Total Amount Of 137Cs Research Articles

Refinement of source term and atmospheric dispersion simulations of radionuclides during the Fukushima Daiichi Nuclear Power Station accident

To assess the radiological dose to the public resulting from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident in Japan, especially for the early phase of the accident when no measured data are available for that purpose, the spatial and temporal distributions of radioactive materials in the environment need to be reconstructed through computer simulations using the atmospheric transport, dispersion, and deposition model (ATDM). For the ATDM simulation, the source term of radioactive materials discharged into the atmosphere is essential and has been estimated in many studies. In the present study, we further refined the source term estimated in our previous study and improved the ATDM simulation with an optimization method based on Bayesian inference, which used various measurements such as air concentration, surface deposition, fallout, and newly released hourly air concentrations of 137Cs derived by analyzing suspended particulate matter (SPM) collected at air pollution monitoring stations. This optimization improved not only the source term but also the wind field in meteorological calculation, which led to the reduction of discrepancies in plume passage time at monitoring points to less than 3 h between calculations and measurements, by feeding back comparison results between the dispersion calculations and measurements of radionuclides. As a result, the total amounts of 137Cs and 131I by the present study became 1.0 × 1016 and 1.2 × 1017 Bq, respectively, and decreased by 29% and 20%, respectively, in comparison with those by previous study. The ATDM simulation successfully reproduced both the air concentrations at SPM monitoring points and surface depositions by airborne monitoring. FA10 for total samples of air concentrations of 137Cs at SPM monitoring points increased from 35.9% by the previous study to 47.3%. The deposition amount on the land decreased from 3.7 × 1015 Bq by the previous study to 2.1 × 1015 Bq, which was close to the measured amount of 2.4 × 1015 Bq. We also constructed the spatiotemporal distribution of some major radionuclides in the air and on the surface (optimized dispersion database) by using the optimized release rates and ATDM simulations. The optimized dispersion database can be used for comprehensive dose assessment in tandem with behavioral patterns of evacuees from the FDNPS accident by collaborating research group in the Japanese dose assessment project. The improvements in the present study lead to the refinement of the dose estimation.

Estimation of 137Cs source term from Fukushima nuclear accident

Objective To study the 137Cs source term from the Fukushima Daiichi nuclear power plant, based on inverse modeling, so as to provide reference for accident assessment and radiation protection. Methods The 137Cs source term was estimated by means of inverse modeling of nuclear accidents based on variational data assimilation combined with truncated total least squares (TTLS-VAR). The environmental monitoring data was balanced, and the dispersion model operator and monitoring data vector were corrected, in order to reduce the influence from atmospheric dispersion model error, and then improve the accuracy of inverse modeling of source term. Results The total amount of 137Cs released was estimated to be 1.74×1016-3.73×1016 Bq, with the highest peak of release rates estimated appearing on March 18, 2011 and the average release rate in exceed of 1.00×1012 Bq/s. The estimated total amount of 137Cs was close to the data published by IAEA and UNSCEAR. Also, the estimated release sequences were in good consistent with Japanese analytical results of source terms and sequence of events. The highest peak of the estimated release rate curve corresponds to the leakage incident of unit 3. Conclusions In this study, the 137Cs source term from the Fukushima Daiichi nuclear power plant is estimated by using TTLS-VAR inverse modeling, which could provide the basis for accident assessment and radiation protection. Key words: Fukushima nuclear accident; Inverse modeling; Source term for nuclear accidents; Variational data assimilation; Truncated total least squares

Accumulation of Chernobyl-derived 137Cs in bottom sediments of some Finnish lakes

The amount and vertical distribution of Chernobyl-derived 137Cs in the bottom sediments of some Finnish lakes were studied. Sediment and surface water samples were taken in 2000 and 2003 from 12 stations in nine lakes and the results were compared with those obtained in corresponding surveys carried out in 1969, 1978, 1988 and 1990. Each of the five deposition categories of Chernobyl fallout in Finland were represented. The depth profiles of 137Cs in the sediments showed considerable variety in the lakes studied. The peak values varied between 1.5 and 46 kBq kg −1 dry wt. The size and shape of the peak did not always correlate with the amount of deposition in the area, but on the other hand, reflected differences in sedimentation processes in different lakes. In some of the lakes the peak still occurred in the uppermost (0–2 cm) sediment layer, but in an extreme case the peak occurred at a depth of 22–23 cm corresponding to a sedimentation rate of 16 mm year −1 during the 14 years after the Chernobyl accident. The total amounts of 137Cs in sediments varied from 15 to 170 kBq m −2 at the sampling stations studied. Since 1990, the amounts have continued to increase slightly in two lakes, but started to decrease in the other lakes. In most of the lakes, the total amounts of 137Cs in sediments were about 1.5–2 times higher than in local deposition. In two lakes, the ratio was below 1, but in one case 3.2. Compared with the total amounts of 137Cs at the same stations in the late 1960s and 1970s, the values were now at their highest, at about 60-fold. The most important factors affecting 137Cs values in sediments were the local amount of deposition and the type of the lake and the sediment, but in addition, there were a number of other factors to be considered.

