High-burnup Fast Reactor Metal Fuel

Abstract

The disclosure discloses a high-burnup fast reactor metal fuel, wherein the reactor core is loaded with metal fuel made of natural uranium alloy U-50Zr. The metal fuel manually controls the temperature to realize phase transition, increase burnup, and extend the service life of fuel; increases the fuel burnup to increase uranium utilization and reduce the pressure of disposing nuclear waste; extends the fuel life cycle to reduce nuclear power costs and improve the economy of nuclear energy; effectively carries out the timely release of fission gas and the periodic elimination of fuel defects, thus reducing the fuel-cladding mechanical interaction caused by swelling, and increasing the safety.

Claims

1. A high-burnup fast reactor metal fuel, characterized in that: the reactor core is loaded with metal fuel made of natural uranium alloy U-50Zr.

2. The high-burnup fast reactor metal fuel of claim 1, characterized in that: The operation mode of the reactor core is as follows: After the first-loaded reactor core runs for a certain time under normal conditions, when a certain amount of fission gas is accumulated, the temperature rise is controlled manually to cause phase transition of the fuel and keep it in the γ phase for a period of time, which effectively accelerates the release of fission gas; After the fission gas is released, manually cool it down to cause phase transition, and then return to the δ-phase for normal operation; the process of phase transition during cooling-down is also the driving force to promote the rapid movement and release of fission gas, and the phase transition can effectively eliminate the accumulated irradiation defects; Repeat the above actions for release of fission gas after operating for a period of time in the δ-phase and cycle on and on.

3. The high-burnup fast reactor metal fuel of claim 2, characterized in that: the control temperature range is 550-630° C.

4. The high-burnup fast reactor metal fuel of claim 2, characterized in that: the fuel temperature is controlled within an ideal temperature range through operating power regulation, so as to allow response to the power of fast reactor metal fuel and controlled release of gas fission products.

5. The high-burnup fast reactor metal fuel of claim 2, characterized in that: the pulse-type phenomenon of repeatedly accelerating the release of fission gas by repeatedly regulating the temperature.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is the U—Zr phase diagram (as a reference basis for innovation points);

[0019] FIG. 2 is a schematic diagram of fission gas release during the whole process of reactor core operation mode in the disclosure;

[0020] FIG. 3 is a schematic diagram of the fission gas release in the disclosure as a function of fuel burnup;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] In order to make the contents of the disclosure easier to be clearly understood, technical schemes in embodiments of the disclosure will be described clearly and completely in conjunction with drawings in embodiments of the disclosure.

[0022] The drawings show a high-burnup fast reactor metal fuel, wherein the reactor has a typical pool-type fast reactor core and is loaded with metal fuel made of natural uranium alloy U-50Zr.

[0023] The operation mode of the reactor core is as follows: After the first-loaded reactor core runs for a certain time under normal conditions, when a certain amount of fission gas is accumulated, the temperature rise is controlled manually to cause phase transition of the fuel and keep it in the γ phase for a period of time, which effectively accelerates the release of fission gas; after the fission gas is released, manually cool it down to cause phase transition, and then return to the δ-phase for normal operation; the process of phase transition during cooling-down is also the driving force to promote the rapid movement and release of fission gas, and the phase transition can effectively eliminate the accumulated irradiation defects; repeat the above actions for release of fission gas after operating for a period of time in the δ-phase and cycle on and on.

[0024] The range of fuel core temperature is 550-630° C.

[0025] The core temperature of metal fuel is controlled within an ideal phase transition temperature range through the reactor power regulation to trigger large release of fission gas.

[0026] The pulse-type phenomenon of repeatedly accelerating the release of fission gas by repeatedly regulating the temperature.

[0027] The fuel is U-50% Zr alloy, and due to the extremely low neutron absorption cross section of Zr, the self-breeding of fast reactors loaded with high-burnup metal fuel can be realized even at such a low proportion of uranium. Due to the excellent irradiation and corrosion resistance of Zr, the high-Zr fuel itself has a lower swelling rate than the general fuel. In addition, due to the excellent mechanical properties of Zr, the mechanical properties of fuel are also quite good.

[0028] The release of fission gas is dependent on the migration of fission gas atoms and bubbles, and the high migration rate can accelerate the release of fission gas and reduce the swelling of fuel. However, the migration rate of fission gas is not only related to temperature, but also affected by irradiation, defects and the movement of fuel metal matrix atoms. During the phase transition, the fission gas migration can be promoted due to violent diffusion and migration of the atomic system. The reason why high-Zr alloy U-50% Zr is selected as the fuel is that, according to the U—Zr phase diagram shown in FIG. 1, the U—Zr alloy can change from δ to γ phase at 620° C. in this ratio, and the spinodal decomposition can occur at 550° C. in the chemical environment with fission gas and defects. In this ratio, there are only two phases in U—Zr alloy.

[0029] At higher temperatures, the migration rate of fission gases is higher, which can promote the movement and release of bubbles. The short-range movement of atoms can exacerbate the movement of fission gas atoms and bubbles when phase transitions occur. After the phase transition to γ phase, the migration rate of bubbles and fission gas atoms in the γ phase is also relatively high, and this can further promote the release of fission gas. Therefore, the unique phase transition of high-Zr U—Zr alloy at a certain temperature can be realized by manually controlling the temperature rise. The high randomness and rapid movement of atoms in the phase change process can be utilized in combination with high temperature to accelerate the migration and release of bubbles, so as to reduce the FCMI problem caused by the swelling of fission gas. After the fission gas is released, the temperature will be reduced, and the fuel phase will be converted into δ phase. This phase transition can remove the defects introduced by irradiation in the crystal, so that the fuel defect level will return to the initial level of the fuel, and continue the operation under normal conditions. The phase transition process in this step can also accelerate the migration of fission gas and promote the release.

[0030] After operating under normal conditions for a certain period of time, the natural uranium alloy U-50Zr realizes temperature rise control by power regulation. In case of ULOF (unprotected loss of flow) accident, the reactor core loaded with metal fuel will not have sodium boiling, because the negative feedback mechanism of the metal fuel itself makes its Doppler effect small. The ULOF test at 100% power without emergency shutdown on EBRII (experimental breeder fast reactor II) demonstrated that the reactor core loaded with metal fuel was automatically shut down without emergency shutdown measures and sodium was not boiling. In the ULOF test, the fuel temperature can reach 0.5-0.6Tm (Tm>1400K, representing the melting point of the fuel) of U-50Zr fuel, which is sufficient to cause phase transition from δ to γ phase. Therefore, the fuel temperature control can be realized through power regulation under the premise of safe operation, so as to promote periodic release of fission gas and periodic elimination of defects.

[0031] The above are only preferred embodiments of the disclosure and are not intended to limit the disclosure. Any modifications, equivalents, improvements made within the spirit and principles of the disclosure shall fall within the scope of protection of the disclosure.