Approximation of Fast Reactor Spectra at the JHR

Due to the limited availability of fast reactors, some experiments supporting fast reactor development have to be conducted in MTRs whenever possible. At the Jules Horowitz Reactor, currently under construction in Cadarache, studies are underway to determine the range of possibilities at this reactor for basic neutron cross section, material and fuel behaviour experiments before ASTRID, the presently studied fast reactor prototype, becomes operational. One of the examined options is to aim for a similar neutron physics environment by hardening the neutron spectrum with Cd and Hf shields. Because reactor is designed to be strongly under moderated with a fast flux of 5.5 1014 n/cm2/s in core, the neutron flux conditions come reasonably close to low power density fast reactors as long as the thermal part of the spectrum can be excluded. This paper presents calculations for adjusting the neutron spectrum in the JHR with neutron shields and compares it to a SFR core spectrum. The examined irradiation positions are located in the reflector close to the core, in the central tube into a fuel element and as a replacement of a fuel element. An estimation of the effect on the neutron economy of the reactor is also given. (author)