Abstract: In a method of and an apparatus for checking the degradation of the pressure vessel of a nuclear reactor with the pressure vessel of the nuclear reactor being directly measured in a non-destructive manner, a magnetic yoke having an exciting coil and a magnetic flux measuring coil is closely placed in contact with the inner wall of the pressure vessel of the nuclear reactor. The hysteresis magnetization characteristics of the closed magnetic path formed by the magnetic yoke and the pressure vessel of the nuclear reactor are measured. The coercive forces are obtained by the hysteresis characteristics. The hardness of the material comprising the pressure vessel of the nuclear reactor at the part of the magnetic path formed in the pressure vessel of the nuclear reactor is obtained from the coercive forces and the degradation of the material comprising the pressure vessel is checked from the hardness.

Abstract: A method of and an apparatus for measuring the thickness of the overlay clad of the pressure vessel of a nuclear reactor with good accuracy are disclosed. A magnetic yoke having an appropriate length and cross-sectional area of the magnetic path is placed closely in contact with the surface of the overlay clad of the pressure vessel of the nuclear reactor to form a magnetic path by the magnetic yoke and the pressure vessel of the nuclear reactor, the magnetic yoke is magnetized, the distribution of the magnetic field on or near the surface of the overlay clad in contact with which the magnetic yoke is closely placed is measured and the thickness of the overlay clad of the pressure vessel of the nuclear reactor is identified from the medium value or the half value width of the distribution of the magnetic field thus measured.

Abstract: A method and a system for fine control of the thermal power of a nuclear boiling water reactor (BWR) with natural circulation. The reactor vessel, in which the core of such a reactor is enclosed, embodies an in-vessel part of a water level gauge containing a water level sensor, such that together with the out-of-vessel part of the system, which is a signal conditioning and processing unit, the effective water level in the vessel can accurately be measured and adjusted either automatically or by hand. The in-vessel part of the system comprises a water level gauge, such as a vertical standpipe, in which the "steam-collapsed" or "effective" water level is accurately created. The effective water level is typically defined for a reactor vessel of a normally operating boiling water reactor (BWR), while partly containing liquid water, partly a mixture of steam and water, and partly just steam.

Abstract: A method of manufacturing a heat resisting magnetic scale is disclosed which comprises a manufacturing process in which at least a part of a heat resisting base is heated and immediately cooled for the purpose of fusing the heated part to the base and changing both the magnetic characteristics of the part of the base which has been heated and the Curie point of the part which has been heated is raised to 100.degree. C. or higher.

Abstract: A method of manufacturing a heat resisting magnetic scale is disclosed which comprises a manufacturing process in which at least a part of a heat resisting base is heated and a manufacturing process in which the part which has been heated is immediately cooled down for the purpose of changing the magnetic characteristics of the part of the base which has been heated and the Curie point of the part which has been heated is raised to 100.degree. C. or higher.A heating resisting magnetic scale which cannot be demagnetized at high temperatures and cannot be separated even if it is subjected to rapid change in temperatures, and which exhibits excellent stability and measuring precision.

Abstract: Method and apparatus for sensing liquid level of the invention includes a plurality of thermocouple elements that are formed by connecting two kind of thermocouple wires alternately in series into a plurality of thermometric contacts. The two kind of thermocouple wires have different thermoelectric powers SA and SB and have a variety of predetermined lengths. The invention can sense with high reliability a liquid level of a sensed liquid by changing electromotive forces from these thermocouple elements into binary signals by using fewer thermocouple elements than the conventional apparatus. The invention also includes thermocouple elements for parity check to self-diagnose the sensed result to inspect easily and securely errors in operation due to disconnections in the thermocouple elements or external noises.