System performance assessment of final repository for radioactive wastes using first-order reliability method

When a final option for radioactive waste is determined, it is necessary to demonstrate compliance of disposal system chosen with relevant regulations. Considering the large number of physical and chemical factors involved, the complexity of their interrelationships, and long time periods, a system approach is required. A stochastic analysis is also needed to ensure that these regulatory criteria can be met with confidence. Among a variety of models developed to treat the effect of uncertainty on system performance, the first-order reliability method is suggested as an attractive tool to stochastic problems incorporating any amount of probabilistic information. Based on the first-order approximation, the method can give a probability of failure against a preselected target value, and information concerning the sensitivity of the outcome to variations in the input random variables and their statistical moments. In this paper, for reliable prediction of the performance of repository for radioactive wastes, first-order reliability method is applied in treating the parameter uncertainties of predictive models. First, a thickness of canister corrosion and breach time of canister is calculated using a uniform corrosion model, combined with the diffusional transport modeling of radionuclides in the backfill material. Second, a fractional release rate for each radionuclide is derived from the evaluation of the performance of a waste package which consists of canister and backfill material. Third, a cumulative release rate at the accessible environment is obtained by geosphere transport modeling with the source term given as a fractional release rate. The proposed first-order reliability method can be applicable to a full range of problems occurring in radioactive waste management and beyond.     

Stochastic Modeling Concepts in Groundwater and Risk Assessment: Potential Application to Marine Problems

Parameter uncertainty is ubiquitous in marine environmental processes. Failure to account for this uncertainty may lead to erroneous results, and may have significant environmental and economic ramifications. Stochastic modeling of oil spill transport and fate is, therefore, central in the development of an oil spill contingency plan for new oil and gas projects. Over the past twenty years, several stochastic modeling tools have been developed for modeling parameter uncertainty, including the spectral, perturbation, and simulation methods. In this work we explore the application of a new stochastic methodology, the first-order reliability method (FORM), in oil spill modeling. FORM was originally developed in the structural reliability field and has been recently applied to various environmental problems. The method has many appealing features that makes it a powerful tool for modeling complex environmental systems. The theory of FORM is presented, identifying the features that distinguish the method from other stochastic tools. Different formulations to the reliability-based stochastic oil spill modeling are presented in a decision-analytic context.     

Analysis of a system for remote, dry removal of solidified mixed waste

This paper describes a novel technology for the removal of solidified radioactive waste from underground storage tanks at the DOE Hanford site in southeast Washington. The process involves the use of a unique high pressure system which pulverizes the hardened saltcake with stainless steel pellets to a powder for easy vacuum removal. The steel pellets can be magnetically separated from the waste material for re-use. Specifically this study analyzes the effects of various steel abrasives, pressure of the air stream, and stand-off distance on removal rates and penetration depth on simulated saltcake samples using the high pressure technique. A full-scale test set-up and protocol were implemented to allow for comprehensive testing. To insure reproducibility of the method, tests were then run for the optimum removal parameters. A time-dependent test was also conducted to determine the relationship of removal rates to length of pressure blasts. The results of these tests revealed that stand-off distance and pressure could be positively correlated to removal volumes. Additionally, a statistical analysis confirmed that nozzle angle is independent of removal rate. This study demonstrated that the pellet ‘blaster’ technique is a safe, effective method for removal of radioactive wastes without any increase in either waste mass or volume.     

Fuzzy multicriteria disposal method and site selection for municipal solid waste

The use of fuzzy multiple criteria analysis (MCA) in solid waste management has the advantage of rendering subjective and implicit decision making more objective and analytical, with its ability to accommodate both quantitative and qualitative data. In this paper a modified fuzzy TOPSIS methodology is proposed for the selection of appropriate disposal method and site for municipal solid waste (MSW). Our method is superior to existing methods since it has capability of representing vague qualitative data and presenting all possible results with different degrees of membership. In the first stage of the proposed methodology, a set of criteria of cost, reliability, feasibility, pollution and emission levels, waste and energy recovery is optimized to determine the best MSW disposal method. Landfilling, composting, conventional incineration, and refuse-derived fuel (RDF) combustion are the alternatives considered. The weights of the selection criteria are determined by fuzzy pairwise comparison matrices of Analytic Hierarchy Process (AHP). It is found that RDF combustion is the best disposal method alternative for Istanbul. In the second stage, the same methodology is used to determine the optimum RDF combustion plant location using adjacent land use, climate, road access and cost as the criteria. The results of this study illustrate the importance of the weights on the various factors in deciding the optimized location, with the best site located in Çatalca. A sensitivity analysis is also conducted to monitor how sensitive our model is to changes in the various criteria weights.     

