JPH0580123B

An electromagnet for a nuclear reactor shutdown system, which comprises upper and lower cores disposed in an axially symmetrical arrangement and capable of latching with and delatching from each other. When an ambient temperature increases, the upper and lower iron cores are delatched from each other and a control rod connected to the lower iron core falls down into a reactor core. The lower iron core is provided with a plurality of slits to form a plurality of fins therebetween. A temperature sensitive magnetic material (TSMM) is disposed in the outer circumferential lower corner portion of the lower iron core. An interface between the TSMM and an iron core material takes the form of a side surface of a cone whose central axis is coincident with the symmetry axis and whose apex angle lies in the range of 60 DEG to 120 DEG .