Hitachi, Ltd.

Hitachi-ge Nuclear Energy, Ltd.

Yoshihiko Ishii

Sadao Uchikawa

Motoo Aoyama

Yasunori Bessho

Setsuo Arita

Renzo Takeda

Osamu Yokomizo

Junjiro Nakajima

Tadaaki Ishikawa

Yuichiro Yoshimoto

Koji Fujimura

Hiromi Maruyama

Yuichi Morimoto

Ryota Kamoshida

Atsushi Fushimi

Tomohiko Ikegawa

Kazuaki Kito

Masaki Kanada

Shin Hasegawa

Takahisa Matsuzaki

Sohei Fukui

Masataka Hidaka

Kenichi Katono

Atsushi Zukeran

Kouji Fujimura

Tomoyuki Matsumoto

Katsuki Hamada

Atsutoshi Mizuide

Kazuhiko Ishiii

In view of above problems, an object of the invention is to provide a primary containment vessel venting system having a structure capable of continuously discharging vapor in a primary containment vessel out of the system and continuously reducing pressure of the primary containment vessel without discharging radioactive noble gases to the outside of the containment vessel and without using an enclosing vessel or a power source. In order to achieve the above object, an nuclear power plant of the invention includes a primary containment vessel which includes a reactor pressure vessel, a radioactive substance separation apparatus which is disposed inside the primary containment vessel and through which the radioactive noble gases do not permeate but vapor permeates, a vent pipe which is connected to the radioactive substance separation apparatus, and an exhaust tower which is connected to the vent pipe and discharges a gas, from which a radioactive substance is removed, to the outside.

Nuclear power plant

An operator of a nuclear plant is provided with an action margin time up to the execution of a next action to be performed in response to a detected accident based on sensor signals received from sensors for the plant. The operator is provided with a displayed graph showing the received sensor signals, estimated sensor signals for the future, the action margin time and an action threshold value corresponding to the next action. Accordingly, the operator can readily grasp how much time is available to perform the next action before the received sensor signals are predicted to exceed the action threshold value.

Operation assistance apparatus at time of accident in plant

In order to provide a reactor power control apparatus which can maintain a stable water level when reactivity control based on control rod operation and water level adjustment is performed, this invention comprises a turbine control which calculates the load set error signal from the error between the set target generator power value and the generator power that was fed back and outputs to the turbine control apparatus; control rod control in the natural circulation boiling water reactor which calculates the control rod operation signal and outputs it to the control rod drive control apparatus; water level control inside the natural circulation boiling water reactor which calculates the water level set signal and outputs it to the feed water control apparatus; and the switch determining device which selectively outputs one of the control rod control and water level control based on the generator power that was fed back, the reactor power and water level, as well as switching rules and determination values.

Reactor power control apparatus of a natural circulation boiling water reactor and a feed water control apparatus and nuclear power generation plant

A fuel assembly comprises a plurality of fuel rods which contain nuclear fuel material inside, a lower tie plate which holds the lower end of the fuel rods and has a path inside to lead coolant between the fuel rods, and a channel box which encloses a bundle of the fuel rods. An orifice, in which a plurality of round rods are arranged to cross the coolant flow path, is installed in a through hole at a side wall of the lower tie plate by connecting to the side wall. Orifice coefficient of the orifice becomes large at small flow rate of coolant which supplied to the fuel assembly, and becomes small at large flow rate of coolant. By using the fuel assembly described above, void fraction in a gap region between fuel assemblies can be altered during beginning and end of an operation cycle of the nuclear reactor.

Fuel assembly and boiling water reactor

A high conversion nuclear reactor core has fuel assemblies made up from large numbers of axially-extending uranium-plutonium mixed oxide fuel rods. The fuel rods are densely packed so as to give a high conversion ratio of fissile substances, preferably approaching unity. The average plutonium enrichment in the assemblies is higher in their bottom, upstream halves, than in their top downstream halves. This has the effect of reducing a potentially dangerously high void coefficient in the core.

Fuel assembly and nuclear reactor

A fuel assembly of the present invention comprises a plurality of fuel rods which are held by an upper tie plate and lower tie plate at the ends thereof and a moderating rod which is arranged between the fuel rods and held by the lower tie plate at its lower end. The fuel rods are arranged in a lattice form having 9 rows and 9 columns, and the moderating rod contains a passage for a coolant and has a cruciate cross-sectional form. The ratio A.sub.M /A.sub.C of the area A.sub.M of a moderator region in the moderating rod in the cross-sectional plane in which the moderator is present to the area A.sub.C of the coolant passages in said fuel assembly is within the range of 0.07 to 0.11, and the area A.sub.M is 75% or more of the total area of the fuel lattice units in which none of the fuel rods is arranged, but the moderating rod is arranged.

Fuel assembly

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.

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Tokyo, Japan

Yoshihiko Ishii