HEAT DEPOSITION RATE MEASUREMENTS USING A GRAPHITE QUASI-ADIABATIC CALORIMETER AND THERMOLUMINESCENT DOSIMETERS IN A FUSION ENVIRONMENT OF THE LOTUS FACILITY

Heat deposition rate measurements are made by an extremely sensitive q uasi-adiabatic graphite calorimeter and thermoluminescent dosimeters ( TLDs) in the fusion environment of the LOTUS facility. The response of a bare calorimeter and the response inside a large graphite cylindric al block are measured by irradiating with a mixed neutron and gamma fi eld of the Haefely neutron generator. The reproducibility of these mea surements is found to be better than 1% for a dose rate more than 60 c Gy/min and better than 3.8% for dose rates in the range of 6 to 60 cGy /min. The heating rates are found to vary linearly with neutron source strength. The calculation to experiment (C/E)for the bare calorimeter is found to be 1.05, whereas inside the graphite block, C/E varies fr om 1.11 to 1.32. These measurements are analyzed by the MCNP Monte Car lo neutron and photon transport code using the BMCCS2, PHOTXS2, and EL 2 cross-section libraries. The influence of wall-returned neutrons and gammas is found to be negligible.The origin of the discrepancies is f ound by measuring the gamma component of the heating at identical loca tions by conducting special geometry irradiation using several TLDs-70 0. The conditions that are employed considerably simplify the transfor mation of the TLD results to that of the graphite medium. A detailed d ata treatment is done with the TLD outputs to arrive at the gamma heat ing component at different locations in the graphite by employing the Burlin theory. The gamma production is found to be well represented in the calculations. On the other hand, measured and calculated net nucl ear heating in the graphite differ considerably. A downward revision o f the neutron kerma factor would be desirable.