## Aspects of the use of different types of regenerated fuel (RUF, REMIX, MOX) in high power VVER

Four steady state fuel loadings with the campaign length of 500 effective days and 72 FAs make-up are developed for 18-month cycle of VVER-1200. The make-up FAs are fabricated using enriched natural uranium, regenerated uranium, REMIX fuel and MOX fuel. The average content of U-235 and Pu isotopes in the make-up fuel is as follows: 4.69% and 0%; 4.84% and 0%; 4.53% and 1%; 2.46% and 4.54% respectively. The share of fissionable isotopes of plutonium in Pu is 68%. In the cycle with MOX fuel the share of MOX FAs in the core is 44%, other FAs are made of enriched natural uranium. Maximum content of plutonium in fuel rods of MOX FA is 9.5%.

The results of calculations of neutron-physic characteristics of the developed fuel cycles are compered. It is noted that verification of codes for neutronic calculations of cores with REMIX and MOX fuel is far from complete. That is why calculations for these cores should be considered as preliminary. According to the results obtained the most of the neutron-physic characteristics of the cycles considered are close to one another. The exception is point kinetics parameters, critical and shutdown concentration of boric acid and efficiency of boric acid for loadings formed from REMIX and MOX fuel. It is necessary to point out the significant increase in boric acid concentration in coolant when MOX fuel is used. In particular, the boric acid concentration providing 5% cold state subcriticality reaches 26 g/kgH2O in the loading with 44% of MOX FAs in the core. This value is substantially dependent on the share of MOX FAs in the core and on the isotopic composition of the plutonium used. The efficiency of the emergency protection decreases with the increase of the plutonium amount in the core. However, this decrease is small for the developed MOX and REMIXES loadings.

Calculations of the cooling pond containing FAs used in four developed steady state loadings show that nuclear safety requirements are fulfilled.

According to the calculations the heat and power of the neutron source of fresh and burnt REMIX and in particular MOX FAs are many times greater than the corresponding values for the FAs of enriched uranium.

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