Low-level Radioactive Solid Waste Research Articles

プラズマ加熱による雑固体廃棄物溶融処理時のセシウム蒸発挙動

プラズマ加熱による雑固体廃棄物溶融処理時のセシウム蒸発挙動

DRINK: a biogeochemical source term model for low level radioactive waste disposal sites

Interactions between element chemistry and the ambient geochemistry play a significant role in the control of radionuclide migration in the geosphere. These same interactions influence radionuclide release from near surface, low level radioactive waste, disposal sites once physical containment has degraded. In situations where LLW contains significant amounts of metal and organic materials such as cellulose, microbial degradation in conjunction with corrosion can significantly perturb the ambient geochemistry. These processes typically produce a transition from oxidising to reducing conditions and can influence radionuclide migration through changes in both the dominant radionuclide species and mineral phases. The DRINK (DRIgg Near field Kinetic) code is a biogeochemical transport code designed to simulate the long term evolution of the UK low level radioactive waste disposal site at Drigg. Drigg is the UK's principal solid low level radioactive waste disposal site and has been receiving waste since 1959. The interaction between microbial activity, the ambient geochemistry and radionuclide chemistry is central to the DRINK approach with the development of the ambient pH, redox potential and bulk geochemistry being directly influenced by microbial activity. This paper describes the microbial aspects of the code, site data underpinning the microbial model, the microbiology/chemistry interface and provides an example of the code in action.

DRINK: a biogeochemical source term model for low level radioactive waste disposal sites.

Interactions between element chemistry and the ambient geochemistry play a significant role in the control of radionuclide migration in the geosphere. These same interactions influence radionuclide release from near surface, low level radioactive waste, disposal sites once physical containment has degraded. In situations where LLW contains significant amounts of metal and organic materials such as cellulose, microbial degradation in conjunction with corrosion can significantly perturb the ambient geochemistry. These processes typically produce a transition from oxidising to reducing conditions and can influence radionuclide migration through changes in both the dominant radionuclide species and mineral phases. The DRINK (DRIgg Near field Kinetic) code is a biogeochemical transport code designed to simulate the long term evolution of the UK low level radioactive waste disposal site at Drigg. Drigg is the UK's principal solid low level radioactive waste disposal site and has been receiving waste since 1959. The interaction between microbial activity, the ambient geochemistry and radionuclide chemistry is central to the DRINK approach with the development of the ambient pH, redox potential and bulk geochemistry being directly influenced by microbial activity. This paper describes the microbial aspects of the code, site data underpinning the microbial model, the microbiology/chemistry interface and provides an example of the code in action.

Radiological Impact of Low Level Solid Radioactive Waste Disposed of with Ordinary Hospital Refuse

A method for the measurement of radioactivity contained in cardboard boxes used to store hospital refuse was developed, testing its reliability with sources of known activity and geometry. The method was applied to a random sample of about 2000 boxes taken from those which are not considered to contain radioactive material and are disposed of without checks, in order to evaluate the amount of activity which is released into the environment. It was found that it is about 0.06% of the total activity administered to patients. Radiation protection quantities were calculated on this basis, showing that the radiological effect is small, not requiring routine analysis of all waste boxes produced in the hospital, but suggesting that measurements on a random sample are advisable to monitor the process.

The Design, Manufacture and Testing of a New Generation of ISO Freight Container for Certification as an IP-2 Package in Compliance with the IAEA Regulations for the Safe Transport of Radioactive Material, 1985 Edition (As Amended 1990)

