Speaker
Description
In this work, we describe how experiments where the energy response function and the angular response function of a neutron REM counter were modified, led to the improvement and validation of the computational model of the TCV facility. Due to an upgrade of the plasma heating system at TCV and a subsequent order-of-magnitude increase in neutron production, an upgrade of the radiological shield was needed. The upgraded radiological shield, made from polyethylene (PE), was designed using Monte Carlo neutron and gamma transport simulations and was installed in 2023.
During the design process of the radiological shield, the attenuation coefficient of the H*(10) neutron dose by PE was measured by placing the Lupin BF3 REM counter inside PE boxes of varying thickness. However, a significant discrepancy outside the statistical uncertainty was observed when these experiments were recreated with the MCNP code. This led to the realization that a significant amount of neutron moderators is missing in the MCNP model of the device, mainly the graphite protection tiles. After their addition, the relative ratio between calculations and experiments (C/E) for stacked PE boxes decreased from the range [1, 4.5] to the range [1, 2.5].
Additionally, the computational model of the TCV facility was validated using a shaded detector setup, where the Lupin BF3 counter was placed inside the PE box with one of the 6 sides left open, which enabled us to quantify the angular contribution to the neutron dose. A good agreement between experiments and calculations was observed with C/E ratios in the range [0.75, 2.0], for 10 measurements at 5 positions across the TCV facility. We propose a method with which these measurements can be used to determine the moisture content of the TCV hall concrete, which is expected to be a large source of error in dose calculations. Finally, we justify the use of the TCV experiments and the computational model we have developed as benchmark experiments by comparing them to existing benchmark experiments in fusion devices such as the JET neutron streaming experiments.
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