UN-UO2 dual-phase structure fuel rod

Abstract

The invention discloses a UN-UO2 dual-phase structure fuel rod, which comprises an inner ring, an outer ring, a plurality of inner rings and a plurality of outer rings, the outer ring wraps the outer part of the inner ring, and the outer ring is filled with a UO2 fuel layer; and the cladding is wrapped in the outer ring, and a helium layer is arranged between the cladding and the inner ring. According to the UN-UO2 dual-phase structure fuel rod, the service life of a reactor can be prolonged, and the economical efficiency of a reactor core is improved. The stability of the axial non-uniform coefficient, the radial non-uniform coefficient and the total non-uniform coefficient of the reactor core added with the UN pellet fuel along with time change is better than that of a pure UO2 fuel reactor core, and the risk of accidents during operation of the reactor core can be reduced. The reactor core loaded with the UN-UO2 dual-phase structure fuel rod has lower instantaneous neutron lifetime and faster transient response, and the system can trigger a negative feedback mechanism more quickly, so that rapid increase of power is inhibited. In general, the UN-UO2 dual-phase structure fuel rod is suitable for a 177 reactor core, and the safety of the reactor core can be improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nuclear reactor fuel, and more particularly, the present application relates to a UN-UO2 dual-phase structure fuel rod. BACKGROUND

[0002] The occurrence of nuclear leakage accidents will bring extremely serious consequences to global nuclear power industry and natural environment, so it is necessary for people to improve the safety of nuclear power plant core and the safety of UO2-Zr fuel, and the development of accident tolerant fuel (ATF) with better high-temperature mechanical properties and chemical stability and stronger fission product containment capacity is our goal. An important means to improve the accident tolerance capacity of fuel is to use high uranium density fuel, and the main types of high uranium density fuel are U3Si2, UN and UN-U3Si2 composite fuel.

[0003] In the early development of ATF fuel, researchers first studied U3Si2. However, the research results show that when the fuel cladding fails due to failure, the reaction activity of U3Si2 fuel pellets in the reactor will affect its operation in the reactor and stability in the event of a serious accident. In addition, Nelson et al. found that the oxidation resistance of U3Si2 is lower than that of UN and UO2. From the above conclusion, it is concluded that pure U3Si2 is not suitable for ATF fuel. In addition, considering the improvement of uranium loading, the reduction of core temperature, the resistance to water and water vapor oxidation, the improvement of accident tolerance, the optimization of material selection and the control of the proportion of high uranium density nuclear fuel, UN is more suitable for ATF fuel than U3Si2.

[0004] The U.S. Nuclear Regulatory Commission (U.S. NRC) considers UN material as a candidate for ATF fuel for the following reasons: ① Using UN can increase the uranium density, so that the reactor core can operate at a higher power or have a longer fuel cycle; ② UN has the advantage of high melting point; ③ UN has the advantage of low parasitic neutron absorption; ④ The increase in fuel thermal conductivity helps to reduce the operating temperature.

[0005] Before the 1990s, the stability of UN in high temperature water was controversial. As the research went deeper, it was found that the corrosion rate of UN in boiling water was higher than that of the oxide and beyond the acceptable range, thus UN was not suitable for light water reactors. In the published articles, Watkins and Gonzales et al. pointed out that the premise of applying UN to light water reactors was to solve the problem of poor oxidation resistance of UN. After discussing three schemes of pure UN fuel pellets, adding other oxidation-resistant materials to UN except UO2, and UN-UO2 composite fuel pellets, it was considered that UN-UO2 composite pellets were one of the feasible improvement schemes. By making UN and UO2 into composite pellets, it was possible to simultaneously exert the advantages of the two materials: increasing the uranium density and thermal conductivity of the pellets by UN and playing a barrier role between water and UN by UO2. SUMMARY

[0006] An object of the present application is to solve at least the above problems and / or defects, and to provide at least the advantages to be described later.

