FAQs

Uranium-235 and cobalt-60 are both radioactive, insoluble metals.

Naturally occurring radioactive uranium-235 is extracted from the uranium ore mined for use by the nuclear power industry. This process leaves behind 'depleted uranium' (depleted of uranium-235) that is still radioactive but at a lower level than in nature. The density of depleted-uranium is 1.7 times that of lead. Because of its extremely high density it is used to trim the balance of commercial aircraft and it makes a very effective shielding for containers used to transport radioactive material. The depleted uranium is encased in steel as part of the container design, and in this form it is a benign material that emits much less radiation than the mined ore.

Cobalt-60 is a man-made radioisotope that is made for two principal applications in medical sterilization and cancer therapy. It is made by putting natural cobalt metal (cobalt-59) in a nuclear reactor to convert it to radioactive cobalt-60. It takes 5¼ years for 50% of the resulting radioactive cobalt-60 atoms in a sealed source to decay to non-radioactive nickel-60. After 50 years 99.9% of the original cobalt-60 has converted into non-radioactive nickel.

REVISS transport containers are large well-shielded flasks weighing 3.5 to 14 metric tonnes, which are used to transport sealed radiation sources from the point of manufacture to our warehouse and on to our customers. They use heavy lead or depleted uranium to shield the environment from gamma radiation. They are robustly designed to international standards, to withstand potential accident conditions. Part of the design process is to test by dropping them from a height of 9m at a temperature of -200°C onto a steel spike on a concrete floor. In transit they are bolted onto a truck base. They cannot be breached in normal use or road accident conditions and they are never left unattended outside the REVISS warehouse. They are opened under water to shield the operator from gamma radiation emitted by the sealed sources contained inside. Once the sources are removed from the container it is safe to handle the container without special procedures.

In the UK the average natural background dose of radiation that we all absorb each year is 2,500 units (micro-sieverts). This comes from natural cosmic and terrestrial emissions, medical treatments, food and radon emissions from granite. The contribution to the total from the nuclear industry is less than 10 units. Compare this with up to 20 units per hour that we absorb from cosmic emissions on a transatlantic flight or the 5 units we receive in a routine dental x-ray. Specialist medical diagnostic treatments deliver much higher doses: 1000 units from a CT-scan of the head, and up to 10,000 units from a barium meal. REVISS employees in everyday contact with sealed sources absorb an additional dose equivalent only to the UK natural background levels.