RU2315373C1 - Core of high-temperature thermal reactor using finely dispersed solid coolant - Google Patents

Abstract

FIELD: nuclear power engineering; cores of high-temperature thermal reactors using finely dispersed solid coolant.

SUBSTANCE: proposed reactor core has bottom supporting plate with side neutron deflector as well as control and protection system rod tubes fixed with supporting plate. Fuel assemblies are disposed between tubes and are assembled of vertically mounted graphite-clad fuel elements by means of spacer members forming clearances for passing graphite-containing coolant and for accommodating turbulizing members. Fuel elements are made in the form of cylinders, (5-30)D long, where D is fuel element diameter. Cladding wall thickness ranges between 2 and 10 mm. Each fuel element is provided with two turbulizers in the form of cowlings, for instance, conical in shape, mounted at its ends. Fuel elements are assembled to form fuel assemblies in layer-by-layer manner so that top cowlings of bottom layer are disposed between bottom cowlings of upper layer of fuel elements. Spacer members are installed between layers in vicinity of cowlings and fuel assemblies are loosely mounted one on top of other between tubes as guides and rest on bottom.

EFFECT: enhanced uniformity and effectiveness of heat removal, as well as specific power of reactor core without increasing coolant flow velocity.

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Description

1. The technical field to which the invention relates.

The invention relates to the field of nuclear energy, in particular to the active zones of high-temperature thermal neutron reactors with solid finely divided coolant.

2. The level of technology

The active zone of a high-temperature thermal neutron reactor with a solid finely dispersed heat carrier is known, consisting of fuel assemblies assembled from vertically arranged fuel rods using spacer parts that form gaps for the passage of a graphite-containing coolant and lean on the reactor vessel through transition parts with the possibility of partial lifting coolant assemblies for reactivity control (see, Rigg S., Greenlees FM Nuclear reactor. UK patent and No. 1309883, MKI G21D 5/00, NCI G6C30X363, Declared February 18, 1971, published March 14, 1973]. In this design, fuel rods in height occupy almost the entire active zone, the heat carrier is prone to sticking, which results in uneven heat removal in height fuel rods and increases the likelihood of their thermal destruction, especially when removing fuel rods above the coolant level to regulate reactivity.

This design coincides with the claimed core according to the following essential features:

- there is a reactivity control system (by partial extraction of fuel elements from the coolant);

- fuel assemblies are assembled from vertically arranged fuel rods with the help of spacer parts, forming gaps for the passage of graphite-containing coolant.

Also known is the design of the core of a high-temperature thermal neutron reactor with a finely dispersed solid coolant, consisting of a lower support platform with a lateral neutron reflector, fuel assemblies placed between the pipes of the reactor control and protection system and assembled from vertically arranged plate fuel elements with a graphite sheath using distance parts forming the gaps for the passage of graphite-containing coolant, in which turbulent elements are installed you made in the form of one-sided fins, spiral fins or screws. The heat-carrying elements are made of graphite mass coated with pyrolytic carbon with a restriction in diameter and non-sphericity, which eliminates sticking (see, for example, Nuclear Power Reactor. RF Patent No. 2166806, IPC G21C 15/24, dated 09.02.2000). This design of the active zone is also associated with significant local inhomogeneities of heat removal along the length of the fuel rod due to the formation of voids under the turbulators and zones of stationary particles above them in the gravitationally moving coolant layer.

This design coincides with the claimed core according to the following essential features:

- lower support platform

- lateral neutron reflector;

- pipes of rods of the reactor control and protection system;

- fuel assemblies placed between the pipes;

- fuel assemblies are assembled from vertically arranged fuel rods with a graphite cladding using spacers that form gaps for the passage of a graphite-containing coolant;

- turbulizing elements installed in the gaps.

The latter design is closest to the claimed core in terms of essential features and is selected as a prototype.