[0007] To achieve these objects and other advantages according to the present application, a UN-UO2 dual-phase structure fuel rod is provided, comprising:

[0008] an inner ring, the inside of which is dispersed with UN pellets;

[0009] an outer ring, which is wrapped outside the inner ring, the outer ring being filled with a UO2 fuel layer;

[0010] a cladding, which is wrapped inside the outer ring, a helium layer being arranged between the cladding and the inner ring.

[0011] Preferably, the UN pellets in the inner ring are filled with 235 UO2 fuel with a U enrichment of 4.4%.

[0012] Preferably, the diameter of the UN pellets is 435.4-590.8 μm.

[0013] Preferably, the diameter of the inner ring accounts for 80% of the diameter of the UN-UO2 dual-phase structure fuel rod.

[0014] Preferably, the filling volume of the UN pellets is 30%-50% of the volume of the inner ring.

[0015] Preferably, the UO2 fuel layer has 235 a U enrichment of 4.4%.

[0016] Preferably, the material of the cladding is Zr-4 alloy.

[0017] The application of a UN-UO2 dual-phase structure fuel rod is applied to the loading of a fuel assembly in a nuclear reactor; wherein the fuel assembly is in a 17x17 arrangement, comprising 264 UN-UO2 dual-phase structure fuel rods and 25 control guide tubes; and the core of the nuclear reactor comprises 289 fuel assemblies arranged in a 17x17 arrangement.

[0018] The present application has at least the following beneficial effects: the UN is designed to be dispersed in the UO2 fuel matrix in the form of small balls to form a UN-UO2 composite pellet. eff The k eff The k 235 The neutron spectrum of the UN-UO2 dual-phase structure fuel core is only harder than that of the pure UO2 fuel core, and the difference in the high-energy region is not large, indicating that the UN-UO2 dual-phase structure fuel has limited effect on the neutron spectrum of the core. 239 Pu, 240 Pu and 241Pu gradually increase, indicating that each scheme can increase the service life of the reactor to some extent and improve the economy of the core. From the statistics of the delayed neutron effective fraction of each scheme, the change of the delayed neutron effective fraction of each scheme is relatively stable, and the change of the delayed neutron effective fraction when the UN fuel volume accounts for 20% and 30% of the inner circle volume is more stable than that when the UN fuel volume accounts for 40% and 50% of the inner circle volume, which is more conducive to the control of the core. From the statistics of the moderator temperature coefficient and the fuel temperature coefficient of each scheme, each scheme has a negative temperature coefficient, so that the core has sufficient negative reactivity when the temperature rises during operation, improving the safety of the core. The axial non-uniformity coefficient, radial non-uniformity coefficient and total non-uniformity coefficient of the core with added UN ball fuel change more stably over time than those of the pure UO2 fuel core, and the coefficients are relatively low, having good safety and reducing the risk of accidents during operation of the core. The core with added UN fuel has a lower prompt neutron lifetime, indicating that the core has a faster transient response, so that the system can trigger a negative feedback mechanism more quickly to suppress the rapid growth of power, and also requires a more precise real-time monitoring and rapid adjustment mechanism.

[0019] The present application simulates and analyzes the 177 core overall loading of UN-UO2 dual-phase structure fuel rods, and finds that the core has a k eff and a slight shortage in burnup depth, but overall can improve the safety of the core, and can reduce the spatial self-shielding effect of the fuel by adjusting the UN pellet diameter. Overall, the UN-UO2 dual-phase structure fuel rod is suitable for the 177 core, and can improve the safety of the core.

[0020] Other advantages, objects, and features of the present application will be apparent from the following specification, and will be understood by those skilled in the art. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A UN-UO2 dual-phase structure fuel rod transverse cross-section structure schematic diagram is provided for the present application;

[0022] Figure 2 A UN-UO2 dual-phase structure fuel rod arrangement schematic diagram in a fuel assembly is provided for the present application;

[0023] Figure 3 A core k eff over time diagram;

[0024] Figure 4 A core k eff over burnup diagram;

[0025] Figure 5 A core neutron energy spectrum loaded with UO2 fuel rods of Comparative Example 1;

[0026] Figure 6 A core neutron energy spectrum loaded with UN-UO2 dual-phase structure fuel rods of Example 1;

