During the 1970s, a wide range experimental program (GCFR-PROTEUS) was carried out at PSI's critical facility PROTEUS to study the physics characteristics of gas-cooled fast reactors. This paper presents the results of a series of new calculations based on the analysis of the reference test lattice in these experiments, viz. a regular hexagonal array of steel-clad, 15%-total-Pu PuO₂/UO₂ rods in air. The current study has been carried out using the deterministic fast-reactor code system ERANOS-2.0, largely employing the cell code ECCO and the Monte Carlo code MCNPX-2.5e, in conjunction with different modern nuclear data libraries.

Globally, good agreement is obtained between the different calculations for most of the important reaction rates which were measured at the center of the test lattice (relative to the fission of ²³⁹Pu). For these reaction rate ratios, ERANOS-2.0 results obtained in conjunction with adjusted JEF-2.2 data (adjustments primarily made from the analysis of sodium-cooled fast-spectrum systems) have been found to be in good agreement (i.e. within -1σ), with both MCNPX-2.5e using the (unadjusted) JEF-2.2 data library and, even more important, with the experimental results. This provides useful indication that existing computational tools show an adequate level of accuracy for design studies of advanced gas-cooled fast reactors using conventional fuel pins.