3. The invention

The proposed active zone consists of a lower support platform with a lateral neutron reflector, rigidly connected to the tube platform of the reactor control and protection rods, fuel assemblies placed between the tubes and assembled from vertically arranged fuel rods with a graphite cladding using spacers that form gaps for the passage of graphite-containing coolant in which turbulizing elements are installed. The fuel rods are made in the form of cylinders with a length of (5 ÷ 30) D, where D is the diameter of the fuel rod, the wall thickness of the claddings is selected in the range of (3-10) mm, each fuel rod is equipped with two turbulators in the form of fairings, for example, conical, mounted on it At the ends, the fuel rods are assembled in layers so that the upper fairings of the lower layer of the fuel rods are located between the lower fairings of the upper layer, the spacers are installed between the layers in the region of the fairings, and the assemblies are placed loosely on each other between the pipes as guides and with a stop at the bottom.

This device differs from the prototype in that the fuel rods are made in the form of cylinders with a length of (5 ÷ 30) D, where D is the diameter of the fuel rod, the shell wall thickness is selected in the range (3-10) mm, each fuel rod is equipped with two turbulators in the form of fairings, for example, of a conical shape mounted on its ends, the fuel rods are assembled in layers so that the upper fairings of the lower layer of the fuel rods are located between the lower fairings of the upper layer, the spacers are installed between the layers in the area of the fairings, and the assemblies are placed freely on each other between pipes as guides and with an emphasis below.

The implementation of the fuel elements in the proposed core of the reactor with the ratio of the outer diameter to the length, determined by the ratio L = (5 ÷ 30) D, provides efficient heat removal by a solid heat carrier. When shortening the length below 5D, the core structure is oversaturated with spacers of short fuel rods; with a length of more than 30D, the efficiency of heat removal by a solid heat carrier begins to really decrease.

The choice of the wall thickness of graphite shells in the range of 3 ÷ 10 mm makes it possible to ensure reliable stiffness of short fuel rods without loss of coolant velocity.

The presence of turbulizers in the form of conical fairings mounted on the ends of the fuel rods, and the arrangement of the fuel rods in assemblies with the displacement of the layers provides mixing of the coolant in the gaps between the layers, aligning the temperature of the coolant in a horizontal plane at the entrance to the flushing region of the cylindrical surface of the fuel rods.

This design of the active zone provides an increase in the uniformity and efficiency of heat removal and specific power of the active zone of a nuclear reactor without increasing the speed of the coolant.

4. The list of drawings.

Figure 1. Scheme of the active zone. In the diagram:

1 - lower support platform;

2 - side neutron reflector;

3 - pipe rods of the control system and reactor protection;

4 - fuel assembly;

5 - fuel rod;

6 - turbulizers in the form of fairings;

7 - spacer parts.

Figure 2. Cross section of a core section.

5. Information confirming the possibility of carrying out the invention

The possibility of carrying out the invention is illustrated by a specific example.

Figure 1 shows a diagram of the active zone of the inventive reactor. It contains a lower support platform 1 on which a lateral neutron reflector 2 is mounted and graphite tubes 3 are mounted to accommodate the rods of the control system and emergency protection. The fuel assembly 4 consists of two layers of vertically arranged fuel elements 5. Each fuel element has a tubular cladding with an external diameter of 20 mm and an internal 12.7 mm, a length of 33 cm, in which there are 6 fuel assemblies with a diameter of 12.5 mm and a height of 50 mm made of microfuel and graphite binder. The ends of the shells are drowned out by turbulators 6 in the form of conical fairings with a height of the conical part of 25 mm.

The fuel rods are assembled into a fuel assembly of 15 pieces in a row in a square grid with a step of 30 mm in two layers with a height of 225 fuel rods in each layer. Of the total number of fuel rods in the assembly (450 pieces), part (8 pieces) are removed from the corners. The lattice pitch at the indicated fuel rod sizes is determined on the basis of computational studies of the neutron-physical characteristics of a reactor with a solid coolant and a fuel cycle based on enriched uranium. The fuel elements in the assembly are offset relative to each other, for example, as shown in FIG.

