Selection of nuclear power valve materials

Release time:

2024-04-08

The materials selected for nuclear grade valves must meet the requirements of corrosion resistance, radiation resistance, high temperature resistance, damp heat resistance and fatigue resistance of nuclear power plants.

1. Metal materials

1) quality assurance certificate and conformity certificate. Pressure bearing materials must have quality assurance certificate of chemical composition and mechanical properties that meet the requirements. Materials without quality assurance certificate shall be subject to chemical composition analysis and mechanical property inspection. Non pressure bearing materials shall have certificates of conformity, and those without certificates of conformity shall be subject to chemical composition analysis. Copies of quality assurance certificate, conformity certificate, chemical composition analysis report and mechanical property inspection report must be provided with the materials.

2) impact toughness requirements of materials. V-notch impact test must be carried out for pressure bearing materials and the materials to be welded. When some conditions are met, V-type confirmatory impact test may not be carried out. There are seven provisions for safety level I (see ASME nb-2300), and nine provisions for safety level II and safety level III valves (see as-menc-2300 and ASME nd-2300 wre)

3) inspection of materials.

A. non destructive testing must be carried out for pressure bearing materials and their welding materials, but for valves with inlet nozzle not more than NPS2 (50mm) specified in ASME nb-2500, non-destructive testing may not be carried out according to the requirements of this section. According to rcc-mb3513, valves with inner diameter less than 25 mm can be accepted as long as they meet the requirements of minimum wall thickness.

China's nuclear industry standard EJ 405-1989 basically conforms to the corresponding standards of ASME and rcc-m. Non destructive inspection items and inspection scope of various parts and materials of nuclear grade valves specified in ej405-1989.

B. inspection of bolts and nuts. According to relevant standards, all bolt and screw connection materials shall be subject to visual inspection, and materials with diameter greater than 25mm shall be subject to magnetic particle inspection or liquid penetrant inspection; materials with diameter greater than 50mm shall be subject to ultrasonic inspection in addition to magnetic particle inspection or liquid penetrant inspection.

The above requirements are basically in accordance with the requirements of ASME nb-2580 and m5140 in Volume II m of rcc-m.

2. Non metallic materials

1) the packing and gasket shall be made of flexible graphite with low chloride ion and sulfur ion meeting the service conditions of nuclear power plant.

2) the lubricating oil and grease used in rubber sealing ring and electric device must meet the requirements of radiation resistance and high temperature resistance.

3. Prohibited and restricted materials EJ / T 1022.9-1996 are as follows:

1) soft mercury compounds are not allowed to be used in the reactor containment. Because it is easy to react with various metal alloy generators at room temperature, resulting in rapid corrosion and possible rupture; no steam (especially at high temperature) is harmful to human health; Mercury will be activated in neutron flow.

2) aluminum and coating containing aluminum shall be avoided in the reactor containment, because aluminum will be strongly corroded by alkaline spray liquid, and the corrosion product is hydrogen. For aluminum that cannot be replaced by other materials due to process reasons, there must be a certain amount, from which the hydrogen after the design basis accident can be estimated.

3) zinc and galvanized parts shall not be used in reactor containment. Because boric acid spray solution corrodes zinc greatly, hydrogen is released.

4) other low melting point metals shall be avoided in the reactor containment.