新风换气对室内氡浓度的影响

使用RAD7测氡仪对氡模拟实验房进行氡浓度连续测量,研究不同新风换气率对室内氡浓度的影[JP2]响。结果表明：氡模拟实验房内氡浓度最高可累积至2 000 Bq/m³,墙面平均氡析出率为14.5 Bq·m^-2·h^-1;氡模拟实验房在连续均匀地通入新风情况下,室内氡浓度随时间呈指数递减趋势;当新风换气率变化时,氡模拟实验房内的平衡氡浓度和平衡时间随新风换气率的增加呈指数递减趋势;当新风换气率由大变小时,室内氡浓度会再次累积增加。     

成都地区室内氡浓度调查

采用固体核径迹法,对成都市不同建筑类型、建筑结构、装修材料以及不同楼层的100间居室进行了室内氡浓度测量。调查结果表明:成都市居室环境中氡浓度的最高值为177.1 Bq/m3,最低值为8.4 Bq/m3,算术平均值为(39.4±22.9)Bq/m3;不同类型房屋室内氡浓度水平有显著差异;氡及其子体照射所致的人均年有效剂量为0.99 mSv,低于世界平均水平。     

MC法计算γ射线外照射剂量转换因子

以剂量转换数学模型为基础,针对骨、软组织和水的等效组织球体剂量计算,采用蒙特卡罗软件MCNP5构建0.01~10 MeV的γ射线在这三种物质中的通量和能量沉积模拟模型,进而计算这三种物质的γ外照射剂量转换因子。同时给出这三种物质的γ外照射剂量转换因子对不同能量γ光子的拟合计算公式,并进行了数据验证。结果表明:剂量转换因子在γ射线能量低于0.15 MeV时,随着能量的增加按幂函数降低;高于0.15 MeV时,按指数函数上升;剂量转换因子模拟值与参考值随γ射线能量的变化规律相同。     

长白山γ辐射空气吸收剂量率初步调查

结合我国长白山主峰地区典型地形地貌特征,较全面的开展γ辐射空气吸收剂量率水平调查,掌握了第一手的调查数据。调查结果表明长白山主峰的北坡、南坡及西坡海拔高度800m以上各测点地表环境γ辐射剂量率结果随海拔高度变化呈明显的正相关性。本工作的开展也为后续山林地区γ辐射空气吸收剂量率水平测量工作积累经验。     

Measurement of Soil Concentration Profile of Radon-222 and Its Effect on Exposure Rate

The concentration profiles of ²²²Rn in the soil air are measured at several selected sites in different parts of Japan, together with the ²²⁶Ra concentrations in soil, ²²²Rn escape-to-production ratios of soil and the characteristic physical properties of the soil. The resulting data are used to derive the vertical soil concentration profile of ²²²Rn, which is found to differ distinctly from site to site. Measurements are also made of the concentrations in soil of ²³²Th and ⁴⁰K.

Based on these data, the exposure rates due to the nuclides in the soil are calculated for a level 1m above ground at each site. The lowering of exposure rate due to the diffusion loss of ²²²Rn is estimated to be 2~13% of the total exposure rate due to naturally occurring radionuclides in the soil.     

Simple Empirical Expression to Evaluate Effective Dose Equivalent for External Photon Irradiation

In the CABRI-FAST and CABRI-RAFT programs within a collaboration with the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) and Forschungszentrum Karlsruhe (FZK), five pulse-type transient overpower tests were performed in order to study fuel pin behavior and failure condition in the Unprotected Loss-of-Flow (ULOF) accident. In these tests, two types of low-smear-density fuels irradiated in the French Phénix reactor at different burn-up levels were used so that an experimental database extension from the former CABRI-1 and CABRI-2 programs can be obtained. Pin failure took place in three of these tests giving information on the failure threshold. In two tests, no pin failure took place and useful information related to the transient fuel behavior up to failure and failure mechanism was obtained. These test results were interpreted through detailed analysis of experimental data and PAPAS-2S code calculations. In these calculations, pretransient fuel characteristics obtained from the sibling fuels were reflected, such that the uncertainty of the boundary condition can be minimized. Through the comparison among these tests and formerly existing CABRI tests, generalized understanding on the transient fuel behavior was obtained. It was concluded that the low-smear-density fuel mitigates cavity pressurization, thereby enhancing the margin-to-failure. It was also understood that this failure-thresholdenhancing capability is dependent on the type of transient.     

Wide Range Wave-Number Spectra of Place-to-Place Variations in Terrestrial Gamma-Ray Exposure Rate

The precipitation behavior of Pu. Np and Am during the denitration of high-level radioactive liquid waste (HLW) by formic acid was studied using a simulated HLW. The dissolution of the precipitate formed in denitrated HLW was also studied using oxalic acid to recover transuranium (TRU) elements from the precipitate. In the denitration, the precipitated fractions of TRU elements increased with decreasing acidity of the denitrated HLW. In the denitration at [HCOOH]/[HNO₃]=1.5, which was adopted in the partitioning process developed in JAERI, the precipitated fractions of Np and Am were only 0.6% and 0.06%, respectively, whereas that of Pu was 90 %. The precipitation fractions of Pu and Np did not depend on their concentrations in the range of 6x10^?5–6x10^?4 M for Pu and 10^?5–10^?3 M for Np. Plutonium was not precipitated itself by polymerization or hydrolysis but coprecipitated with other elements such as Mo and Zr. It was found that the precipitate formed during the denitration of 1 l of HLW could be dissolved in a 800 ml of 0.5 M oxalic acid solution.     

Dose Conversion Coefficients for External Photons Based on ICRP 1990 Recommendations

Monte Carlo calculations were performed to estimate the effective doses E for external photons based on the recent proposals in the ICRP 1990 Recommendations. Twelve photon energies between 17 keV and 8.5 MeV and eleven irradiation geometries were selected to be applicable to many exposure conditions encountered in the working and living environment. A MIRD-based unisex phantom was used in conjunction with the Monte Carlo transport code MORSE-CG. The results were presented as a form of dose conversion coefficients transforming the air kerma or fluence in free air to the effective dose. These coefficients were given in graphical and tabular forms. Analyses of organs' fractional contribution to E showed that the gonadal exposure has generally a great contribution for all the geometries except the incidence from above. A comparison of conversion coefficients with other results gave a reasonably satisfactory agreement. Finally, the ambient dose equivalent H ^*(10), one of the operational quantities proposed by the ICRU, was found to give conservative estimates of E for most of the irradiation geometries considered, but it gives a considerable overestimate of E at the incidences from above and below.     

Development of a Detector for Measuring Effective Dose (Equivalent) for External Photon Exposures in Natural Environment

We have developed a new shaped NaI(Tl) scintillation detector for the direct measurement of “effective dose, (E)” or “effective dose equivalent, (H^E )” for external photon exposures. These quantities related to human risk are generally difficult to be evaluated directly from measurements, because these depend not only on the energy distribution but also on the angular distribution of the gamma ray field. The present work, however, solved the problem concerning the angular dependence, by considering a detector shape that satisfies the angular response similar to human body's. The optimum dimensions of NaI(Tl) crystal for H_E and for E were determined respectively by a Monte Carlo simulation. The detector subject to H_E was manufactured and tested. The angular characteristics of the developed detector indicate a fairly good coincidence with those of the theoretical values, H_E . Together with the dose conversion method, so called “G(E) Function method”, it was made possible to directly measure effective dose (equivalent).