**4.3. Change of resonant absorption in raw materials**

As it can be seen from charts of figures 1 equal reproduction coefficient is achievable with different fission materials contents in fuel. It is done by changing of resonant absorption in raw nuclides. Described results are made for cases with no resonant absorption. Theoretically these characteristics remain constant at the same durability and neutron flux with increase of resonant absorption and achieving the same reproduction coefficient:


188 Nuclear Power – Practical Aspects

reached.

Positive reactivity margin in this campaign is decreasing at its beginning because of 233Ра contents increase and its comparatively long half-life. After 2000 work hours reactivity fluctuation is small because all fuel nuclides has stabilized. The reached duration of this

Let us compare some campaign characteristics of three shown variants of reactors with different fuel type, which are significant for its working out for applying in practice. This comparison is needed because the choice of initial conditions for campaign characteristics

Portion of raw uranium usage is usage rationality of this fuel kind (at this campaign). It is

Only the first of three considered campaigns can be used in the open cycle, i.e. without

Closed fuel cycles with raw thorium or raw uranium can work without 235U usage. Thus, the complete use of natural uranium, which used at the initial stages of these campaigns, is

At the base of 238U+235U fuel simplest campaign cannot reach high raw uranium usage. Reproduction of fission materials is too small, neutron losses in reactor control elements is

Characteristics of reactors campaign with initial contents of 239Pu and 241Pu sum in the uranium-plutonium fuel, which is equal to equilibrium, which can be formed from the

Fission reproduction coefficient in this campaign is equal to unity practically always during campaign. Neutron absorption in control rods increases up to 3.3 %. Reactor power is

Optimization of campaign with fuel on the base 233U + 232Th by the same means is also

Equilibrium of fission materials in the campaign with equilibrium contents of 233U, 235U and thorium is achieved after 2000 work hours. Neutron absorption in control rods is 5.8 %. Reactor power decreases to 93.2 % from initial value at 2000 work hours and remains stable.

Large reactivity margin with increase possibility of neutron losses in construction materials

Power decrease is caused by 233U formation and role of 233Ра with long half-time.

and for leakage is significant difference between this and previous campaign.

calculation is, in principle, not equivalent. Comparisons can delete this shortage.

important because uranium is unique natural material containing fission isotope 235U.

campaign is considerably higher than it of the previous campaigns.

too big. Reached burn-up is minimal among all suggested variants.

campaign by picture 3, are presented at string 4 of application's table 1.

interesting. These data are shown at string 5 of application's table 1.

practically constant. Its decrease is not more than 1 %.

**4. Analysis of hypothetic reactors campaign** 

**4.1. Variants of campaigns for figures 2, 3, 4** 

nuclides, which were gotten from the spent fuel.

**4.2. Variants with equilibrium fuel** 

Burn-up of fuel nuclides is changed. Reactor work with high burn-up is desirable. For campaign search with increased resonant absorption in raw nuclides data from figures 1 is not sufficient, because it is based on two nuclide campaign when its real number is six in campaign with uranium-plutonium fuel with limitation of 240Pu.

Described cases are not common in reactors with low reproduction coefficient, where resonant absorption in raw nuclides leads to multiplication factor decrease in the campaign beginning and decreases campaign durability.
