CN100578681C - "Water boiler" solution nuclear reactor with intrinsic safety - Google Patents

Abstract

The invention discloses a 'water boiler' solution nuclear reactor with intrinsic safety, using concentrated UO₂(NO₃)₂Solutions or UOs₂SO₄The solution is nuclear fuel, a flat reactor core structure is adopted, the ratio of the height of the reactor core solution to the diameter of the reactor core is 0.3-0.8, when the volume ratio power is maintained at 2.0-2.5 kW/L, the volume of the reactor core solution can reach 50-200L, and the reactor power is more than 100 kW.

Description

Intrinsically Safe "Water Boiler" Solution Nuclear Reactor

technical field

The invention relates to a "water boiler" solution nuclear reactor, in particular to a "water boiler" solution nuclear reactor with inherent safety.

Background technique

The homogeneous solution nuclear reactor using uranium brine solution as nuclear fuel is also called "water boiler" reactor. It is characterized in that the fuel solution transfers the fission heat to the cooling pipe or the cooling wall by convection through natural convection of the fuel solution (including the disturbance of the rising air flow).

This "water boiler" reactor concept was first proposed in the world in 1943, and a Lopo (zero power) reactor fueled by uranyl sulfate aqueous solution was built in Los.Alamos National Laboratory in the United States in 1944. It provides not only critical mass data but also manipulation and control experience.

In December 1944, the Hypo reactor with power operation was built. Based on the Lopo reactor, the fuel was changed from uranyl sulfate aqueous solution to uranyl nitrate aqueous solution, and the reactor power was increased to the range of 1-5.5kW. The hydrogen and oxygen gas produced by the fragments in the solution bombarding the water and the radioactive gas produced by the fission are discharged into the atmosphere through the chimney through dilution and filtration. After running for several hundred kW-h, the nitrogen content in the original solution is reduced by 30% and is taken away by the air, so 6cm ³ of acid water/kW-h is required to make up to ensure continuous operation.

In order to solve the problems of nitrogen loss and hydrogen-oxygen composite water return to the reactor, the Hypo reactor was converted into a Supo reactor in 1950. The maximum reactor power was 45kW, and the fuel solution was still uranyl nitrate aqueous solution. The stack establishes a closed gas circuit, hydrogen and oxygen are combined into water through the catalytic bed, and the stack is returned under condensation to seal the radioactive gas, nitrogen, and nitrogen oxides in the gas circuit to avoid the loss of nitrogen in the solution. U-235 is rich in The concentration was changed from 14.5% to 88.7%, which greatly reduced the gas produced by the decomposition of nitric acid.

Some of the above-mentioned reactor types start from the pursuit of the minimum critical mass, and do not emphasize the inherent safety of introducing negative reactivity under the condition of dilution and concentration of the fuel solution.

Solution reactors are mainly used for neutron activation analysis, neutron imaging and various research work. Due to the successful development of solid fuel research reactors, which can provide higher power levels and neutron fluence rate levels, research reactors have gradually replaced solution reactors. heap. In the 1990s, as most of the research reactors in the world were aging, they faced the problem of the source of medical isotopes in the future. The United States proposed the conceptual design of the Medical Isotope Production Reactor (MIPR). This creates an opportunity for the redevelopment and utilization of solution reactors. As the world attaches great importance to nuclear safety, the redevelopment of solution reactors must be based on a more secure and reliable foundation.

The Russian "Argus" heap is an inherently safe solution heap. That is, fuel solutions, whether concentrated or diluted, introduce negative reactivity. Another feature is that under the conditions of failure of the cooling system and failure of the control and protection system, the heating of the fuel solution introduces negative reactivity and reduces the power of the stack. The negative reactivity introduced by temperature rise counteracts the positive reactivity introduced by the reduction of cavitation share in power reduction, and the stack power is automatically adjusted to a power level balanced with natural heat dissipation. At this time, the temperature of the fuel solution is still lower than the boiling temperature of the fuel solution. The Russian "Argus" reactor is 20kW, and the ratio of height to diameter is 1:1, that is, the diameter of the core is 30cm, the height of the solution is about 30cm, and the volume of the solution is about 20L. The uranium-235 content is 90%, and the initial uranium loading is 1.5kg. From the change curve of the uranium-235 concentration in the solution and the reserve effective reactivity (K _eff ), the critical mass of the uranium-235 in the range of 60-85g/l is the smallest, namely Solution concentration can be achieved or dilution can introduce negative reactivity. Although the stack has inherent safety, the stack power is only 20kW, and the production capacity is low. To increase the production capacity, the stack power must be increased, so that the stack has both inherent safety and high stack power. At present, there are no relevant reports on solution reactors with a reactor power greater than 100kW and inherent safety at home and abroad.