Solid low level radioactive waste (LLW) which arises at nuclear power stations and other nuclear facilities in the UK, is routinely transported to British Nuclear Fuels' site at Drigg in Cumbria for disposal. A requirement was identified for the use of a refurbished ISO freight container of the full-height design, to transport drummed LLW to the site of a supercompaction facility prior to disposal at Drigg. This paper describes the reasoned technical justification employed for certifying the refurbished ISO freight container, Design No. 2912B, as an IP-2 package under Paragraph 523 of the IAEA Transport Regulations and the development of a new generation of ISO freight container, Design No. 2044. It was recognised that the use of a refurbished container was only an interim measure and because of significant changes in the acceptance criteria for disposal, the increased use of high force compaction techniques and the proposed amendments to the IAEA Transport Regulations, Nuclear Electric embarked upon the development of a new generation of ISO freight containers. The new container design (Design No. 2044) incorporates a readily decontaminable stainless steel interior, a comprehensive load restraint system designed for the transport of single and multiple packages, and is lined with a polyurethane foam between the inner and outer skins. It is designed to transport 70 off, 200 litre drums of LLW (stacked in two layers) and other payloads of size not greater than 4 m long × 2 m wide and 20 tonnes in weight. The container was subjected to a range of tests to prove compliance with the ISO standard and the IAEA Transport Regulations. Following the preparation of the required documentation, in particular a Safety Case and comprehensive Operating and Maintenance Instructions, a Certificate of Regulatory Compliance was issued by the appropriate authority certifying the container as an Industrial Package Type 2 (IP-2) suitable for the transport of drummed LLW and other materials within LSA-II/SCO-II limits.

Predicting the Performance of a Site Closure System Through Engineering Risk Assessment

ABSTRACTSince 1959 British Nuclear Fuels pie (BNFL) have operated a disposal site for solid low level radioactive wastes (LLW) at Drigg, approximately 6 kilometres south of Sellafield in West Cumbria. Prior to 1988 the disposal method involved the excavation of a series of parallel trenches across the site which were back filled with LLW and covered with an interim, water resistant cap. Since 1988 the disposal method has changed and waste is now compacted and placed into steel isofreight containers into which a highly fluid cement based grout is added prior to the containers being disposed of in a series of open concrete lined vaults. It is proposed that, when full, each vault will also be capped. The change in disposal method has extended the life of the site and final closure is therefore not anticipated until about the middle of the next century.

The Design, Manufacture and Testing of a New Generation of ISO Freight Container for Certification as an IP-2 Package in Compliance with the IAEA Regulations for the Safe Transport of Radioactive Material – 1985 Edition (as Amended 1990)

Solid low level radioactive waste (LLW) which arises at nuclear power stations and other nuclear facilities in the UK, is routinely transported to British Nuclear Fuels site at Drigg in Cumbria for disposal. A requirement was identified for the use of an ISO freight container of the full-height design, to transport drummed LLW to the site of a supercompaction facility prior to disposal at Drigg. This was initially accomplished using refurbished containers incorporating a number of enhanced features. It was recognised that the use of a refurbished container was only an interim measure and as a result of significant changes in the acceptance criteria for disposal, the increased use of high force compaction techniques and the proposed amendments to the IAEA Transport Regulations, Nuclear Electric embarked upon the development of a new generation of ISO freight container. The new design of container, Design No. 2044, incorporates a readily decontaminable stainless steel interior, a comprehensive load restraint system designed for the transport of single and multiple packages, and is lined with a polyurethane foam between the inner and outer skins. It is designed to transport 70 off, 200 litre drums of LLW (stacked in two layers) and other payloads of size not greater than 4 m long × 2 m wide and 20 tonnes in weight. The container was subjected to a range of tests to prove compliance with the ISO standard and the IAEA Transport Regulations. Following the preparation of the required documentation, in particular a Safety Case and comprehensive Operating and Maintenance Instructions, a Certificate of Regulatory Compliance was issued by the appropriate authority certifying the container as an Industrial Package Type 2 (IP-2) suitable for the transport of drununed LLW and other materials within LSA-II/SCO-II limits.

