Computed neutron spectra and dose distribution in the ion-chamber basket of Dhruva reactor

The neutron spectra in the ion-chamber (IC) basket of Dhruva reactor have been computed, adopting a hybrid approach, using ANISN code to study the transport of neutrons up to the region of interest and employing MORSE code to track them in the more complicated geometry region of the IC basket. ICRU based fluence-to-dose conversion factors are used to obtain the neutron dose distribution. A neutron dose of 500 rads per 100 Mwd of reactor operation is obtained in the paraffin used in the IC basket. Assuming a limiting dose of 108 rads for 25 per cent radiation damage in paraffin and the contribution of gamma radiation to the total dose to be twice that of neutrons, the irradiation period for paraffin to attain the limiting dose is estimated to be about 180 years. Further work is in progress to obtain the gamma dose distribution. 5 refs., 9 tables, 10 figures. (author)