[en] Purpose: To enable to respond to the abnormal high temperature of coolants within a short operation period in a LMFBR type reactors thereby surely scram the reactor. Constitution: In a structure having a curie point magnetic material contained at the lower portion of a control rod extension pipe, so as to interrupt the magnetic fluxes of an electromagnet that always attracts to hold a magnetic body disposed to the upper portion of a control rod, an annular curie point magnetic material is disposed to the upper outside of the electromagnet. Since the curie point magnetic material is disposed near the surface of the electromagnet where the temperature rises most significantly, the abnormal temperature at the exit of the fuels can rapidly be detected to deenergize the electromagnet and the response time can remarkably be shortened. Since this device operates as a gravitationally falling type reactor shutdown system independent from other reactor shutdown systems, high reliability can be obtained as a multiple safety system. (Moriyama, K.)

[en] Purpose: To prevent the occurrence of thermal stresses to the reactor core upper mechanisms in LMFBR type reactors. Constitution: A coolant flow rete limiter is mounted to a control rod handling rod, which is abutted against a secured plate in the course of withdrawing a control rod main body for limiting the flow rate of coolants passing through the central aperture, such that the coolant flow rate is limited by the coolant flow rate limiter when the insertion amount of the control rod main body into the reactor core region is small. Accordingly, the exit temperature of the coolants in the control rod assembly can be increased at the withdrawing stroke position with less heat generation amount of neutron absorbers. Accordingly, the maximum temperature difference between the temperature at the exit of the control rod assembly and the temperature at the exit of the fuel rod assembly can be reduced than usual to thereby enabling to moderate the thermal stresses and the theremal fatigue in the nuclear reactor structure to improve the reactor reliability. (Takahashi, M.)

[en] Purpose: To reduce the size of a reactor core and, thus, that of an entire nuclear reactor by decreasing the number of control rods without impairing the reactor shutdown function in an FBR type reactor. Constitution: The scram operation is carried out by a scram operation signal. Even in a case if the scram signal should fail to be outputted, coolant temperature rises due to the abnormality of the reactor and, when it rises above a curie point, the curie point electromagnet of the curie point electromagnet mechanism is demagnetized. Then, magnetic adsorption between this mechanism and the adsorbed plate is released causing an inside extension tube to fall thereby releasing the engagement between a latch filter and a handling head, by which a control rod is inserted to the inside of the reactor core to surely conduct scram operation. In this way, by providing both of the function, i.e., the scram operation due to the scram signal and the scram operation in a case if the scram signal should fail to be outputted by some or other reason, control rods and appendant mechanism for a reserved reactor shutdown device are no more necessary thereby enabling to reduce the size of the nuclear reactor. (Horiuchi, T.)

[en] Purpose: To shutdown nuclear reactors by gravitationally lowering control rods upon occurrence of abnormality, by constituting a chuck mechanism for connecting control rods with a combination of a magnetic body having a certain curie point and a magnet. Constitution: To the inside of a lower guide tube constituting a reactor core, a control rod incorporating neutron absorbers is inserted. A magnetic body with a curie point in the temperature range of 600 - 800⁰C is provided to the upper end of the control rod and adapted so that its magnetic force is decreased at the curie point. Just above the lower guide pipe, a guide pipe having an extension pipe disposed therein is supported on an upper mechanism. The lower end of the extension pipe is secured with an electromagnet that constitutes a chuk mechanism for attracting the magnetic body. During normal operation, the control rod is in extracted state and, if the temperature in the core fuels increases upon abnormality, the magnetic force of the magnetic body is weakened by the high temperature coolants, whereby the control rod falls gravitationally to shutdown the reactor. (Kawakami, Y.)

[en] Purpose: To provide a device for detecting the position of failed fuel, which is capable of being loaded on a rotary plug and accurately indexing the position of a failed fuel element, and is compact in construction, easy in maintenance, and high in accuracy. Constitution: When the existence of failed fuel has been detected, the reactor is operated at a low power or is stopped, and the detection cylinder of a failed fuel detector is inserted into a hole of a fuel exchanger on the double rotary plug. Then, a predetermined piping is applied. Thereafter, a tracer is injected therein and circulated in the part required to be detected, thus the object position being detected. (Aizawa, K.)

