KR820001369B1 - Integral nuclear fuel element assembly - Google Patents

Abstract

A fuel assembly for a pressurized water fast breeder reactor has parallel pins each with tubular metal cladding(12) having a longitudinal fin with its extremity brazed to the cladding of an adjacent pin to form an integral assembly(10) with a moderator. The pins contain Pu as fuel and water is heavy water. One or more pins may have a number of longitudinal fins. The assembly prefers to include an Al alloy block with first channels for fuel and second channels for coolant arranged such that neutrons can pass between first channels without traversing coolant channels.

Description

Integral Nuclear Fuel Assembly

1 is a partial cross-sectional view of a fuel assembly.

2 is a partial perspective view of a fuel body having several fins arranged in accordance with another embodiment of the present invention.

3 is a partial perspective view of several fuel bodies arranged in accordance with another embodiment of the present invention.

4 is a partial cross-sectional view of a fuel assembly with a fuel body in accordance with another embodiment of the present invention.

5 is a partial plan view of a block core arrangement for a low temperature reactor.

TECHNICAL FIELD The present invention relates to the design of nuclear fuel assemblies for use in nuclear reactors, and more particularly, to fast breeding reactors using polotonium as nuclear fuel and pressurized or heavy water as reactor coolants and moderators.

The advantages of converting fertile materials into fissile materials to generate heat for power generation have been extensively studied in view of the limited global fissile material resources. The richer fuel-friendly uranium-238 can be converted to fissile plutonium-239 for fuel use, and can be used as fuel with the plutonium produced in other conventional reactors, and more nuclear than the fissile material consumed. The development of propagation reactors that multiply fissile material is highly desirable. Extensive technology development and experience has been applied to the design and construction of pressurized hard water and heavy water nuclear power plants, and the use of pressurized water technology in propagation reactor applications has had a very good effect on the development of propagation raw materials.

Heavy water, or deuterium oxide (D ₂ O), has essentially the same physical and chemical properties as hard water (H ₂ O). Their nuclear properties, however, differ, with the neutron absorption section and deceleration capacity of the heavy water being significantly lower than that of hard water. Accordingly, the use of heavy water as a coolant in a fast propagation reactor is desirable in terms of nuclear properties and applications of pressurized water technology. In a plutonium-uranium-heavy water (Pu-uD ₂ O) nuclear power plant, the reduction of coolant to fuel atomic ratio increases the conversion or growth ratio. Proliferation ratio is the ratio of generated fissile atoms to spent fissile atoms. A fast multiplication ratio of 1.40 was found in the plutonium-uranium-heavy water reactor system when the geometry of the fuel rod lattice allowed the volume ratio of the moderator to fuel to be adjusted to yield a moderator-to-fuel ratio of 1.0 or less. Can be used. The choice of moderators for fuel atomic ratios limits the amount of coolant per mass of nuclear fuel, making it difficult to design fuel rod grids that can produce adequate cooling flow rates at low moderator-to-fuel ratios. The high flow rates required to ensure adequate reactor core cooling require high velocity flows in the flow passages which are quite limited when relatively low moderator to fuel ratios are achieved. In a very tightly close fuel rod grid, the use of conventional spacer grids is limited in fuel rod compaction due to the inserted grid, flow tendencies caused by spacer grid vibration, parasitic absorption of grid plates and limited flow passages. This is very disadvantageous due to an increase in hydraulic pressure loss due to grid insertion.

The prior art relates to a reactor design that is slowed down and cooled by heavy water by forming a specific fuel rod diameter and spacing such that the moderator-to-fuel ratio is in the range of 0.35-4.0. It has been proposed to be made in a fuel rod grid using contact fuel rods arranged therein. However, reducing the heat flux to the extent necessary to eliminate potentially destructive hot spots at the fuel rod contact points severely limits the core's ability to operate in pressurized water reactors. Furthermore, the dense arrangement of fuel rods is blocked by solid particles carried by the coolant and requires very high reactor coolant pumping (pumping) power. Other problems also appear to a considerable extent. Removal of the spacer grid, on the other hand, is desirable to approach the moderator-to-fuel atomic ratio, which leads to a high conversion ratio of the contact fuel rod structure, while removal of the spacer grid incorrectly spaces the fuel rod and eliminates vibration-induced flow. Causing uneven cooling.

