Fuel Composition for Water-Cooled Reactors of NPPs on Thermal Neutrons

Abstract

The fuel of NPPs on thermal neutrons. A fuel composition is proposed, which includes a mixture of regenerated plutonium and enriched uranium in the form of oxides, in which the enriched natural uranium is used as enriched uranium as well as regenerated plutonium, with a ratio of components, determined by the energy potential, equal to the potential of freshly prepared NPP fuel from enriched natural uranium, which provides the loading of the reactor core up to 100%. Possible options of the specified components are claimed, including unlimited cycling of the secondary regenerated plutonium and uranium. The use of the proposed composition makes it possible to use of the uranium and plutonium energy potential at maximum level, including accumulated SNF, and sharply reduce the volume of warehouses, up to their decommissioning, as well as significantly simplify the logistics and technology of manufacturing nuclear fuel from recycled materials.

Claims

1. Fuel composition for NPP water-cooled power reactors on thermal neutrons, comprising a mixture of plutonium oxides, when plutonium was regenerated in the processing of uranium spent nuclear fuel from such reactors, and enriched uranium. And this composition is characterized by that, at providing 100% load of the reactor core, it contains enriched natural uranium at a ratio with the regenerated plutonium, providing equal energy potential with freshly prepared fuel from enriched natural uranium, whereas the enriched regenerated uranium is included in the composition, used at the NPP, that does not contain plutonium and also provides equal energy potential with freshly prepared fuel from enriched natural uranium, with unlimited cross-cycling of both regenerated materials in the specified compositions.

2. Composition according to claim 1, characterized in that the secondary regenerated uranium, extracted from the irradiated claimed composition after the refueling interval in the reactor, is part of the general composition of the regenerated uranium, while the secondary regenerated plutonium, extracted from the irradiated composition of the regenerated uranium is part of the claimed composition.

3. Composition according to claim 1, characterized in that for the VVER-1000/1200 reactor at standard SNF burnup of 47 GW*days/t and 504 days refueling interval between the SNF reloading, contains regenerated plutonium from 5 to 12% at the content of enriched uranium from 3.5 to 2% .sup.235U only of natural origin and at providing equal energy potential with fresh fuel from natural uranium with enrichment of 4.6% .sup.235U or other content of .sup.235U, matching the fuel cycle of VVER-1000/1200 reactors.

4. Composition according to claim 1, which further comprises a part of natural uranium without enrichment.

5. Composition according to claim 1, characterized in that the mixture of regenerated plutonium and enriched natural uranium contains the latter in the form of a finished composition for the fuel of the WWER-1000/1200 NPP.

6. Composition according to claim 1, characterized in that it contains plutonium, that has been regenerated at various times, including from SNF of different type reactors and/or batches, and mixed according to calculation with natural and naturally enriched uranium in any combination to achieve the required energy potential.

7. Composition according to claim 1, which, at its optimal proportion, is intended for loading into a reactor with an increased RCS number with an extended refueling interval and subsequent disposal without processing.

8. Composition according to claim 1, characterized in that its use is not time-bound with the use of a composition, containing enriched regenerated uranium.

Description

EXAMPLE 1

[0029] The fuel composition MIX-B consists of the regenerated plutonium dioxide, extracted from VVER-1000 SNF in the amount of 3.87 t HM (the initial total result of actinides amount in the load) with a burnup of 47 GW*days/t HM and exposure of 5 years, contains 5.0% mass. Pu (3.4% .sup.239+241Pu) in a mixture with enriched natural uranium, containing 2.9% .sup.235U (the rest is .sup.238U). The composition (1 t HM) has an equal energy potential with a standard fresh fuel, containing 4.6% .sup.235U, and is suitable for loading 100% of the VVER-1000 reactor core, when the reactor operates at refueling interval of 504 effective days (1.5 years) at two re-loads (a total of 5 years per each FA).

[0030] Simultaneously 3.82 tons HM of regenerated uranium, having a composition of 1.27% .sup.235U, as well as 0.65% .sup.236U and 3 ppb .sup.232U (the rest is .sup.238U), are being extracted from such a quantity of SNF. From such a quantity, 0.83 HM regenerated uranium fuel is being produced.

