Applicable feasibility of HKED to the measurement of special nuclear material in pyro-processing products

It is essential to measure precisely the nuclear materials present in spent nuclear fuels at an engineering-scaled pyro-processing facility, such as the one constructed at KAERI (Korea Atomic Energy Institute), for safeguard purposes. However, for the realization of high proliferation resistance, the products at each pyro processing stage have nuclear materials including some actinides and fission products. These elements prevent us from carrying out precise measurements of uranium and plutonium in the processing products, which is troublesome. Although some countries are trying to develop new methods, precise measurements have not been satisfied yet. Thus, applying Hybrid K-edge Densitometry (HKED) to nuclear material measurements at a pyro-processing facility has been reviewed as an alternative solution. HKED, combined with KED (K-edge densitometry) and XRF (X-ray fluorescence), has already proven itself to be useful at the Euratom-OSL (on-site laboratory). However, the HKED used in the wet PUREX process cannot be applied directly to the pyro process because the pyro-processing products are of a solid state. Therefore, the samples taken from the products should be dissolved and diluted by nitrogen acid. In this feasibility study, HKED technology was reviewed as a precondition to dissolve some solid state samples into liquid samples. When a solid state sample of pyro-processing products is employed in an HKED measurement, the absorption of X-rays in the sample itself takes place largely because of heavy elements including U and Pu. The high absorption results in a poor uncertainty in the KED measurements, and thus a solid state sample should be dissolved and diluted to reduce the absorption. If the sample is to be transformed into a liquid state, the HKED method can be an alternative method for the measurement of special nuclear materials at a pyro-processing facility owing to the high measurement precision. Although it may be annoying to have to prepare dissolved and diluted samples, it is necessary for a more precise analysis of nuclear materials. In conclusion, it is desirable to apply HKED technology with other technologies to the measurement of pyro-processing products for a high degree of confidence and for transparency of nuclear material management.