[0027] Figure 7 A core neutron energy spectrum loaded with UN-UO2 dual-phase structure fuel rods of Example 2;

[0028] Figure 8 A core neutron energy spectrum loaded with UN-UO2 dual-phase structure fuel rods of Example 3;

[0029] Figure 9 A core neutron energy spectrum loaded with UN-UO2 dual-phase structure fuel rods of Example 4;

[0030] Figure 10Spectrum at beginning of core life (BOC) for a core loaded with UN-U02 dual- phase fuel rods of Examples 1-4, U02 fuel rods of Comparative Example 1;

[0031] Figure 11 Spectrum at mid of core life (MOC) for a core loaded with UN-U02 dual- phase fuel rods of Examples 1-4, U02 fuel rods of Comparative Example 1;

[0032] Figure 12 Spectrum at end of core life (EOC) for a core loaded with UN-U02 dual- phase fuel rods of Examples 1-4, U02 fuel rods of Comparative Example 1;

[0033] Figure 13 Plot of core fissile mass as a function of burnup for a core loaded with U02 fuel rods of Comparative Example 1;

[0034] Figure 14 Plot of core fissile mass as a function of burnup for a core loaded with UN-U02 dual-phase fuel rods of Example 1;

[0035] Figure 15 Plot of core fissile mass as a function of burnup for a core loaded with UN-U02 dual-phase fuel rods of Example 2;

[0036] Figure 16 Plot of core fissile mass as a function of burnup for a core loaded with UN-U02 dual-phase fuel rods of Example 3;

[0037] Figure 17 Plot of core fissile mass as a function of burnup for a core loaded with UN-U02 dual-phase fuel rods of Example 4;

[0038] Figure 18 Plot of core delayed neutron fraction as a function of time for a core loaded with UN-U02 dual-phase fuel rods of Examples 1-4, U02 fuel rods of Comparative Example 1;

[0039] Figure 19 Plot of core moderator temperature as a function of time for a core loaded with UN-U02 dual-phase fuel rods of Examples 1-4, U02 fuel rods of Comparative Example 1;

[0040] Figure 20 Plot of core fuel temperature reactivity coefficient as a function of time for a core loaded with UN-U02 dual-phase fuel rods of Examples 1-4, U02 fuel rods of Comparative Example 1;

[0041] Figure 21The core axial non-uniformity coefficient varies with time for the UN-UO2 dual-phase fuel rods of Examples 1-4 and the UO2 fuel rod of Comparative Example 1.

[0042] Figure 22 The diagram shows the change of the radial non-uniformity coefficient of the reactor core loaded with UN-UO2 dual-phase fuel rods of Examples 1-4 and UO2 fuel rods of Comparative Example 1 over time.

[0043] Figure 23 The graph shows the change of the total inhomogeneity coefficient of the reactor core loaded with UN-UO2 dual-phase fuel rods of Examples 1-4 and UO2 fuel rods of Comparative Example 1 over time.

[0044] Figure 24 The graph shows the change in the core transient neutron lifetime over time for reactors loaded with UN-UO2 two-phase fuel rods of Examples 1-4 and UO2 fuel rods of Comparative Example 1. Detailed Implementation

[0045] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0046] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0047] Example 1

[0048] like Figure 1 As shown, a UN-UO2 dual-phase fuel rod includes:

[0049] The inner circle contains UN microspheres 1, each with a diameter of 435.4 micrometers. All UN microspheres occupy 20% of the volume of the inner circle. Figure 1 The grid in the model is used for modeling. When actually filling, the distribution of UN sphere 1 in the inner circle is random and irregular.

[0050] The outer ring is wrapped around the inner ring and is filled with a UO2 fuel layer 3. The diameter of the inner ring is 80% of the diameter of the UN-UO2 dual-phase fuel rod. The fuel pellet composed of the UN spheres 1 in the inner ring and the UO2 fuel layer in the outer ring has a diameter of 8.192 mm.

[0051] The outer shell 5 is wrapped inside the outer ring. The outer shell is made of Zr-4 alloy and has a thickness of 0.572 mm. A helium layer 4 with a thickness of 0.082 mm is provided between the outer shell 5 and the inner ring.

