Health physics procedures and experience on Princeton tokamaks

Princeton tokamaks have produced radiation levels of interest to health physicists since 1977. However, increases in the neutron flux and associated tritium production from deuterium-deuterium (DD) reactions have heightened the level of health physics requirements around machines such as Princeton's Tokamak Fusion Test Reactor (TFTR). The graphite tiles used within the vessel have retained tritium produced by DD operations and thereby created contamination control challenges during vessel openings. From January to July 1987, approximately 3 × 10 18 DD fusion neutrons were produced in TFTR operations. For each DD neutron produced, one would expect to see the production of one triton since the cross-sections for the D-D fusion reactions are approximately equal. This would imply 5.4 GBq (145 mCi) of tritium produced from DD reactions in 1987. Procedures for vessel entry, contamination control, removal of activated hardware from the test cell and exposure control have been upgraded to meet the changes resulting from the success of producing higher neutron fluxes. Measurements continue to be made of bremsstrahlung profiles within the test cell, general radiation levels in potentially occupied areas, and environmental baselines in preparation for the introduction of tritium as a fuel. However, the tritium produced from DD reactions already produces measurable tritium levels in vacuum pump oils, neutral beam injector boxes, the vessel itself, and within the test cell when the vessel is opened and vented to the test cell. This paper describes the increased activities of the health physics staff in providing measurement techniques, contamination control, written procedural requirements, and the radiation training instituted for ensuring the safety of the employees.