METHOD OF CLEANING POWER GENERATION TURBINE OF NUCLEAR POWER GENERATION EQUIPMENT

Abstract: A method of removing material attached to the surface of a power generation turbine of a nuclear power generation equipment by blasting particles comprising a melamine resin along with a gas stream against said turbine surface. The melamine residue can then be incinerated to a fraction (e.g. 2 %) of the particles weight before combustion. The volume of stored waste is therefore reduced.

Description: Background of the Invention This invention relates to a method of cleaning a power generation turbine of a nuclear power generation equipment, particularly a boiling water nuclear power generation equipment. In a nuclear power generation plant, thermal energy generated as a result of nuclear fission is taken out from a reactor core by primary cooling water and converted in a steam plant into element energy. For instance, in a boiling water type nuclear power generation equipment, primary cooling water is boiled by heat received from nuclear fuel, it rises along the core to be separated by a steam/water separator provided on core top into steam and water, and separated steam is supplied through a steam pipe to a direct power generation turbine. Consequently, it is necessary to clean the turbine each few years to remove material attached to it. This done to remove contaminants attached to the turbine and also to inspect damage thereto. Heretofore, the cleaning was done by a dry blasting process, in which sintered alumina is used as a polishing agent and blown along with an air stream against the turbine surface. One operation of cleaning the turbine by this process requires 3 to 6 tons of polishing material. When sintered alumina is used as polishing material, however, the turbine surface is soon worn. The polishing material used after cleaning cannot be transported from the place in which it was used. Also, it cannot be incinerated. Therefore, it is stored in a concrete. This means that a large storage area is required. FR-A-2 127 021 discloses a method of cleaning parts of a nuclear power generating plant by a blasting process which uses sintered alumina. This method therefore suffers from the disadvantage mentioned above. GB-A-1 571 239 discloses the use of resin coated particles in a blasting technique but these particles are sand or slag which increase the indentation depth of a surface which is blasted and hence would cause wear. An object of the invention is to provide a method of removing material attached to a power generation turbine of a nuclear power generation equipment, particularly of the boiling water type, without causing wear of the turbine surface, and without causing a problem of disposal after treatment. Summary of the Invention According to the invention, there is provided a method of removing and disposing of material attached to the surface of a turbine, the method including the step of blowing particles in a gas stream against the turbine surface, characterised in that: a) said particles consist of thermosetting melamine resin or a mixture of a melamine resin with a different thermosetting resin and are blown against the turbine of a nuclear power generator to remove contaminated material; b) after said particles have been used to remove said contaminated material, said particles and said material are together incinerated in a furnace, the exhaust gas of the incineration being discharged to atmosphere through gas treatment equipment; and c) the residue of incineration is stored in concrete. According to the invention, a thermosetting resin is used, which is suitably a melamine resin. The melamine resin may be of a single composition, or it may be a mixture of a melamine resin with a different thermosetting resin. The melamine resin may slightly contain a urea resin When the content of a urea resin is high, however, the capacity of the particles to remove material is reduced, and also the ratio of breakage of particles at the time of removal of attached material is increased, thus increasing the amount of particles used. Thus, the content of a urea resin in the particles is suitably no greater than 30% by weight. Further, the grain size of melamine resin particles is not particularly limited, but is suitably 20 to 120 meshes as prescribed by JIS R-6001-1973. The particles may have any shape. Their hardness is not particularly limited, but is suitably 3 to 4 in Mohs scale. The particles may be obtained by pulverizing solidified meramine resin masses, pellets, etc. with a pulverizer. The particles may be blasted along with a gas stream by various blasting processes, but the dry blasting processes are best suited. Among the dry blasting processes are (A) A gravity type blasting process, in which particles are charged into a tank held at a position higher in level than a nozzle, and particles falling on a discharge port provided at the tank bottom is blasted from the nozzle together with compressed gas. (B) A direct pressure type blasting process, in which particles are sealed in a particle force-out tank, compressed gas is supplied to the tank, and particles discharged from a discharge port provided at the tank bottom are blasted from the nozzle together with compressed gas. (C) A siphon type blasting process, in which particles are charged into a tank held at a lower level than a nozzle, and