[0052] Example 2

[0053] A UN-UO2 dual-phase structure fuel rod, comprising:

[0054] an inner ring, inside which UN pellets are dispersed, the diameter of the UN pellets being 498.4 microns, and all the UN pellets accounting for 30% of the volume of the inner ring;

[0055] an outer ring, wrapped outside the inner ring, the outer ring being filled with a UO2 fuel layer, wherein the diameter of the inner ring accounts for 80% of the diameter of the UN-UO2 dual-phase structure fuel rod, and the fuel pellet composed of the UO2 fuel layer in the inner ring and the outer ring has a diameter of 8.192 mm;

[0056] a cladding, wrapped inside the outer ring, the material of the cladding being Zr-4 alloy, the thickness of the cladding being 0.572 mm, and a helium layer being arranged between the cladding and the inner ring, the thickness of the helium layer being 0.082 mm.

[0057] Example 3

[0058] A UN-UO2 dual-phase structure fuel rod, comprising:

[0059] an inner ring, inside which UN pellets are dispersed, the diameter of the UN pellets being 548.6 microns, and all the UN pellets accounting for 40% of the volume of the inner ring;

[0060] an outer ring, wrapped outside the inner ring, the outer ring being filled with a UO2 fuel layer, wherein the diameter of the inner ring accounts for 80% of the diameter of the UN-UO2 dual-phase structure fuel rod, and the fuel pellet composed of the UO2 fuel layer in the inner ring and the outer ring has a diameter of 8.192 mm;

[0061] a cladding, wrapped inside the outer ring, the material of the cladding being Zr-4 alloy, the thickness of the cladding being 0.572 mm, and a helium layer being arranged between the cladding and the inner ring, the thickness of the helium layer being 0.082 mm.

[0062] Example 4

[0063] A UN-UO2 dual-phase structure fuel rod, comprising:

[0064] an inner ring, inside which UN pellets are dispersed, the diameter of the UN pellets being 590.8 microns, and all the UN pellets accounting for 50% of the volume of the inner ring;

[0065] an outer ring, wrapped outside the inner ring, the outer ring being filled with a UO2 fuel layer, wherein the diameter of the inner ring accounts for 80% of the diameter of the UN-UO2 dual-phase structure fuel rod, and the fuel pellet composed of the UO2 fuel layer in the inner ring and the outer ring has a diameter of 8.192 mm;

[0066] A cladding is wrapped inside the outer ring, the material of the cladding is Zr-4 alloy, the thickness of the cladding is 0.572mm, a helium layer is arranged between the cladding and the inner ring, and the thickness of the helium layer is 0.082mm.

[0067] Comparative Example 1

[0068] The present comparative example is a traditional UO2 fuel rod, that is, the fuel of the fuel pellets of the present comparative example is UO2 compared with Examples 1-4. The overall size parameters of the UO2 fuel rod of the present comparative example are the same as those of Examples 1-4.

[0069] As shown in Figure 2 , referring to the classic 17x17 arrangement of the Hualong No.1 reactor core, the reactor core is composed of 289 fuel assemblies, each of which contains 264 fuel rods UN-UO2 dual-phase structure fuel rods or UO2 fuel rods and 25 control rod guide tubes, the thickness of the guide tube is 0.5mm, the inner diameter of the guide tube is 11.9mm, and the center distance of the fuel rods is 12.6mm. The enrichment of uranium dioxide fuel used in the whole reactor core is 4.4%.

[0070] The fuel burnup calculation of each scheme is carried out for 1500 days, and the change of the effective multiplication factor of the reactor core with time and the change of the effective multiplication factor of the reactor core with burnup are shown in Figure 3 and Figure 4 .

