Self-operation type electromagnet for control rod supporting mechanism

In a control rod mechanism used for FBR type reactor, heat sensitive magnetic material is incorporated in a part of a bisectable core for attaching/detaching two core halves depending on the peripheral temperature. However, since a certain magnetic permeability is present in a magnetic circuit different from electric circuits, magnetic fluxes passing through the space are remained even if a part of the core is shielded magnetically. Then, the residual magnetic fluxes have to be sufficiently decreased. In this invention, heat sensitive magnetic material is disposed between each of the attaching faces of cores with coils and the portions for attaching the coils respectively. If the peripheral temperature becomes higher than the curie point of heat sensitive magnetic material, since the coils and all of the attaching faces are not magnetically short-circuitted directly by the cores and interrupted from coils, the density of magnetic fluxes is composed only by the magnetic fluxes leaked from the coils to the space, to scarcely cause attaching force. Accordingly, changes of the attaching force near the curie point is increased extremely, and the reliability can be improved. (N.H.)