The development of integrated digital Instrumentation and Control (I & C) systems for Advanced Pressurized Water Reactor (APWR) and Advanced Boiling Water Reactor (ABWR) have been promoted to meet the requirements for increased reliability, enhanced operability and maintainability. The systems integrate state-of-the-art technologies for man-machine interface, digital plant control and protection, optical multiplexing signal transmission and ergonomics. The systems have been systematically built on the hierarchically distributed architecture. This paper describes the design philosophy and the features of the integrated digital I & C systems for APWR and ABWR, focusing on improved man machine interface and newly developed digital systems for plant control and protection.

View full abstract

Magnetic properties of ternary uranium oxides with the fluorite-type structure or the perovskite-type structure are summarized to discuss the behavior of 5f electrons in solids. The magnetic susceptibility data for M_yU_1-yO_2+x solid solutions (M=rare earth ion, alkaline earth ion) with the fluorite-type structure are reviewed and the charge transfer phenomena found in Ce_yU_1-yO₂ solid solutions are discussed. The magnetic susceptibility and the electron paramagnetic resonance (EPR) data for MUO₃ (M=alkali metal ion) and the ordered perovskites Ba₂MUO₆ (M=rare earth ion, transition metal ion, alkaline earth ion) are reviewed. The magnetic exchange interactions between uranium ions at low temperatures and the g-value for EPR are discussed, and the critical distance between uranium ions is derived.

View full abstract

The ⁶⁰Co γ-ray radiolysis of simulated nitric acid solutions was examined with a laboratory-scale apparatus in order to evaluate the amount of hydrogen released from high-level liquid waste (HLLW) in nuclear fuel reprocessing. The authors studied the effects of several factors on hydrogen release from aqueous nitric acid solution with bubbling. In the experiment, nitric acid concentration ranged from 0.1 to 8.0M, dose rate ranged from 0.24 to 4.5kGy/h, and the temperature was 30°C.
The amounts of hydrogen released increased linearly with dose. The primary molecular hydrogen yield, per energy absorption of 100eV, G(H₂), was indepent of the dose rate, and decreased nearly exponentially with increasing the nitric acid concentration. The G(H₂) values for 2 to 5M nitric acid concentration corresponding to that of HLLW were in the range from 0.01 to 0.044. These values are about 20% less than reported data on radiolysis of deaerated nitric acid solutions in glass ampoules.

View full abstract

The concentration of ²²²Rn in air sampled within a very short period of time was measured using activated charcoal as the adsorber. The detector is the plastic canister containing mixture of the activated charcoal and the silica gel. The radon gas was adsorbed in the charcoal in the radon chamber at the temperature of 25°C. A little amount of liquid scintillation cocktail was added into the vial of liquid scintillation counter with the canister. The radon in the charcoal was extracted in the liquid scintillation cocktail. Alpha particles emitted from radon and its daughter nuclei in the cocktail were detected using the liquid scintillation counter. Present method has advantages of not only short sampling time of air but also adsorption of radon in charcoal under a constant temperature. The concentration of radon in air down to 2Bq/m³ could be detected. A kinetic model for adsorption of radon in the charcoal is also presented. The ratio of radon concentration in the charcoal to that in air under the equilibrium state of adsorption was estimated to be from 6.1 to 6.8m₃/kg at the temperature of 25°C.

View full abstract

Fast imaging techiques with a linear array type ultrasonic probe and character recognition using a coded dot pattern have been developed for an automated reading of fuel ID numberson fuel assemblies in nuclear fuel reprocessing facilities etc. As fast imaging techniques, electronic and mechanical scanning of ultrasonic beam (hybrid ultrasonic beam scanning) and associated signal processing were developed using the linear array ultrasonic probe which consists of a one-dimensional array with 64 transducer elements of 1mm thick and 9mm wide. Fast imaging within 3s, which is about 1/20 of the conventional full mechanical scanning method, was realized for fuel assemblies of the present light water reactors. The coded dot pattern expressed by 2×3 dots was proposed as a method for the fast recognition of fuel ID numbers, and it gave the fast recognitions within 1s.

View full abstract