KERNREAKTOR MIT EINER SCHUETTUNG KUGELFOERMIGER BRENNELEMENTE SOWIE VERFAHREN ZUM BETREIBEN DIESES REAKTORS

1483506 Nuclear reactors KERNFORSCHUNGSANLAGE JULICH GmbH 20 Sept 1974 [22 Sept 1973] 41068/74 Heading G6C In a pebble bed nuclear reactor comprising graphite-coated fuel elements which pass downwardly through a core surrounded by reflector walls, neutron absorbing or retarding material is provided to operate at an upper part of the core to avoid damage to the reflector at this point. Rods or coated particles containing B, Hf, Gd, Mn, Fe, or Ni may be embedded in the top reflector or at the top of the side reflectors. Alternatively, the fuel elements charged to the reactor may contain neutron absorbing or retarding material, either incorporated in the fuel elements or as separate bodies. Suitable additives are graphite, Th-232, and Pu containing a high proportion of Pu-240. Such material may be added to a marginal zone adjacent the side reflector.