According to the principles of the present invention can be effectively solved by the practice of the present invention the disadvantages of the prior art. The fuel assembly according to the present invention is bonded to each other by soldering fins formed in the fuel rods and other fuel rods formed in a continuous state or interrupted in one fuel rod using a cover tube of nuclear fuel rods having fins formed in the longitudinal direction. Thus forming an integral fuel assembly. The fuel rod assemblies integrally formed by soldering the pins of the nuclear fuel rod sheathing tube may be designed to meet the thermal and hydraulic conditions of the very close lattice required to achieve a high growth rate.

In another embodiment, the fuel rod fins are directly connected to the tubular portion of the other fuel rods such that the final assembly has a moderator-to-fuel volume ratio that tends to increase the growth ratio at the plutonium-uranium-heavy water reactor core.

In another embodiment of the present invention, the core is assembled from a solid material having a channel suitable for the presence of coolant and fuel storage. The present invention provides a means for obtaining a moderator-to-fuel ratio conducive to a high polotonium-uranium-heavy water reactor propagation ratio, while at the same time providing a means to form a precise space in the fuel rod without the parasitic absorption associated with the prior art using spacer grids. Solve it. The arrangement of the present invention also eliminates the hydraulic losses associated with conventional spacer grids and reduces the tendency of nuclear fuel rod vibration. Finned fuel rod arrangements increase fuel rod strength, increase the available heat transfer surface, and improve overall heat transfer efficiency.

Various advantages of the invention are pointed out in particular in the appended claims, which form part of this specification.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 partially shows the fuel assembly 10 of the nuclear fuel rods 1 densely arranged in parallel with the longitudinal axis. Each fuel rod 11 consists of a tubular cladding tube 12 which is formed as part of the outer surface and has a plurality of longitudinally extending fins 13 which form a constant space around the fuel rod. The nuclear fuel 14, which is a mixture of fissile material and nuclear fuel parent material, is infiltrated into the covering tube 12. In FIG. 1, the fuel rods 11 are arranged such that the tips of each pin 13A are adjacent to the tips of the pins 13B of the nuclear fuel rods arranged adjacently. The fins 16, 17 at the edges shown in FIG. 1 are individually soldered to the fins of another fuel rod and to the coating structure of the nuclear fuel assemblies within the reactor to form an integral fuel assembly 10.

In one embodiment, the fin 13 extends uninterruptedly (continuously) along the longitudinal surface of the fuel rod to form a passageway 20 in the space between the fuel rods allowing the reactor coolant to flow parallel to the longitudinal axis of the fuel rod. have. However, the fins 13 need not extend continuously along the length of the fuel rods but are pinned as shown in FIGS. 2 and 3 to allow the coolant to transversely flow and mix with each other through the spaces between the fuel rods. (21) may be sufficient. The axially interrupted pins 21 of the adjacently arranged nuclear fuel rods are soldered to different pins at 22 (FIG. 2) or the tubular portion of the fuel rods at 23, as shown in FIG. Can be soldered directly to Aggregates using any arrangement shown in FIGS. 2 and 3, i.e., a combination of pin-in contacts and pin-to-tub contact, may also be used.

4 shows a nuclear fuel rod 26 having a wide fin 24 coupled to it by soldering to each other at the portion 25. Wide fins can be used to limit the fraction of moderator volume, taking into account some loss of specific core power. The removal of conventional spacer grids and the formation of fins as part of the tubing cladding allows the fraction of reactor core moderator volume to be reduced to a value consistent with a desired moderator to fuel atomic ratio.

