Corresponding author: Valery V. Korobeynikov (vvkorobeynikov@ippe.ru)

Academic editor: Georgy Tikhomirov

The paper presents the results of studies on the burning of minor actinides (

Disposal of radioactive waste in nuclear power is becoming a growinglysensitiveissue as spent nuclear fuel builds up, the nuclear reactor fleet is enlarged, and NPP units are decommissioned after their design life expires. Specifically challenging in addressing this issue are minor actinides (

An important peculiarity of the approach proposed for the

Note that this paper does not discuss any issues involved in the practical implementation of and the arrangement of operations in such facility. A number of additional studies are required to justify in detail the conceptual approach described. Studies are primarily required for justifying the safety and functionality of FAs with

MAs are isotopes of americium, curium and neptunium formed as the result of the reactor operation and affecting significantly the SNF and RW handling methods.This is explained by the fact that, despite being produced in small quantities in reactors, MAs contribute greatly to the SNF decay heat power and radiotoxicity in a longer term. Table

Critical masses of nuclides in metallic form

Nuclide | _{1/2}, years |
Decay heat power, | Critical mass |
---|---|---|---|

W/kg | kg | ||

U-233 | 1,59E+05 | 2,81E-01 | 1,56E+01 |

U-235 | 7,04E+08 | 6,00E-05 | 4,65E+01 |

Np-237 | 2,14E+06 | 2,10E-02 | 5,89E+01 |

Pu-238 | 8,77E+01 | 5,60E+02 | 9,76E+00 |

Pu-239 | 2,41E+04 | 2,00E+00 | 9,96E+00 |

Pu-240 | 6,56E+03 | 7,00E+00 | 3,70E+01 |

Pu-241 | 1,43E+01 | 6,40E+00 | 1,28E+01 |

Pu-242 | 3,75E+05 | 1,20E-01 | 8,71E+01 |

Am-241 | 4,33E+02 | 1,15E+02 | 6,18E+01 |

Am-242m | 1,41E+02 | 4,50E+00 | 1,26E+01 |

Am-243 | 7,37E+03 | 6,40E+00 | 1,83E+02 |

Cm-242 | 162,8 сут | 1,21E+05 | 1,32E+01 |

Cm-243 | 2,91E+01 | 1,86E+03 | 6,14E+00 |

Cm-244 | 1,81E+01 | 2,80E+03 | 2,51E+01 |

Cm-245 | 8,50E+03 | 5,70E+00 | 1,26E+01 |

Cm-246 | 4,76E+03 | 1,00E+01 | 8,33E+01 |

An analysis into the dependence of the capture and fission cross-sections on energy for the nuclides, MAs are composed of, shows (

the fission cross-section for fast neutrons (Am-241 and Np-237) is much greater than the capture cross-section (for other energies, the capture cross-sections are higher than the fission cross-sections);

a similar dependence of cross-sections exists as well for the Am-243, Cm-242 and Cm-244 nuclides;

for the Am-242, Am-242, Cm-243 and Cm-245 nuclides, the fission cross-section is higher than the capture cross-section across the region of energies and grows as energy decreases.

Since the Am-241 and Np-237 fission cross-sections are higher than the capture cross-sections only in the “fast” region of energies, and these nuclides account for the most part of the MAs, the reactor with

Therefore, fast neutron reactors, the fuel in which consists of only minor actinides with no traditional uranium and/or plutonium, will be capable to burn efficiently the MAs accumulated in SNF of thermal neutron reactors.

It is important that most of the MAs in such reactor will be converted to fragments in the process of fission. Another major argument in favor of a reactor with

The results of the studies into the possibility for using Am-241 and Np-237 (

The Table

Composition of isotopes in unloaded VVER fuel. Five year cooling

Isotope | Mass fraction in SNF | Initial composition for calculations, metallic fue, 10^{24} 1/cm^{3} |
Initial composition for calculations, oxide fuel, 10^{24} 1/cm^{3} |
---|---|---|---|

