Abstract: An improvement in a liquid metal mechanical pump which includes a hydrostatic bearing immersed in liquid to rotatably support the lower end of a pump drive shaft and is constructed such that a part of liquid forced out of a diffuser is supplied to the bearing to lubricate it by the liquid. A cylindrical partition wall is disposed around the bearing with a clearance therebetween. The areas inside and outside the partition wall are communicated at a position remote from the diffuser. The partition wall prevents the liquid discharged from the diffuser from being directly supplied to the bearing, thereby reducing thermal shocks to the bearing.

Abstract: A complex personal dosimeter including a gamma- and beta-ray dosimeter block and a neutron dosimeter block. These two blocks are enclosed in a badge case type package so that a person can secure the dosimeter on his clothing. The gamma- and beta-ray dosimeter block consists of four thermoluminescent elements in combination with plastic filters having different thickness. The neutron dosimeter block consists of four thermoluminescent elements in combination with cadmium and tin filters. This complex dosimeter can individually measure or estimate the radiation doses such as gamma-rays, beta-rays, thermal neutrons, epithermal neutrons and fast neutrons over a wide range of doses, and can also obtain information on the energy of the radiation.

Abstract: A method of producing an oxide fuel pellet having a low density is provided which comprises adding a manganese compound to an oxide fuel powder selected from a group consisting of uranium dioxide powder and a mixed powder of uranium dioxide and plutonium dioxide, in an amount of 0.01 to 5.0% by weight based on the weight of the oxide fuel powder, molding the resulting mixture into a pellet form, and sintering the pellet-formed mixture at a temperature of 1,200.degree. to 1,700.degree. C.

Abstract: A freeze valve for a molten glass discharging nozzle is disposed at the bottom of a glass melting furnace. The freeze valve has at least two sets of temperature control units provided around the nozzle and arranged in series in the longitudinal direction of the nozzle, and an ejector for ejecting a high-pressure gas disposed at the lower end of the nozzle and adapted to eject the high-pressure gas toward the axis of the nozzle. Each of the temperature control units includes heating and cooling means so as to heat and cool independently both the upper and lower portions of the nozzle.

Abstract: A system for denitrating a starting nitric acid solution by irradiation of microwaves to obtain oxide product of the solution comprises a receiver for receiving the solution, a rectangular oven vessel provided with a bottom plate on which the receiver is put, and a conveying mechanism located below the bottom plate for continuously conveying the receiver on the bottom plate throughout the oven vessel. A microwave generator is operatively connected to the oven vessel for generating microwaves to irradiate the content of the receiver when it passes throughout the oven vessel. The receiver may be rotated and vertically moved when it is subjected to denitration and calcination in the oven vessel.

Abstract: A nuclear fuel conversion system comprises a unit for heating and denitrifying a nitric acid solution of uranyl nitrate, plutonium nitrate, or mixture thereof, a unit for grinding denitrified products, a unit connected to the grinding unit through a first conveying unit for roasting and reducing ground products, a unit connected to the roast-reduction unit through a second conveying unit for further grinding and then sieving the roasted and reduced products, and a unit for disposing of waste gases and waste liquor. The denitrification unit includes a microwave generator for heating and denitrifying the nitric acid solution and for cooling the denitrified product, and the first and second conveying units comprise pneumatic carrier means each of which consists of a suction nozzle, cyclone connected to the nozzle through a pipe, and a blower for creating a reduced pressure condition in the pipe.

Abstract: A cold trap including a section for cooling inflowing liquid sodium, a section for trapping impurities in the sodium, and a double-walled cylindrical structure disposed between the cooling section and the trapping section. The double-walled structure is filled with a heat-insulating gas, and is closed at its upper end but open at its lower end. An expanded portion designed for storing the heat-insulating gas is formed at the open lower end or in the vicinity thereof of the double-walled structure.

Abstract: A method of ascertaining the state inside a melting furnace of a radioactive waste, which method comprises: blowing a gas into a molten matter in the melting furnace by using at least two slender tubes disposed at an upper and lower points with a gap .DELTA.h between said points; detecting a back pressure difference .DELTA.P at the slender tubes to determine the density .rho. of the molten matter; and determining the level h of the molten matter in the furnace using the density .rho.. It is also possible to detect the formation of a bridge inside the furnace due to a non-molten solid matter of the waste charged into the furnace.

Abstract: A substance such as radioactive liquid waste is heat treated using microwave by introducing the substance into a vessel made of a material reflective to microwave and containing spherical bodies made mainly of a material transmissive (i.e. transparent) to microwave. Microwave is applied to the substance while imparting movement to the spherical bodies. The substance is heat treated while in contact with the spherical bodies and is separated from the spherical bodies and pulverized by the friction and collision between the moving spherical bodies. An apparatus for carrying out the method is described.

Abstract: Nitrates, such as alkali metal nitrates and ammonium nitrate, are electrolytically reduced to the corresponding nitrites by a process wherein an aqueous solution containing a nitrate is supplied into a cathode chamber of an electrolytic cell including cathode and anode chambers separated by a cation exchange membrane and an electric current is applied to the electrolytic cell, while maintaining the pH of the aqueous solution at a value of at least about 4. This process can be advantageously applied not only to the manufacture of nitrites but, also, to the treatment of waste nitrates. In the treatment of waste ammonium nitrate, the ammonium nitrite so formed is conveniently further treated by subjecting the electrolytically reduced catholyte to thermal decomposition outside the electrolytic cell, and removing the so formed nitrogen and water from the reaction system.