The physical parameters of the examples of the present invention are as described in the following table (1).

TABLE 1

In the example of table 1, the fuel rod is in the form of a rod. The fuel rods of Examples (1) and (2) are formed of fins that continue along their length. Example 3 specifically illustrates another example of Example 2, where only about 30% of the rod length is laterally arranged.

The values for the moderator to fuel atomic ratios shown in Table (1) are typical, including the primary coolant temperature and pressure, the type of fuel pellets, the gap between fuel pellets and sheaths, and the percentage of theoretical UO ₂ density obtained from the pellets. This value approximates the operating conditions of the pressurized water reactor.

The nuclear fuel assembly shown in Table (1) is a presbyopic brazing furnace using a brazing alloy under the trade name "Nicro-Braz 50" (Wil-Klemonie, Detroid, Mich.) In a hydrogen gas body of 1065.6 degrees Celsius to 1093.5 degrees Celsius. It is formed by brazing, which is also used as a jig and fixture, and presbyopic soldering uses a solder alloy placement method that is well known in the art.

In another example, FIG. 5 shows a design for a low temperature reactor for the purpose of generating low heat by propagating polotonium, ie suitable for residential heating. In this example the fuel fuel assembly is made of a block of metal 32, i.e. an aluminum alloy. In this block, a second passage 31 for flowing coolant and a first passage 30 for charging fuel are formed in parallel in the longitudinal direction. The surface of the second passageway may be roughened where necessary to increase the critical heat flux. Exemplary design parameters for such a block reactor are shown in Table (2).

TABLE 2

The moderator-to-fuel atomic ratio in Table (2) corresponds to the primary coolant temperature of about 121.1 degrees Celsius at low pressure. The other parameters are similar to those in table (1).

The coolant and fuel passage geometry in the block fuel assembly can increase the degree of etch “moderator escape probablity” that acts to harden the neutron spectrum and improve core conversion or growth ratio. Occurs because the neutrons generated in the fuel passage can pass into another fuel passage without passing through the volume containing the moderator, thereby increasing the average neutron energy during nuclear fission. These fuel assemblies, combined with a moderator-to-fuel ratio that is somewhat less than that achieved by contact fuel rods, can achieve a uniform high growth rate for hard or heavy water cooling.

Due to the moderator-to-fuel atomic ratio made by this method of the present invention possible for fuel assembly design, fast reactor physics can be used in pressurized water reactor technology. The combination of these has the following important advantages.

a) avoiding gas or fluid metal coolants other than those used for high-speed reactors,

b) slowed coating operating temperature,

c) the use of additional methods of radiation control, ie chemical composition and spectrum conversion control.

The use of additional methods of radiation control can lower the conventional dependence on fast reactors for control rods. They reduce the cost at a given control rod price and provide a means of making continuous adjustments of the excess response to the minimum value, thereby greatly improving the stability of the fast reactor core. This allows control rods that are very expensive from the core to work better.

Claims (1)

In an integrated nuclear fuel assembly in a fast-growing nuclear reactor decelerated and cooled by pressurized water, a plurality of nuclear fuel rods (11) are arranged in parallel to the longitudinal axis so that the nuclear fuel rods (11) are densely arranged, and the nuclear fuel rods (11) are tubular sheathed tube ( 12) so that the nuclear fuel 14 is loaded therein, and the pin 13 protruding from the covering tube to the adjacent fuel rod in the longitudinal direction is coupled with the pins of the adjacent fuel rod to form the integral fuel assembly 10 At the same time forming the coolant passageway 20 by the cladding tube and the fin, the fuel assembly having a structural volume fraction of less than about 0.166 and a fuel coolant volume in the range between about 2.43 and about 3.20. A monolithic fuel assembly constructed of the above-described fuel rods having fins having a fraction ratio.

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