[en] Purpose: To reduce the thermal stresses and improve the reliability of dip plates in LMFBR type reactors by constituting the dip plates with a plurality of segments and a plurality of auxiliary members while leaving them set free. Constitution: Arc-shaped segments are suspended by way of cylindrical supports respectively from the lower surface of a shielding plug disposed in the upper portion of a reactor container and dipped below the level of coolants. Each of the segments is supported approximately at its center of gravity by one support from the lower surface of the shielding plug. The support has a sufficient regidity to horizontal shock waves in the segment and is bonded to the plate by welding. The segment is formed so thin that thermal stresses due to the temperature slope along the plate thickness may be decreased and it is movable radially so that it can avoid severe thermal bendings when displaced radially due to heat expansion. (Moriyama, K.)

[en] Purpose: To prevent involvement of a cover gas into a coolant by simplifying the dip plate support structure, preventing the thermal stress load to the coolant and flattening the free liquid level of the coolant. Constitution: The dip plate suspended on the lower surface of a shield plug provided on the upper part of the reactor vessel and dipped below the liquid surface of sodium is divided into a plurality of segments, which are installed at a specific interval. In this manner, in place of the dip plate of an one-sheet structure, one having a structure of a plurality of divided dip plate segments is used, and therefore the plate supporting structure becomes simple, thus the thermal stress load being prevented. (Aizawa, K.)

[en] Purpose: To alleviate the production of thermal stress at the upper mechanism for a reactor core by mitigating the axial temperature gradient of a connecting body when the nuclear reactor is started or stopped. Constitution: A thermal resistor, e.g., ceramic plate having small thermal conductivity is interposed between a shielding body of the upper mechanism for the core of a liquid metal cooled reactor and an end plate of the coupling part with a connecting body connected to the shielding body, and are connected with bolts, etc. Thus, abrupt temperature change will not occur in the vicinity of the coolant liquid surface of the connecting body, and the thermal resistor changes temperature slowly. (Sekiya, K.)

[en] Purpose: To improve the safety of reactor container upon earthquakes. Constitution: A reactor container is suspended from and joined to the lower surface of a roof slab not rigidly but softly. Specifically, the lower surface of the roof slab is provided with support structures for suspending the shell. The container is provided with seats at the upper end thereof for engagement with the support structures. Since the support structures and the upper end of the container are merely engaged, this provides a soft connection. Bellows are also provided between the roof slab and the container for preventing gases from leaking through the joining portions. In the above structure, the earthquake shocks can be damped in the soft joining portions to decrease the effects on the container. (Ikeda, J.)

[en] Iodine and alkyl iodine compounds are removed from a gas phase or aqueous solution containing salts, iodine and iodine compounds, such as the ambient gas in a reactor, if an accident should occur. The process comprises contacting the phase or solution: (a) with a hydrogen type strongly acidic cationic exchange resin, (b) with an anionic exchange resin containing quarternary ammonium and (c) with an anionic exchange resin containing free basic type tertiary amine, in this order or by reversing the order of the two anionic exchange resins. Although no problems arise in the liquid phase reaction, the ion-exchange resins in the gas phase reaction are desired in the moist state in order to stable maintain the migration speed of the materials to be removed regardless of the relative humidity of the amibent gas. In example I, Amberlite IRA-900 of 200 mm thickness as the lowermost bed, Amberlite IRA93 of 200 mm thickness as the middle bed and Amberlite 200 of 200 mm thickness as the uppermost bed were filled respectively, in a methacrylate resin cylinder with an inner diameter of 25 mm. A solution containing 15.9 mg/1 of iodine, 41.2 mg/1 of methyl iodine and 550 mg/1 of sodium carbonate flows at a rate of 15 liter/hr downward through the beds. As a result of testing, no iodine, iodine ions, iodic acid ions and methyl iodine were detected. The amount of water the beds could treat was 60 times the total quantity of the filled resins. (Iwakiri, K.)

