IRR17 (30) - Keeping and Moving of Radioactive Substances
Published: Sep 29, 2021
Sources must be kept in a suitable receptacle and in a suitable store. Sources being moved as opposed to transported (i.e. within a site) must be in a suitable receptacle.
As noted for IRR17 (Regulation 29) a common system can be employed which meets the needs of IRR17 and the relevant environmental legislation. However, IRR17 Regulation 30 does provide some specific guidance on a suitable receptacle and suitable store.
(a) radiation shielding – it is advisable that the surface dose rate never exceeds 2 mSv / h and usually it should be much less
(b) the ability to withstand damage from normal use and foreseeable misuse or accident
(c) fire resistance
(d) prevention of unauthorised access, exposure or dispersal
Special considerations are also required where:
(a) the radioactive substance is corrosive, self-heating or pyrophoric
(b) there could be pressure build-up inside the receptacle
(c) the storage environment itself is corrosive
Pressure build-up. This can occur in aged alpha emitting sources such as encapsulated Am-241. The encapsulation means that alpha particles never escape (this source is either designed for its 60 keV gamma radiation, or is combined with beryllium to form a neutron AmBe source). As the alpha decay proceeds over many years there is pressurisation of the capsule due to helium production which is the end point of alpha particle interaction. The design of the capsule takes pressurisation into account, but an aged source in a fire could result in containment failure in a worse case scenario.
(a) protection from the weather;
(b) resistance to fire sufficient to minimise dispersal and loss of shielding, taking into account combustible materials in the vicinity and the likely temperatures that would be reached
(c) shielding to achieve the lowest dose rate that is reasonably practicable outside the store. Where non-classified persons may approach the outside of the store, it is suggested that the dose rate does not exceed 2.5 μSv per hour. A further goal would be to reduce this to < 1 μSv per hour and therefore approach background levels.
(d) ventilation for both radioactive and non-radioactive substances that have accumulated as both may be harmful. Ventilation should also be provided for a radioactive substance that has been spilt or accidentally dispersed. Ventilation may also be required for substances that emit radon gas.
(e) physical security so that access is only possible to people permitted by the employer. There may be interaction between this requirement and that of the CTSA (counter terrorism security adviser) who will work and advise on behalf of the UK environmental agencies.
IRR17 ACoP paragraph 594 states ‘… a sign prominently displayed on the outside of the store (preferably on the door) will warn people that the store may contain radioactive substances. Such signs must conform to the Health and Safety (Safety Signs and Signals) Regulations 1996…’ It is the experience of Ionactive that the size and location of such signs can cause strong debate between the HSE and Environmental regulators (the environmental regulators and their security advisers do not like advertising the location of radioactive material).