[0071] As can be seen from Figure 3 and Figure 4 , the core life of the core added with UN and the core without UN can reach more than 1100 days, which meets the design standard of 540 days of the pressurized water reactor life, and the burnup depth is about 38GWd / MTU. Due to the limitation of the experimental software, there will be a certain degree of error. The specific core performance parameters of each scheme are shown in Table 1:

[0072] Table 1 Core performance parameters

[0073] Scheme UN 20% UN 30% UN 40% UN 50% No UN Days on stream / day 1137.82 1126.51 1113.15 1112.27 1139.57 Fuel consumption / GWd / MTU 39.3468 38.9214 38.5321 38.5009 39.3839 initial k eff ]] 1.3243 1.31747 1.31747 1.29961 1.34369

[0074] In combination with Figure 3 , Figure 4 and Table 1, two points can be seen, one is that the initial effective multiplication factor k eff of the core added with UN fuel pellets is lower than that of the core without UN fuel pellets, and the initial effective multiplication factor k eff of the core gradually decreases with the increase of the content of UN fuel, but no matter which content in the experimental scheme, the effective multiplication factor k eff is less than 1.0, and the effective multiplication factor k effThe burnup depth of the UN fuel core is slightly lower than that of the pure UO2 fuel core, and the burnup depth gradually decreases with the increase of the UN fuel content.

[0075] The UN fuel core has higher safety than the pure UO2 fuel core.

[0076] The neutron energy spectrum of each scheme and the neutron energy spectrum of each lifetime are shown in Figures 5-12 It can be seen from Figures 5-12 that in the low-energy region of E-9MeV to 1E-8MeV, the neutron energy spectrum of the UN-UO2 dual-phase structure fuel core is harder than that of the pure UO2 fuel core, and the energy spectrum difference in the high-energy region is not large, which shows that the UN-UO2 dual-phase structure fuel has limited influence on the neutron energy spectrum of the core.

[0077] In the present application, the core fuel is UN-UO2 dual-phase structure fuel, and thorium-based fuel is not used, 233 U is 232 converted from Th, so the statistical nuclide is 235 U, 239 Pu, 240 Pu and 241 Pu, which are fissile nuclides and secondary fissile nuclides. The fissile nuclides are directly driven nuclides of the chain reaction, and the concentration and capture-fission ratio determine the neutron utilization rate, and under the action of low-energy neutrons, 238 U has a higher fission probability than 239 Pu, but in the fast neutron energy spectrum, 239 Pu has a significant increase in fission advantage. The secondary fissile nuclides are generated from non-fissile nuclides (such as 238 U) through neutron capture and beta decay during the burnup process, gradually replacing the consumed 238 U, extending the core lifetime, and when the burnup is deepened, the fissile nuclides are continuously consumed, and the generation rate and consumption rate of the secondary nuclides determine the trend of the core reactivity. The statistics of the fissile nuclides and the secondary fissile nuclides of each scheme are shown in Figures 13-17 It can be seen from Figures 13-17 that with the operation of the core, the fissile nuclides 235 U in the initial loaded uranium dioxide fuel are gradually consumed, and 238 Pu, 239 Pu and 240 Pu generated from non-fissile nuclides (such as 241 U) through neutron capture and beta decay gradually increase, wherein 239Pu production is the most, the trend of nuclide change of each scheme is consistent, indicating that each scheme increases the core life and improves the economic performance of the reactor to some extent.

[0078] In the process of nuclear reactor operation, U-235 in uranium fuel will undergo fission after absorbing neutrons. The fission process releases a large number of prompt neutrons and a small amount of delayed neutrons. The proportion of delayed neutrons is called the effective fraction of delayed neutrons. Delayed neutrons can extend the millisecond chain reaction to minutes, so that the operator can have enough time to adjust the reactor operation according to the situation during the actual operation of the reactor, making manual control possible. The effective fraction of delayed neutrons of each scheme changes with time as shown in Figure 18 Figure 18 It can be seen from Figure 18 that the overall change of the effective fraction of delayed neutrons of the four schemes is relatively stable. The change of the effective fraction of delayed neutrons when the UN fuel volume accounts for 20% and 30% of the inner circle volume is more stable than that when the UN fuel volume accounts for 40% and 50% of the inner circle volume. Except for the scheme with UN small ball volume accounting for 50% of the inner circle volume, the last data fluctuates greatly from 0.00494 to 0.01127. All schemes show a decreasing trend, which is beneficial to the control of the reactor.