[0031] The MIX-B spent fuel contains 4.1% of the mass. Pu (2.4% of .sup.239+241Pu) in the mixture with uranium, containing 1.4% of .sup.235U, as well as 0.33% of .sup.236U and 3 ppb .sup.232U (the rest is .sup.238U). After processing, the regenerated uranium is being sent for enrichment together with the uranium from VVER-1000 regular SNF in a separate chain and thus provides, during the subsequent production, another 0.25 t HM of equipotential fuel from regenerated uranium. Regenerated plutonium from such spent fuel is being returned for the production of MIX-fuel. 1.08 t HM of fuel from regenerated uranium is being produced in total.

[0032] From the secondary regenerated plutonium, 0.39 t HM of the secondary mixed fuel MIX-B2 is being produced, containing 100 kg Pu/t HM in a mixture with natural uranium, enriched to 3.0% .sup.235U. Regenerated from it uranium is also being sent into the enrichment chain with an additional production of 0.12 tons of fuel.

[0033] The extracted plutonium, by the isotope combination, still has a small energy potential (1 kg of .sup.235U equivalent per 5 kg Pu), but its use for VVER reactors becomes unprofitable, and it is being sent to storage, and then goes to the production of starting fuel for Fast Neutron Nuclear Reactors.

[0034] Secondary regenerated uranium with a double predominance of .sup.236U over the residual .sup.235U is sent to the disposal site.

[0035] Such recycling can take place in a stationary state as long as necessary without the reactor load ratio distortion by different fuels.

[0036] Thus, the fuel with regenerated plutonium can be loaded into 36% of the total number of thermal neutron reactors, and the fuel from enriched regenerated uranium ˜34% of the total number of VVER reactors. The balance of NFC occurs when 53% of the VVER reactors total number are loaded with fresh uranium fuel, and 47%—with regenerated fuel, including 25% of reactors—with plutonium-containing fuel of type MIX-B and MIX-B2 and 22%—with regenerated uranium fuel.

EXAMPLE 2

[0037] The fuel composition MIX-B consists of the regenerated plutonium dioxide, extracted from VVER-1200 SNF in the amount of 7.0 t HM (the initial total result of actinides amount in the load) with a burnup of 47 GW*days/t HM and exposure of 5 years, contains 9.0% mass. Pu (6.1% .sup.239+241Pu) in a mixture with enriched natural uranium, containing 1.36% .sup.235U (the rest is .sup.238U). The composition (1 t HM) has an equal energy potential with a standard fresh fuel containing 4.6% .sup.235U, and is suitable for loading 100% of the VVER-1200 reactor core, when the reactor operates at refueling interval of 315 effective days (1 year) at 5 re-loads (a total of 6 years per each FA) with a burnup of 60 GW*days/t HM. Such fuel is loaded into 14% of the total number of VVER reactors, which does not exceed the total number of VVER-1200 reactors in the total number of VVER reactors. The increase in the energy plutonium content in the MIX-B fuel has been achieved due to the doubled number of RCS in the VVER-1200 reactor in comparison with the VVER-1000 reactor.

[0038] Simultaneously 6.9 tons HM of regenerated uranium, having a composition of 1.27% .sup.235U, as well as 0.66% .sup.236U and 3 ppb .sup.232U (the rest is .sup.238U), are being extracted from such a quantity of SNF. From such a quantity, 1.5 HM regenerated uranium fuel is being produced, which is being loaded into 20% of the total number of VVER reactors (preferably VVER-1000).

[0039] The spent fuel contains 6.4% of the mass. Pu (3.6% of .sup.239+241Pu) in the mixture with uranium, containing 0.68% of .sup.235U, as well as 0.18% of .sup.236U and 4 ppb .sup.232U (the rest is .sup.238U). The energy potential of the extracted plutonium is equivalent to 10.4 kg .sup.235U, i.e. 1 kg .sup.235U per 6 kg Pu, which, as in the Example 1, makes its further cycling economically impractical, so that it is removed from the cycle and used as in the Example 1.

[0040] After processing, the secondary regenerated uranium can be sent to enrichment in a separate chain, resulting in the subsequent production into 0.1 t HM of equipotential fuel, but this may also be considered economically inappropriate, and then, instead of enrichment, it is to be disposed of.

[0041] Thus, if there is an excess of plutonium in the warehouse, all secondary SNF can be sent for long-term storage and subsequent disposal without processing, and, instead of it, the excess plutonium from previous years of activity, taken from the nuclear materials warehouse, can be involved into the NFC.