Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Patent
1989-12-14
1992-07-07
Hunt, Brooks H.
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
376434, 376446, 376448, G21C 334
Patent
active
051280973
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a reactor core, a fuel assembly and a fuel spacer and, more particularly, to a reactor core, a fuel assembly and a fuel spacer which find their suitable applications to a boiling water reactor.
BACKGROUND ART
As a fuel assembly for fuel burn-up extension, there has been proposed the structure which is shown in FIGS. 1 and 7 of Japanese Patent Laid-Open No. 217186/1987. This fuel assembly is arranged at its central portion with two water rods of large diameter and therearound with a number of fuel rods. This fuel assembly has its seven fuel rods replaced by the two larger water rods. With this structure, the fuel economy can be improved because the number of fuel rods replaced by the water rods is small. Moreover, the fuel assembly can reduce a local power peaking.
Another structure for the fuel assembly of high burn-up exposure is disclosed in Japanese Patent Laid-Open No. 202386/1985. This fuel assembly has its fuel rods arrayed at a small pitch at its peripheral portion. The structure shown in FIG. 3 of Japanese Patent Laid-Open No. 202386/1985 will be described in the following. In this fuel assembly, two water rods are arranged at the central portion whereas fuel rods and water rods are arranged in the form of a square lattice so that the pitch of the fuel rods is large at the central portion where the utilization of thermal neutrons is low but is high at the peripheral portion where the utilization of thermal neutrons is high. The small pitch of the fuel rods in the peripheral portion improves the average utilization of thermal neutrons of the fuel assembly, thus leading to the high burn-up exposure of the fuel assembly.
DISCLOSURE OF INVENTION
A first object of the present invention is to provide a reactor core and a fuel assembly which have the minimum critical power ratio increased and the local power peaking decreased.
A second object of the present invention is to provide a fuel assembly which has a fuel economy improved.
A third object of the present invention is to provide a fuel assembly which has a core shut-down allowance augmented.
A fourth object of the present invention is to provide a fuel assembly which can prevent the fuel inventory from decreasing and can increase the slowing-down region in a water rod.
A fifth object of the present invention is to provide a fuel assembly which can prevent the fretting corrosion of two water rods to decrease the local power peaking.
A sixth object of the present invention is to provide a fuel assembly which holds a fuel spacer easily with the water rods.
A seventh object of the present invention is to provide a fuel spacer which can facilitate the arrangement of fuel rods to augment the minimum critical power ratio and decrease the critical power peaking.
An eighth object of the present invention is to provide an initial inventory core extending a discharged exposure.
The first object of the present invention can be achieved by forming a fuel assembly with a central region arranged with a plurality of fuel rods in the form of a square lattice and a peripheral region arranged with a plurality of fuel rods in the form of a triangular lattice and surrounding the central region.
Since the square lattice arrangement of the fuel rods at the central region and the triangular lattice arrangement of the fuel rods at the peripheral region are used together in the fuel assembly, the amount of fuel substance in the vicinity of the periphery is augmented. As a result, the high power in the vicinity of the periphery is decreased to reduce the local power peaking. Since, moreover, the combination of the square lattice arrangement and the triangular lattice arrangement of the fuel rods can equalize the pitches of the fuel rods at the central region and the peripheral region, thus leading to an augmentation of the minimum critical power ratio (which will be shortly referred to as "MCPR").
The object of the present invention can be achieved by arranging two water rods adjacent to each other in the central region s
REFERENCES:
patent: 4111594 (1978-09-01), Sforza
patent: 4255236 (1981-03-01), Robbins
patent: 4285771 (1981-08-01), Downs
patent: 4585614 (1986-04-01), Helmersson
patent: 4714585 (1987-12-01), Kast
patent: 4863680 (1989-09-01), Sakurada et al.
patent: 4968479 (1990-11-01), Ogiya et al.
Fukasawa Yukihisa
Nishimura Akira
Ozawa Michihiro
Yamashita Jun-ichi
Chelliah Meena
Hitachi , Ltd.
Hunt Brooks H.
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