Valves Used for Spent Fuel Reprocessing Processes

(1) Globe valves
A globe valve is the most common valve in post-processing engineering. It has great flow resistance and is used on horizontal pipelines that do not require good flow resistance. Globe valves are suitable for small and medium pipelines (not greater than DN200), and the application of cone seals or flat seals is more common, which are usually packing-type globe valves and bellows globe valves. Pure packing globe valves are rarely used and are used in non-radioactive or medium and low-level environments to transport low-temperature and low-pressure media, for example, deionized water. Bellows globe valves are widely used to transport radioactive or corrosive media, compressed air, or steam with high temperature and pressure. The globe valve adopts the upper threaded stem to avoid contact between the medium and the thread, which will cause radioactive contamination. According to the requirements for the pipeline layout, straight-through globe valves are used most, and some pipelines use angle globe valves.
 
(2) Ball valves
Ball valves are common valves in post-processing and are often used for opening and closing. Ball valves have the lowest flow resistance and are used on pipelines with a nominal diameter not greater than DN80. They are installed on vertical or horizontal pipelines. For no special reason, full-bore ball valves are used. Considering the convenience of maintenance, the top entry is adopted for welded ball valves, which is convenient for online maintenance. When the nominal diameter and nominal pressure are low, consider floating ball valves. When the nominal diameter or nominal pressure is high, consider the trunnion ball valve. Hard alloys that are resistant to radiation and acid and alkali corrosion should be selected for the sealing surface of the ball valve.
 
(3) Butterfly valves
Butterfly valves are used in pipelines with a nominal diameter greater than or equal to DN80 in the post-treatment process system to transport gases such as steam, exhaled exhaust and evaporated tail, as well as liquids containing particles such as powder and suspension. Butterfly valves have the advantage of being short, simple, light, and fast opening and closing compared with other valves, but the flow resistance is relatively great. Butterfly valves can be installed vertically or horizontally on pipelines, and are suitable for post-processing plants with limited space. In the radioactive environment, the check valve with a hard seal and triple eccentric structure is selected. Compared with the center line, single eccentric and double eccentric structures, the triple eccentric structure has better sealing performance, and the operating torque is smaller, which can reduce wear of the sealing surface at the moment of opening and closing.
 
(4) Check valves
Check valves are widely used in post-treatment process systems to prevent backflow of media and discharge of container media. The check valve is generally installed horizontally or vertically on the pipeline according to the direction mark, and most of them are lifting or swinging check valves. Swing check valves are generally used on pipelines with a nominal diameter of not less than DN80. When the swing check valve is installed in a horizontal pipeline, there should be an included angle between the valve sealing pair and the vertical direction to ensure that the disc is in contact with the vertical direction. The valve seat can be in good contact. When the swing check valve is installed on the vertical pipeline, it is only suitable for the medium flowing from bottom to top. The nominal diameter of the lift check valve is generally not greater than DN80, and it is divided into two types: with spring and without spring. The lifting check valve without spring has a simple structure, but it is easy to get stuck and cannot be reset normally. The lift check valve with spring is reliable in reset, but it is easy to cause the disc to not fully open under low-pressure differential conditions, resulting in increased flow resistance. When the check valve is used on the boundary between the red zone and the orange zone (vertical pipelines, the normal flow direction of the medium is from top to bottom), while preventing the reverse flow of the material, it should also ensure that the sealing pair is under the condition of extremely low-pressure difference. The vertical lifting structure is adopted, and the valve disc is reset by the spring. There are high requirements for the material selection and calculation of the spring, the flatness and the roughness of the sealing surface. It is required that the check valve can realize the opening, closing and sealing of low-pressure difference.
 
(5) Safety valves
Safety valves are generally used in pipelines where the flow medium is water, compressed air, kerosene, TBP, etc. Most of them are spring-loaded safety valves with angular structure and direct action, and micro-opening or full-opening safety valves are selected according to process requirements. The vast majority are non-safety (NR, NR(S)) valves. The nominal diameter is generally DN10 to DN50; the nominal pressure does not exceed PN20, and the working temperature is 330°C. A safety valve can be installed vertically or horizontally on the pipeline according to the direction to prevent the pressure in the system from exceeding the predetermined safety value.
 
(6) Pressure reducing valves
In spent fuel reprocessing projects, pressure-reducing valves are used in pipelines where the flow medium is compressed air to reduce the incoming pressure and keep the outlet pressure at the set value required by the process. Most of them have membrane structures. The vast majority are non-safety (NR, NR(S)) valves. The nominal diameter is generally DN6 to DN80; the nominal pressure does not exceed PN20, and the working temperature is 100℃.
 
(7) Traps
Steam traps are used in steam pipes or equipment and heat tracing pipes in process systems. They are installed on horizontal pipes according to the direction mark, which is used to transport saturated steam and steam condensate, discharge condensed water and air in steam, and ensure steam quality. The vast majority are non-safety (NR, NR(S)) valves. The nominal diameter is generally DN10 to DN65; the nominal pressure does not exceed PN20, and the working temperature is 200 ℃.