particles discharged from a discharge port provided at the tank bottom by suction of compressed gas are blasted along with compressed gas from the nozzle. Any of the above blasting processes can be used. As compressed gas, usually compressed air is used. Usually, its pressure is set to 3 to 10 kg/cm² in gauge pressure, and the speed of jet of compressed gas from the nozzle is 50 to 240 m/sec. The amount of particles used for cleaning, pressure of compressed gas and speed of jet can be suitably selected in dependence on the characteristics of particles used and state of attachment of material to the turbine. Particles after use for removal of attached material contain the removed material such that the particles and removed material form a non-homogeneous mixture. When this mixture is incinerated in an incinerating furance, a residue of melamine resin after incineration remains with the removed material as overall residue of incineration. The exhaust gas discharged from the incinerator is discharged into atmosphere through a suitable discharge gas treatment equipment such as a filter. The residue of melamine resin particles is several per cent at most of the quantity of resin particles before incineration. The incinerator may be of various types, and it is suitable to use an electric furnace. The residue of incineration containing attached material can be treated by a suitable process such as holding in a concrete. When particles comprising a thermoplastic resin are used, incineration of particles after use for cleaning in the incinerator causes melting of the thermoplastic resin in the incinerator and adhering the melted resin to the bottom of the incinerator. This means that the treatment of the residue after incineration is very difficult. Therefore, it is indispensable to use particles comprising a thermosetting resin. The method according to the invention is applicable to a nuclear power generation equipment, particularly to a boiling water type nuclear power generation equipment. Brief Description of the Drawing The drawing is a schematic view showing a blast apparatus suited for carrying out the invention. Detailed Description of the Preferred Embodiment Now, an embodiment of the invention will be described in detail with reference to the drawing. Using melamine resin particles with a grain size of 42 to 90 meshes, material precipitated and attached to the surface of a power generation turbine of a boiling water type nuclear power generation equipment was removed. The removal was carried out using direct pressure type blaster 20. Particles 10 were charged into tank 22, and compressed air was forced from a compressed air source into tank 22 and transport pipe 26. The rate of supply of compressed air from the compressed air source was set to 1 Nm³/min., and the pressure to 5 kg/cm² in gauge pressure. The rate of use of particles was 300 kg/hour. Particles discharged from a discharge port provided at the bottom of tank 22 were transported by compressed air along the transport pipe and discharged from nozzle 24. The nozzle inner diameter was 5 mm, the speed of jet of compressed air from the nozzle was set to 150 m/sec., and the distance from the nozzle to the turbine surface was held at 200 to 800 mm. Particles from the nozzle were blown against the turbine surface to remove material attached to the turbine surface. The rate blowing with particles per 1 m² of turbine surface was set to 40 to 60 kg. No wear was recognized on the turbine surface after removal of attached material. Neither material remaining attached to the turbine surface nor particles attached thereto were recognized. Combustion residue of particles used for the removal was only about 2 % by weight of the particles before the combustion. For the sake of comparison, removal of material attached to turbine surface under the same conditions as above was carried out using sintered alumina of 80 to 150 meshes. In this case, wear due to sintered alumina was recognized on the turbine surface. Since sintered alumina could not be incinerated, it was inevitable to store sintered alumina after use for removal of the attached material in concrete in all quantity.

Claims: A method of removing and disposing of material attached to the surface of a turbine, the method including the step of blowing particles in a gas stream against the turbine surface, characterised in that: a) said particles consist of thermosetting melamine resin or a mixture of a melamine resin with a different thermosetting resin and are blown against the turbine of a nuclear power generator to remove contaminated material; b) after said particles have been used to remove said contaminated material, said particles and said material are together incinerated in a furnace, the exhaust gas of the incineration being discharged to atmosphere through gas treatment equipment; and c) the residue of incineration is stored in concrete. The method according to Claim 1, wherein the grain size of said particles is in the range of from 20 to 120 mesh. The method according to Claim 1 or 2, wherein said nuclear power generation equipment is a boiling type nuclear power generation equipment.

Inventors: MIYASAKA, YOSHIO, ONIZAWA, MASAO
Applicants: KABUSHIKI KAISHA FUJI KIHAN, SANYO TRADING CO., LTD.
Application year: 1989
Main classification: F01D25
IPC codes: F01D25, B08B9, B24C1, B08B7, B24C11