INTERNAL DOSIMETRY FOR URANIUM FUEL MANUFACTURE AT BNFL

At its Springfields Works, near Preston, UK, BNFL manufactures uranium fuels and fuel intermediates, in a range of chemical and metallurgical processes. Uranium ore concentrate is converted to uranium metal for the Magnox reactors, uranium hexafluoride (UF6) to uranium dioxide (UO2) for AGR and other oxide reactors, and various intermediate products are produced to meet customer requirements. Thus, uranium compounds with biological retention periods ranging from days (UF6) to years (UO2) are handled on multi-hundred, or thousand, tonne per year scales. Control and minimisation of workforce exposure is exercised primarily by engineered methods (e.g. total enclosures and high integrity plant), backed up by use of respiratory and other protective equipment. A high profile is given to good standards of housekeeping. Assessment of intake is by methods approved by HSE (NII) in the Approved Laboratory Statement on internal dosimetry. The principal method is assessment by use of continuous air sampling combined with occupancy. This is backed up by routine personal air sampling (PAS) in selected relevant areas in which ceramic UO2 is handled. Further assurance is provided by programmed PAS in other areas and by systematic, and routine, urinalysis and whole-body monitoring of all relevant members of the workforce. The results of the above are presented in detail. In summary, average internal dose for 1992 was 1.4 mSv compared with 2.3 mSv in 1986. Additionally, in the areas of highest dose (the oxide plants) average internal doses now range from 4.6 to 5.8 mSv (1992), compared with 6.8 to 10.6 mSv (1986). Reductions of a similar order have been made in the Uranium Casting Plant which, in former years, was another area of relatively high dose. These results demonstrate the Site's commitment to dose reduction wherever it is justifiable on ALARA principles.