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The "Projects and Calculations" labs (BPC) has two main roles : achievement of innovative projects and carrying out complex calculations in many physical fields for all ILL divisions.

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The BPC has developed high-level expertise in neutronic simulation in a number of areas, such as instrument design, reactor safety or radiation protection (as suppliers for ILL's Health Physics service in this case). We use Monte-Carlo codes, for example, to model the ILL reactor, beam tubes or even whole instruments, and obtain quantitative information on neutron and gamma spectra or deposited doses.

HFR modelling

Exhaustive 3D modelling of the ILL High-Flux Reactor (HFR) has recently been carried out using MCNPX 2.6d code and the ENDF/ B-VII library. All the in-pile elements have been taken into account, including beam tubes (H,IH,V), safety rods, cold and hot neutron sources and so on. . . Material densities, compositions and fuel specificities comply with the Safety Report or have been updated if needed. The HFR fuel element has been detailed with a high degree of accuracy. All 280 fuel plates have been modelled with the closest geometry available (involutes were modelled by cylinder sections). Control and safety rod positions can be adjusted to fit experimental conditions.The cross-section library used in these calculations is ENDF/ B-V II at 300K. We
used the latest available release of thermal structure factors for low energy neutrons.

The HFR has 5 safety rods (BS) which have all been weighted using subcritical approaches. The weight has been determined by substracting the keff of the "all BS up" configuration from the considered keff. Most calculations match the experimental values with a shift of less than roughly 500 pcm. We can thus conclude that we have very good agreement between simulations and experiments for these configuration series. When all BS are up, the fit is excellent with only 31 pcm of difference between simulation and experiment. For a better view of the neutron distribution in-pile, we scored mesh tallies for several configurations in the median plane.

Neutron spectrum in the heavy water tank

We have performed a benchmark study of the ILL in collaboration with ILL's Science Division for MCNP and TRIPOLI codes. In the framework of this study, we matched our simulation results in the heavy water tank with measurements and calculations carried out in the past by P. Ageron. We obtained good agreement, except perhaps for epithermal neutrons.



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