Neutron flux monitoring system of the French GEN-IV SFR: Assessment of diverse solutions for in-vessel detector installation

• The expression of need of the ASTRID neutron monitoring system is presented.
• Performance criteria of neutron detector are proposed.
• Neutronics computational models are described in details.
• Study of diverse solutions for in-vessel neutron detector installation is carried out.
• The location behind the lateral shielding with neutron guide and that at the lower part of the above-core structure are preferred.

The neutron flux monitoring (NFM) system of any reactor must, in any situation, permit both reactivity control and power level monitoring. It also has to monitor the change in neutron flux distribution within the core region in order to prevent any local melting accident. This paper presents the recent output of the design of the NFM system of the French Generation-IV sodium-cooled fast reactor (SFR). The expression of need of such a system is first specified. Its main functions and important requirements for safety and detection are defined. Diverse solutions for detector installation into the reactor vessel and the performance criteria for their assessment are proposed. This work relies mostly on simulation results obtained with the use of various computational models that are described. The detailed study and the selection of detector locations are carried out. It is shown that two locations have passed a majority of those criteria: the outer part of the lateral neutron shield and the lower part of the above-core structure.