Abstract
A gamma thermometer suitable for very high gamma heating levels (up to 20 W/g) has been designed and modelled by means of detailed finite element calculations. Based on a sensitivity analysis, the predicted accuracy of this gamma thermometer is better than 5 %. A novel miniaturized gamma thermometer is proposed in which a single thermocouple is used as the gamma absorption element, allowing a reduction of the sensor diameter down to 3 mm. Monte Carlo calculations (by MCNP) have been performed to assess the relative contribution of neutrons to the nuclear heating in a gamma thermometer. Calculations have been performed for gamma thermometers with an inner body made of various materials, such as stainless steel, tungsten, molybdenum and rhodium. By using gamma thermometers made of different materials, it will be possible to deduce the nuclear heating rates in these materials and also to separate out the neutron and gamma heating contributions. The Monte Carlo calculations show that nuclear heating of rhodium is mainly due to neutrons, converting the rhodium gamma thermometer effectively in a neutron thermometer. The sensitivities of the gamma thermometers with W, Mo or Rh as heated materials have been modelled by finite element calculations. It is found that both the Mo and the Rh based sensor have a very linear response up to a nuclear heating of 20 W/g.
Highlights
Nuclear heating measurements in material test reactors are important for various reasons
A detector with Rh as inner body material could serve as a neutron detector
The sensitivity of the SCKCEN type gamma thermometer has been calculated over the gamma heating range from zero to 20 W/g
Summary
Nuclear heating measurements in material test reactors are important for various reasons. For the design of experimental rigs, a good knowledge of the gamma heating is required in order to predict the correct irradiation temperature of samples. For power calibrations of test fuels, the knowledge of the contribution of gamma heating is crucial in order to attain the required precision. It is important to know the nuclear heating of various materials such as for tungsten, copper, graphite, chromium, etc. Discrepancies between measured and calculated gamma heating levels (such as by MCNP) have regularly been observed in the past and are partly related to imprecise nuclear data. In order to contribute to a better understanding and predictability, modified gamma thermometers (GT) containing different materials have been designed and modelled
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