Spectral shift apparatus and method for a nuclear reactor fuel assembly.

摘要

The invention relates to a method and apparatus for effecting spectral shift in a nuclear reactor core.
<??>Displacer rods (50) precharged with a quantity of water equivalent to a minor fraction of rod volume have associated therewith sealing means (70) designed to cause flooding of the displacer rods with primary moderator/coolant when the differential between the pressure of moderator/coolant in the core and the internal pressure of the displacer rods increases above a predetermined level. When reverse spectral shift toward higher reactivity is desired, the reactor is made subcritical to an extent substantially equivalent to the amount of reactivity added through flooding of the displacer rods, and said pressure differential is then elevated above said predetermined level, preferably by reducing the primary moderator/coolant temperature while maintaining system pressure.