Nuclear Reactor Fuel Assembly Manufacturing Method

Abstract

Method of fuel elements installation into fuel assemblies including fuel elements fabrication and control operations, application of a protective coating on each fuel element, installation of prepared fuel elements into a fuel assembly, attachment of top and bottom nozzles, washing off of the protective coating and drying. The protective coating application and fuel elements installation are combined using a water soluble lubricant containing nonylphenol ethoxylate and monobasic unsaturated fatty acids as protective coating, which is applied on the surface of the fuel element being moved during fuel elements installation in the fuel assembly on an assembly stand in horizontal direction along its own axis to the cells of grids through a protective coating application device installed on the assembly stand. The protective coating is washed off using water jets under pressure at room temperature.

Claims

1. A method for manufacturing nuclear reactor fuel assembly, the method comprising the steps of fuel elements fabrication and control operations, application of a protective coating on each fuel element, installation of prepared fuel elements in a fuel assembly, attachment of top and bottom nozzles, and washing off of the protective coating and drying; wherein the operations of protective coating application and fuel elements installation into the fuel assembly are combined, by moving each fuel element during the fuel elements installation into the fuel assembly on an assembly stand in a horizontal direction along its own axis to the cells of grids through a protective coating application device installed on the assembly stand, wherein water soluble lubricant consisting of nonylphenol ethoxylate and monobasic unsaturated fatty acids is used as the protective coating.

2. The method according to claim 1, wherein the protective layer is washed off using water jets under pressure at room temperature.

Description

THE BEST EMBODIMENT OF THE INVENTION

[0013] The method of nuclear reactor fuel assembly manufacturing is implemented as follows.

[0014] Fuel elements in the form of long tubes made primarily of zirconium alloy, sealed at both ends, pre-charged with fuel pellets and having passed all inspection operations are collected in a bundle—a set of fuel elements intended for assembling in one cassette (fuel assembly), packed in inter-operation cassette and then transported to FAs assembly stand.

[0015] Installation of fuel elements into fuel assembly on assembly stand is performed by pushing fuel elements moved by pushing mechanism in horizontal direction along their own axis through protective coating application device and grid cells into fuel assembly frame. Protective coating application device may be, for example, a drawing die with inner surface lined with porous elastic material saturated with water soluble lubricant of proposed composition which may be installed on the assembly stand immediately before the first grid located in the frame in the direction of fuel element movement, or similarly located container filled with lubricant of proposed composition and provided with coaxial opening for fuel element passing through.

[0016] After installation of all fuel elements forming a single fuel assembly, top and bottom nozzles are attached to the fuel assembly.

[0017] Then water soluble lubricant is washed off from the fuel assembly with water jets under pressure at room temperature on jet washing unit. Washing off is also possible on jet washing unit with subsequent cassette placement in a retort with water at room temperature and bubbling during 30 minutes with subsequent water drainage. Washing off is repeated twice with the last washing off performed using hot water having the temperature of 80 to 90° C.

[0018] Fuel assemblies are dried at the temperature of 100 to 120° C. for 40 minutes.

INDUSTRIAL APPLICABILITY

[0019] Proposed method of nuclear reactor fuel assemblies manufacture using water soluble lubricant of proposed composition as protective layer instead of lacquer application has passed type tests in production environment.

[0020] Dummy fuel assemblies moved on assembly stand through protective coating application device were pushed through the grids of TVS-2M frame consisting of the grids attached on guide channels and central tube. Pushing force along the frame length was recorded. Statistical characteristics of the pushing force applied to dummy fuel assemblies when performing type tests of TVS-2M assembly using a lubricant were as follows: [0021] average value—244.7 N; [0022] standard deviation from average value—47.9 N; [0023] minimum value—68.6 N; [0024] maximum value—358.5 N.

[0025] Lubricant containing 30% of nonylphenol ethoxylate and 70% of monobasic fatty acids mixture was used.

[0026] Lubricant coating application quality was controlled in the course of assembly. Results of control have proven lubricant viscosity values necessary and sufficient for retention thereof on fuel element surface and its integrity during contact with spring elements of grid, which allows single application of lubricant on fuel element surface. Inspection of fuel elements having passed assembly operation has shown that maximum scratch marks depth measured using cast method was 9 to 13 μm. Most of scratch marks have a depth of 5 to 8 μm which does not exceed allowable values in respect of mechanical damages (30 μm) and potential risk of corrosion. Pilling-ups and tears were not observed.

[0027] Lubricant ability to cover fuel element surface with a thin layer ensures its minimum consumption in manufacturing process: 1.0 to 1.51 for assembling one fuel assembly.

[0028] Operation of fuel elements installation into fuel assembly using a lubricant of proposed composition does not require any design changes of existing assembly stands. Assembly is performed on standard equipment.

[0029] Therefore, implementation of proposed nuclear reactor fuel assembly manufacturing method allows solving the allotted task: ensure fuel assembly manufacturing quality and, at the same time, ensure manufacturing process efficiency and related decrease of fuel assemblies manufacturing cost. This method offers an opportunity for creation of continuous cycle of fuel elements fabrication and installation thereof into fuel assemblies.