Method for producing ceramic multilayered tube used as cladding for fuel element in nuclear power plant

A method for producing ceramic multilayered tube used as a cladding fora fuel element in nuclear power plant, comprising successive formation of layers, the method comprising the steps of:

• forming an inner monolithic layer having a thickness of 250-500 μm and being comprised of crystals of beta phase stoichiometric silicon carbide on a carbon substrate being a rod, by chemical methylsilane vapor deposition in a sealed tubular hot-wall chemical vapor deposition reactor (CVD reactor) at a forming the inner monolithic layer operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 60-100 hours,
• wherein the step of forming the inner monolithic layer comprises the step of feeding gaseous argon to the CVD reactor at an operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 60-100 hours, when the CVD reactor at the forming the inner monolithic layer operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 60-100 hours is heated from room temperature to the forming the inner monolithic layer operating temperature and is cooled from the forming the inner monolithic layer operating temperature to the room temperature,
• forming a central composite layer having a thickness of 300-500 μm over the inner monolithic layer,
• wherein the step of forming said central composite layer comprises the steps of:
• twisting continuous stoichiometric fibers of beta phase silicon carbide having a diameter of 10-15 μm into tows of 500-1500 fibers,
• transporting the tows to a braiding machine for biaxial or triaxial braiding,
• forming a cord as a reinforcing thread framework by the braiding machine,
• arranging the cord over the inner monolithic layer disposed on the carbon substrate, the cord having fixed ends,
• building up a pyrocarbon interface coating on the cord to a thickness of 100-200 nm by chemical methane vapor deposition in a sealed tubular hot-wall chemical vapor deposition reactor (CVD reactor) at a building up the pyrocarbon interface operating temperature of 1000-1050 degrees C. and pressure of 100-200 Pa for 1.5-2 hours,
• wherein the step of building up the pyrocarbon interface comprises the step of feeding gaseous argon to the CVD reactor at the building up the pyrocarbon interface operating temperature of 1000-1050 degrees C. and pressure of 100-200 Pa for 1.5-2 hours when the CVD reactor at the building up the pyrocarbon interface operating temperature of 1000-1050 degrees C. and pressure of 100-200 Pa for 1.5-2 hours is heated from the room temperature to the building up the pyrocarbon interface operating temperature, and
• forming a matrix from crystals of beta phase stoichiometric silicon carbide inside the cord by chemical methylsilane vapor deposition in a sealed tubular hot-wall chemical vapor deposition reactor (CVD reactor) at a forming the matrix operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 5-10 hours,
• wherein the step of forming the matrix comprises the step of feeding gaseous argon to the CVD reactor at the forming the matrix operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 5-10 hours when the CVD reactor at the forming the matrix operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 5-10 hours is cooled from the forming the matrix operating temperature to the room temperature;
• forming a protective outer monolithic layer with the thickness of 100 μm from crystals of beta phase stoichiometric silicon carbide over the central composite layer by chemical methylsilane vapor deposition in a sealed tubular hot-wall chemical vapor deposition reactor (CVD reactor) at a forming the protective outer monolitihic operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 10-20 hours so as to form a fabricated semi-finished product on the carbon substrate,
• wherein the step of forming the protective outer monolithic layer comprises the step of feeding gaseous argon to the CVD reactor at the forming the protective outer monolitihic operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 10-20 hours when the CVD reactor at the forming the protective outer monolitihic operating temperature of 660-730 degrees C. and pressure of 50-100 Pa for 10-20 hours is heated from the room temperature to the forming the protective outer monolitihic operating temperature and cooled from the forming the protective outer monolitihic operating temperature to the room temperature;
• and
• removing the carbon substrate from said fabricated semi-finished product, said fabricated semi-finished product being comprised of the inner monolithic layer, the central composite layer, and the protective outer monolithic layer.