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Radioactive Waste

Author: Dr Kelvin Klemm

( Article Type: Explanation )

Radioactive waste covers a spectrum from very low-level waste to very high-level waste and there are different challenges to be faced at the two ends of this spectrum. Low-level waste includes items such as gloves, syringes and cotton wool that have been used in the radiotherapy department of a hospital. By law all such items used in radiotherapy are assumed to be potentially radioactive even if they are not. These items have to be disposed of in a waste disposal process that is strictly controlled by law. Generally there are large quantities of low-level waste produced in a busy radiotherapy department in a hospital, which easily accumulates to a number of drums of waste per day. This whole process presents management and control problems because it is relatively easy for gloves or similar items to be accidentally disposed of outside the official waste process, unless strict control is exercised at all times.

A rather different type of challenge faces the issue of very high-level waste. High-level waste is typically spent fuel elements from a nuclear reactor. In contrast to low level waste there are very small quantities of high level waste produced, but the high level waste is very radioactive and if a human being came in direct contact with unprotected high level waste, it would be lethal. High-level waste is also controlled by a disposal process that is strictly controlled by law. A potential problem often cited in relation to high-level waste is its long life. The intensity of a source of radiation is measured by a term called half-life. As radiation intensity dies down it does so rapidly initially and then more slowly as time passes. This is the principle of the half-life measurement. A short half-life material (which could have a half-life measured in seconds) could be highly radioactive for a day, but can then have died off to a low intensity after a week. Some materials have half-lives measured in years, and will stay radioactive for thousands of years.

As a result, most countries now have disposal policies that stipulate that any radioactive waste placed in safekeeping in a repository must be able to be picked up and moved to another place in the future, should this ever become necessary. In years gone by some radioactive waste was sealed into concrete blocks and then disposed of in the sea. This is now considered an irresponsible way of dealing with such waste.