Licentiatseminarium: Segmented HPGe detector for gamma emission tomography of nuclear fuel

Vikram Rathore defends his licentiate thesis titled "Segmented HPGe detector for gamma emission tomography of nuclear fuel". The external reviewer is Prof. Peter Dendooven, Helsinki Institute of Physics.

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Gamma emission tomography (GET) is a non-destructive post-irradiation examination technique that, in recent times, has been proved to be an effective tool for spent nuclear fuel characterisation. Spent nuclear fuel characterisation is carried out to validate and evaluate the performance of the fuel. This is both necessary for the evaluation of safe operational limits of conventional reactor fuel, and qualification and licensing of the new fuel, such as for the upcoming advanced reactors.

The technique of GET is continuously being improved and applied to characterise the different properties of the spent fuel which will help in designing safer fuel. In particular, the improvement in spatial resolution of GET can help in imaging fuel rod-internal features and examination of smaller irradiated fuel samples.

In this thesis, a novel electronically segmented coaxial HPGe (High Purity Germanium) detector for GET measurements is proposed. The proposed detector aims for achieving faster examination of a fuel object with excellent spectroscopic capabilities to obtain the goal of high spatial resolution.

The performance of the proposed concept was studied through simulations performed using Monte Carlo N-Particle (MCNP) code. The important performance parameters relevant for GET measurement, detection efficiency and misidentification/mislocalisation rate were evaluated by using different methods of detector data analysis. The results from the simulations indicate that the proposed detector is a viable option for GET measurements. Furthermore, the dimensions of the proposed detector were optimised considering various measuring parameters and anticipated measurement scenarios.

Considering some foreseeable measurement scenarios, detector performance was analysed, and optimal ranges of the segment dimensions were determined. For demonstration purpose, a smaller segmented HPGe detector (prototype) in the planar shape has been proposed and its spatial response obtained through a simulation study.