[0079] Temperature reactivity coefficient refers to the change of reactivity with the change of core temperature during reactor operation. In the design process of the core, it is necessary to ensure a reasonable reactivity coefficient to avoid accidents caused by temperature rise of the core. The range of temperature coefficient value will directly affect the control and safety of the core.

[0080] Three groups of temperature coefficients are calculated respectively: fuel temperature 1200K and moderator temperature 600K; fuel temperature 900K and moderator temperature 600K; fuel temperature 1200K and moderator temperature 550K.

[0081] Moderator temperature reactivity coefficient (MTC) is usually expressed in terms of reactivity change per degree Celsius (per degree Celsius). This coefficient is an important parameter to ensure the safe operation of nuclear reactors. Therefore, in the design process of the core, it is necessary to ensure that MTC is negative to prevent the core from losing control due to temperature rise. The MTC parameters of each scheme in this study are shown in Figure 19

[0082] As can be seen from Figure 19 , with the increase of time and burnup, the moderator temperature coefficient has a trend of first decreasing and then slowly rising, and the five schemes all have negative moderator temperature coefficients, so that the reactor has enough negative reactivity when the temperature rises during operation.

[0083] Fuel temperature reactivity coefficient (FTC) refers to the influence of the change of the reactor fuel temperature on the reactivity. With the increase of the core temperature, the volume of the nuclear material will expand due to thermal expansion and contraction, so the density of the nuclear material will decrease, the possibility of neutron collision will also decrease, and finally the change of the nuclear reaction activity will be caused. In the process of core design, the reasonable range of FTC value should be ensured, so as to reduce the risk of reactor accidents. The physical properties of nuclear fuel and the operating state of the reactor will affect the FTC. The FTC parameters of the schemes of the present application in the service life are shown in Figure 20 From Figure 20 it can be seen that, with the increase of time and burnup, the fuel temperature coefficient has the trend of first decreasing and then slowly rising, and the fuel temperature coefficient of the five schemes is negative, so that the reactor has sufficient negative reactivity when the temperature rises during operation.

[0084] From the above analysis, it can be seen that the moderator temperature coefficient and the fuel temperature coefficient both meet the design standard of the pressurized water reactor, and have sufficient negative reactivity, which improves the safety performance and economy of the core.

[0085] The neutron flux non-uniformity coefficient of the core is composed of two parts, which are the axial neutron flux non-uniformity coefficient and the radial neutron flux non-uniformity coefficient. This parameter represents the energy distribution state of the core, and is a parameter for measuring the uniformity of the neutron flux density distribution in the reactor. In the process of core design, the lower the value is, the more uniform the neutron flux density distribution is, and the more stable and safer the operation of the reactor is.

[0086] The axial non-uniformity coefficient, the radial non-uniformity coefficient and the total non-uniformity coefficient of the schemes of the present application in the service life are shown in Figure 21 , Figure 22 and Figure 23 respectively. From the above figures, it can be seen that the stability of the axial non-uniformity coefficient, the radial non-uniformity coefficient and the total non-uniformity coefficient of the core with UN pellet fuel changes better than that of the core with pure UO2 fuel, and the coefficients are relatively low, which has good safety. Among them, the scheme with UN pellet fuel volume ratio of 50% in the inner circle volume is the most stable, because the whole core uses fuel with enrichment of 4.4%, and there is no partition loading, so the total non-uniformity coefficient is higher than 4, which exceeds the design range. In the later stage, partition loading and other means can be used to reduce the non-uniformity coefficient, so that it is reduced to the design range below 2.6. Overall, the change of the core non-uniformity coefficient is relatively stable, which can reduce the risk of local overheating, helps to ensure that the reactor can remain stable under various operating conditions, and reduces the risk of accidents. It is also helpful to prolong the service life of the fuel rod and increase the economy of the reactor.

