The International Commission on Radiological Protection (ICRP) published the 2007 Recommendation of ICRP as the publication 103 of Annals of ICRP at the end of the year 2007. Owing to the transparency of revision process for the 1990 recommendation (Publ. 60) the understanding of as well as the interest in the new recommendation prevailed widely in the past 9 years. The Japan Health Physics Society (JHPS) made contribution to the revision by providing valuable comments on the drafts. Now members of the society are expected to express their insights on the future regulatory aspects of radiological protection and safety based on deep understanding of the new recommendations. In this issue of the Japanese Journal of Health Physics authors who participated in the Symposium of JHPS describe various aspects of new recommendations and its applications to future regulations in Japan. The authors wish that this article will help members of JHPS for better perception of the new recommendation and deep insight on the new principles of radiological protection and their application to regulations.
In the field of radiation protection, quality factor Q (L) and radiation weighting factor wR are important coefficients for estimating both radiation protection and operational quantities to the mixed types of radiation exposure. However, some inconsistencies might be found between Q (L) and wR for estimating effective dose, for example. Some inconsistencies are attributed to incomplete definition of terms Q (L) and wR. This report presents the root and evolution of quality factor Q (L) and radiation weighting factor wR for the years 1931-2007, to clarify the current issues of inconsistencies to be solved.
The International Commission on Radiological Protection (ICRP) has recommended ‘protection quantities’, such as equivalent dose and effective dose. These quantities have been amended to give the dose limits for exposures of workers and the public. Many discussions have been continuously made on protection quantities and their meanings at the time when ICRP defined new protection quantities (e. g., effective dose replaced effective equivalent dose in ICRP 1990 Recommendations). In addition, ICRP just published new recommendations for radiological protection (ICRP 2007 Recommendations). This paper reviews historical transition of protection quantities, including the ICRP 2007 Recommendations.
Since the late 1980s, the International Atomic Energy Agency has sponsored programmes in the area of environmental modelling and assessment. The recent EMRAS (Environmental Modelling for Radiation Safety) programme was started in 2003 and ended in 2007. This paper firstly describes the historical background of international exercises aimed at the testing and validation of models to assess the transfer of radionuclides in the environment and to predict the potential routes and levels of human exposure to the radionuclides. Chernobyl fallout data collected in various regions of Europe have provided a unique opportunity to test the reliability of environmental assessment models for contamination of terrestrial and aquatic environments. The paper also describes the activities undertaken by the 131I Working Group in the EMRAS programme, which were focused primarily on evaluating the predictive capability of environmental transfer and dosimetry models and on applying models to evaluating the effectiveness of countermeasures.
Current principle of radiation protection systems is protection of human, because the human is assumed as the most sensitive organism. Protection framework of human is also believed to be effective for protection of non-human species. On the other hand, it is recently attracting the international interests how sustainability of the ecological services is influenced by environmental disturbances such as chemicals and radiation. Therefore, international concern about protection framework of non-human biota has arisen. By the international concern, European and American countries were respectively developed models to evaluate effects of radiation to biota. However, the models are based on their own assumptions, so that the international validity has not been confirmed. Therefore, in IAEA, biota dosimetry working group (BWG) was established in Environmental Modeling for Radiation Safety (EMRAS) program, which aimed to intercompare the models to validate their assumptions and estimations. This paper reports summary of the activity in EMRAS biota dosimetry working group.
Before the 1995 Hyogoken-Nanbu earthquake, various geochemical precursors were observed in the aftershock area: chloride ion concentration, groundwater discharge rate, groundwater radon concentration and so on. Kobe Pharmaceutical University (KPU) is located about 25km northeast from the epicenter and within the aftershock area. Atmospheric radon concentration had been continuously measured from 1984 at KPU, using a flow-type ionization chamber. The radon concentration data were analyzed using the smoothed residual values which represent the daily minimum of radon concentration with the exclusion of normalized seasonal variation. The radon concentration (smoothed residual values) demonstrated an upward trend about two months before the Hyogoken-Nanbu earthquake. The trend can be well fitted to a log-periodic model related to earthquake fault dynamics. As a result of model fitting, a critical point was calculated to be between 13 and 27 January 1995, which was in good agreement with the occurrence date of earthquake (17 January 1995). The mechanism of radon anomaly before earthquakes is not fully understood. However, it might be possible to detect atmospheric radon anomaly as a precursor before a large earthquake, if (1) the measurement is conducted near the earthquake fault, (2) the monitoring station is located on granite (radon-rich) areas, and (3) the measurement is conducted for more than several years before the earthquake to obtain background data.