Independent Monitoring of Solid Low Level Radioactive Waste Disposals in The UK

AbstractThe independent monitoring of solid low level radioactive waste (LLW) disposals in England and Wales is undertaken by Taywood Environmental Consultancy (TEC) on behalf of Her Majesty's Inspectorate of Pollution (HMIP). To ensure that LLW disposals are within authorised limits, as defined in the Radioactive Substances Act 1993, consignments of waste are seized by HMIP before disposal and the contents are assessed by TEC. Waste consignments are transported to the Waste Quality Checking Laboratory (WQCL) operated by TEC at Winfrith in Dorset where they are analysed by both destructive and nondestructive testing. The testing performed at the laboratory is encompassed by a NAMAS accredited quality system and all test results are reported to HMIP. This paper outlines the work of the laboratory and describes some of the techniques used for radioactive waste assessment.

Fundamental research on thermal plasma technology for treatment of low‐level radioactive solid waste

The technology for treatment of low-level radioactive solid waste generated in nuclear power plants is expected to be established. The main problems are volume reduction and stabilization of radionuclides acceptable for final disposal. Thermal plasma technology offers advantages for such waste treatment because of the easy supply of heat at high temperature independent of chemical and physical properties of the waste. New, noncontaminated waste, such as metallic, inorganic and combustible materials, have been melted in a crucible furnace. A transferred-type of a dc plasma torch with a solid electrode was used as heat source and rated up to 50 kW. The main results obtained are as follows: 1 (1) Metallic and inorganic materials can be melted and vitrified. Combustible materials can be pyrolyzed. Consequently, high-volume reduction rates can be attained. 2 (2) Compressive strength of solidified products is more than twice as great as that of cement composites used for solidification of the liquid waste. Leaching rate of main components of the slag layer is in the same order of that of the high-level radioactive waste glass. 3 (3) To obtain a guiding principle for design of an off-gas treating system, compositions of the off-gas and properties of the dust entrained in the off-gas are clarified. From these results, technical prospects so that plasma heating technology can be applied for treatment of low-level radioactive solid waste have been obtained.

Low-Impact Sampling Under an Active Solid Low-Level Radioactive Waste Disposal Unit Using Horizontal Drilling Technology

AbstractThe purpose of this project was to determine the performance of a 5.5 year old active solid low-level radioactive waste disposal unit (Pit 37) located on a mesa top at Los Alamos National Laboratory (LANL), Los Alamos, NM, and to provide in-situ (vadose zone) site characterization information to Technical Area 54, Material Disposal Area (MDA) G's Performance Assessment. The vadose zone beneath Pit 37 was accessed by utilizing low-impact, air-rotary horizontal drilling technology. Core was sampled at approximately 5-foot intervals via wire-line core method in 3 horizontal holes fanning out below Pit 37. Samples were screened and prepared in-field following LANL Environmental Restoration Project guidelines. Samples were transferred from the field to the Mobile Radiation Analysis Laboratory for initial radiological screening. Following screening, samples were delivered to an analytical lab for analyses including moisture content, 23 inorganic compounds, 60 volatile organic compounds, 68 semivolatile organic compounds, tritium, lead 210, radium 226 's Pit 37 is performing well and no significant liquid phase migration of contaminants has occurred.

The Identification and Degradation of Isosaccharinic Acid, a Cellulose Degradation Product

AbstractNirex is seeking to develop a deep underground repository for the disposal of solid intermediate-level and low-level radioactive wastes (ILW and LLW) in the UK. One possible influence on the behaviour of radionuclides is the formation of water-soluble complexants by the degradation of the solid organic polymers that will be present in the wastes. The degradation products of cellulose have been shown to increase the solubility of plutonium and other radionuclides and to reduce sorption onto near-field and far-field materials. Degradation of cellulose under anaerobic alkaline conditions produces a range of organic acids. In this paper 2-C-(hydroxymethyl)-3-deoxy-D-pentonic acid (isosaccharinic acid, ISA) is identified by High Performance Liquid Chromatography as a significant component of cellulose leachates. A combination of fractionation of cellulose leachates and plutonium solubility determinations shows that ISA is responsible for the majority of the enhancement of plutonium solubility observed in such leachates. Further degradation of ISA by chemical or microbial action may lessen the effect of degraded cellulose leachates. Experimental studies on the chemical degradation of this compound under alkaline conditions suggest that the presence of oxygen is required. Microbial degradation studies show that the plutonium solubility in solutions of ISA is reduced by their exposure to microbial action.

