Neutronic Analysis to Replace Cobalt Radioisotope Facility by Iridium Radioisotope Facility at ETRR-2

Abstract

The Egyptian Second Research Reactor (ETRR-2) is a pool-type reactor, 22 MW thermal, with 27 fuel elements loaded with 60Co production facility in the most relative highest flux position for the production of 200 Ci/g specific activity. The production of this specific activity needs a very long irradiation time and continuity of operation to produce useful quantities of 60Co over a reasonable period, which means that the reactor would have to operate 24 h a day, for 5 to 7 days a week. This requirement for the production of cobalt with the required specific activity is difficult to meet in ETRR-2, so this position needs to be reused for the production of other radioisotopes that require shorter irradiation times compared to cobalt. Iridium-192 is the most important radioactive isotope of iridium; it can be used in the production of “sealed sources” for industrial or medical applications. In this study, we did a full neutronic analysis of the ETRR-2 reactor core with iridium and with cobalt and compared both cases. We used two different models: a model using the MCNP code (Monte Carlo Neutron Photon), and another model using the WIMS/CITVAP code (a deterministic code). The models were validated with the results of the experiments done during the commissioning of the radioisotope production facility. We concluded that 500 g of iridium could be used instead of 577 g of cobalt in the core, and 24 molybdenum production plates would fulfil the fixed experiment design criteria, which is lower than 1200 pcm. The average axial/radial flux inside the tube was lower when using iridium disks than when using cobalt pellets because of the difference between the neutron absorption cross sections of 191Ir, 193Ir, and 59Co. When comparing the average radial flux inside the irradiation position near the edge of the iridium pellets inside the tube, we found that the flux would be higher for iridium than cobalt because of the empty part of the tube. We also calculated the power peaking factor over the whole core and found it was 2.12, which fulfilled the design criteria (must be less than 3).