Eric Mauerhofer

An improved method for the non-destructive characterization of radioactive waste by gamma scanning

A method to improve the reliability and accuracy of activity results in segmented gamma scanning of radioactive waste drums with non-uniform isotope and matrix distribution has been developed. The improved method which is based on numerical simulations of the measured angular dependent count rate distribution during drum rotation in segmented gamma scanning has been validated through the measurement of Cs-137 and Co-60 activities in 13 real radioactive waste drums with heterogeneous activity and matrix distributions. The results were compared to that obtained for the conventional method assuming homogeneous activity and matrix distributions.

Prompt gamma neutron activation analysis of toxic elements in radioactive waste packages.

The French Alternative Energies and Atomic Energy Commission (CEA) and National Radioactive Waste Management Agency (ANDRA) are conducting an R&D program to improve the characterization of long-lived and medium activity (LL-MA) radioactive waste packages. In particular, the amount of toxic elements present in radioactive waste packages must be assessed before they can be accepted in repository facilities in order to avoid pollution of underground water reserves. To this aim, the Nuclear Measurement Laboratory of CEA-Cadarache has started to study the performances of Prompt Gamma Neutron Activation Analysis (PGNAA) for elements showing large capture cross sections such as mercury, cadmium, boron, and chromium. This paper reports a comparison between Monte Carlo calculations performed with the MCNPX computer code using the ENDF/B-VII.0 library and experimental gamma rays measured in the REGAIN PGNAA cell with small samples of nickel, lead, cadmium, arsenic, antimony, chromium, magnesium, zinc, boron, and lithium to verify the validity of a numerical model and gamma-ray production data. The measurement of a ∼20kg test sample of concrete containing toxic elements has also been performed, in collaboration with Forschungszentrum Jülich, to validate the model in view of future performance studies for dense and large LL-MA waste packages.

Reconstruction of the activity of point sources for the accurate characterization of nuclear waste drums by segmented gamma scanning.

This work improves the reliability and accuracy in the reconstruction of the total isotope activity content in heterogeneous nuclear waste drums containing point sources. The method is based on χ(2)-fits of the angular dependent count rate distribution measured during a drum rotation in segmented gamma scanning. A new description of the analytical calculation of the angular count rate distribution is introduced based on a more precise model of the collimated detector. The new description is validated and compared to the old description using MCNP5 simulations of angular dependent count rate distributions of Co-60 and Cs-137 point sources. It is shown that the new model describes the angular dependent count rate distribution significantly more accurate compared to the old model. Hence, the reconstruction of the activity is more accurate and the errors are considerably reduced that lead to more reliable results. Furthermore, the results are compared to the conventional reconstruction method assuming a homogeneous matrix and activity distribution.

Reconstruction of the isotope activity content of heterogeneous nuclear waste drums

Radioactive waste must be characterized in order to verify its conformance with national regulations for intermediate storage or its disposal. Segmented gamma scanning (SGS) is a most widely applied non-destructive analytical technique for the characterization of radioactive waste drums. The isotope specific activity content is generally calculated assuming a homogeneous matrix and activity distribution for each measured drum segment. However, real radioactive waste drums exhibit non-uniform isotope and density distributions most affecting the reliability and accuracy of activities reconstruction in SGS. The presence of internal shielding structures in the waste drum contributes generally to a strong underestimation of the activity and this in particular for radioactive sources emitting low energy gamma-rays independently of their spatial distribution. In this work we present an improved method to quantify the activity of spatially concentrated gamma-emitting isotopes (point sources or hot spots) in heterogeneous waste drums with internal shielding structures. The isotope activity is reconstructed by numerical simulations and fits of the angular dependent count rate distribution recorded during the drum rotation in SGS using an analytical expression derived from a geometric model. First results of the improved method and enhancements of this method are shown and are compared to each other as well as to the conventional method which assumes a homogeneous matrix and activity distribution. It is shown that the new model improves the accuracy and the reliability of the activity reconstruction in SGS and that the presented algorithm is suitable with respect to the framework requirement of industrial application.

Measurement of thermal neutron capture cross sections of 237Np and 242Pu using prompt gamma neutron activation

Several samples of 237Np and 242Pu were irradiated in the guided cold neutron beam of the prompt gamma activation analysis facility at the Budapest Research Reactor. The thermal neutron capture cross sections of 237 Np and 242Pu were evaluated from the obtained prompt and delayed gamma ray data. The thermal neutron capture cross sections for 237Np(n,γ)238Np was found to be

TANDEM: A mutual cooperation effort for transactinide nuclear data evaluation and measurement

\sigma_{0} ({}^{237}{\text{Np}}) = 170.4 \pm 7.4\,{\text{b}}

A priori calculation of the thermal neutron die-away time of large samples irradiated in the facility MEDINA

and for 242Pu(n,γ)243Pu to be