[en] Purpose: To prevent the reduction in the activity of radioactive iodine adsorbent material at high temperature. Constitution: Regenerated cellulose type fiberous activated carbon with the pore volume of 0.08 cc/g is reactivated by impregnating to support 10% by weight of magnesium acetate to obtain fiberous activated carbon with the pore volume 0.40 cc/g for the pores having diameter between 30 - 300 A. 60 parts of the activated carbon, 40 parts of breaching graft pulp made of coniferous trees and 7 parts by weight of polyvinyl alcohol fibers are subjected to a paper- making process to obtain activated carbon paper. Then, it is molded into a single side corrugated sheet, which is immersed in an ethanol solution containing 20% by weight of triethylenediamine then dried and molded into a honeycomb filter. It is necessary that the activated carbon material has pore volume of more than 5 cc/g for the pores having diameter between 30 - 300 A. (Horiuchi, T.)

[en] Purpose: To improve the methyl iodide removing efficiency by the use of absorber materials comprising fiberous activated carbon having a specified pore distribution and incorporated with amines. Constitution: Amines are added to fiberous activated carbon comprising fine pores of more than 0.68 cc/g with diameter less than 300 A and fine pores of between 0.16 - 0.95 cc/g with diameter between 30 - 300 A, and the ratio of the fine pore volume with diameter between 30 - 300 A to the fine pore volume with diameter less than 300 A being more than 28%. The amine-incorporated fiberous activated carbon is highly effective to the removal of gaseous methyl iodide, reduced in weight due to its fiberous structure and scarcely fallen by vibrations or like other external forces. In addition, since the fiberous carbon can be fabricated into a paper-like sheet and further molded into a honeycomb structure with less pressure loss, it can be used with no trouble while being inserted in an exhaust duct. (Yoshihara, H.)

[en] Alkyl iodides and mixtures of iodine and alkyl iodides are removed from a gas phase and an aquous solution phase by using solely an anion exchange resin containing a tertiary amine or together with an anion exchange resin containing quarternary ammonium compound. The resin containing the quarternary ammonium compound is employed mainly to remove iodine, and the resin containing the tertiary amine serves mainly to remove alkyl iodides. The method can be applied to collecting a majority of the methyl iodide as well as the radioactive iodine produced in the atmosphere of a reactor in case of a fuel accident. In embodiments, it is desirable to maintain the sufficient moisture content of the anion exchange resins at a sufficient moisture level so as not to reduce the migration speed of the iodine and alkyl iodides. The iodine and alkyl iodide can be produced with high efficiency and stability independently of the relative humidity of the gas phase. In examples, a solution which consists of 20.5 mg/l of iodine and 42.2mg/l of methyl iodide flew through a column of Amberite IRA-93 alone or blended with IRA-900 at a speed of 15 /hr. respectively. The resins were able to treat 400 times their equivalent in water. (Iwakiri, K.)

[en] Purpose: To maintain the positional relationship constant between equipments mounted on a roof slab and incore structures so that no undesired thermal stresses may be exerted thereto. Constitution: A control device for a cooling gas recycling system is disposed so that the temperature of cooling gases flowing through a cooling gas communication space within a roof slab is changed by the amount of change in the temperature inside of a reactor upper chamber. Since this enables to maintain the temperature gradient on both of the upper and lower faces of the radiation shielding layer in the roof slab, particularly, to prevent the warp fluctuation of the roof slab dependent on the temperature in the reactor upper chamber, no undesired thermal stresses are produced. (Kamimura, M.)

[en] Purpose: To detect the abnormality in the suspended body or reactor core supporting structures thereby improve the safety and reliability of tank type LMFBR reactors. Constitution: Upon inspection during reactor operation period, the top end of the gripper sensing rod of a fuel exchanger is abutted against a supporting bed and the position of the reactor core supporting structures from the roof slab is measured by a stroke measuring device. Then, the sensing rod is pulled upwardly to abut against the arm portion and the position is measured by the stroke measuring device. The measuring procedures are carried out for all of the sensing rods and the measured values are compared with a previously determined value at the initial stage of the reactor operation. As a result, it is possible to detect excess distortions and abnormal deformation in the suspended body or reactor core supporting structures. Furthermore, integrity of the suspended body against thermal stresses can be secured by always measuring the coolant liquid level by the level measuring sensor. (Kamimura, M.)