[0087] The prompt neutron lifetime represents the average time from the release to the absorption or leakage of the prompt neutron generated by fission, which is a key parameter in nuclear reactor physics and is mainly determined by the moderation time and the diffusion time. The prompt neutron lifetime of each scheme changes with time as shown in Figure 24 From Figure 24 It can be seen that the prompt neutron lifetime of each scheme is relatively stable within 1100 days without dramatic changes, and meets the design standard (10 -5 s order) of the pressurized water reactor. The prompt neutron lifetime of the UN-free scheme is higher than that of the scheme with UN. With the increase of the UN fuel addition amount, the prompt neutron lifetime is lower. The reason may be that UN has a higher uranium density, and its fission cross-section characteristics reduce the neutron moderation requirement, which can more efficiently utilize neutrons and shorten the moderation process time.

[0088] Through the safety performance parameter analysis of the reactor equipped with UN-UO2 dual-phase structure fuel, including the effective fraction of delayed neutrons in the core, the temperature reactivity coefficient, and the core non-uniformity coefficient, the following conclusions are drawn: In terms of the effective fraction of delayed neutrons, the data show that when the UN pellet fuel volume accounts for 20% and 30% of the inner circle volume, both have good stability of the effective fraction of delayed neutrons, which is conducive to the control of the reactor; the analysis results show that when the UN pellet fuel volume accounts for 20% and 30% of the inner circle volume, the fuel temperature coefficient, the moderator temperature coefficient, and the total temperature coefficient are more stable, so the negative reactivity is better, and the safety performance of the core is higher; by comparing the non-uniformity coefficients of the five schemes, it can be found that the scheme with UN pellet fuel volume accounting for 50% of the inner circle volume has the best stability, which has a positive effect on improving the safety and economy of the reactor; the prompt neutron lifetimes of the five schemes all meet the design standard (10 -5 s order) of the pressurized water reactor, and the prompt neutron lifetime of the scheme with UN is lower. The safety and economy of the 177 core equipped with UN-UO2 dual-phase structure fuel perform well.

[0089] The number of devices and the scale of processing described herein are used to simplify the explanation of the present application. Applications, modifications, and variations of the present application that are obvious to those skilled in the art are intended to be within the scope of the present application.

[0090] Although the embodiments of the present application have been disclosed as above, they are not limited only to the applications listed in the specification and the embodiments, and can be fully applied to various fields suitable for the present application, and additional modifications can be easily realized by those skilled in the art, and therefore the present application is not limited to specific details and the figures shown and described herein, without departing from the general concept defined by the claims and the equivalent scope.

Claims

1. A UN-UO2 bi-phase structured fuel rod characterized in that, The application relates to a UN-UO2 dual-phase structure fuel rod, which comprises the following parts: an inner ring, the inside of which is filled with UN small balls; an outer ring, which is wrapped outside the inner ring, and the outer ring is filled with a UO2 fuel layer; a cladding, which is wrapped inside the outer ring, and a helium layer is arranged between the cladding and the inner ring.

2. The UN-UO2 bi-modal fuel rod of claim 1 wherein, The UN pellets of the inner ring are filled with UN pellets between them 235 UO2 fuel with U enrichment of 4.4%.

3. The UN-UO2 bi-modal fuel rod of claim 2, wherein, The diameter of the UN small balls is 435.4-590.8 mu m.

4. The UN-UO2 bi-modal fuel rod of claim 1 wherein, The diameter of the inner ring accounts for 80% of the diameter of the UN-UO2 dual-phase structure fuel rod.

5. The UN-UO2 bi-modal fuel rod of claim 2, wherein, The filling volume of the UN small balls is 30%-50% of the volume of the inner ring.

6. The UN-UO2 bi-modal fuel rod of claim 1 wherein, The UO2 fuel layer has a 235 U enrichment of 4.4%.

7. The UN-UO2 bi-modal fuel rod of claim 1 wherein, The material of the cladding is Zr-4 alloy.

8. Use of a UN-UO2 bi-phase structured fuel rod as claimed in any one of claims 1 to 7 for loading of a fuel assembly in a nuclear reactor; wherein, The fuel assembly is arranged in a 17*17 mode and comprises 264 UN-UO2 dual-phase structure fuel rods and 25 control guide tubes; the core of the nuclear reactor comprises 289 fuel assemblies, and the fuel assemblies are arranged in a 17*17 mode.

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