Contents of the invention

The object of the present invention is to provide an inherently safe "water boiler" solution nuclear reactor with a stack power greater than 100 kW.

A "water boiler" solution reactor with inherent safety of the present invention has a flat core, the core solution height/core diameter ratio is 0.3-0.8, and the concentrated UO ₂ (NO ₃ ) ₂ solution is used Or UO ₂ SO ₄ solution as nuclear fuel, when the volume specific power is maintained at 2.0-2.5kW/L, the volume of the core solution can reach 50-200L, and the stack power is greater than 100kW.

The above-mentioned "water boiler" solution reactor with inherent safety adopts a flat-bottomed cylindrical core or a dish-bottomed cylindrical core, and the core is divided into inner and outer areas, and the inner area has no cooling pipes Cooling pipes are arranged in the outer area; control rod guides are arranged in the inner area without cooling tubes, and the control rod guides are sealed and welded with the upper cover of the core vessel and the lower bottom of the core vessel. The inside of the control rod guides is cooling water, and the outside is in contact with the fuel solution; The radially outer area of the core solution is arranged with a cooling pipe fuel inner area, and the cooling pipe is coiled longitudinally in a helical shape. The upper reflective layer is provided with a water or graphite reflective layer outside the core vessel.

The inherently safe "water boiler" solution reactor as described above has a combustible neutron poison Gd-155 added to its core solution.

In the inherently safe "water boiler" solution reactor as mentioned above, the combustible neutron poison Gd-155 added to the core solution is in the form of Gd(NO ₃ ) ₃ .

The "water boiler" solution reactor with inherent safety as mentioned above operates in the mode of variable solution uranium concentration and variable power operation.

When designing a solution nuclear reactor whose reactor power is greater than 100kW and which is inherently safe, if only expanding the volume of the core solution is designed according to the normal core height-to-diameter ratio (1:1), the effective reactivity (K _eff ) of the reactor backup will be large. to the point where it is difficult to control. In order to reduce K _eff , the present invention adopts a flat core structure, through the increase of neutron leakage, the maximum value of K _eff along with the solution uranium concentration change curve moves to the direction of uranium-235 concentration reduction, so as to facilitate the expansion of the core solution volume . When the stack specific power is maintained at 2-2.5kW/L, the volume of the core solution can reach 50-200L. Because the reactivity change caused by the flat core when the solution is concentrated is composed of two parts: one is the positive reactivity introduced by the solution concentration, and the other is that the decrease of the solution height increases the ratio of leakage surface to fuel volume and introduces negative reactivity. The superposition of the two parts of reactivity gradually introduces negative reactivity under the condition of solution concentration. The invention utilizes this principle to realize the inherent safety of introducing negative reactivity in both the dilution and enrichment of the fuel solution at a lower solution uranium concentration. The flat core structure that the present invention adopts also makes the solution surface area/solution volume ratio increase, and the cavitation in the solution overflows easily, and is more conducive to keeping the core solution temperature lower than the boiling temperature when the accident power failure control rod refuses to move, and the reactor power can Automatically drops to a power level balanced with natural heat dissipation.

In the present invention, the core is divided into inner and outer areas, the inner area has no cooling pipes, and the outer area is arranged with cooling pipes, which is beneficial for the maximum value of the curve of K _eff changing with the concentration of uranium in the solution to move to the low concentration direction and reduce the loading of uranium-235. Adding a local reflective layer to the upper air cavity of the core solution is also beneficial to reducing the uranium-235 loading.

In order to prolong the refueling period under small K _eff , the present invention also adds combustible neutron poison Gd-155 (for example in the form of Gd(NO ₃ ) ₃ ) in the core solution, because the Gd-155 neutron absorption cross section is moderate, The reactivity that can cause the loss of uranium-235 fuel can be compensated by the positive reactivity of Gd-155 to reduce the release. It is calculated that under the backup reactivity of less than 1 effective delayed neutron fraction (β _eff ), it can be used at 1000 EFPD (Effective full power days) Do not replenish the solution.

During isotope extraction, in order to reduce the loss of solution, the solution on the isotope extraction column should be rinsed with dilute nitric acid, and this part of the uranium-containing flushing solution should be returned to the stack, which will cause the dilution of the stack solution, and use variable solution uranium concentration and variable power The operation mode can solve the problem of solution dilution, that is, the concentration of uranium in the solution changes, and the stack power gradually changes. When the concentration of uranium in the solution increases, the stack power increases automatically or manually. Adopting such an operation mode is conducive to reducing the initial backup reactivity, enabling the reactor to have a relatively large reactor power (greater than 100kW), and has inherent safety.

