**3.3. Fuel 232Th + 233U**

0

0,02

0,04

0,06

0,08

**K-1**

0,1

0,12

0,14

0

0,01

0,02

0,03

**K-1**

0,04

0,05

0,06

186 Nuclear Power – Practical Aspects

**3.2. Fuel 238U + 239Pu** 

0

0,2

0,4

0,6

**C FM**

0,8

1

1,2

0

0,2

0,4

0,6

0,8

**C FM**

1

1,2

1,4

Multiplication factors for RC=1 is increased.

235U.

figure 3.

**Figure 2.** Reactor campaign characteristics with initial contents 235U in fuel 0.47 % and absence of

0 2000 4000 6000 8000 10000 12000 **time, h**

U 235 Pu 239 Pu 241 Ряд6 K-1 SZ K-1 oper

Region with reproduction coefficient equal unity for fuel on the base of mix 238U + 239Pu relocates to less value of fission materials contents comparing to fuel on the base of 238U and

Reactor campaign characteristics with initial fuel containing 238U and 239Pu are shown at

**Figure 3.** Reactor campaign characteristics with initial contents of 239Pu in uranium-plutonium fuel 0.37

Pu 239 Pu 241 W K-1 SZ K-1 oper

0 2000 4000 6000 8000 10000 12000 **time, h**

% and absence of absorption in 238U of epithermal neutrons (string 2 of application's table 1).

absorption in 238U on epithermal neutrons. (string 1 of Attachment Table 1)

For the fuel on the base of mix 232Th + 233U the region with reproduction coefficient equal to unity relocates to higher contents of fission materials. Multiplication factor in this region also shows increase comparing to variants with fuel on the base of 238U and 235U.

Reactor campaign characteristics with 233U + 232Th in initial fuel is shown at figure 4. Contents change of 233U during campaign is not big. Reactor power change is also not big. But power is decreasing at the campaign beginning and after that returns to its initial value. Power decrease at the campaign beginning is caused by 233U contents decrease, and return is caused by 235U accumulation. Comparatively small accumulation of 235U is well explained by small neutron absorption cross-section of 233U, from which produces 235U.

**Figure 4.** Reactor campaign characteristics with initial contents of 233U in uranium-thorium fuel equal to 1.55 % (string 3 of application's table 1).

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 campaign is considerably higher than it of the previous campaigns.

Thermal Reactors with High Reproduction of Fission Materials 189

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

campaign with uranium-plutonium fuel with limitation of 240Pu.


beginning and decreases campaign durability.


**reproduction** 

neutron losses.

and 238U).

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:

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

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

The basic difference of real reactors is presence of neutron absorption in construction materials and neutron leakage from reactor. These factors can be researched in the described models without reference to the reactor design by additional term insertion for these

Neutron flux values used in previous calculations are not always applicable. Possibility of

Arrangements for reactor campaign improvements and its effects should be also considered.



Campaign characteristics calculations, which were presented above, use ~9\*1013 sm-2sec-1 neutron flux. Flux increase allows improving economical issues – decrease of fuel

neutron flux change and its influence on campaign characteristics must be examined.

Without reference to a reactor design following arrangements can be considered:



**5.1. Neutron flux influence on campaign characteristics** 

portion. In the cycle each portion is used once;


**5. About possibility of practical campaign realization with high** 