Strategies for the municipal waste management system to take advantage of carbon trading under competing policies: The role of energy from waste in Sydney

Climate change is a driving force behind some recent environmental legislation around the world. Greenhouse gas emission reduction targets have been set in many industrialised countries. A change in current practices of almost all greenhouse-emitting industrial sectors is unavoidable, if the set targets is to be achieved. Although, waste disposal contributes around 3% of the total greenhouse gas emissions in Australia (mainly due to fugitive methane emissions from landfills), the carbon credit and trading scheme set to start in 2010 presents significant challenges and opportunities to municipal solid waste practitioners. Technological advances in waste management, if adopted properly, allow the municipal solid waste sector to act as carbon sink, hence earning tradable carbon credits. However, due to the complexity of the system and its inherent uncertainties, optimizing it for carbon credits may worsen its performance under other criteria. We use an integrated, stochastic multi-criteria decision-making tool that we developed earlier to analyse the carbon credit potential of Sydney municipal solid waste under eleven possible future strategies. We find that the changing legislative environment is likely to make current practices highly non-optimal and increase pressures for a change of waste management strategy.     

A cost study for enhanced sludge washing of high-level radioactive waste at the U.S. Department of energy Hanford Site

Enhanced Sludge Washing (ESW) with caustic has the potential to significantly reduce the amount of sludge-based underground storage tank (UST) high-level radioactive waste at the Hanford Site. The alternative to ESW is a simple sludge wash, a process that does not take advantege of recent dissolution development efforts. During the past several years, studies have been conducted to determine the remediation cost savings derived from the development and deployment of ESW. The tank waste inventory and ESW process performance continues to be revised as waste characterization, and ESW development efforts advance. This study provides a new cost savings estimate based upon the most recent waste inventory and ESW process performance revisions, an estimate of the associated cost savings uncertainty, and an estimate of the rate of return (ROR) on the investment in technology development. The revised remediation cost savings estimate due to ESW of all UST waste at Hanford is $4.8 billion ± $0.7 billion within 95 percent confidence in 1998 dollars. The ROR on investment was estimated to range from 100 percent to 130 percent. A sensitivity analysis indicated that it would be difficult to imagine a remediation scenario for which ESW did not yield a significant remediation cost savings and ROR.     

Application of a Proposed Generic LLW Waste Package Analysis With Changing Infiltration in a Humid Environment

Corrosion of carbon steel boxes filled with low‐level radioactive waste and buried within a near surface disposal facility in a humid environment was evaluated using an integrated systems approach framework. The time to hydraulic failure from initial burial to development of holes through the wall of a given waste package from pitting corrosion was calculated for four corrosion scenarios under two different corrosion cases. The two corrosion cases chosen were a constant rate of corrosion and a slowing rate of corrosion. Corrosion rates were estimated for carbon steel buried in soil from several historical studies and related to the corrosivity and aeration profile of the soil. The scenarios were chosen to represent a range of possible conditions at current and future U.S. Department of Energy disposal facilities. For each scenario, once the time to hydraulic failure had been estimated, the amount of liquid present in each waste package at the time of failure was calculated as an estimate of leachate available for subsurface transport. The Savannah River E‐Area Engineered Trench was used as a basis for the hypothetical disposal facility. © 2016 Wiley Periodicals, Inc.     

Investigating the length of data collection period with respect to rate constant in the first-order decay model

The first-order decay model is the only highly recommended method for estimating landfill gas emissions from solid waste disposal sites according to 2006 IPCC (Intergovernmental Panel on Climate Change) Guidelines. It is also encouraged to collect relevant activity data over the past 50 years to apply the first-order decay model. Even though it is beneficial to facilitate the accuracy of landfill gas emissions estimation, it may not be an easy task to collect reliable data for such a long period of time. It is discussed in this study that a data collection over a shorter period of time may yield a comparable accuracy for emissions estimation depending on methane generation rate or half-life of landfill wastes. Based on the analysis of mathematical properties of the first-order decay model, the estimation accuracy with respect to the length of data collection period has been investigated. Finally, it is also proposed how to estimate the amount of landfill gas emissions and analyze the level of estimation accuracy considering the length of time period since the deposition of wastes.     

