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Heat Deposition Rate Measurements Using a Graphite Quasi-Adiabatic Calorimeter and Thermoluminescent Dosimeters in a Fusion Environment of the LOTUS Facility

O. P. Joneja, M. Rosselet, A. Luethi, J. Ligou, R. P. Anand, T. Buchillier

Fusion Science and Technology / Volume 28 / Number 4 / Pages 1663-1673

November 1995


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Heat deposition rate measurements are made by an extremely sensitive quasi-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 cylindrical block are measured by irradiating with a mixed neutron and gamma field of the Haefely neutron generator. The reproducibility of these measurements is found to be better than 1% for a dose rate more than 60 cGy/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 from 1.11 to 1.32. These measurements are analyzed by the MCNP Monte Carlo neutron and photon transport code using the BMCCS2, PHOTXS2, and EL2 cross-section libraries. The influence of wall-returned neutrons and gammas is found to be negligible. The origin of the discrepancies is found by measuring the gamma component of the heating at identical locations by conducting special geometry irradiation using several TLDs-700. The conditions that are employed considerably simplify the transformation of the TLD results to that of the graphite medium. A detailed data treatment is done with the TLD outputs to arrive at the gamma heating 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 nuclear heating in the graphite differ considerably. A downward revision of the neutron kerma factor would be desirable.

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