What is radiolysis and what does it have to do with nuclear waste?
--Wired in Winnipeg

Dear Wired:

For everyone but the nuclear establishment, radiolysis refers to a highly effective hair-removal technique that involves sitting next to a very loud radio and having body hair simply blown off your body. It was popularized by dancers at Radio City Music Hall in the 1950s.

In the nuclear establishment, where hair is relatively scarce anyway, radiolysis refers to something else: a process by which radioactivity breaks down and hence changes chemical compounds.

Radiolysis is a principal cause of certain kinds of waste management problems, notably in relation to liquid radioactive wastes and wastes containing mixtures of radioactive materials and non-radioactive chemicals. Chemicals present in the waste break down over time due to the action of radiation unless they are in very stable forms. The breakdown products in turn create new chemical reactions with each other and with pre-existing chemicals. These processes make estimation of the chemical make-up of the waste very difficult. Radiolysis of waste and organic compounds frequently results in the generation of hydrogen gas, as well as of other toxic and flammable compounds. Such radiolytic decomposition is one of the main sources of risk of fires and/or explosions in some of the high-level waste tanks at Hanford and Savannah River Site. Build-up of dangerous chemicals due to radiolysis has also affected plutonium storage at Rocky Flats, as well as TRU waste at various sites. One of the problems has been the breakdown of plastics into flammable and toxic gases by radiolysis. Radiolysis can actually render waste more hazardous over time, or it can create hazardous waste from what was originally non-hazardous waste. Furthermore, depending on the half-life of the radionuclide (and decay products), this process can continue for a very long time.

The chemical changes undergone by vinyl-chloride and polyvinyl chloride (PVC), the material used to make items like plastic containers, tubing, and car dashboards (as well as TRU waste packaging) provide an example of radiolysis that results from the production of a wide variety of chemicals. When irradiated by alpha particles, these PVC materials release gases containing molecules such as benzene, acetone, and hydrogen chloride (HCl). Such radiolysis can change the status of waste from initially non-hazardous to hazardous under the Resource Conservation and Recovery Act (RCRA), the United States hazardous waste law (see box on WIPP). Wastes can be classified as "hazardous" under RCRA either because of the specific process or chemicals used to make them or because they meet one of the four defined characteristics of "hazardous waste:" toxicity, ignitability, corrosivity, and reactivity.

If RCRA-regulated radiolysis products are created in sufficient concentrations to meet any of the four characteristics, it would render the waste hazardous under federal law. This would mean that the management and disposal of the waste would require a RCRA permit. The RCRA permit would be in addition to other permits and waste packaging requirements relating to the radioactivity of the waste.

Ghost written by Hisham Zerriffi