Economical Radioisotope Power

In the Phase I NIAC grant, the CSNR has evaluated the feasibility of using a low power, commercially available nuclear reactor to produce 1.5 kg of Pu-238 per year. The impact on the neutronics of the reactor have been assessed, the amount of Neptunium target material estimated, and the production rates calculated. In addition, the size of the post-irradiation processing facility has been established. Finally, as the study progressed, a new method for fabricating the Pu-238 product into the form used for power sources has been identified to reduce the cost of the final product. In short, the concept appears to be viable, can produce the amount of Pu-238 needed to support the NASA missions, can be available within a few years, and will cost significantly less than the current DOE program. The alternative method to produce Pu-238 is to continuously flow an encapsulated aqueous solution containing a high concentration of dissolved Np-237 in a water carrier stream. Once the optimum irradiation period is completed, the encapsulated target slowly moves through the reactor's water tank which allows for time for the decay of Np-238 to Pu-238. This process allows small quantities of Pu-238 to be processed on a weekly basis so that a much smaller, and less costly, facility is needed to accumulate the Pu-238. One other aspect that has come out of the Phase I effort is the recognition that the new process will produce a substantially smaller waste stream of radioactive acidic solution, mixed waste, which has to be stored or processed. Thus, the method will produce substantially reduced costs. In addition to the technical assessment of the production, the study sought to determine the answers to two major issues: 1) given a sufficient price per kg of Pu-238, could a sufficient return on investment (ROI) be possible so that private venture would pay the up-front capital costs saving the government this requirement in times of diminished budgets, and 2) is it more cost effective to install the new reactor on private land with private operations rather than locating the reactor at a DOE facility? The results of the study indicate that a 20% ROI is possible if the price per kg paid for the material is commensurate with the last known, circa 2007, asking price from Russia. The results also show that, due to lower security and transportation costs, the only responsible option is to locate the reactor at the Idaho National Laboratory site of the DOE. The Phase I effort utilized experimentally measured neutron spectra from a 1 MW TRIGA reactor at the Kansas State University to estimate the Pu-238 production. Although several reactor types may be available for Pu-238 production, the TRIGA was used to model the production rates due to the large database regarding neutron flux and costs. By assuming a linear scaling of the neutron flux but keeping the neutron spectra the same, the production rate of the Pu-238, the concentration of Pu-236, and the amount of fission products could be calculated. The calculations show that an irradiation time of between 15 to 18 days with a 12 day decay time is optimum. Pu-236 contamination should be less than 2 ppm. The amount of fission products is estimated to be 150 gms/yr. Using an 18 day irradiation time, the production rate versus neutron flux, i.e. reactor power, was determined. The trade studies indicate that a reactor at 3.8 or 10 MW can produce 1.5 or 6.25 kgs/yr of Pu-238 respectively. If a 20% return on investment is required, i.e. if the facility is privately funded, the price of the Pu-238 sold to the DOE would have to be 10 $M/kg and 4.3 $M/kg respectively. If no ROI is required, i.e. the US government funds the facility, then the price is 4.9 $M/kg and 1.6 $M/kg for the 1.5 kg and the 6.25 kg respectively. In either case, the results of this study indicate that the 1.5 kgs/yr of Pu-238 can be produced in a new facility within a 3-4 year timeframe for around $50M and return a 20 % ROI to an investor group.