Mikio Murata

Physicochemical speciation of airborne 131I in Japan from Chernobyl

The physicochemical form of airborne 131I, released during the Chernobyl accident, was investigated in Japan during the period 6 to 19 May 1986. The proportions of 131I species identified during that period were: 19% particulate iodine, 5% I2, 6% HOI and 70% organic iodides. These results are similar to those obtained in previous studies of airborne stable iodine in inland regions. A fraction of 131I2 which was adsorbed on particulate matter desorbed from it during the sampling process.

Behavior of Sodium Oxide Aerosol in a Closed Chamber

The behavior of sodium oxide aerosol in a closed chamber was studied for the safety analysis of a Na-cooled fast reactor. The experimental apparatus and techniques are first described. The aerosol was released during a short time by blowing air onto heated Na in a 1 m3 chamber. The maximum mass concentration of the aerosol in the form of Na2O ranged of 0.05 ∼ 10g/m3. The particle size distribution, the aerosol mass concentration and the mass deposition rates were measured as a function of time. It was found that the mass median diameter of the aerosol was related to the maximum mass concentration. To determine the character of the behavior of sodium oxide aerosol in the chamber, the density of the aerosol material and the thickness of the boundary layer through which the particles deposit on the chamber wall were observed. The initial half-time of the aerosol mass concentration was compared with the values numerically calculated under certain assumptions.

Behavior of Sodium Aerosol in Atmosphere

Experiments have been made to determine the behavior of sodium aerosol under various atmospheric conditions, with the view to establishing an air monitoring technique to be used in sodium-cooled fast reactors. Changes in both size and form of sodium aerosol particles released into the air were studied. At levels of humidity below 40%, the particles were observed to be in solid state, constituted of sodium oxides and sodium hydroxide. When sodium aerosol particles are exposed for more than 1 min in an atmosphere containing more than 60% humidity, they are mostly converted into droplets of sodium hydroxide. The size of the droplets increases with humidity, the diameter becoming at 95% humidity about 1.4 times that at 40% (2. 7 times in volume). The final state of sodium aerosol suspended in air with a humidity exceeding 90% is in the form of droplets of sodium carbonate. When the CO2 concentration in the air is as high as 1.0v/o, the droplets solidify even at a humidity of 70%. The droplets can be made to s...

COMPARISON OF PERFORMANCE CHARACTERISTICS OF SOME FILTERS USING THORON DAUGHTERS AS RADIOACTIVE AEROSOL

Abstract —The important characteristics of air sampling filters are collection efficiency, flow resistance and surface collection efficiency. A comparison was made for these performance characteristics between the filters used at present in JAERI for air sampling (mostly imported) and those (made in trial) by a Japanese manufacturer. Collection efficiency, and surface collection efficiency and also alpha energy resolution were tested using the Millipore AA filter as a reference filter and thoron decay daughters as a test aerosol; the significant particles were less than 0.1 micron in diameter. In the cellulose filters tested, Toyo No. 5A and Toyo No. 1 showed nearly the same performance characteristics as Whatman 41, and the collection efficiencies of these three types of filters were over 90% at face velocities larger than 64 meters per minute. In the cellulose asbestos filters tested, for alpha air sampling Toyo HE-40 proved superior to HV-70. This filter has a collection efficiency greater than 99.5%, and about the same surface collection efficiency as the glass fiber filter Gelman E, generally used for alpha air sampling. On the basis of these tests, it was decided to use the cellulose asbestos filter Toyo HE-40 for alpha air sampling in JAERI.

Generation of Smoke and Clogging of Ventilation Filter under Burning of Bitumen/Salt Mixture

The fire and explosion accident happened at the bituminization demonstration facility of Power Reactor and Nuclear Fuel Development Corporation (PNC) of Japan on March 11, 1997. To elucidate smoke generation and clogging mechanism of ventilation filters under burning of bitumen/salt mixture in the PNC facility, small-scale simulation experiments were performed. The mock mixtures were prepared by referring to the composition of the real liquid waste and were burnt by heating. The burning behavior of the mixture was observed and the filter pressure drop, which was caused by loading smoke, was measured. Moreover, mass, energy and smoke release rate as direct source term from the burnt mixture and the empirical equation, which could represent the relationship between the pressure drop and burnt mass, were determined by comparing between the calculation results based on a one-dimensional thermofluid analysis code CELVA-1D, and the experimental results.

Calibration of Cascade Impactor by Two-Stage Method

A simple method of calibrating the cascade impactor has been developed by applying Hongo et al.s two-stage method to evaluate the particle-size distribution. The constants ψ and σfor a function representing the impaction efficiency were determined for the UNICO cascade impactor, using the test particles produced by a spinning-disc aerosol generator. The values were ψ=0.35, σ=1.46, respectively. The validity of the method for the UNICO cascade impactor was confirmed from microphotographic observation of a sample artificial aerosol containing different sizes of uranine methylene-blue particles. Both the mass median aerodynamic diameter and the geometric standard deviation obtained with the method agreed with the microphotographie measurements with relative errors not exceeding 10%.