3. Conclusion and outlook

The first materials to be considered for use as absorbers were primarily based on criteria of neutron efficiency and availability. Other aspects (materials, radiotoxicity, etc.) were only really taken into account after the necessary feedback. Two examples will illustrate this approach:

• the boron carbide pellets used in French RNRs have been reduced in diameter from 42 mm in Rapsodie to 23 mm in Phénix and then 17 mm in SuperPhénix, to less than 10 mm in experimental assemblies. This development was made possible by the observation and analysis of material behavior in the reactor, which led to efforts to reduce thermal gradients: the extra manufacturing cost was offset by an increase in the lifetime of the absorbing elements;

• AIC was invented to compensate for scarce Hf resources. The radiotoxicity of silver...