Fuel design for high power density forced circulation boiling water reactor

摘要

A fuel bundle of square cross section and standard vertical dimension is disclosed. The fuel bundle includes a matrix of upstanding vertical rods, a lower tie plate for supporting the matrix of vertical rods and permitting the inflow of liquid moderator coolant (preferably light water) , and upper tie plate for holding the matrix of vertical fuel rods upright and permitting the outflow of liquid and vapor moderator coolant (water and steam), and a preferably square sectioned channel extending between the tie plate for confining the flow path between the tie plate around the fuel bundle. The novel characteristics of the invention is the introduction of a corresponding matrix of water rods (cylindrical rods with liquid phase water flow) positioned between the fuel rods, as opposed to the current practice of using or displacing a subset of fuel rods with large central water rod(s) for this purpose. This matrix of water rods preferably has each water rod of smaller diameter than the adjoining fuel rods and is dispersed at intervals uniformly in the matrix of fuel rods. This geometry provides for more uniform (flat) power distributions within the bundle, as a result of the greater similarity of the neutron spectrum in the vicinity of the individual fuel rods. This geometry yields increased design margins for MLGHR and MCPR relative to current fuel designs. The design margins can be traded off to permit achievement of higher core power density. The design also results in less negative void coefficients, which improves core stability.