High Temperature Doppler Effect Experiment for 238U at FCA, (I)

The experimental device for Doppler effect measurement was developed for the Fast Critical Assembly of Japan Atomic Energy Research Institute. The Doppler effect up to 1,500°C can be measured with this device. The experimental data is to be used for evaluating and improving the calculation method of the Doppler effect in higher temperature range. The measurement technique is based on a reactivity worth measurement with a heated sample. The device is made of tungsten for the high temperature parts and stainless steel for the other structural parts. The measurements were carried out in a mock-up core of an oxide-fueled fast reactor.In the analysis of the experimental data, the Doppler reactivity worth was calculated by a first order perturbation theory and JENDL-3.2 library. A collision probability cell code with ultra-fine group structure, PEACO-X, was used to obtain the precise effective cross sections in a pin cell model of the Doppler sample. The calculation underestimates Doppler effect by about 5% in high temperature range.The Doppler effect above 1,500°C was estimated by the extrapolation of the measured data below this temperature. When the calculated and extrapolated Doppler reactivity worths at 2,000°C were compared, a good agreement between them was obtained. The significant improvement of calculation reliability of the Doppler effect in the higher temperature range was achieved by this experiment.