Modelling of activation processes for GR-280 graphite at Ignalina NPP

Ignalina Nuclear Power Plant (INPP) operates two RBMK-1500 water-cooled graphite-moderated channel-type power reactors. The total mass of graphite in the cores of both units at INPP is about 3600 tons. Modelling of activation processes in the reactor's structural materials is necessary for decommissioning planning, because large amounts of activated structural materials (graphite, stainless steel, concrete, etc.) should be managed as radioactive waste. Knowledge of radiological characteristics and a radioactive inventory of irradiated materials are essential in planning of the decommissioning processes. The purpose of this work was to perform conservative neutron activation analysis for decommissioning purposes of INPP. ORIGEN computer code was used for the calculations. Activity levels were calculated for different nuclides present in the graphite and estimates were made how these activity levels depend on irradiation time, neutron flux value and other parameters. Obtained results were compared with the data available from other investigations for GR-280 graphite.     

Dynamic reliability and risk assessment of the accident localization system of the Ignalina NPP RBMK-1500 reactor

The paper presents reliability and risk analysis of the RBMK-1500 reactor accident localization system (ALS) (confinement), which prevents radioactive releases to the environment. Reliability of the system was estimated and compared by two methods: the conventional fault tree method and an innovative dynamic reliability model, based on stochastic differential equations. Frequency of radioactive release through ALS was also estimated. The results of the study indicate that conventional fault tree modeling techniques in this case apply high degree of conservatism in the system reliability estimates.One of the purposes of the ALS reliability study was to demonstrate advantages of the dynamic reliability analysis against the conventional fault/event tree methods. The Markovian framework to deal with dynamic aspects of system behavior is presented. Although not analyzed in detail, the framework is also capable of accounting for non-constant component failure rates. Computational methods are proposed to solve stochastic differential equations, including analytical solution, which is possible only for relatively small and simple systems. Other numerical methods, like Monte Carlo and numerical schemes of differential equations are analyzed and compared. The study is finalized with concluding remarks regarding both the studied system reliability and computational methods used.     

Generation of radioactive dust by lava-like fuel-containing materials at the Shelter Object of Chernobyl NPP

During 2011–2013, the α-activity of dust that was accumulated on the sample surface of lava-like fuel-containing materials in room 304/3 of the Shelter Object of Chernobyl NPP over a period of 1–284 days was measured. The α-activity of the dust collected during the 823 days was 495.5 Bq, or 2.15 kBq m^?2 per year, with the annual increment exceeding 3%. The maximal activity of the dust is in the period immediately after condensation moisture removal from the lava. The supposed source of the dust is fragmentary dispersion of lava areas with high fuel concentration. Disintegration of lava fragments continued after their detachment.     

Decontamination of radioactive waste solutions using pottery

The sorption of microamounts of Eu spiked with ^152,154Eu on the artificial stone, pottery, was studied at varoius conditions. Three kinds of pottery (red, black, and white), in addition to the raw material (potter’s clay) of the red kind, were tested. The pottery shows high sorption power with respect to the radiotracer depending on the kind of pottery. The uptake percentages gradually increase with the contact time, weight of pottery, or pH of the aqueous solution, attaining saturation at certain values. The amounts of Eu³⁺ required for the saturation are 7.38, 7.00, 5.93, and 1.64 (mmol Eu) (g pottery)⁻¹ for raw, red, black, and white samples, respectively. This sequence is parallel to that of the uptake percentage, which is related to the surface area of each material. The sorption presumably occurs via adsorption and ion exchange. The results were applied to decontamination of low-level liquid radioactive waste by filtration through a pot of red pottery; the effluent was free from the radiotracer. Published in Russian in Radiokhimiya, 2006, Vol. 48, No. 4, pp. 352–356. The text was submitted by the authors in English.     

Development and trials of a technology for reprocessing of NPP liquid radioactive wastes

Laboratory trials of a process for sorption decontamination of real NPP bottom residues from Cs radionuclides with Termoksid-35 ferrocyanide sorbent and rig and pilot trials of the technology for reprocessing of bottom residues from a number of Russian nuclear power plants were performed. The efficiency of the Cs sorption drastically decreases in the presence of organic complexing agents (EDTA, oxalate ions). Preliminary ozonation of the bottom residue allows the working life of Termoksid-35 sorbent in the decontamination process to be increased by a factor of several tens. Rig and pilot trials showed that ozonation of bottom residues, followed by microfiltration separation of the precipitate formed, ensures efficient decontamination of the solutions from Co, Mn, and Sr radionuclides and from α-emitters. A technology was suggested for decontamination of NPP bottom residues from radionuclides, involving ozonation, microfiltration, and selective sorption of Cs radionuclides on Termoksid-35 ferrocyanide sorbent. Process and technical solutions obtained in the course of trials were implemented in an industrial installation for reprocessing of bottom residues from the Kola NPP.     

