Calorimetric measurement of afterheat in target materials for the accelerator production of tritium

Abstract

The estimate of afterheat in a spallation target of lead (Pb) or tungsten (W), by calorimetry, is the purpose of this experiment in support of the Accelerator Production of Tritium (APT). Such measurements are needed to confirm code calculations, these being the only practical way of gaining this type of information in a form suitable to aid the design of the APT machine. Knowledge of the magnitude and duration of afterheat resulting from decay of activation products produced by proton bombardment of the target is necessary to quantify APT safety assumptions, to design target cooling and safety systems, and to reduce technical risk. Direct calorimetric measurement of the afterheat for the appropriate incident proton energies is more reliable than the available alternative, which is indirect, based on data from gamma-ray spectroscopy measurements. The basic concept, a direct measurement of decay afterheat which bypasses the laborious classical way of determining this quantity, has been demonstrated to work. The gamma-ray energy given off by the decay products produced in the activation of lead or tungsten with high-energy protons apparently does represent a significant fraction of the total decay energy. A calorimeter designed for measurement of isotopes decaying by alpha emission must be modified to reduce energy lost with escaping gamma rays. Replacement of the aluminum liner with a tungsten liner in the SSC measurement chamber resulted in a 270% increase in measured heat, proving that the energy loss in the earlier (1992) measurements was significant. Gamma-ray measurements are needed to confirm the gamma-ray absorption calculations for the calorimeter to determine the correction for loss of heat due to transmission of high-energy gamma rays through the calorimeter walls. The experiments at BLIP have shown that calorimetry can be a useful tool in measuring the afterheat in APT target materials.