Hydroponic experiments were conducted to examine root-uptake of 14C in the form of acetic acid by 3 kinds of plants (marigold, tall fescue, and paddy rice) based on buried transuranic (TRU) waste disposal. Also, chamber experiment was conducted to examine loss of 14C as vaporized carbon dioxide (CO2) from the experimental tessera (spatially heterogeneous environment). The distribution of radioactivity in the plant, mediums, and carbon dioxide (14CO2) in the chamber were determined, and the distribution of 14C in the plant was visualized by the autoradiography. The plants absorbed and assimilated 14C through the roots. The amount of 14C in marigold and tall fescue were higher than that of paddy rice. However, the amounts of 14C-acetic acid absorbed by all the plants through their roots were considered to be very small. More so, 14CO2 gas was released from the culture solution to the atmosphere; however, it was not enough for the plant to perform photosyn-thesis. Assimilation of 14C in the plant shoots would be because of 14C movement of inorganic forms such as CO2 and HCO3-via the roots. Thus, the results indicated that the plants absorbed 14C through the roots and assimilated it into the shoots or edible parts not because of uptake of 14C-acetic acid but because of uptake of 14C in inorganic forms.
The aim of the present study is the development of the reliable calibration method for lung counting systems. In this study, a lung set that was constructed using a lung equivalent material was developed to simulate various source distributions within the lung. Counting efficiencies of a lung counting system were also evaluated for heterogeneous distributions of Pu and 241Am within the lung. The size of the developed lung set is similar to that of the lung for the JAERI phantom, the IAEA Asian torso phantom. The mass density of the lung set is 240kgm-3. It was found that counting efficiencies of the lung counting system for Pu/241Am loaded lung's apex are one tenth/three tenth of those for the homogenous distributions within the lung.
We examined applicability of established assessment tools to Japanese environment, which are developed to evaluate radiological impact for biota.. In this study, we chose two assessment tools, the one is RESRAD-BIOTA which was developed by US-DOE, and the other is ERICA assessment tools which developed by EURATOM. We considered paddy field as the typical Asian environment and used maximum of global fallout nuclide concentrations which were monitored in Joetsu. From our trial calculation for general screening, Tier 1 of ERICA suggested that concentration of 137Cs in aquatic systems is exceeded the screening level. On the other hand, RESRAD-BIOTA, concentration of 90Sr, and terrestrial systems in ERICA were less than screening levels. Thus, we proceeded to apply the ERICA Tier 2 using with same parameter set in Tier 1, and found that each species was not exceeded the screening level. Finally, we calculated dosimetries of considerable species living in paddy field. We tested both tools and we adopted ERICA because of flexibility in body dimensions of adding organism. From our calculation, we concluded that graded approaches which are adopted in RESRAD-BIOTA and ERICA are effective to apply Japanese environment.
Present ALARA (As Low as Reasonably Achievable) activities in three US nuclear power plants were investigated, which were Vogtle (PWR), ANO (PWR), and Quad Cities (BWR). They have been developing and continuing their own activities for over 20 years, and they have been in fact succeeding in reducing the collective doses of workers to certain levels. They are now focusing on “reducing dose” in this stage through the wide campaign under the cooperation between the authority and operators. Some of their recent attempts would provide Japanese nuclear power plants with useful information. A next discussion point would be “what is the real meaning of “ALARA”?”, which we concluded after the information-exchange and discussion with health physics experts in the three US plants. The US experts also agreed to this. The key is especially the term of “reasonably”. With referring to their experiences as well as understanding any difference of both countries, we should go toward the better dose control for workers in nuclear power plants.
The Committee on Radiation Protection and Public Health (CRPPH) of the OECD Nuclear Energy Agency (NEA) organised the fourth Asian Regional Conference on 13-14 December 2007 to discuss the next steps following the publication of new ICRP recommendations, to discuss aspects of their implementation, and to provide a dedicated forum for the collection and discussion of Asian views. The results of this conference provided useful and practical viewpoints for implementing the new ICRP recommendations to NEA member countries in the Asian and Pacific region, and highlighted those areas where further dialogue and discussion would be necessary in order to effectively implement the new formulation of the Commission's principles.