The effect of the present invention is: since medical isotopes such as molybdenum-99, sulfur-131 and strontium-89 are the pillar products of nuclear medicine, the "water boiler" solution nuclear reactor with inherent safety of the present invention can improve molybdenum-99, The production capacity of medical isotopes such as iodine-131 and strontium-89 can meet the needs of the market, and the economic and social benefits are considerable. At the same time, it also has good application prospects for neutron activation analysis, neutron photography and neutron cancer treatment.

Description of drawings

Figure 1 is a schematic diagram of the structure of a flat-bottomed cylindrical core.

Figure 2 is a schematic diagram of the cylindrical core structure with a dish bottom.

In the figure: 1. Inner area without cooling tube; 2. Core container; 3. Fuel inner area with cooling tube; 4. Control rod conduit; 5. Cooling tube manifold; 6. Cooling tube inlet and outlet pipe; Upper reflective layer; 8. Water or graphite reflective layer.

Detailed ways

Now in conjunction with accompanying drawing, the present invention will be further described:

Taking the 200kw reactor power as an example, the specific core design is carried out.

Example 1

As shown in Figure 1, a flat-bottomed cylindrical core structure is adopted, and the flammable neutron poison Gd-155 is not contained in the core solution. The UO ₂ (NO ₃ ) ₂ solution or UO ₂ SO ₄ solution of enriched uranium is placed in the core vessel 2, the diameter (inner diameter) of the core is 70cm, the height of the core vessel is about 70cm, and the height of the core solution is 25-32cm (depending on the solution uranium concentration), the core solution is radially divided into inner and outer areas, and only 3 to 6 control rod conduits 4 are arranged in the inner area without cooling tubes. The lower bottom is sealed and welded, the inside of the control rod conduit 4 is cooling water, the outside of the control rod conduit 4 is in contact with the fuel solution, the radially outer area of the core solution is arranged with a cooling pipe in the fuel inner area 3, and the cooling pipe has 20 branches in a spiral shape Coiled lengthwise. Arrangement of radiation lines, arranged in the range of R = 13.5 ~ 35.0cm, each radiation line is wound 13 times, and the pipe diameter is Φ8×1.5. The 20 branch cooling pipes flow into the cooling pipe manifold 5, and then the cooling water inlet and outlet pipes 6 in and out. Above the core solution is the upper core reflective layer 7, and outside the core vessel is a water or graphite reflective layer 8.

Initial conditions for nuclear design: uranium-235 initial charge 4.44kg, uranium-235 enrichment 90%, UO ₂ (NO ₃ ) ₂ aqueous solution, containing 0.2mol/L nitric acid. The calculation results of K _eff with the concentration of uranium in the solution are shown in Table 1. The maximum point of K _eff corresponds to a uranium concentration of 54gU/L, and the operating point of the reactor can be selected at 46gU/L, corresponding to a solution volume of 111.8L.

Table 1 The change of K _eff with uranium concentration in a flat-bottomed cylindrical core (without Gd-155)

serial number Uranium concentration in solution gU/L Solution height Hcm   Full lifting stick K_eff Uranium-235 loading Kg Solution volume L 7H7046F 46 32.00 1.000085 4.437 111.86 7H7048F 48 30.67 1.007643 4.437 107.17 7H7050F 50 29.44 1.007942 4.439 102.91 7H7052F 52 28.31 1.009530 4.441 98.96 7H7054F 54 27.26 1.009798 4.437 95.29 7H7056F 56 26.29 1.009109 4.439 91.90 7H7058F 58 25.38 1.007536 4.440 88.71

Example 2

As shown in Figure 1, a flat-bottomed cylindrical core structure is adopted, and an appropriate combustible neutron poison Gd-155 (in the form of Gd(NO ₃ ) ₃ ) is added to the core solution.

The core structure is the same as in Example 1, except that gadolinium-155 is added to UO ₂ (NO ₃ ) ₂ . The nuclear design calculation result K _eff varies with the concentration of uranium in the solution, see Table 2. The maximum point of K _eff corresponds to a uranium concentration of 52gU/L, and the operating point of the reactor can be selected at 46gU/L, corresponding to a solution volume of 122.3L, and a Gd-155 content of 9.13 gram. At the concentration of 46gU/L, the fuel consumption is uniform at full power, and the K _eff changes with the fuel consumption are shown in Table 3.

