Radioactive Waste Storage Areas Research Articles

Ge-Doped Optical Fibers for Passive and Active Radiation Detection Modes

Silica-based optical fibers made by Modified Chemical Vapor Deposition (MCVD) technique have been doped with different concentrations of germanium (Ge). After characterization of the thermoluminescence (TL) process in each of these fibers, their real-time responses were studied by radioluminescence (RL) under X-rays. First, the same counterintuitive trend was observed for the intensity of the two phenomena as a function of the Ge content, namely the decrease in TL and RL signals with increasing Ge content. This behavior was explained by the existence of thermally disconnected traps. Then, the RL response as a function of the dose-rate of the fiber doped with 1% Ge was judiciously chosen and investigated in detail. The results show that up to Total Ionizing Dose (TID) of 1.9 kGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), this response is not only insensitive to the accumulated dose effect but also exhibits an afterglow decay at the end of the radiation much faster than that of a Ce-doped fiber, a very useful feature where irradiations are repetitive as in the medical field of flash-therapy. In addition to the medical field where the Ge-doped fiber seems to be quite suitable, slightly larger core diameters would also allow this same fiber to meet the challenge of high sensitivity in the environmental radiation monitoring around nuclear power plants or radioactive waste storage areas.

Environmental Remediation of the difficult-to-return zone in Tomioka Town, Fukushima Prefecture

Temporal variations in ambient dose rates in a restricted area designated as “difficult-to-return” for residents of Tomioka Town, Fukushima Prefecture were evaluated in a car-borne survey during 2018–2019. The median dose rates in the “Decontaminated area” in the difficult-to-return zone decreased rapidly from 1.0 μSv/h to 0.32 μSv/h; however, the median dose rates in the “Non-decontaminated area” and “Radioactive waste storage area” fluctuated between 1.1–1.4 μSv/h and 0.46–0.61 μSv/h, respectively. The detected rate of the cesium-137 (137Cs) (137Cs-detected points per all measuring points) in the “Decontaminated area” also decreased rapidly from 64% to 6.7%, accompany with decreasing in ambient dose rates. On the other hand, the detection of 137Cs in the “Radioactive waste storage area” and “Non-decontaminated area” decreased from 53% to 17% and 93% to 88%, respectively. We confirmed that the dose rates in the Decontaminated area dramatically decreased due to decontamination work aiming to help residents return home. Moreover, the estimated external exposure dose of workers during the present survey was 0.66 mSv/y in the Decontaminated area and 0.55 mSv/y in the Radioactive waste storage area, respectively. This case of Tomioka Town within the “difficult-to-return zone” may be the first reconstruction model for evaluating environmental contamination and radiation exposure dose rates due to artificial radionuclides derived from the nuclear disaster.

344. Application of Monte Carlo techniques to the calibration of airborne radioactivity monitoring systems

Purpose Air monitoring systems are mandatory in all areas potentially contaminated with airborne radioactivity, such as hot laboratories, treatment rooms, and radioactive waste storage areas. The calibration of such systems may be practically complicated or require the application of correction factors, obtained by means of approximated analytical calculations. Monte Carlo techniques provide an effective way to check the calibration and the impact of the approximations used in the calculation. Methods The present work compares two different systems: a continuous air monitoring system, composed by a NaI detector located inside a chimney, and an air pumping system that measures the sample activity in a Marinelli beaker geometry, equipped with NaI detector. This setup allows to calibrate the continuous air monitoring system using the measurements provided by the Marinelli beaker system. A self-absorption correction factor, applied in the calibration of the Marinelli beaker system, is derived for gamma and beta+ radiation and compared with approximated analytical calculation available for gamma [1] . The cross-calibration of the two systems is complicated by the presence of F18 that sticks to the duct’s walls, producing a background that continuously increases during the air flow, therefore the calibration constants are checked using an approximate analytical calculation and a Geant4 simulation. Results Calibration factors are computed for ducts of different sizes and lengths, and validated using the IRST monitoring system. These coefficients represent a useful estimate in the calibration of continuous air monitoring systems in all cases where the cross-calibration of two systems is not possible. Conclusions Monte Carlo techniques help in overcome challenging aspects in the calibration of air monitoring systems, providing reliable results that can be used to cross-check the calibration constants of the system in case of large experimental uncertainties.

