Control blade for nuclear reactor

• US 5,180,544 A
• Filed: 08/21/1991
• Issued: 01/19/1993
• Est. Priority Date: 06/30/1986
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Nakamura, Mitsuharu, Yoshioka, Ritsuo, Ueda, Makoto, Motora, Yuichi
• Primary Examiner(s): Behrend, Harvey E.
• Application Number:
  US07/752,218
• Time in Patent Office: 517 Days
• Field of Search: 376/333, 376/327, 376/287, 376/288
• US Class Current: 376/333
• CPC Class Codes: G21C 7/113 Control elements made of flat elements; Control elements having cruciform cross-section
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

In the field of commercial nuclear reactors, there is an increasing demand for long-life control blades in order to meet the requirements of higher economy and reduction in the disposal of radioactive wastes. A control blade proposed by the invention stands a long use by virtue of the use of a long-life neutron absorber which is typically made of hafnium. Despite the use of hafnium which has a large specific weight (13.3 g/cm³), the size, shape and weight of the control blade are substantially the same as those of conventional control blades which employ boron carbides B₄ C as the neutron absorber, so that the control blade can be back-fitted in existing boiling water reactors without difficulty. The control blade of this invention is a flux-trap-type control blade in which long-life neutron absorber plates or sheets are arranged to oppose each other in the thicknesswise direction of the wing within the sheath plate such that a water gap is preserved between the opposing neutron absorber plates, so that the weight of the hafnium, which occupies most part of the total weight of the control blade, is reduced by an amount corresponding to the volume of the water gap. The thickness of the neutron absorber plates or sheets is increased at the upper portion of the control blade where the neutron exposure is specifically high and where a large neutron absorption power or capacity is required for ensuring a sufficient reactor shut-down margin, while the thickness is reduced in other portions so as to increase the size of the water gap. In consequence, the weight of the control blade incorporating heavy hafnium as the neutron absorber is reduced almost to the same level as that of ordinary control blades, without being accompanied by any reduction in the reactivity worth.

Claims

1. A control blade for use in nuclear reactors comprising:

an upper structure means provided with a handle for handling of the control blade;

a lower structure means provided with a speed limiter;

a central tie rod means for connecting integrally said upper and lower structure means together, having radial projections so as to exhibit a substantially cross-shaped cross section;

a sheath plate means having a substantially U-shaped cross-section and secured to the end of each projection of said central tie rod means;

a hafnium neutron absorber means disposed in each sheath plate means and divided into a plurality of neutron absorber elements along the axis of said central tie rod means, each neutron absorber element being composed of a pair of substantially parallel adjacent neutron absorber plates or sheets spaced from and opposing each other so that a space is defined therebetween and an end tie rod means provided between outer facing end portions of the respective neutron absorber plates so as to close an outer end opening of the space, said end tie rod means being disposed for effectively increasing reactivity, each of said neutron absorber plates being provided with an inner facing end adjacent to said central tie rod, said inner facing ends of each pair of adjacent neutron absorber plates being curved to approach each other and said inner facing ends are spaced from each other so that thermal expansion of the neutron absorber plates is absorbed, the respective adjacent ones of said neutron absorber elements being arranged with gaps therebetween in the axial direction of said central tie rod means so that axial ends of the absorber elements of adjacent neutron absorber plates occupy different horizontal planes; and

supporting spacer means provided inbetween said adjacent opposing neutron absorber plates at a predetermined interval in the axial direction of said central tie rod means so as to define the space as a water gap for guiding flow of a moderator.