SECURE Project

Deliverable 3.3

EXECUTIVE SUMMARY

Production of W-188 is performed by irradiating enriched W-186 targets in high flux reactors. Traditionally tungsten oxide targets have been used, but stability issues have occurred in the past for some of the irradiated ampoules. Thus, tungsten metal targets are sought as alternative to tungsten oxide targets. However, large volume targets of massive tungsten are disfavoured in terms of neutronics and dissolution strategy respectively.
Notably massive and dense parts of W-186, that is a relatively strong neutron absorber, would lead to significant neutron self-attenuation in the target and consequently to a considerable reduction of yield and specific activity of the produced W-188. The neutron self-attenuation effect has been studied for different geometries by analytical estimates and Monte Carlo simulations respectively.
After irradiation the tungsten targets need to be chemically processed and the first step of this processing requires a chemical dissolution of the solid target to bring the W-188 into aqueous solution, as necessary precondition before subsequent chemical separation and/or generator loading steps. Dissolution of massive dense parts of metallic tungsten is challenging and slow since the surface-to-volume ratio is small and provides only limited liquid-solid interface area for chemical attack.
Advanced metal targets should compensate these intrinsic drawbacks of simple bulk metal targets by reducing the average physical density of the targets and/or using hollow targets to enhance their surface-to-volume ratio.
Different strategies can be followed to achieve both of these goals, namely targets of reduced physical density like foams, felts or mixtures with other materials that are weak neutron absorbers. Test samples produced by different methods have been obtained and supplied to NCBJ for dissolution tests and chemical analysis.

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.