Determination of burn-up of irradiated thoria using TIMS

The Indian nuclear fuel cycle aims at the large scale utilization of thorium for the sustained growth of nuclear energy in the country. This implementation of Th fuel cycle requires development of new technologies including post-irradiation studies. Burn-up is one such important parameter and it is defined as the atom percent fission of heavy elements (mass >225) during the life of the fuel in a reactor. The experimental data with high accuracy on burn-up is essential to develop the computer codes for thoria-based fuels as well as it helps in evaluating the performance of the fuel in the reactor. The procedure for the experimental determination of burn-up involves the determination of the total heavy-element composition after irradiation and the concentration of a fission product in the irradiated fuel that can be related to the total number of fissions in the fuel. Isotope dilution mass spectrometry (IDMS), being a very accurate and sensitive method, was utilised for carrying out these measurements. The advantages of this method such as low limits of detection and non-essentiality of quantitative recovery reduce the problems associated with handling of radioactive samples. Stable fission product 148Nd was chosen as the monitor for determining the burn-up of thoria-based fuel