GB1327196A - Safety devices for nuclear reactors - Google Patents

Abstract

1327196 Controlling reactors REYROLLE PARSONS Ltd 6 Jan 1971 [14 Oct 1969] 50463/69 Heading G6C A reactor safety device operates automatically in response to a relative displacement between the reactor pressure vessel and the superstructure above it from which the control rods are suspended, for releasing the control rods to allow them to fall under gravity into the reactor core in response to the occurrence of a relative displacement in excess of a predetermined amount. In the embodiment shown, a control rod 10 is releasably latched within the lower end of a support tube 11 by means of three latch members 13 whose heads are held against a chamfered abutment 14 inside the support tube 11 by means of a conical end 15 on a plunger rod 16. The latch members 13 have cross-bars 13A at thier lower end which are engaged in an annular recess 10A beneath abutment surfaces in the head of the control rod 10. The rod 16 is biased upwardly by means of a spring 21 which bears against an abutment portion 22 of the rod 16 and a ring 23 biased within the support tube 11. The upper end of the rod 16 is tapered at 16A and has a flat end face 24 on which the conical end 25A of a detent strut 25 abuts. The upper end of the strut 25 is attached by a chain (not shown) to a motor-driven winch on a concrete superstructure above the pressure vessel. The strut 25 has a part-spherical intermediate portion 26 which bears against an inwardly tapering end cap 27 screwed to the top of support tube 11 and thus forms a fulcrum about which the strut 25 may move. Upon the occurrence of a displacement of the superstructure relative to the pressure vessel, caused for example by an earthquake, an explosion in the vicinity of the reactor or a structural fault in some part of the reactor, a tilting of the strut 25 will occur about the fulcrum 26 causing its conical end 25A to move across the face 24 of the plunger rod 16. Should the tilting exceed a predetermined amount, e.g. 2 degrees, the end 25A will move beyond the edge of the face 24 and the rod 16 will be driven upwards by the spring 21 thus releasing the latch members 13 and allowing the control rod 10 to fall into the reactor core.