On-line early fault detection and diagnosis of municipal solid waste incinerators

A fault detection and diagnosis framework is proposed in this paper for early fault detection and diagnosis (FDD) of municipal solid waste incinerators (MSWIs) in order to improve the safety and continuity of production. In this framework, principal component analysis (PCA), one of the multivariate statistical technologies, is used for detecting abnormal events, while rule-based reasoning performs the fault diagnosis and consequence prediction, and also generates recommendations for fault mitigation once an abnormal event is detected. A software package, SWIFT, is developed based on the proposed framework, and has been applied in an actual industrial MSWI. The application shows that automated real-time abnormal situation management (ASM) of the MSWI can be achieved by using SWIFT, resulting in an industrially acceptable low rate of wrong diagnosis, which has resulted in improved process continuity and environmental performance of the MSWI.     

A Review Of The Management Of Radioactive Wastes In Medical Institutes

Amongst the waste from health care institutions, radioactive waste represents a special category since it cannot be modified or neutralized by any available conventional means. Accordingly, disposal of radioactive waste can mean only its transfer from a place where it represents some hazard to somewhere else where it can be retained without undue risk. Radioactive waste arises in health care institutes as a result of diagnostic, therapeutical or research uses of unsealed radioactive substances. Sometimes, sealed sources withdrawn from further use might also be subject to disposal. Most radionuclides used in medicine are short-lived beta-, or beta-gamma emitters and represent a low risk, if properly handled, that is if due care is taken to prevent significant contamination of the workplace and personnel. Low-activity gaseous and liquid waste can usually be discharged to the environment directly; medium-activity or high-activity waste should be stored for variable periods to allow natural decay before specialized disposal.This paper presents a review of the different types of radioactive wastes produced in hospitals, and introduces many of the sources of generation and subsequent disposal options. An example is given of the wide range of guidance available, both by national bodies in Hungary and international agencies, such as the International Atomic Energy Agency (IAEA), World Health Organisation (WHO) and International Committee on Radiological Protection (ICRP).     

An Updated Cost Study for Enhanced Sludge Washing of Radioactive Waste

This article updates previous cost savings studies conducted to evaluate the use of enhanced sludge washing (ESW) of high‐level radioactive waste at the United States Department of Energy Hanford Site. The cost savings estimate was updated using stochastic analysis based on new information from the Independent Review of Hanford High Level Waste Volume and the more recent Tank Waste Remediation System Operation and Utilization Plan. It is estimated that implementation of ESW in the tank waste remediation system (TWRS) at the Hanford Site can save approximately $4.8 billion compared to the use of an alternative, simpler water wash. The simpler water wash dissolution was found to be 85 percent as effective as the ESW dissolution. Further, the updated remediation cost estimate of $4.8 billion savings is uncertain only within ±$1.6 billion at the 95 percent confidence interval. © 2002 Wiley Periodicals, Inc.     

Report: The assessment of hospital waste management:a case study in Tehran

Hospital waste management is an important process that must be dealt with diligently. The management of hazardous waste material requires specific knowledge and regulations and it must be carried out by specialists in the field. In this cross-sectional study, we assessed the main stages of hospital waste management including separation, containment, removal and disposal of waste materials in public hospitals affiliated with Tehran University of Medical Sciences (TUMS). We selected 108 units of six hospitals (three general hospitals and three subspecialty hospitals) from those hospitals supervised by TUMS using the cluster sampling method. The measurement was conducted through a questionnaire and direct observation by researchers. Association analysis was done by statistical tests; Fisher exact test and chi-squared using SPSS software. According to the results obtained by the questionnaire, most of the studied wards scored moderately in terms of quality of their performance in all stages of waste management. About one-fifth of the wards were suffering from poor management of their medical waste and only a minority of wards obtained good scores for managing their waste materials. The findings also revealed significant associations between temporary waste storage and collection and the level of education of the managers (P = 0.040, P = 0.050, respectively). In summary, the study indicated a moderate management in all processes of separation, collection, containment, removal and disposal of waste materials in hospitals with several observed problems in the process.     