137Cs tracing of lacustrine sediments in the Dalian Lake, Qinghai Province, China

Based upon the analysis of137Cs and grain-size parameters, the total amounts of137Cs deposition by wind and water in the Dalian Lake of Gonghe Basin, Qinghai Province are defined. The vertical profile of Cs in the lacustrine sediments exhibits three137Cs activity maxima and one minimum. The major maximum corresponds to the global137Cs fallout in 1963; the two secondary maxima correspond to the leakage of the Chernobyl reactor in 1986 and complete desiccation of the lake in 1994, respectively. The minimum corresponds to aeolian deposition caused by extensive reclamation in the late 1980s and early 1990s. The137Cs data set was used to evaluate average sedimentation rate of the Dalian Lake since 1963. The deposition was stable in 1963–1986 and 1994–1998, and it was rapid during 1986–1994. This preliminary study reveals that137Cs has the same potential to trace environmental changes introduce by human interference in arid/semiarid regions as in humid regions.

Model testing using Chernobyl data: I. Wash-off of 90Sr and 137Cs from two experimental plots established in the vicinity of the Chernobyl reactor.

The "Wash-off" scenario is designed to test models concerned with the movement of trace contaminants from terrestrial sources to bodies of water, specifically the contamination of surface water by wash-off of radionuclides initially deposited onto soils. Particular emphasis is placed on chemical speciation and on the geochemical and geophysical processes affecting transfer of contaminants from soil to water. The scenario gives descriptions of two experimental plots near the Chernobyl power plant, one using heavy rain and one using snow melt, together with characteristics of the initial aerial deposition of the radionuclides and data on topography, soil type and characteristics, and time-varying precipitation. Predictions are requested for (1) the vertical distribution of concentrations of exchangeable and nonexchangeable forms of 137Cs and 90Sr in the soil of the experimental plots, (2) concentrations of 137Cs and 90Sr in runoff water from the experimental plots, and (3) total amounts of 137Cs and 90Sr removed by runoff from the experimental plots. Test data (field measurements) are available for all endpoints.

Leaching of Used Candu Fuel: Results from a 19-Year Leach Test Under Oxidizing Conditions

ABSTRACTA fuel leaching experiment has been in progress since 1977 to study the dissolution behaviour of used CANDU fuel in aerated aqueous solution. The experiment involves exposure of 50-mm clad segments of an outer element of a Pickering fuel bundle (burnup 610 GJ/kg U; linear and peak power ratings 53 and 58 kW/m, respectively), to deionized distilled water (DDH2O, ∼2 mg/L carbonate) and tapwater (∼50 mg/L carbonate). In 1992, it was observed that the fuel in at least one of the leaching solutions showed some signs of deterioration and, therefore, in 1993, parts of the fuel samples were sacrificed for a detailed analysis of the physical state of the fuel, using SEM and optical microscopy. Leaching results to date show that even after >6900 days only 5 to 7.7% of the total calculated inventory of 137Cs has leached out preferentially and that leach rates suggest a development towards congruent dissolution. Total amounts of 137Cs and 90Sr leached are slightly larger in tapwater than in DDH2O. SEM examinations of leached fuel surface fragments indicate that the fuel surface exposed to DDH2O is covered in a needle-like precipitate. The fuel surface exposed to tapwater shows evidence of leaching but no precipitate, likely because uranium is kept in solution by carbonate. Detailed optical and SEM microscopy examinations on fuel cross sections suggest that grain-boundary dissolution in DDH2O is not prevalent, and in tapwater appears to be limited to the outer %0.5 mm (pellet/cladding) region of the fuel. Grain boundary attack seems to be limited to microcracks at or near the surface of the fuel. It thus appears that grain-boundary attack occurs only near the fuel pellet surface and is prevalent only in the presence of carbonate in solution.

Distribution of137Cs and239,240Pu in the sediment of the Seto Inland Sea

The contents and distribution patterns of137Cs and239,240Pu in the sediments of the Seto Inland Sea were determined. In most of the sediment columns, approximately uniform concentrations were found to a depth of around 20 cm, probably due to bioturbation. Total amounts of137Cs in the sediment column are considerably lower than the global fallout inputs. It is suggested that a significant portion of137Cs input was removed from the Seto Inland Sea to the open ocean. Large excess inventories of239,240Pu over fallout input were observed in the investigated sediment columns.