Use of electric-arc plasma for radioactive waste immobilization

We analyze the basic trends in the use of electric-arc plasma for radioactive waste decontamination. We present a scheme and performance figures of a process for a shaft-type furnace with fuel-plasma heating. We present the results of numerical and experimental investigations for a 150-kW direct-flow plasma reactor.     

Neutron measurements around storage casks containing spent fuel and vitrified high-level radioactive waste at ZWILAG

Spectrometric and dosimetric measurements were made around a cask containing spent fuel and a cask containing high-level radioactive waste at the Swiss intermediate waste and spent fuel storage facility. A Bonner sphere spectrometer, an LB 6411 neutron monitor and an Automess Szintomat 6134A were used to characterise the n-gamma fields at several locations around the two casks. The results of these measurements show that the neutron fluence spectra around the cask containing radioactive waste are harder and higher in intensity than those measured in the vicinity of the spent fuel cask. The ambient dose equivalents measured with the LB 6411 neutron monitor are in good agreement with those obtained using the Bonner spheres, except for locations with soft neutron spectra where the monitor overestimates the neutron ambient dose equivalent by almost 50%.     

Processes for treatment of liquid radioactive waste containing seawater

The main sources of formation of liquid radioactive waste (LRW) containing seawater are determined, and the main problems arising in management of such waste are analyzed. Sorption methods for removing long-lived Cs and Sr radionuclides from highly mineralized (>1 g L^–1) LRW are determined. The main physicochemical and sorption characteristics, advantages, and drawbacks of candidate sorbents for removing Cs and Sr radionuclides are described. Examples of using SRM and VS-5 chemical reaction sorption materials developed for removing Sr from LRW with the mineralization of up to 60 g L^–1 are given. The results of studying composite materials based on BaSiO₃ and resorcinol–formaldehyde resins, intended for removing Cs and Sr radionuclides from seawater, are analyzed. Composite sorbents of such type efficiently remove Cs and Sr radionuclides from seawater. Processes developed by the authors and brought into practice at various plants of the Far East for treatment of multicomponent LRW formed in the course of operation, repair, and decommissioning of nuclear-powered surface ships and submarines are described.     

Nuclear-physical properties of borobasalt systems containing radioactive waste components

A significant nuclear-physical feature of boron-containing systems, distinguishing them from all other, except fluoride, systems, is considerable flux of fast neutrons generated by the (α,n) reaction on boron nuclei. The neutron flux generated on boron nuclei is higher by approximately an order of magnitude than that excited on nuclei of other components of the borobasalt matrix. The calculated and measured neutron flux values are well consistent. The neutron generation is mainly determined by the reaction of α-particles with O, Si, and Al nuclei and is thus characteristic of any aluminosilicate system.     

Reduction of radioactive waste volume using selective crystallization processes

Satisfactory combination of small volume of compositions incorporating ¹³⁷Cs, ⁹⁰Sr, and ²⁴⁴Cm with the admissible heat release rate can be attained by crystallization of definite compounds from high-level solutions. The concentrate of cesium isotopes is obtained by their precipitation in the form of phosphoromolybdate and, after additional storage, in the form of CsMgPO₄·6H₂O; the concentrate of Am, Cm, Sr, Ba, and Ln can be obtained using the known but somewhat modified (increased pH of solution) OXAL process. It is appropriate to remove Am and long-lived Cm isotopes from this concentrate also after storage ensuring the decay of ⁹⁰Sr and ²⁴⁴Cm. The remaining rare-earth elements with traces of Am and Cm and stable isotopes of Sr and Ba can be disposed of, e.g., in the form of a mineral-like phosphate.     

Microbiological treatment of oil-containing radioactive waste prior to cementation

Microbiological oxidation of liquid organic radioactive waste (ORW), spent vacuum and transformer oils, is described. The physicochemical properties of oils and their structural-group composition before and after using in the process cycle were studied. Changes in the structural-group composition and physicochemical parameters of oils upon microbiological treatment were determined. The distribution of radionuclides between the organic and aqueous phases upon microbiological treatment was studied by the example of model ORW containing ¹³⁷Cs, ⁹⁰Sr, ²³⁸Pu, and ²⁴¹Am. The compatibility of oils subjected to microbiological treatment with the cement compound intended for ORW disposal was evaluated. The biological step of the radioactive oil processing leads to a decrease in the weight and volume of the organic radioactive waste and increases its amount that can be incorporated into the cement compound (to 30 vol %) without deterioration of the strength characteristics of the cement.     