Spacer parts 7 made of graphite materials (or refractory metals, or oxides) connect the fuel rods in the assemblies, are located in the area of the fairings and form the gaps between the fuel rods for the coolant passage, acting as additional turbulators, as well as the role of the distance and support elements between the fuel assemblies.

Each lower layer of fuel rods is located relative to the upper layer with a shift so that the lower layer of fuel rods is located in the middle of the space along the coolant of the upper layer. The upper fairings of the lower layer fuel rods are at or above the end of the lower fairing of the upper fuel layer.

A fuel assembly with an outer dimension of the sides of a square-truncated corner of ~ 460 mm is installed between graphite tubes 2 with an outer diameter of 55 mm and an inner diameter of 25 mm. Pipes have a height of about 6 meters and form a supporting frame of the core. Inside the pipes are rods of the control and protection system. Each fuel assembly has an installation height of 67 cm and 8 fuel assemblies, mounted vertically, form an active zone with a height of 5.36 meters, while the height of the fuel compacts is 4.8 meters. Due to the layer-by-layer shift and the arrangement of the spacer parts in the area of the fairings, 16 layers of fuel rods mix the coolant well and special turbulators in the area of the cylindrical surfaces of the fuel rods are not required. The mounting gaps between the fuel assemblies and the pipes of the reactor control and protection system are about 1 mm, which makes it possible to freely assemble the assemblies into the active zone and compensate for the temperature and radiation effects of the shape change.

In the cross section, the area of the fuel rods is 32% of the area of the assembly cell, and the area of the pipes under the channels of the protection and control rods is ~ 1%. Thus, in comparison with the prototype, the gap area under the coolant is increased in the proposed design from 40 to 67%, which at a fixed speed allows you to increase heat removal from the core by ~ 65%.

The outer diameter of the active zone is ~ 9 meters, and the entire active zone consists of fuel assemblies placed freely between the pipes with an emphasis below on the spacing elements of the lower fuel assemblies. In total, the active zone contains ~ 2388 fuel assemblies arranged vertically, each of 8 pieces in 299 fuel assemblies.

The active zone of the design proposed and described in this example provides the thermal power of the 3750 MW reactor at a coolant speed of 17 cm / sec. At temperatures of the coolant at the inlet and outlet of 500 and 900 ° C, the flow rate of the coolant will be 5.2 t / s. The coolant passes the core in ~ 33 sec, the heating rate on average in the core is ~ 12.5 ° C / s.

It is easy to show that the thermal relaxation time of heat-carrying particles with a decrease in the thermal conductivity of pyrographite to ~ 8 W / m · deg due to the effect of neutron irradiation is about 0.3 s.

Thus, the thermal inertia of the heat-carrying particles does not play a significant role in the proposed design and core parameters.

Experiments were performed that showed that the proposed design of the active zone achieves efficient mixing of the coolant and heat exchange between the heat-carrying particles (equalizing the temperature at the outlet of the reactor) practically without using special turbulators in the areas of the side surfaces of the fuel rods and without the formation of stagnant coolant zones over the fuel rods and voids below the fuel rods, i.e. uniformity of the uranium-graphite ratio in the core of the proposed type is ensured.

Claims (1)

The active zone of a solid-state high-temperature thermal neutron reactor consisting of a lower support platform with a lateral neutron reflector rigidly connected to the tube platform of the reactor control and protection rods, fuel assemblies placed between the tubes and assembled from vertically arranged graphite clad fuel rods with using spacers that form gaps for the passage of graphite-containing coolant, in which turbulizing elements are installed, in that the fuel rods are made in the form of cylinders with a length of (5 ÷ 30) D, where D is the diameter of the fuel rod, the wall thickness of the claddings is selected in the range (3-10) mm, each fuel rod is equipped with two turbulators in the form of fairings, for example, conical in shape installed on its ends, the fuel rods are assembled in layers so that the upper fairings of the lower layer of the fuel rods are located between the lower fairings of the upper layer, the spacers are installed between the layers in the area of the fairings, and the assemblies are placed freely on each other between the pipes as guides and rum down.

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