Individual RCCA rodlets contain the neutron-absorbing material that controls the rate of reactor power production. These rodlets are brazed to precise position on the arms of the spider assembly. The lower end plug of the rodlet is tapered to guide rodlet insertion into the fuel assembly. The multiple rodlet RCCA provides spatial distribution of absorber material within a fuel assembly in the reactor core. Control rod drive mechanisms position the RCCAs for control of core reactivity during reactor startup, shutdown, and power-level change.
Control rod drive mechanisms move RCCAs into and out of the core.
When the reactor is shut down, the RCCAs are inserted into thimble tubes in nuclear fuel assemblies, and are partly or fully withdrawn during reactor operation. The lower end of each rodlet remains partly inserted in the top of a fuel assembly thimble tube when the RCCA is fully withdrawn. Westinghouse Electric Company, LLC, part of the BNFL Group. All rights reserved.