低レベル放射性雑固体廃棄物のプラズマ溶融処理技術の基礎検討

The technology for treatment of low-level radioactive solid waste generated in nuclear power plants is expected to be established. The main problems are volume reduction and stabilization of radionuclides acceptable for final disposal. Thermal plasma technology offers advantages for such waste treatment because of the easy supply of heat at high temperature independent of chemical and physical properties of the waste. New, noncontaminated waste, such as metallic, inorganic and combustible materials, have been melted in a crucible furnace. A transferred-type of a dc plasma torch with a solid electrode was used as heat source and rated up to 50 kW. The main results obtained are as follows: 1 (1) Metallic and inorganic materials can be melted and vitrified. Combustible materials can be pyrolyzed. Consequently, high-volume reduction rates can be attained. 2 (2) Compressive strength of solidified products is more than twice as great as that of cement composites used for solidification of the liquid waste. Leaching rate of main components of the slag layer is in the same order of that of the high-level radioactive waste glass. 3 (3) To obtain a guiding principle for design of an off-gas treating system, compositions of the off-gas and properties of the dust entrained in the off-gas are clarified. From these results, technical prospects so that plasma heating technology can be applied for treatment of low-level radioactive solid waste have been obtained.

Containers for Packaging of Solid Low and Intermediate Level Radioactive Wastes — IAEA Technical Reports Series NO. 355.

Containers for Packaging of Solid Low and Intermediate Level Radioactive Wastes — IAEA Technical Reports Series NO. 355.

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.

A system optimization model for low-level nuclear waste disposal

The development of waste management systems for the disposal of low-level radioactive waste (LLW) is becoming an increasingly complex problem in decision-making. The complexity is the result of increasing considerations for the protection of water quality and remedial actions for system failures. The process becomes more complex as the points of regulatory compliance are moving closer to the disposal unit instead of the boundary of disposal site. This trend would result in every disposal unit being regulated as a discharge point, similar to the National Pollutant Discharge Elimination System (NPDES). The Oak Ridge Reservation (ORR) is in the process of developing a disposal complex for solid LLW. The complex will be a combination of disposal sites, disposal units, and disposal unit technology. Disposal unit technology includes the waste package (waste form and disposal container) and other engineered barriers added to the trench to prevent or control the transfer of radionuclides from the disposal unit into the environment. The combination of waste inventory and engineered barriers is called a waste facility. The waste facility is viewed as confinement systems and is the focal point in waste confinement studies. A disposal strategy has been developed as a framework for segregation of solid LLW according to the isotope and level of contamination in the waste. The objective of this framework is that different waste can be disposed of differently, according to the performance of the disposal site and disposal technology. A system optimization model has been developed as a portfolio of objective functions to provide insights into the implementation of the waste disposal strategy for the ORR complex. The model is aimed at making best use of the developable disposal capacities while providing for regulatory compliance, support operational continuity of the waste generators, and cost-effectiveness. This model is being designed to function as a strategic planning framework for the development of the specialized model system needed to provide the necessary data for decision making. This optimization model can be extended to the management of chemically hazardous and mixed (radioactive and chemically hazardous) waste.

Medical waste: socioeconomic impact.

The proper disposal and management of medical waste is a never-ending problem and one which is of grave concern to the general public. The amounts that are produced each day by hospitals and other small-generators are staggering, e.g., in the U.S. ca. 6000 tons per day. Approximately fifteen (15%) percent of this waste is considered infectious. This latter type of waste is usually incinerated or autoclaved (steam sterilization). In addition to the daily accumulation of solid waste, chemical wastes (liquids) and low-level radioactive wastes are generated. The proper disposal of all types of wastes is discussed as well as the overall cost and its impact on society.

