THE BIOKINETICS OF CORROSION PRODUCTS FROM A WATER-COOLED REACTOR AFTER DEPOSITION IN THE RAT LUNG

Corrosion of steels used in the fabrication of the primary cooling cir cuit of certain types of nuclear reactor results in the formation of o xide bearing debris which contains neutron activation products. These present a potential inhalation hazard during maintenance and decommiss ioning of the reactors. In this study, the biokinetics of a residue co ntaining (by activity) Cr-51 (6.8%), Mn-54 (12.7%), Co-58 (4.8%), Fe-5 9 (4.6%), Co-60 (60.2%) and Zn-65 (10.9%) have been investigated in ra ts after intratracheal instillation. Transfer rates to blood for Mn-54 , Fe-59. Co-60 and Zn-65 were obtained up to 282 days after exposure. Combination of these with the mechanical clearance rates from the alve olar region of the lung in the proposed ICRP lung model, provided esti mates of biological half-times in the lung. Predicted biokinetics in m an for Co-60, Zn-65, and Fe-59 were consistent with human data obtaine d after accidental intakes and experimental studies and hence would ap pear to validate the model used. Using the biokinetics predicted here, an Annual Limit on Intake (ALI) for the respirable residue aerosol mi xture containing a range of particle sizes of 2.5 x 10(6) Bq was obtai ned. This is 1.5 times that which would have been obtained using stand ard ICRP W and Y classifications for the material.