Abstract: A method for monitoring flow condition of a liquid metal which employs a detector consisting of an excitation coil applied with an a.c. current and at least two detection coils disposed on both sides of said excitation coil. The detector is disposed in the flowing direction of the liquid metal and a peak point of the cross-correlation function of fluctuation signals occurring in said detection coils is examined. By detecting the moving direction, the polarity and the magnitude of the peak point, the flow condition can be comprehensively ascertained, such as a change in flow velocity, a change in void fraction, the presence of voids and transit velocity of void.

Abstract: A method for sealing an object having a peripheral surface, surfaces substantially perpendicular to the peripheral surface and infinite enlongated bodies projecting from the surfaces perpendicular to the peripheral surface, which method comprises: wrapping the peripheral surface with a heat-shrinkable film in such a manner that both side edges of the film extend beyond the side edges of the peripheral surface; bonding longitudinal edges of the film to each other; and heating the heat-shrinkable film to permit the film to shrink to thereby seal the peripheral surface and a peripheral portion of the surfaces perpendicular to said peripheral surface, except said infinite elongated bodies.

Abstract: A method for the heat treatment of a radioactive substance by microwave power comprising preparing a nitrate solution of uranium, thorium, plutonium or a mixture thereof, and applying to the nitrate solution microwave energy sufficient to directly convert the nitrate solution into an oxide powder of uranium, thorium, plutonium or a mixture thereof, respectively. Such oxide powder is suitable for the manufacture of nuclear fuel pellets.

Abstract: An alpha-ray radiation source photographing device comprising a glove box having an optical window formed in a part of a wall thereof, alpha-ray radiation scintillator, on which an alpha-ray radiation source-containing sample is placed, disposed within the glove box and adjacent to the optical window, and photographing mechanism which includes an optical multiplier tube, a close-up lens system and a camera and is disposed outside the glove box such as to oppose the scintillator. According to this photographing device, the postion of the alpha-ray radiation source can be photographed from the outside of the glove box without inserting a film therein.

Abstract: A process for improving decarburization resistance of chrome-molybdenum steel in sodium is provided which comprises subjecting the chrome-molybdenum steel to cold working to attain a working ratio of not less than 5%, thereby forming numerous nuclei for carbide formation in the steel material, and heat-treating the cold-worked steel to form stable, fine carbide particles. Alternatively, by subjecting the steel material to warm working at a temperature of 600.degree. to 750.degree. C., both the working step and the heat treatment step can be accomplished in one step.

Abstract: A microwave melter in which a material charged in a crucible is heated and melted by irradiation of microwaves, the melter including a melting furnace having an upper furnace body fixedly mounted on a support structure and a lower furnace body detachably connectable with the upper furnace body, a waveguide for guiding microwaves from a microwave generator toward the furnace, a crucible received rotatably and in a suspended state in the lower furnace body, and a feed pipe for feeding untreated material to the crucible.

Abstract: Disclosed is a multi-stage hydrogen water isotopic exchange column suitable for use in producing heavy water. It comprises, at each stage, an overlying vapor-and-water contact bed, an underlying catalyst bed and means for collecting the water dripping from the overlying contact bed and guiding to and sprinkling the water on the upper-surface of the vapor-and-water contact bed of the lower adjacent stage.The vapor-and-water contact bed consists of a closely compacted fine network structure, and the water dripping from an overlying contact bed is transferred through the catalyst bed via water channel and is sprinkled over the upper-surface of the vapor-and-water contact bed of the lower adjacent stage. With this arrangement a multi-stage exchange column according to this invention is guaranteed little amount of gas pressure loss and elimination of water splashing which otherwise would be caused by increasing the flow rate of hydrogen gas.

Abstract: A method for wearing and taking off a protective suit which is used when entering the inside of a working zone segregated from the outside thereof. The protective suit has a cylindrical portion made of a film-like fusible material and is designed so that one can get into or out of the suit by passing through the cylindrical portion. When wearing the protective suit, one gets into the suit by passing through the cylindrical portion, with the protective suit being kept joined to an entrance/exit section of the working zone, and then part of the cylindrical portion is fused and closed to segregate the inside of the suit from the outside thereof while sealing the entrance/exit section with a pouch-like member.

Abstract: A method for detecting the flow instability in steam generators is provided. First, a number of limit values on the differential pressure between the water-side inlet and outlet of the steam generator are determined at different feedwater flow rates. The limit values define the onset of the flow instability. By connecting the thus determined limit values, a boundary line defining the occurrence of the flow instability is obtained. Second, it is checked whether the measured differential pressure between the inlet and outlet at an actual feedwater flow rate is above or below the boundary line so as to determine if the flow instability has occurred or not in the steam generator. An apparatus for accomplishing the method is also provided.

Abstract: A nuclear fuel element is provided which comprises a cladding tube having end plugs for sealing ends of the cladding tube and a multiplicity of fuel pellets stacked within the cladding tube. Each of the fuel pellets has a substantially cylindrical external lateral surface and a plurality of longitudinal recesses having rounded root portions on the external lateral surface, and has a height within the range from 1/2 to 1/3 of the outer diameter thereof. These fuel pellets with the floral petal shape are stacked in such a manner that the recesses of one pellet are not aligned with the recesses of adjacent upper and/or lower pellets.