Hitachi, Ltd.

Hiromi Maruyama

Sadao Uchikawa

Motoo Aoyama

Yasunori Bessho

Renzo Takeda

Junichi Koyama

Akinobu Nakajima

Kikuo Umegaki

Yuichi Morimoto

Michihiro Ozawa

Mitsunari Nakamura

Masayuki Izumi

Tadahiro Ohnishi

Junichi Yamashita

Kanji Kato

Yoshihiko Ishii

Motomasa Fuse

Michiro Yokomi

Atsushi Zukeran

Kouji Fujimura

Tomoyuki Matsumoto

A nuclear fuel assembly has an array of fuel rods comprising a plurality of first fuel rods each containing nuclear fuel material but not containing burnable poison and a plurality of further fuel rods each containing both nuclear fuel material and burnable poison. The further fuel rods comprise second fuel rods and third fuel rods, and each second fuel rod has at a lower region of the fuel assembly a burnable poison concentration which is a minimum burnable poison concentration in the further fuel rods. To increase the effectiveness of the second fuel rods in controlling axial power peaking, as seen in plan view on the array, the first fuel rods are the nearest neighbors of each further fuel rod.

Nuclear fuel assemblies and reactor cores including them

A core of boiling water reactor is divided into a central region and a peripheral region surrounding it in the radial direction thereof. The loading fraction of new first fuel assemblies containing burnable poison and loaded in the central region is greater than the loading fraction of the new first fuel assemblies loaded in the peripheral region. The loading fraction of second fuel assemblies loaded in the central region of the core and operating in a second operation cycle is smaller than the loading fraction of the second fuel assemblies loaded in the peripheral region of the core and operating in the second operation cycle. The second fuel assemblies contain no burnable poison. In such a core, the reactivity of the peripheral region is greater than that of the central region in the beginning of an operation cycle. Contrary, the reactivity of the central region is greater than that of the peripheral region in the end of an operation cycle.

Core loading strategy

A fuel assembly has a plurality of first fuel rods each of which contains nuclear fuel material but does not contain burnable poison, and a plurality of second fuel rods each of which includes nuclear fuel material and burnable poison. The amount of burnable poison in a lower region of the fuel assembly is smaller than that in an upper region thereof. When each of the second fuel rods is divided into an upper region and a lower region, a region of the divided regions in the second fuel rods containing a maximum burnable poison concentration Gmax and a region of the divided regions in the second fuel rods containing a minimum burnable poison concentration Gmin are located in the lower region of the fuel assembly. The burnable poison concentration of the upper region of each second fuel rod is between Gmax and Gmin. The fuel assembly may moderate a maximum linear heat rating with an increased spectral shift effect.

Fuel assembly

In a light water moderation type nuclear reactor with the once-through method, the reactor core is divided into a central area and a peripheral area by a partition member, a first fuel assembly is arranged in the central area (high conversion area) and a second fuel assembly is arranged in the peripheral area. The ratio (r.sub.H/U) of the number of hydrogen atoms to that of uranium atoms in the central area is smaller than that of the ratio in the peripheral area and the second fuel assembly in the peripheral area is formed of fuel rods of the first fuel assembly having been previously burned in the central area and moved into the peripheral area. The plutonium production increases and uranium consumption is reduced during the first half of the lifetime of the fuel rods in the high conversion area with the take-up burn up increasing during the second half of the lifetime of the fuel rods in the burner area.

Light water moderation type nuclear reactor

A fuel assembly comprises a channel box, upper and lower tie plates fixed to the upper and lower portion of the channel box and a bundle of fuel rods enclosed in the channel box and retained by the upper and lower tie plates. The bundle of fuel rods includes ordinary fuel rods containing fissile material not containing gadolinia, and gadolinia-containing rods each containing gadolinia therein and having a larger outer diameter than that of the ordinary fuel rod. The gadolinia-containing rod has pellets enclosed in a closed cladding, and the outer diameters of the pellets also are larger than these of fuel pellets of the ordinary fuel rods.

A fuel assembly comprises a plurality of fuel rods, moderator rods disposed among the fuel rods, upper and lower tie plates for holding both end portions of the fuel rods and the moderator rods, and fuel spacers for keeping distances between the fuel rods and the moderator rods constant. The fuel assembly is characterized in that there is provided a space region extending from the upper tie plate to the lower tie plate and having a space enough to dispose at least one of the fuel rods. At least one of the moderator rods being disposed adjacent to the space region. The fuel rods, the moderator rods, and the space region are disposed in a grid form.

A fuel assembly is composed of first fuel rods containing nuclear fuel material and burnable poison material and second fuel rods containing nuclear fuel material but no burnable poison material. The fuel assembly is charged in a high conversion area of a boiling water type nuclear reactor having a reactor core having the high conversion area and a burner area surrounding the high conversion area. A ratio V.sub.C /V.sub.F is not greater than 1.5 in the fuel assembly where V.sub.C is the volume occupied by coolant flow paths and V.sub.F is the volume occupied by the nuclear fuel material per unit length in an axial direction of the fuel assembly. In addition, the burnable poison material is composed of neutron absorption nuclides having at least one resonant energy in a neutron energy region of one electron volt or less.

Fuel assembly and nuclear reactor

A fuel assembly having a plurality of fuel rods arranged in a lattice state and being charged into a core of a nuclear reactor using light water as a coolant, which comprises the fuel rods consisting of a first group of fuel rods and a second group of fuel rods, an average concentration of U.sup.236 in the first group being lower than an average concentration of U.sup.236 in the second group, and the first group and the second group being arranged unevenly in the fuel assembly, preferably, a fuel assembly wherein the first group is arranged at the periphery of the fuel assembly, and the second group being arranged at positions other than the periphery, has a low reactivity penalty due to U.sup.236 and can reduce the requirements for natural uranium.

A control rod for a nuclear reactor according to the present invention is such that neutron absorbing rods are surrounded with a second neutron absorber which differs in material from the neutron absorbing rods. In a case where the neutron absorbing rod is composed of boron carbide powder and a cladding for receiving the powder therein, the second neutron absorber is a sheet of a material having a neutron irradiation lifetime longer than that of boron carbide, for example, hafnium. In a case where the neutron absorbing rod is a round hafnium rod, the second neutron absorber having a neutron absorption worth higher than that of hafnium is located so as to surround the round hafnium rods. Thus, the neutron absorbing rods are effectively used, and the lifetime of the control rod can be prolonged in the former.

Control rod for nuclear reactor

A method of operating a nuclear reactor adapted to use cross-shaped control rods. The control rods are grouped into a plurality of groups having a first group consisting of a control rod located at the center of the core, a second group consisting of 8 control rods surrounding the control rod of the first group, a third group consisting of control rods located adjacent to and outside of the control rods of the second group, and other groups determined successively in the same manner as in the third group. During the operation period other than the period in which the number of the control rods to be inserted for realizing the critical condition of said nuclear reactor is less than 6, the nuclear reactor is operated with control rod patterns in which the inserted control rods are selected from control rods of alternate or every other groups of said groups so as to include at least a pair of control rods which are located in a similar manner to that of the KNIGHT's movement on a chess board.

Method of controlling operation of nuclear reactor

A method of operating a nuclear reactor wherein the reactor is operated for more than 50% of its operating period with the control rod patterns in which, in the central region of the reactor core accounting for at least 50% thereof, the control rods inserted from the bottom of the reactor core are at the depths of between 16/24 and 21/24 of the height of the reactor core with eight control rods surrounding each of said inserted control rods being fully withdrawn.

Growing community of inventors

Katsuta, Japan

Hiromi Maruyama