Controlled use of explosive techniques in the decommissioning of nuclear facilities

The decommissioning of nuclear facilities calls for the controlled removal of activated and/or contaminated materials from the inside of biological shielding structures whilst relying on the outer layers of non-activated or contaminated material to contain the activity. This paper describes development work being carried out on the controlled use of explosives to cut and remove selected parts of biological shielding structures without impairing the overall containment integrity. The technique being developed is also applicable to other controlled cutting of concrete requirements outside the nuclear industry. The paper reviews work carried out to optimise the concrete cratering effectiveness of the explosive charges and reports on investigations carried out on concrete removal from re-entrant corners, on curved surfaces and from behind reinforcement and steel liners. Procedures for achieving a required level of material removal without impairing the remaining structure are reported. The use of explosives for the provision of charge holes is discussed together with reports on tests to assess the particle size distribution in the dust generated during blasting. To substantiate and to add credibility to the development work being carried out, analytical studies have been performed to investigate the effects of firing an explosive charge buried in a concrete mass. The paper describes analytical results from this exercise and compares the results with experimental results from field trials. (author)