High conduction neutron absorber to simulate fast reactor environment in an existing test reactor

Abstract

A new metal matrix composite material has been developed to serve as a thermal neutron absorber for testing fast reactor fuels and materials in an existing pressurized water reactor. The performance of this material was evaluated by placing neutron fluence monitors within shrouded and unshrouded holders and irradiating for up to four cycles. The monitor wires were analyzed by gamma and X-ray spectrometry to determine the activities of the activation products. Adjusted neutron fluences were calculated and grouped into three bins-thermal, epithermal, and fast-to evaluate the spectral shift created by the new material. A comparison of shrouded and unshrouded fluence monitors shows a thermal fluence decrease of *11 % for the shielded monitors. Radioisotope activity and mass for each of the major activation products is given to provide insight into the evolution of thermal absorption crosssection during irradiation. The thermal neutron absorption capability of the composite material appears to diminish at total neutron fluence levels of *8 9 10 25 n/m 2 . Calculated values for dpa in excess of 2.0 were obtained for two common structural materials (iron and nickel) of interest for future fast flux experiments.

Measurement and Simulation of Thermal Conductivity of Hafnium-Aluminum Thermal Neutron Absorber Material

“…[13] Specimens were fabricated with three different volume percentages of Al 3 Hf (20, 28.4, and 36.5 pct) using a powder metallurgy technique. [14] The 28.4 vol pct material was found to be optimum from a neutronics and thermal standpoint.…”

“…The integer beside each curve corresponds to the number of irradiation cycles to which the samples were subjected. Samples were irradiated for 0 (i.e., unirradiated), 2, 3, and 4 cycles in the ATR, corresponding to 0, 1965.5, 3184.0, and 3984.6 megawatt days, [13] respectively. The error bars for the irradiated samples correspond to a systematic error of ±5 pct for each set of measurements and are due to the high sensitivity of the differential scanning calorimeter to the position of the sample within the apparatus.…”

Thermomechanical Properties of Neutron Irradiated Al3Hf-Al Thermal Neutron Absorber Materials

“…One goal of this research is to evaluate the tensile properties of unirradiated and irradiated Al 3 Hf-Al MMCs. Although the neutron absorber block is not planned for use in structural components, maintaining acceptable mechanical properties is important since spent absorber blankets will need to be periodically inspected and replaced with fresh ones [ 14 ]. The results presented here provide mechanical and thermal properties needed for component design.…”