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At least 397 records · Page 22Linked to original sources
PubMed1993

Determination of regional myocardial blood flow using fluorescent microspheres.

Determination of blood flow in tissues at risk for infarction is necessary for in vivo studies of the pathologic effects of vascular occlusion. Such blood flow measurements are traditionally carried out using radioactive microspheres. These are expensive and may pose a significant hazard to laboratory personnel. In addition, disposal of radioactive wastes, especially radioactive carcasses, is an increasingly expensive and inconvenient process. To avoid these problems, we have developed a modified procedure using fluorescent microspheres. To measure blood flow, spheres are injected intravenously and a blood sample is taken. Following cardiectomy, appropriate segments of left ventricular myocardium are digested with proteases to release the spheres, which are then purified through sucrose gradients. The spheres may be counted manually using an epifluorescence microscope, or by flow cytometry. Comparison of this method with the traditional radioactive microsphere procedure reveals similar results for the two methods. Fluorescent microspheres should provide a useful and accurate alternative method for measuring blood flow in studies of vascular disease.

Animals↗
PubMed2005

An additional performance of HTRS: the waste radiotoxicity minimisation.

The management of radioactive waste is a key issue for the present and future use of nuclear energy. In this frame, high temperature reactors (HTRs) have, among others, the capability to burn actinides. After a short introduction on HTRs, the performances of two MC-based burnup codes (Monte Carlo continuous energy burnup and MONTEBURNS) in assessing the ability of these reactors to burn actinides are compared. These codes are necessary for performing ultra-high burnup calculations on HTRs. The best one, in this specific case, results to be MONTEBURNS. It was analysed using HTRs loaded with the following: (1) 1st generation Pu, 600 equivalent full power days; (2) 2nd generation Pu, 645 equivalent full power days; and (iii) 33% 1st generation Pu and 67% Th, 705 equivalent full power days. Finally, it is possible to conclude that HTRs can reduce time when the waste is considered dangerous. Even if the amount of reduction does not solve the whole problem, it represents an important step in the management of radioactive waste.

Computer Simulation↗
PubMed2001

Non-combustible waste vitrification with plasma torch melter.

Non-combustible radioactive wastes generated from Nuclear Power Plants (NPPs) are composed of concrete, glass, asbestos, metal, sand, soil, spent filters, etc. The melting tests for concrete, glass, sand, and spent filters were carried out using a 60 kW plasma torch system. The surrogate wastes were prepared for the tests. Non-radioactive Co and Cs were added to the surrogates in order to simulate the radioactive waste. Several kinds of surrogate prepared by their own mixture or by single waste were melted with the plasma torch system to produce glassy waste forms. The characteristics of glassy waste forms were examined for the volume reduction factor (VRF) and the leach rate. The VRFs were estimated through the density measurement of the surrogates and the glassy waste forms, and were turned out to be 1.2-2.4. The EPA (Environmental Protection Agency) Toxicity Characteristic Leaching Procedure (TCLP) was used to determine the leach resistance for As, Ba, Hg, Pb, Cd, Cr, Se, Co, and Cs. The leaching index was calculated using the total content of each element in both the waste forms and the leachant. The TCLP tests resulted in that the leach rates for all elements except Co and Cs were lower than those of the Universal Treatment Standard (UTS) limits. There were no UTS limits for Co and Cs, and their leach rate & index from the experiments were resulted in around 10 times higher than those of other elements.

Chemical Phenomena↗
PubMed2002

Efficiency of a blast furnace slag cement for immobilizing simulated borate radioactive liquid waste.

The efficiency of a blast furnace slag cement (Spanish CEM III/B) for immobilizing simulated radioactive borate liquid waste [containing H3BO3, NaCl, Na2SO4 and Na(OH)] has been evaluated by means of a leaching attack in de-mineralized water at the temperature of 40 degrees C over 180 days. The leaching was carried out according to the ANSI/ANS-16.1-1986 test. Moreover, changes of the matrix microstructure were characterized through porosity and pore-size distribution analysis carried out by mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) and thermal analysis (TG). The results were compared with those obtained from a calcium aluminate cement matrix, previously published.

Borates↗
PubMed1996

Complete decay of radionuclides: implications for low-level waste disposal in municipal landfills.

The time required for the complete decay of a radioactive source can be quantified by specifying an acceptable probability and using an original derivation. The physical phenomenon of complete decay may be used as the technical basis to change regulations and permit, with public acceptance, the inexpensive disposal of short half-lived radioactive waste into municipal landfills. Current regulations require isolation of trash from the biosphere for 30 years during the post-closure control period for municipal landfills. Thirty years is sufficient time for complete decay of significant quantities of short-lived radionuclides, and there is a large decay capacity in the nation's landfills. As the major generators of low-level radioactive waste with relatively short half-lives, the academic, medical, and research communities likely would benefit most from such regulatory relief. Disposal of such waste is prohibited or costly. The waste must be specially packaged, stored, transported, and disposed in designated repositories. Regulatory relief can be initiated by citizens since the Administrative Procedures Act gives citizens the right to petition for regulatory change.

Radioactive Waste↗
PubMed2002

Volume and activity of buried transuranic-contaminated wastes at U.S. Department of Energy facilities.