Experience with radioactive waste incineration at chalk river nuclear laboratories

Chalk River Nuclear Laboratories is a nuclear research centre operated by Atomic Energy of Canada Limited. A full-scale waste treatment centre has been constructed to process low- and intermediate-level radioactive wastes generated on-site. A batch-loaded, two-stage, starved-air incinerator for solid combustible waste is one of the processes installed in this facility. The incinerator has been operating since 1982. It has consistently reduced combustible wastes to an inert ash product, with an average volume reduction factor of about 150:1. The incinerator ash is stored in 200 L drums awaiting solidification in bitumen. The incinerator and a 50-ton hydraulic baler have provided treatment for a combined volume of about 1300 m 3/a of solid low-level radioactive waste. This article presents a review of the performance of the incinerator during its six years of operation. In addition to presenting operational experience, an assessment of the starved-air incineration technique will also be discussed.

Radiation Dose to Small Mammals Inhabiting a Solid Radioactive Waste Disposal Area

(1) Radiation dose rates received by deer mice (Peromyscus maniculatus (Wagner)) and Ord's kangaroo rats (Dipodomys ordii (Woodhouse) inhabiting a solid radioactive waste disposal area and a control area in south-eastern Idaho were determined by surgically implanting lithium-floride thermoluminescent dosimeter (TLD) packets. Fifty-three percent of the 542 and 135 TLD packets implanted in deer mice and kangaroo rats, respectively, were recovered. (2) The radiation dose rates received by animals from the radioactive waste disposal area varied from 4 to 418 000 gGy day-' (0-4-42 000 mrad day-') and were significantly (P < 0.01) higher than the dose rate of 4 gGy day-' (0-4 mrad day-') received by control animals. Doses resulted primarily from radiation from buried activation and fission products and not from radionuclides in/on tissues. (3) Ninety-six percent of the waste disposal area deer mice in the autumn-winter had radiation dose rates higher than the rates of the control animals, whereas in the spring-summer 73% of the deer mice received dose rates greater than the rates of control animals. Differences in seasonal data were probably related to increased subsurface time in autumn-winter. (4) Autumn-winter dose rates received by kangaroo rats were significantly (P < 0.05) higher than spring-summer rates and were attributed to the species entering torpor beneath the soil surface during winter. (5) Conservative comparisons between the radiation dose rates received by implanted TLD packets in individual small mammals and the potential dose rates received by individual animals on the surface of the area indicated a minimum of 49 and 20% of the deer mice and kangaroo rat populations, respectively, encountered areas of buried activation and fission waste and/or contaminated soil. (6) Data obtained provided an indirect method of measuring biological intrusion into soil covers over solid low-level radioactive waste disposal areas.

Radiological safety assessment for a low-level radioactive solid waste storage facility: preliminary risk evaluation by reliability techniques.

Radiological safety assessment for a low-level radioactive solid waste storage facility: preliminary risk evaluation by reliability techniques.

On radioactive waste management: Model analysis of a proposed site

The proposed waste-management site at the Defence Research Establishment Suffield appears suitable for storing solid low-level radioactive wastes with a half-life for radioactive decay less than 3,000 years. This conclusion is based on model trials which generally indicate that the subsurface environment will be effective in limiting the dispersal of radioactive contaminants in the groundwater system. Contaminant attenuation is produced by the physical process of dispersion, the chemical process of cation exchange and the nuclear process of radioactive decay. A strong measure of contaminant confinement is provided by the relatively low seepage velocity within the porous medium. However, because of the uncertainties inherent in the definition of model parameters, and because there is no historical record with which to calibrate the model, the results of the simulations must be treated in a very general way. Parameters in the model are derived from empirical relationships and a variety of field and laboratory studies conducted over the past two years. Piezometric data indicate that the site is predominantly a recharge area with the permeability of geologic units ranging from 1·10 −5 to 2·10 −8 cm s −1. Measured values of cation-exchange capacity for drift and bedrock units range from 25 to 105 mequiv./100 g. An unsaturated zone up to 36 m thick, a lack of water-level fluctuations, and a semi-arid climate are evidence of the limited quantities of natural recharge to the groundwater system. Soil-moisture data demonstrate the most favourable sites for recharge are depressions within the area.