A method, MIM (magnetic interrogation method), is proposed for nondestructive measurement of radiation damage of nuclear reactor pressure vessels. The method relies on good correlation between the levels of radiation-induced hardness change and magnetic coercivity change in pressure vessel steel. A part of the pressure vessel to be inspected is magnetized with two-pole magnetic yokes through the overlay clad of nonmagnetic stainless steel, and magnetic field distributions on the surface of overlay clad are measured in the vicinity of the poles of magnetic yokes. Then, the coercivity distribution in the direction of thickness in the pressure vessel steel is inversely estimated from the measured magnetic field distribution patterns with aid of static magnetic field analysis. The level of radiation damage such as hardness change is assessed with relation to the estimated coercivity distributions.
A (6)LiF-rich thermoluminescent sheet-type dosemeter ((6)LiF-rich NTL sheet) was developed for neutron 2D dosimetry. The dosemeter utilises the (6)Li(n, alpha)(3)H reaction to detect thermal neutrons. Responses of the (6)LiF-rich NTL sheet to neutrons were measured at the neutron beam irradiation facility for BNCT in JRR-4 Research Reactor at the Japan Atomic Energy Research Institute. Placement of a multi-leaf collimator at the output port of the neutron (beam) irradiation facility, produced either stripe- or round-shaped neutron distributions; the spatial distribution was measured using the developed NTL sheets. Direct measurements of neutron attenuation in water were also carried out using the developed NTL sheet, submersed in a water phantom. In each experiment, NTL sheets having natural abundance (7.9%) of LiF, and (6)LiF-enriched NTL (18.94%) sheet were irradiated under the same conditions. The ratio of thermoluminescence intensities of the (6)LiF-rich NTL sheet to that of the normal NTL sheet was compared to a theoretically calculated value. The experimental measurements are shown to be in good agreement with the calculations.
This paper presents a concept of a Rassive Safe Small Beactor fbr Pistributed energy supply system (PSRD), The PSRD is an integrated-type PWR whh reactor thermal power of 100 to 300 MW aimed at supplying electricitM district heating, etc, In design of the PSRD, high priority is laid on enhancement of safety as well as improvement of economy. Safety is enhanced by the fo11owing means:
Numerical simulation for a hydraulic operation stabilizing system of gas circuit breaker (GCB) driven by a hydraulic operating mechanism is treated . Valve collision and hydraulic column separation, created in hydraulic fluid by the movement of valves, are simulated. Constrictions between main piston and latching mechanism which is used to control the movement of the piston is taken into consideration. Results of simulation agree well with the experiments on the characteristics of the movement of valves, piston and hydraulic pressure. It is confirmed that the hydraulic mechanism with a hydraulic operation stabilizing system is stably operated, not affected by hydraulic column separation. Dimension of return circuit and latching mechanism which constitute a hydraulic operation stabilizing system are investigated. The range of diameter of restrictors in the circuit and latch angle to optimize a hydraulic operation stabilizing system are shown.
Stability of a hydraulic operation stabilization system during valve returning motion was investigated by the measurement and numerical analysis of the hydraulic circuit. Inadequate selection of hydraulic circuit constants causes the returning motion unstable and valves repeat open-close motion periodically. Hydraulic circuit constants related to the valve returning motion were set as parameter and analyzed. The volume of the back space of a discharge valve which is connected with hydraulic return circuit is important on the motion stability, and hydraulic vibration occurs by the combination of the volume with other hydraulic circuit constants. The reach of the constants which influence the motion stability was considered. The small volume and proper selection of other hydraulic circuit constants make a hydraulic operation stabilizing system stable.
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