Collection and analysis of occupational radiation exposure data from the jet tokamak

Estimates of worker dose for future fusion machines have suffered from a lack of an experiential database from operating tokamaks. The need for occupational radiation exposure (ORE) experience was the motivating factor for the present study, which focused on the JET machine. This study of the JET ORE experience has started to address the above need. Much more needs to be done, however. Although preliminary, the results of this initial study are encouraging [A. Natalizio, M.T. Porfiri, JET ORE Data collection, ENEA Report FUS-TN-SA-SE-R-88, December 2003]. We have found that, on average, the machine was in the shutdown state 44% of the time; while most of the shutdown time was planned for maintenance or modifications, about 18% of the total shutdown time, on average, was due to unplanned machine interventions; it would appear about two thirds of the JET annual dose, on average, was accrued by the maintenance staff; about 15% of the average, annual worker dose was accrued during the machine operating state; annual worker doses were significantly reduced after the implementation of the ALARP policy during the 1997 tritium plasma campaign; the long-term averages of the collective and individual worker doses are low (96 and 0.153 mSv/a); and, on average, since 1997, the tritium dose has been about 2% of the total worker dose. (c) 2005 Elsevier B.V. All rights reserved.