[en] The present invention can detect the position of a control rod for controlling the power of a nuclear reactor accurately free from the effect of the dropping speed. That is, the device of the present invention comprises a ultrasonic wave receiving device and a control rod extension rod having a structure of reflecting ultrasonic waves. The ultrasonic waves are transmitted laterally to the extension rod of the control rod. The ultrasonic waves reflected from the control rod extension rod are received and the reflecting signals are detected. With such a constitution, the position of the control rod can be recognized accurately. The determination for the shape by the ultrasonic waves is generally possible up to about 1mm. In view of the above, grooves are formed to the control rod extension rod at 1mm pitch and, if the groove that passes the position of the ultrasonic wave transmission/receiving element is judged, the position of the control rod can be measured on 1mm unit. (I.S.)

[en] An inert gas space is disposed in a wrapper tube. A dropping port for granular or pellet-like neutron absorbers is disposed to the lower end of a neutron absorber-filled portion at an upper level of a reactor core. There are disposed a reactor core constituent element having a plug disposed vertically movably to the dropping port, and a thermally extensible mechanism for opening the dropping port by urging and driving the plug by a thermally expandable medium to drop the neutron absorbers. The neutron absorber-filled portion coaxially comprises, in the wrapper tube, a cylindrical member having a closed upper end and a hopper having the dropping port in the cylindrical member. The thermally extensible mechanism comprises a piston in contact with the upper end surface of a plug-mounting rod, an outer cylinder surrounding the upper portion of the piston with a bellows seal, a sliding guide coaxial with the outer cylinder and a thermally expandable medium at the upper end surface of the piston. Then, neutron absorbers can be dropped by temperature change of the coolants upon failure of scram to conduct passive scram of the reactor by an emergency reactor scram system of a BWR reactor without relaying control rods. (N.H.)

[en] The film structures, magnetic properties, and noise characteristics of soft magnetic multilayers with alternately stacked FeCSi soft magnetic layers and non-magnetic intermediate layers were investigated. The FeCSi layers in an as-deposited multilayer with C or Ta intermediate layers had the same nano-sized fine crystalline grains and low media noise as an as-deposited FeCSi monolayer. Amorphous C intermediate layers suppressed the amplitude of spike noise especially well. In contrast, FeCSi layers in an as-deposited multilayer with Cr or Ti intermediate layers were composed of coarse crystalline grains, which increased the media noise. The crystallographic match at the interface between the layers in a multilayer could explain these phenomena. The similarity of the atomic arrangement at the interface between layers and the crystallographic match of less than a few percent for the distance between atoms crystallized FeCSi layers with nano-sized fine crystalline grains into ones with coarse crystalline grains during deposition

[en] The present invention provides a device for and a method of directly driving control rods of an FBR type reactor linearly by a cylinder type linear motor while having a driving shaft as an electric conductor. Namely, a linear induction motor drives a driving shaft connected with a control rod and vertically moving the control rod by electromagnetic force as an electric conductor. The position of the control rod is detected by a position detector. The driving shaft is hung by a wire by way of an electromagnet which is attachably/detachably held. With such a constitution, the driving shaft connected with the control rod can be vertically moved linearly, stopped or kept. Since they can be driven smoothly at a wide range speed, the responsibility and reliability of the reactor operation can be improved. In addition, since responsibility of the control rod operation is high, scram can be conducted by the linear motor. Since the driving mechanism can be simplified, maintenance and inspection operation can be mitigated. (I.S.)

[en] We compared the radioresponse of cervical carcinoma that was closely related to local disease control by the tumor regression rate (RR) during intracavitary radiotherapy (ICRT) and external beam radiotherapy (EBRT) on the presumption that ICRT has a stronger treatment impact than EBRT because of its specific dose distribution. A total of 37 patients were treated by EBRT at 45.0 Gy over 5 weeks, followed by high-dose-rate ICRT at 6.0 Gy per weekly insertion at point A three to five times and by boost EBRT. RR was defined as the slope (day^-1) of the tumor-volume shrinkage curve fit to an exponential regression equation. Assuming that the tumors were ellipsoid, the tumor volume was estimated using magnetic resonance (MR) images obtained before treatment, after 45.0 Gy of EBRT, and after the third ICRT insertion. RRs were compared based on the radiotherapy method. RR ranged between -0.008 to 0.093 day^-1 (median 0.021 day^-1) during EBRT and -0.001 to 0.097 day^-1 (median 0.018 day^-1) during ICRT, showing no significant difference or correlation between treatments. Contrary to expectations, RR did not directly relate to the impact of physical treatment. RR could be related to biological factors, such as the amount of tumor clearance and changes in tumor consistency during treatment. (author)