DETERMINATION OF EXTERNAL IRRADIATION FROM SOURCES WITH COMPLEX GEOMETRY CONTAINING RADIOACTIVE WASTE

A combined technique using both Monte-Carlo and quasi-analytic method has been developed for calculation of irradiation from complex objects containing radioactive waste. Monte Carlo method is used to calculate spectral, angular and spatial distributions of γ-quanta close to one of the surfaces of the concrete cask loaded with containers filled with radioactive waste (RW). Radiation characteristics at the prescribed distance are determined by integrating the point sources with calculated distributions over thissurface. Summation of photons of external radiation from individual RW isotopes allows finding the photon flux for any storage time. Application of the technique allows to calculate asymmetric loading of casks with containers filled with RW of different activity and to optimize the arrangement of the casks in the RW storage area. This allows reducing the effect of radiation-absorbed dose on the service personnel and on the areas surrounding RW storage.

Radon effective dose from TENORM waste associated with petroleum industries

Technically enhanced naturally occurring radioactive material (TENORM) associated with petroleum industries can be accumulated with elevated quantities and therefore can threat the workers through external and internal exposure. Measurements of radon-related parameters give information about the radioactivity levels in the TENORM waste using the well-established correlation. Also, it is useful to calculate the internal exposure due to radon inhalation in terms of effective radon dose. Among radon-related parameters, areal exhalation rate is the most suitable for characterising land and objects with only upper surface contamination in the case of petroleum waste. The TENORM in this study is collected from waste storage areas located near oilfields at south Sinai governorate, Egypt. The average values of exhalation rates as measured by Lucas cell based on delay count method are 273 +/- 144 and 38 +/- 8 Bq m(-2) h(-1) for scale and sludge, respectively. Whereas, two count method gives results with 18 and 20 % lower values for scale and sludge, respectively with good correlation coefficient of 0.999 and 0.852, respectively. Sealed cup fitted with CR-39 gives results compatible with Lucas cell with minor deviation in case of scale due to its thoron content. The results of CR-39 are qualified by taking into consideration the correction for back diffusion effect. The effective radon dose was calculated for different simulated radioactive waste storage areas with different contaminated areas and air ventilation rate. Minimising the contaminated areas and building up efficient ventilation systems can reduce the internal exposure even in the case of RWSA-containing TENORM with elevated radioactivity.

HTO Emission from Contaminated Surfaces and Distribution in Environmental Media Around Nuclear Facilities

ABSTRACTField studies were undertaken on both a wetland, which is downgrabient from a radioactive waste storage area at Chalk River Laboratory, and a grassland near Pickering nuclear power station. The purpose for this study was to quantify HTO (tritiated water/vapor) transfer in the land surface environment. The amounts of evaporation and transpiration were separately estimated, because the specific activity of tritium (HTO) is commonly different between surface and subsurface soil. Most of the water and tritium fluxes are attributed to transpiration in the season examined. Measured tritium concentrations in leaves at daytime agreed with predicted values, which are based on a simple equation. The ratios of organically bound tritium (OBT) to free water tritium ranged from 0.2 to 0.8 in this study.

Seasonal Trends in Environmental Tritium Concentrations in a Small Forest Adjacent to a Radioactive Waste Storage Area

Tritium (HTO) concentrations were studied for an entire year in a floodplain forest adjacent to a low-level radioactive solid waste storage area (SWSA No.5) at Oak Ridge National Laboratory (ORNL) near Oak Ridge, Tennessee, USA. Tritium in soil was the principal source of HTO to the deciduous forest. Evaporation from the surface soil along with transpiration from tree leaves both contributed to HTO in the forest atmosphere. During the growing season, transpiration was the principal contributor of HTO to the forest atmosphere, while during the dormant season, the main source of atmospheric HTO was evaporation from the surface soil. Seasonal changes and the characteristics of vegetation will influence die relative importance of evaporation and transpiration as sources of atmospheric HTO near the ground in temperate deciduous forests.