Table 2 Data table of K _eff changing with uranium concentration in a flat-bottomed cylindrical core (containing Gd-155)

serial number Uranium concentration in solution gU/L Solution height Hcm   Full lifting stick K_eff Uranium-235 loading Kg Solution volume L   Full lifting stick K_eff Gd-155 7H7042AGD 42 38.33 0.994550 4.85465 133.981 0.916138 9.13126 7H7044AGD 44 36.59 0.999497 4.85582 127.899 0.922527 9.13117 7H7046AGD 46 35.00 1.002238 4.85311 122.341 0.926179 9.13111 7H7048AGD 48 33.54 1.004490 4.85388 117.238 0.929326 9.13099 7H7050AGD 50 32.20 1.005608 4.85549 112.554 0.931801 9.13118 7H7052AGD 52 30.96 1.005958 4.85652 108.220 0.933199 9.13104 7H7054AGD 54 29.81 1.004269 4.85227 104.200 0.933025 9.13111 7H7056AGD 56 28.75 1.003107 4.85471 100.495 0.931284 9.13102 7H7058AGD 58 27.76 1.001679 4.85649 97.0340 0.931943 9.13101

Table 3 Data table of K _eff variation with burnup of flat-bottomed cylindrical core (including Gd-155)

EFPD   Full lifting stick K_eff Gd-155 0 1.0022 9.13111 2 1.0022 9.11097 100 1.0018 8.19998 200 1.0016 7.69303 300 1.0015 7.22290 400 1.0017 6.78037 500 1.0018 6.36390 600 1.0019 5.97260 700 1.0018 5.60332 800 1.0018 5.25653 900 1.0021 4.93042 1000 1.0019 4.62379

Example 3

As shown in Figure 2, the dish bottom cylindrical core structure does not contain combustible neutron poison Gd-155 in the core solution.

The core structure is basically the same as in Example 1, except that the bottom of the core is changed from a flat bottom to a dish bottom. The bottom R of the dish is 630mm, the r is 63mm, the dish height is 142mm, and the dish volume is 33.70L. The height of the core solution is 21.4-30.5cm (varies with the concentration of uranium in the solution), the initial loading of uranium-235 is 3.00kg, and the enrichment degree of uranium-235 is 90%. The nuclear design calculation results of K _eff changing with the concentration of uranium in the solution are shown in Table 4. The maximum point of K _eff corresponds to a uranium concentration of 44gU/L, and the operating point of the reactor can be selected at 36gU/L, corresponding to a solution volume of 95L. To achieve 100L, the core diameter must be increased.

Table 4 Data table of the change of K _eff with uranium concentration in the dish-bottomed cylindrical core (excluding Gd-155)

serial number Uranium concentration in solution gU/L Solution height Hcm   Full lifting stick K_eff Uranium-235 loading Kg Solution volume L Air cavity height cm E7034 34 30.48 1.002913 2.9511 100.63 9.52 E7036 36 28.91 1.008228 2.9523 95.04 11.09 E7038 38 27.50 1.011884 2.9518 90.02 12.50 E7040 40 26.24 1.014046 2.9511 85.54 13.76

E7042 42 25.09 1.015186 2.9510 81.44 14.91 E7044 44 24.05 1.015231 2.9515 77.74 15.95 E7046 46 23.10 1.013889 2.9496 74.36 16.90 E7048 48 22.23 1.012135 2.9503 71.26 17.77 E7050 50 21.43 1.009611 2.9512 68.41 18.57

Claims (5)

1. " homogeneous solution-type reactor " solution reaction heap with inherent safety is used the UO that concentrates ₂(NO ₃) ₂Solution or UO ₂SO ₄Solution is characterized in that as nuclear fuel: height/core diameter is than the pancaked core that is 0.3～0.8 to adopt reactor core solution, and when volumetric specific power maintained 2.0～2.5kW/L, the reactor core liquor capacity can reach 50～200L, and heap power is greater than 100kW.

2. " homogeneous solution-type reactor " solution reaction heap with inherent safety according to claim 1, it is characterized in that: described pancaked core is a cylindrical reactor core at the bottom of flat cylindrical reactor core or the dish, reactor core is divided into inside and outside two districts, and inner region does not have cooling tube, and outskirt is arranged cooling tube; No cooling tube inner region (1) is furnished with control rod guide tube (4), and control rod guide tube (4) and the loam cake of core vessel (2) and the seal welding of going to the bottom of core vessel (2) are chilled water in the control rod guide tube (4), contact with fuel solution outward; Reactor core solution radially outskirt is furnished with cooling tube fuel inner region (3), and the cooling tube curl vertically coils, and cooling tube water is flowed to cooling tube collecting pipe (5), is passed in and out by cooling water outlet and inlet pipe (6) again; Reactor core solution top is provided with reactor core top reflector (7), and core vessel is provided with water or graphite reflector (8) outward.

3. " homogeneous solution-type reactor " solution reaction heap with inherent safety according to claim 1 and 2 is characterized in that: be added with flammable neutron poison Gd-155 in the reactor core solution.

4. " homogeneous solution-type reactor " solution reaction heap with inherent safety according to claim 3, it is characterized in that: flammable neutron poison Gd-155 is Gd (NO ₃) ₃Form.

5. " homogeneous solution-type reactor " solution reaction heap with inherent safety according to claim 3 is characterized in that: adopt the mode that becomes solution uranium concentration and the operation of change power to move.

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