Development of waste gasification and gas reforming system for municipal solid waste (MSW)

To achieve both high-efficiency power generation and high detoxification performance, advanced-type waste power generation plants such as pyrolysis and gas reforming plants are suggested. Further surveys on actual operational data of these plants are required in terms of reliability of the system when it is introduced to waste disposal sites. To verify the technical effectiveness of advanced-type waste power generation using the pyrolysis and gas reforming method, we evaluated 10?tons/day of municipal solid wastes (MSW) treated in a demonstration plant. A demonstration test was conducted over 100?days including 35?consecutive days of operation treating MSWs. The test results show high recycling performance and harmless nature of the plant which proves it to be an excellent waste recycling system. Major test results are as follows: (1) stabilization of waste treatment is possible with the wastes of various qualities, (2) clean gas is produced from the waste whose energy recovery ratio is approximately 40?%. (3) 99.3?% weight % of dried waste are recovered as valuable materials such as clean gas, char and metal, (4) total amount of dioxin emission to the outside of the plant is very small, down to 0.0051–0.018?μg?TEQ per ton waste.     

Integrating multi-criteria decision analysis for a GIS-based hazardous waste landfill sitting in Kurdistan Province, western Iran

The evaluation of a hazardous waste disposal site is a complicated process because it requires data from diverse social and environmental fields. These data often involve processing of a significant amount of spatial information which can be used by GIS as an important tool for land use suitability analysis. This paper presents a multi-criteria decision analysis alongside with a geospatial analysis for the selection of hazardous waste landfill sites in Kurdistan Province, western Iran. The study employs a two-stage analysis to provide a spatial decision support system for hazardous waste management in a typically under developed region. The purpose of GIS was to perform an initial screening process to eliminate unsuitable land followed by utilization of a multi-criteria decision analysis (MCDA) to identify the most suitable sites using the information provided by the regional experts with reference to new chosen criteria. Using 21 exclusionary criteria, as input layers, masked maps were prepared. Creating various intermediate or analysis map layers a final overlay map was obtained representing areas for hazardous waste landfill sites. In order to evaluate different landfill sites produced by the overlaying a landfill suitability index system was developed representing cumulative effects of relative importance (weights) and suitability values of 14 non-exclusionary criteria including several criteria resulting from field observation. Using this suitability index 15 different sites were visited and based on the numerical evaluation provided by MCDA most suitable sites were determined.     

Field testing of particulate matter continuous emission monitors at the DOE Oak Ridge TSCA incinerator. Toxic Substances Control Act

A field study to evaluate the performance of three commercially available particulate matter (PM) continuous emission monitors (CEMs) was conducted in 1999-2000 at the US Department of Energy (DOE) Toxic Substances Control Act (TSCA) Incinerator. This study offers unique features that are believed to enhance the collective US experience with PM CEMs. The TSCA Incinerator is permitted to treat PCB-contaminated RCRA hazardous low-level radioactive wastes. The air pollution control system utilizes MACT control technology and is comprised of a rapid quench, venturi scrubber, packed bed scrubber, and two ionizing wet scrubbers in series, which create a saturated flue gas that must be conditioned by the CEMs prior to measurement. The incinerator routinely treats a wide variety of wastes including high and low BTU organic liquids, aqueous, and solid wastes. The various possible combinations for treating liquid and solid wastes may present a challenge in establishing a single, acceptable correlation relationship for individual CEMs. The effect of low-level radioactive material present in the waste is a unique site-specific factor not evaluated in previous tests. The three systems chosen for evaluation were two beta gauge devices and a light scattering device. The performance of the CEMs was evaluated using the requirements in draft Environmental Protection Agency (EPA) Performance Specification 11 (PS11) and Procedure 2. The results of Reference Method 5i stack tests for establishing statistical correlations between the reference method data and the CEMs responses are discussed.     

