[en] At present at the Ignalina NPP the process of extensive use of the new uranium - erbium fuel is going on. The loading process of the new uranium - erbium fuel assemblies into the reactor cores is accompanied by experiments and analytical investigation of the behaviour of the main neutron - physical characteristics of the reactor. This article presents the results of independent calculations of different core states obtained using the German code QUABOX/CUBBOX which are compared with the results of similar calculations performed using codes SADCO and STEPAN as well as with experimental data. This is one of the steps in the process of validation of the code QUABOX/CUBBOX for the modeling of the process taking place in RBMK-1500 reactors. (author)