Qiuju Guo

Feasibility for Mapping Radon Exhalation Rate from Soil in China

Radon exhalation rate from soil is one of the most important factors for evaluation of the environmental radon level. For rough estimation of the nationwide radon exhalation rate from soil in China, a simple model was derived under the review and analysis of several previous works on radon exhalation theories. To show the feasibility of the model, some nationwide databases were summarized and discussed, and a trial estimation was made and compared with the measured data for Beijing. The results show that it is possible to map the radon exhalation rate from soil in China based on the present databases.

Radon Levels in China

This paper reviewed and summarized the results and problems of a nation-wide environmental radon survey which was carried out from 1984 to 1990 in China. Indoor radon concentrations were measured in 10,811 dwellings, and which covered 26 provinces and cities all over China. The range of indoor radon concentrations was <LLD-386.8Bq·m−3, the average was 22.5 Bq·m−3 and 19.6 Bq·m−3 for arithmetic mean and geometric mean, respectively. Both outdoor radon concentrations and indoor radon progeny concentrations were also reported. Even though the grab sampling was taken as the main method of the survey, it was still a valuable reference.

The Levels of Indoor Thoron and Its Progeny in Four Areas in China

Small surveys on thoron, radon and their progeny were carried out in four areas in China. Both high thoron concentrations near to walls and high thoron progeny concentrations were found in some dwellings through the surveys. It is suggested from the limited data that attention shall be paid to the exposure from the inhalation of thoron and its progeny in some kinds of dwellings or areas, and much works on thoron study in detail is necessary.

Potential of High Thoron Exposure in China

Compared with radon (222Rn) and its progeny, thoron (220Rn) and its progeny have not been well studied in the natural radiation fields. In this paper, some important factors (232Th content in soil and building material as well as building structure) relating to the level of indoor thoron and its progeny in China are reviewed. Limited results of small-scale surveys are also cited. The facts indicate that the public exposure from the inhalation of thoron progeny may be higher than the representative value in the UNSCEAR 1993 report, and thoron and its progeny may be a significant indoor pollutant in some regions or specific dwellings in China.

Some problems on the measurement of 222Rn concentrations by passive cup method.

A passive cup monitor has been constructed by using a 50 mm radius stainless steel hemisphere. The conductive housing has reduced the scatter in track densities. In dwellings with high 220Rn concentrations, it is particularly necessary to measure 222Rn concentration with a monitor having a radon exchange rate less than 0.1 h-1.

The Effect of Some Soil Characteristics on Soil Radon Concentration and Radon Exhalation from Soil Surface

To find out the impacts of soil characters on radon concentrations in soil and radon exhalation from soil, field measurements on soil radon concentrations (60 cm under the soil surface) and radon exhalation rate from soil surface were carried out in totally 31 points with different types of soil in three cities in both South and North China. Soil radium contents, water contents, soil porosity and grain size were concretely analyzed in our laboratory. The linear simulation was used to analyze the above data. The results showed that radon exhalation rate from soil and radon concentrations in soil have direct proportion to soil radium contents. Rather high radium content and radon exhalation rate were measured in Guiyang area, 67±28Bq/kg and 40±59mBq/m2-s, however no high soil radon concentration was found due to the difficulties in the measurements on clay soils with high water saturation. Compared with soil radium contents, radon exhalation rate from soil and soil radon concentrations are more easily impacted by soil characters and change in a rather large range.

Continuous Observation of Atmospheric 222Rn Concentrations for Analytic Basis of Atmospheric Transport in East Asia

The observation network of atmospheric radon-222 (222Rn) concentration established in East Asia region is introduced, and the characteristics of the observations at two continental sites Beijing and Seoul and three remote sites Cape Ochiishi, Hachijo Is. and Hateruma Is. are discussed in this paper. Higher levels of 222Rn concentrations with typical diurnal variation with early morning maxima were observed on the continent, and lower levels with no diurnal variation at remote islands. Seasonal variations with summer minima and winter maxima were commonly obtained at all five observatories, and they suggested contribution of 222Rn originated from the continent to atmospheric 222Rn over the remote islands isolated in the ocean. A backward trajectory analysis showed clear relationship between variation in wind field and in 222Rn concentration at Hachijo Is., and proved availability of the observation for analysis of atmospheric transport in East Asia.

Indoor Thoron and Radon Concentrations in Zhuhai, China

A field survey of 54 dwellings and 21 points outdoors around Zhuhai area was carried out using a newly developed integrating monitor in the spring of 2001 for a preliminary exposure assessment on 222Rn and 220Rn progeny, focusing especially on 220Rn progeny levels and its contribution to the general public. The flux rates of 222Rn and 220Rn from ground soil and soil nuclide contents were measured simultaneously. The average EECRn and EECTn were 52:9±39:1 Bq-m-3 and 4:0±2:3 Bq-m-3 for dwellings and 7:5±3:6 Bq-m-3 and 0:6±0:2Bq-m−3 for outdoor air, respectively. Rather high 220Rn flux rates from ground surface were measured, the mean value was 2;645:1 + 1;667:6 mBq-m−2-s1. The estimated radiation exposures from the exhalation of 222Rn and 220Rn progeny were 3.3 mSv-a−1 and 1.1 mSv-a−1, respectively. The exposure from 220 Rn progeny was some 1/3 that of 222 Rn progeny, and ought not to be ignored from the viewpoint of radiation protection in Zhuhai area.

Numerical solutions for the kinematic model of pebble flow velocity profiles and its applications in pebble-bed nuclear reactor

ABSTRACT The modular pebble-bed nuclear reactor (PBR) is a candidate Generation IV reactor being developed. The pebble flow in the very slow draining of fuel pebbles draws attention for its implications on core physical design and reactor physics analysis. One of the effective and simplified methods to address this problem is the kinematic model which is based on continuous theory to derive a diffusion equation for vertical velocity. This paper investigates the appropriate numerical solutions for the kinematic model of pebble flow velocity profiles in PBR geometry. Our method is based on a previously proposed transformed Cartesian coordinates and uses the implicit Crank–Nicholson integration scheme with two different treatments of the boundary conditions. Validations show that this numerical solution gives preferable agreements with the experimental results in the reference. Finally, the simulated velocity profiles are applied in the investigation of two pebble burnup-related issues, which are the pebble residence time prediction and the channel scheme in realistic high-temperature reactor pebble-bed modules reactor core geometry.

The temperature dependence of adsorption coefficients of 222Rn on activated charcoal: an experimental study

The radon adsorption coefficient of activated charcoal (K) has exponential relationship with temperature theoretically, but few experiment results of K at temperature below 0 ℃ were given. In this study, K were measured using a flow-through system with activated charcoal in cylindrical adsorption beds at temperature adjusted from room temperature to -48°C using liquid nitrogen. Results are consistent with theory and show that the adsorption coefficient at -48°C is nearly 25 times higher than that at 23 ℃.