Np-237 | 4,95Е–1 | 2,5704Е–2 | 1,1555Е–2 |

Am-241 | 3,16Е–1 | 1,0786Е–2 | 8,14Е–3 |

Am-242m | 1,03Е–3 | 3,501Е–5 | 2,63335Е–5 |

Am-243 | 1,48Е–1 | 5,01Е–3 | 3,7846Е–3 |

Cm-242 | 4,13Е–9 | 1,39Е–10 | 1,089Е–10 |

Cm-243 | 4,36Е–4 | 1,4587Е–5 | 1,14546Е–5 |

Cm-244 | 3,69Е–2 | 1,22938Е–3 | 9,6592Е–4 |

Cm-245 | 2,62Е–3 | 8,694Е–5 | 6,8335Е–5 |

Cm-246 | 4,77Е–4 | 1,576444Е–5 | 1,23963Е–5 |

Cm-247 | 1,01Е–5 | 3,324163Е–7 | 2,61535Е–7 |

O-16 | – | 4,91186E–2 |

Table

Critical masses compared for metallic and oxide

Nuclide | Oxide, kg | Metal, kg |
---|---|---|

Np-237 | 2,82E+02 | 5,89E+01 |

Am-241 | 1,20E+02 | 6,18E+01 |

Am-242m | 1,58E+01 | 1,26E+01 |

Am-243 | 4,85E+02 | 1,83E+02 |

Cm-242 | 1,84E+01 | 1,32E+01 |

Cm-243 | 7,91E+00 | 6,14E+00 |

Cm-244 | 3,73E+01 | 2,51E+01 |

Cm-245 | 1,47E+01 | 1,26E+01 |

Cm-246 | 1,42E+02 | 8,33E+01 |

Cm-247 | 1,08E+01 | 8,91E+00 |

«Вектор» МА | 1,93E+02 | 6,15E+01 |

This section presents the results of computational studies to investigate the efficiency of

Figs

Axial arrangement of materials in the computational model of the BN-600 reactor: 1 – axial reflector; 2 – absorber element end fittings; 3 – absorber elements; 4 – sodium cavity; 5 – fuel element end fittings; 6 – core; 7, 8 – lower end shields with depleted uranium dioxide.

Radial arrangement of the BN-600 reactor core components: 1 – radial reflector; 2, 3 – steel shielding blocks; 4, 5, 7 (8) – FAs with 26%, 21% and 17% U-235 enrichment, respectively; 6 – CPS cluster cell.

Everything in this model that is beyond the core, both axially and radially, is homogenized. The heterogeneous structure has been preserved only for the FAs and the fuel elements within the fuel column. The FA cross-section is shown in Fig.

Cross-section of a BN-600 reactor core model FA: 1 – FA jacket; 2 – fuel cladding (wall thickness δ = 0.4 mm); 3 – fuel (diameter

As fuel, instead of uranium and plutonium, the computational model used the

The computational studies were undertaken for two _{eff} values as a function of irradiation time for the metallic and oxide fuel options.

Variation of _{eff} values as a function of irradiation time for two fuel

The _{eff} value at the irradiation start time grows initially and then drops. This phenomenon is explained by the isotopes produced which prove to be more efficient in terms of contribution to the multiplication factor than the original ones.

Figs

Change in the mass of the nuclides contributing the greatest to the BN-600 MAs (HEZ) as a function of irradiation time for the metallic fuel form.

Change in the mass of the nuclides contributing the greatest to the BN-600 MAs (HEZ) as a function of irradiation time for the oxide fuel form.

Fig.

Change in the mass of the nuclides that contribute the greatest to the MAs for all BN-600 zones as a function of irradiation time for the oxide fuel form.

The change in the mass of Cm nuclides depending on the operating time of a nuclear reactor with

Change in the concentration of Cm nuclides at the end of the irradiation period: +Am – initial option; –Am – americium isolated from the

A question remains what will isolation of Am from the

Neutronic computational studies have been undertaken with respect to burning of minor actinides in a reactor with fuel without uranium and plutonium. Burning of the complete composition of MAs (Am, Np, Cm) isolated from SNF has been investigated.

An important argument in favor of a reactor with minor actinide fuel is that

The computational studies were performed using two BN-600 reactor models. One of the models used metallic

The computational studies have shown that the decay heat from the “complete” set from VVER SNF exceeds that from the same mass of “pure” americium by just 20%.

A major reduction in the mass of Cm nuclides with a high decay power can be achieved by burning MAs with a low Am content. Practical implementation of such approach requires small SNF cooling times prior to the

The problem of developing a real design of a reactor with fuel based only on minor actinides has not so far been resolved.

^{-th}Information Exchange Meeting «Actinide and Fission Product Partitioning and Transmutation». Prague, Czech Republic, 24–27 September.

* Russian text published: Izvestiya vuzov. Yadernaya Energetika (ISSN 0204-3327), 2022, n. 3, pp. 134–145.