From the 1940's through the 1970's, radioactive wastes meeting the current definition of transuranic wastes were disposed of by shallow land burial and other techniques at a number of sites owned and operated by the federal government in support of the nuclear weapons program. After transuranic wastes were identified as a separate category of radioactive wastes (distinct from low-level wastes) in 1970 by the U.S. Atomic Energy Commission, they were generally segregated and placed in retrievable storage pending the availability of a geologic repository. Updated information on buried transuranic wastes was recently developed to support future decisions on how to manage these materials. This paper summarizes the approach used to develop this information for U.S. Department of Energy facilities and presents the volumes and transuranic activities of these wastes. The total volume of buried transuranic wastes at DOE sites is approximately 126,000 m3 with a much smaller volume (about 11,000 m3) disposed of at intermediate depths. The reported transuranic activity in these previously disposed of wastes is about 28,000 TBq.

Radioactive Waste↗
PubMed2003

Radioactive contamination of bottom sediments in the upper reaches of the Techa river: analysis of the data obtained in 1950 and 1951.

A stationary sorption model has been developed for re-evaluating and analysing archive data from 1950-1951 on the radioactive contamination of Techa river bottom sediments close to the site of liquid radioactive waste discharge. In general, good agreement was obtained between calculations and measurements, which substantiates further the assumptions and conclusions in two preceding articles, on the radionuclide composition of discharged liquid radioactive waste. Estimates on the effective liquid radioactive waste discharges given here are significantly different from those deduced in the 1950s, i.e. in summer 1950 and October 1951. The results are discussed in relation to the Techa River Dosimetry System 2000 (TRDS-2000) that has recently been presented to serve as a means for estimating doses to the Techa river residents. Parameter values describing the exponential decrease of bottom sediment contamination along the river due to short-lived radionuclides, such as (106)Ru, and (144)Ce, agree reasonably with those used in TRDS-2000. However, for other radionuclides, such as (95)Zr, (95)Nb, (91)Y, (90)Sr and (137)Cs, substantial differences are found. It is demonstrated that water flow rate, width of the river, and surface area of bottom sediments are important parameters which were not adequately taken into account in TRDS-2000. Also, the stirring-up of contaminated bottom sediments and their subsequent transport by the water flow are seen to be an important mechanism that governs the radionuclide transport downstream. This mechanism was not included in the TRDS-2000 model. It is concluded that the sorption model used in TRDS-2000 for the reconstruction of radioactive contamination of water and bottom sediments of the Techa river in 1949-1951, is subject to considerable errors. While the present paper is focussed on details of the dosimetric modelling, the implications for the Techa river dosimetry are major. They will be further elucidated in a forthcoming paper.

Adsorption↗
PubMed2004

Dose assessment for the Metlino and Muslyumovo populations who lived along the Techa river from 1949 to 1954.

In the period from 1949 to 1956, liquid radioactive waste was routinely and accidentally discharged by the Mayak Production Association, Southern Urals, Russia, into the Techa river. Based on a novel approach, the contamination of the Techa river water, the bottom sediments and the adjacent flood plains was modelled, and internal and external doses were estimated for two villages located downstream of the site of liquid radioactive waste release. Altogether, 11 radionuclides that occurred in the liquid radioactive waste were included in the calculations. The results suggest significantly higher doses than previously assumed, with the major contribution in the year 1951. Radionuclides with half-lives of less than 1 year, such as 89Sr, 131I, 95Zr+95Nb, 103Ru+103mRh, 140Ba+140La, and 144Ce+144Pr, represent the major sources and, in contrast, long-lived radionuclides, such as 90Sr and 137Cs that have so far been assumed to be most important, did not dominate the doses. For adults from the village Metlino, located 7 km downstream of the site of liquid radioactive waste discharge, the committed effective doses due to intake of radionuclides were calculated to be about 2.3 Sv, while the external doses were between about 1.2 Sv and 6.9 Sv. On the other hand, for adults from Muslyumovo, located 75 km downstream, the committed effective doses due to intake of radionuclides were calculated to be about 0.5 Sv, while the external doses were between 0.5 Sv and 2.0 Sv. The values for the skin doses to the Metlino and Muslyumovo populations were about 7.1 Sv and 1.3 Sv, respectively. It is concluded that the current dose estimates for the residents of the Techa river need, therefore, reevaluation.

Algorithms↗
PubMed2001

Spanish LLW and MLW disposal: durability of cemented materials in (Na, K)Cl simulated radioactive liquid waste.

The microstructural stability or durability of a specific backfilling pozzolanic-cement mortar, which is employed in Spain, in concrete containers for the storage of low level liquid wastes (LLW) and medium level liquid wastes (MLW), has been studied by means of the Koch-Steinegger test at the temperatures of 20 and 40 degrees C during a period of 365 days. Mortar samples were immersed in salt solutions of 3.46 M NaCl and 3.46 M KCl to simulate the salinity of some radioactive liquid waste matrices. The resistance of the mortar to the saline solution attack is evaluated by the development of the relative flexural strength. The changes of the microstructure were followed by mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Pore solution was extracted and analyzed at different periods of time to know the possible diffusion of sodium, chloride and potassium inside the microstructure.

Potassium↗