JPS6064292A - Nuclear fuel aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention has a function of removing radionuclides released from the surface of a fuel cladding tube into a primary sodium coolant during operation of a fast breeder reactor. Regarding nuclear fuel assemblies.

[Conventional technology and problems]

In fast breeder reactors that use liquid metal as a coolant, multipotent radioactive I substances are generated when core structural materials, fuel cladding tubes, etc. are irradiated with neutrons. Some of these are eluted into the sodium cooling Murayama due to corrosion on the surface of the coolant, are carried along with the coolant to the primary cooling system, and are deposited on the walls of primary cooling system equipment and piping, causing the first maintenance inspection of the reactor to occur. , causing radiation exposure to workers when performing repair work.

For example, in the case of a large reactor at the level of a commercial reactor, in the third year of operation, the accumulated radioactive corrosion product nuclides cause
The radioactivity level around the equipment and piping of the secondary cooling system is expected to exceed 10 x rays/hour. Under such high radioactivity levels, maintenance, inspections, and repairs are almost impossible. Therefore, in the development of fast breeder reactors, the development of technology to reduce contamination of primary cooling system equipment and piping due to radioactive corrosion products has become an important issue.

Most of the radioactivity in the radioactive corrosion products is due to the Mn-54 radionuclide. It is known that this nuclide deposits very well on the surface of nickel materials in high-temperature IJium.
The development of radionuclide trap devices such as those described in No. 600) is progressing.

This device has multiple holes A on the top and bottom surfaces as shown in Figure 1.
, B. Thin nickel plates are housed in cylinders C and G in multiple concentric circles or in the form of a thin single roll to constitute a removal device E. As shown in FIG. By installing the element F in the downstream region of a nuclear fuel assembly G containing a plurality of elements, and bringing the liquid metal coolant H flowing through each nuclear fuel assembly G into contact with the surface of the nickel plate of each removal device E. , radioactive Mn- mixed in the coolant
54 is adsorbed onto a nickel plate.

However, if such a removal device 4 is attached to the upper part of the nuclear fuel assembly, the fuel assembly becomes correspondingly longer, which causes problems such as increasing the size of the entire plant including the reactor vessel.

[Purpose of investigation]

The present invention aims to reduce the accumulation of radioactive corrosion products in the primary cooling system of a fast breeder reactor, and to reduce the radiation exposure of operators during maintenance, inspection, and repair of the primary cooling system. The purpose is to provide a collective.

The present invention is a nuclear fuel assembly for a fast breeder reactor, in which fins are inserted into the upper blanket and gas plenum of a nuclear fuel element.

〔Effect of the invention〕

According to the present invention, radioactive nuclides are removed in the upper plenum and gas plenum in the downstream part of the fuel elements inside the fuel assembly, thereby satisfying the requirements of high efficiency, easy maintenance, and applicability to existing reactor cores. is possible.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

Fig. 3 shows the concept of the fuel assembly, and Fig. 4 shows its main parts.

A fuel assembly 2 consisting of a large number of fuel elements 1 is attached to a core support plate 3
supported in the core by The coolant flows into the fuel assembly through the orifice hole 4, flows through the lower blanket section 5 of the fuel element 1, cools the core fuel section 6, which is the heat generating section of the fuel element 1, flows through the upper blanket section and the gas plenum section, and exits the fuel assembly. The other aggregates are combined with the coolant that has flowed out and exit the furnace. The coolant temperature shows the highest temperature in the upper blanket and gas plenum part 7 directly below the core fuel part 6, which is a heat generating part.

Also, the flow state of the coolant is turbulent.

CPh wrap fins 8 as shown in FIG. 5 are installed in the upper blanket and gas plenum part 7 downstream of the core combustion part 6, which is a heat generating part. Manganese-54, which is mainly CP in the coolant, tends to deposit on the surface of the nickel material. C.P.
) The surface of the wrap fin 80 is coated with nickel.

In the above CP trap fin, for example, the fuel element diameter is (3.8 mm, the fuel element center-to-center spacing is 7.82 mm,
The coolant flow velocity in the core fuel section 6 is 5 m/sec.

The coolant temperature in the CP trap fin section 8 is set to 540°C.
, The surface of the CPI-wrap fin is nickel plated, and the coolant flow area of the CP trap fin is 0.1 cm.
', the wetted length of the coolant flow path in the CP l-wrap fin part is 2.5 cm, and the length of the coolant flow path in the CP trap part is 5 cm.
The efficiency of the CP concentration in the coolant at 0 cm at the trap entrance to the trap exit is 96%.

Note that similar effects can be obtained even if the CP trap fin portion 8 and the fuel element 1 are integrated.

That is, according to this embodiment, high efficiency is expected by installing the CP trap in the upper blanket of the fuel element and in the gas plenum.

Furthermore, since the CP trap section is integrated with the fuel assembly, maintenance is easy, and the overall pressure loss of the cooling system does not increase significantly. In addition, it has the same dimensions as the existing fuel assembly, so modifications such as fuel exchange materials are required (it can be used in existing reactor cores).

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway perspective view of a radioactive nuclear atom removal device used in a conventional device, Fig. 2 is a schematic diagram of the same device installed in a nuclear fuel assembly, and Fig. 3 is a nuclear fuel removal device of the present invention. FIG. 4 is a partially cutaway perspective view showing the main parts of the assembly, and FIG. 5 is a sectional view taken along line AA in FIG. 4. j... Fuel element, 2... Fuel assembly, 3... Core support plate, 4... Orifice hole, 5... Lower blanket part, 6... Core fuel part, 7... Upper blanket part and gas plenum part, 8... radionuclide trap fin. 9...-Wire spacer. Representative Patent Attorney Noriyuki Chika (and 1 other person) Figure 1 ρ @ Figure 2 H/-/ Figure 3 Figure 4

Claims (1)

[Claims] A nuclear fuel assembly for a fast breeder reactor, characterized in that a fin is inserted into the upper blanket and gas plenum of a nuclear fuel element.