Characterisation of radioactive waste products associated with plant decommissioning

The inventory of radioactivity that must be considered in the decommissioning of a typical 1000 MWe Spanish pressurised water reactor (PWR) was investigated as part of a generic plant decommissioning study. Analyses based on DORT models (in both R-Z and R-theta geometries) were used with representative plant operating history and core power distribution data in defining the expected neutron environment in regions near the reactor core. The activation analyses were performed by multiplying the DORT scalar fluxes by energy-dependent reaction cross sections (based on ENDF/B-VI data) to generate reaction rates on a per atom basis. The results from the ORIGEN2 computer code were also used for determining the activities associated with certain nuclides where multi-group cross section data were not available. In addition to the bulk material activation of equipment and structures near the reactor, the activated corrosion-product (or 'crud') deposits on system and equipment surfaces were considered. The projected activities associated with these sources were primarily based on plant data and experience from operating PWR plants.     

Development of geopolymer composites for EMI shielding from steel industry waste

Journal of Materials Science: Materials in Electronics - In this study waste from steel industries, namely, mill scale, red dust, and iron ore fines have been used as additives in geopolymer matrix...     

Geochemical aspects of environmentally safe conservation of liquid radioactive waste

Physicochemical features of the sorption of Sr, Cs, and U radionuclides on natural mineral sorbents (montmorillonites of Na and Ca type, kaolinites, illites) were studied. The main processes responsible for binding and retention of radionuclides are ion exchange and formation of complexes on the mineral surface. The influence of pH, salt composition of the solution, specific surface area of the sorbent, and its pore size on the radionuclide immobilization efficiency was examined.     

Application of generic risk assessment software to radioactive waste disposal

Monte Carlo methods are used in a variety of applications such as risk assessment, probabilistic safety assessment and reliability analysis. While Monte Carlo methods are simple to use, their application can be laborious. A new microcomputer software package has been developed that substantially reduces the effort required to conduct Monte Carlo analyses. The Sensitivity and Uncertainty Analysis Shell (SUNS) is a software shell in the sense that a wide variety of application models can be incorporated into it. SUNS offers several useful features including a menu-driven environment, a flexible input editor, both Monte Carlo and Latin Hypercube sampling, the ability to perform both repeated trials and parametric studies in a single run, and both statistical and graphical output. SUNS also performs all required file management functions.     

卫生填埋场垃圾渗滤液的处理技术

卫生填埋是国内外广泛采用的城市生活垃圾处置方法 ,而渗滤液的处理则是其最大难点。本文总结了当前各种渗滤液处理技术的使用条件及其优缺点 ,并提出了渗滤液处理的改进措施及建议     

Pharmaceutical compound content of municipal solid waste

The occurrence and fate of pharmaceuticals in landfills has been largely neglected. Once discarded in municipal solid waste (MSW), pharmaceuticals within a landfill may undergo degradation, adsorption, or enter the leachate and eventually exit the landfill. The active pharmaceutical ingredient (API) concentration of MSW was predicted using available statistics on medication usage and directly measured by a MSW composition study. Estimation calculations resulted in a potential concentration of APIs from 7.4 to 45 mg/kg of MSW, varying with the percentage of dispensed medications assumed to become unused. Direct measurement resulted in the collection of 22 APIs comprising a total of 22,910 mg. This resulted in a final concentration of 8.1 mg/kg within MSW. Additionally, 45 empty medication containers were collected which potentially contained 33 differing APIs upon disposal.     

Modelling and analysis of a symbiotic waste management system

A municipal solid waste management system is symbiotic when there exists physical exchange of material or by-products between different treatment units. We propose a mathematical model for studying the interactive behaviour of different waste treatment operators in a symbiotic environment. Each operator is a self-interested entity, who sets his gate fee charge to maximise his own payoff. We study the properties and gate fee strategies of the operators, and also perform sensitivity analysis on various model parameters to discuss the local operator behaviour and the effects of various intervention strategies. We also propose a numerical algorithm to solve the model, yielding the optimal equilibrium gate fee charges, payoff and market share levels of different operators. Finally, computational studies based on a two-unit scenario in a case study of organic waste recycling is performed to demonstrate the interactive and dynamic behaviours of different operators. Our results strongly suggest that, to improve new treatment technology utilisation, subsidising the operating cost of the new treatment unit is more effective in the long-run than exerting control on the gate fee upper bounds of the operators by the system regulator. Furthermore, providing residual post-treatment discounts for treatment units can benefit the service users, rather than the waste treatment operators.     

A survey of monitoring technology for subseabed disposal of radioactive waste

The subseabed is currently being considered as a disposal site for nuclear waste, and if it does become an option, monitoring to detect escape of the disposed material will be essential. In this paper, we define types of nuclear waste and present the dimensions of the monitoring problems that would be encountered in ocean disposal. We then summarize the characteristics of a number of physical, chemical, biological, and ecological monitoring methods. We also describe the advances and developments that will be necessary before the monitoring functions and support systems can be employed.