to research this process, because much energy is released if the process is reversed. Previous research had led him to the opinion that this could possibly lead to an underground explosion. When the temperature is raised, chlorine and sodium recombine again into salt. The energy released during this reaction may cause the melting and eventually vaporization of the stored casks with nuclear waste. "At the time we did not know what triggered the explosion, but meanwhile we have proven a number of facts. First, much more salt,15 or more percent, is converted into chlorine and sodium as formerly assumed. We proved that in experiments," he states. This means that much more energy is released if the process is reversed.

A second important discovery is the fact that holes are created when the salt is converted into its two elements. The dimensions of the holes are one thousandth of a millimeter. Those holes are unstable and they will implode, Den Hartog found. This causes locally a rapid rise of temperature, which leads to a shock wave. The shock wave in its turn causes the recombination of chlorine and sodium to salt, which process liberates energy and the shockwave is further enforced.

What happens if a cask with nuclear waste, stored in a salt dome in the north of the Netherlands, explodes? Den Hartog is quite sure that the resulting shockwave might well cause the explosion of another cask. Important is that the salt would surround the casks hermetically. Shockwaves would not subdue for that reason. A salt dome would contain many casks. Virgin salt would conduct shockwaves well; one may expect effects on other casks, even at a distance of 50 meters. "The salt dome will not completely explode," emphasizes Den Hartog, "but the calculated explosive force is not small and expensive damage will be the result."
The governmental appointed Commission Storage of Radioactive Waste (CORA) ommissioned Den Hartog to do the research.
"We have to exclude that explosions will occur in salt domes. That's why I want to know the process as best as I can," concludes Den Hartog. He got the impression that not everybody is of this opinion. There are still people who want to store nuclear waste in salt domes as soon as possible.

Source and contact: Herman Damveld
Selwerderdwarsstraat 18
9717 GN Groningen
The Netherlands
Tel & Fax: +31-50-3125612