Practice of the rotation of assemblies during refuelling in NPP of Paks

Few years ago it turned out that two kk distributions could differ from each other if the kk is calculated using pin-wise burn-up distribution and the pin-wise burn-up distribution is very slanted or using averaged burn-up distribution. In that case when the former manner calculated value of kkmax is higher then the other one, the value of kkmax can be decreased with the rotation of the assembly. As a consequence of the development of computer technique an opportunity presents itself for the practical application of pin-wise burn-up calculation. At the outset the pin-wise burn-up calculation was made for that assembly, where the reactor-physics parameters were near the safety values. Nowadays the further development of the hardware and software devices present opportunity for the full-scope following of the pin-wise burn-up, in all assemblies. In this paper is presented a short historical review of the above mentioned events, practical adaption of the pin-wise burn-up following and display of some used reactor-physics codes.(Author)