Pneumatic transportation pattern of fuel pebbles in a pebble-bed reactor

Pebble-bed high temperature gas-cooled reactors have many advantages such as inherent safety and high efficiency, so it has been considered as a preferred candidate for the Generation IV Nuclear Power Plants. Every day thousands of spherical fuel pebbles are transported pneumatically in the pipes outside the core of a pebble-bed reactor. During the transportation, each pebble will be lifted perpendicularly in a pipe of which the length is tens of meters. The lifting process affects the operation efficiency of the reactor directly, thus it is of great significance to the stability and reliability of the reactor. A pattern widely used nowadays is to lift a single fuel pebble each time, namely at any time there is at most one pebble lifted in a pipe. The efficiency of the pattern is low and it cannot meet the operational requirements, especially during loading and emptying the core. This paper introduces a new transportation pattern named two fuel pebbles lifted together. On this basis we obtain the force conditions of the pebbles. Then the dynamic characteristics of the pebbles are analyzed. The research shows that by controlling the time interval between transporting the two pebbles into the lifting pipe, the collisions between the pebbles can be avoided. In addition the transportation reliability and efficiency can be ensured. The experiment validates that the transportation pattern can meet the operational requirements of the reactor. The research is significant to improving the efficiency and reliability of the transportation of the fuel pebbles and provides an important basis for the design of the reactor.