Minimax regret optimization analysis for a regional solid waste management system

Solid waste management (SWM) facilities are crucial for environmental management and public health in urban regions. Due to the waste management hierarchy, one of the greatest challenges that organizations face today is to figure out how to diversify the treatment options, increase the reliability of infrastructure systems, and leverage the redistribution of waste streams among incineration, compost, recycling, and other facilities to their competitive advantage region wide. Systems analysis plays an important role for regionalization assessment of integrated SWM systems, leading to provide decision makers with break-through insights and risk-informed strategies. This paper aims to apply a minimax regret optimization analysis for improving SWM strategies in the Lower Rio Grande Valley (LRGV), an economically fast growing region in the US. Based on different environmental, economic, legal, and social conditions, event-based simulation in the first stage links estimated waste streams in major cities in LRGV with possible solid waste management alternatives. The optimization analysis in the second stage emphasizes the trade-offs and associated regret evaluation with respect to predetermined scenarios. Such optimization analyses with multiple criteria have featured notable successes, either by public or private efforts, in diverting recyclables, green waste, yard waste, and biosolids from the municipal solid waste streams to upcoming waste-to-energy, composting, and recycling facilities. Model outputs may link prescribed regret scenarios in decision making with various scales of regionalization policies. The insights drawn from the system-oriented, forward-looking, and preventative study can eventually help decision-makers and stakeholders gain a scientific understanding of the consequences of short-term and long-term decisions relating to sustainable SWM in the fast-growing US-Mexico borderland.     

Selection of infectious medical waste disposal firms by using the analytic hierarchy process and sensitivity analysis

While Taiwanese hospitals dispose of large amounts of medical waste to ensure sanitation and personal hygiene, doing so inefficiently creates potential environmental hazards and increases operational expenses. However, hospitals lack objective criteria to select the most appropriate waste disposal firm and evaluate its performance, instead relying on their own subjective judgment and previous experiences. Therefore, this work presents an analytic hierarchy process (AHP) method to objectively select medical waste disposal firms based on the results of interviews with experts in the field, thus reducing overhead costs and enhancing medical waste management. An appropriate weight criterion based on AHP is derived to assess the effectiveness of medical waste disposal firms. The proposed AHP-based method offers a more efficient and precise means of selecting medical waste firms than subjective assessment methods do, thus reducing the potential risks for hospitals. Analysis results indicate that the medical sector selects the most appropriate infectious medical waste disposal firm based on the following rank: matching degree, contractor's qualifications, contractor's service capability, contractor's equipment and economic factors. By providing hospitals with an effective means of evaluating medical waste disposal firms, the proposed AHP method can reduce overhead costs and enable medical waste management to understand the market demand in the health sector. Moreover, performed through use of Expert Choice software, sensitivity analysis can survey the criterion weight of the degree of influence with an alternative hierarchy.     

Test methods to aid in the evaluation of the diversion of biodegradable municipal waste (BMW) from landfill

This response follows on from a recent discussion by Sánchez (2009) on test methods to aid in the evaluation of the diversion of biodegradable municipal waste (BMW) from landfill. Test methods to assess the biodegradability/biodegradable content of organic waste are of great interest across Europe for different purposes, such as landfill acceptance criteria, monitoring treatment facility performance and for monitoring the diversion of biodegradable municipal waste (BMW) from landfill. Many studies have recently attempted to correlate short-term test methods with long-term anaerobic test methods. This response discusses recent findings and conclusions made by Sánchez (2009) and describes recent work undertaken at Cranfield University to develop the enzymatic hydrolysis test (EHT) method. The EHT has previously shown potential as a short-term, non-biological, biodegradability assessment tool, however there is a requirement to further develop this test method. We conclude that aerobic and anaerobic biological test methods are not the only suitable methods of assessing waste treatment process performance; and that alternative methods such as EHT are feasible and potentially suitable.     

Hazard property classification of waste according to the recent propositions of the EC using different methods

Hazard classification of waste is a necessity, but the hazard properties (named “H” and soon “HP”) are still not all defined in a practical and operational manner at EU level. Following discussion of subsequent draft proposals from the Commission there is still no final decision. Methods to implement the proposals have recently been proposed: tests methods for physical risks, test batteries for aquatic and terrestrial ecotoxicity, an analytical package for exhaustive determination of organic substances and mineral elements, surrogate methods for the speciation of mineral elements in mineral substances in waste, and calculation methods for human toxicity and ecotoxicity with M factors.In this paper the different proposed methods have been applied to a large assortment of solid and liquid wastes (>1 0 0).Data for 45 wastes – documented with extensive chemical analysis and flammability test – were assessed in terms of the different HP criteria and results were compared to LoW for lack of an independent classification. For most waste streams the classification matches with the designation provided in the LoW. This indicates that the criteria used by LoW are similar to the HP limit values.This data set showed HP 14 ‘Ecotoxic chronic’ is the most discriminating HP. All wastes classified as acute ecotoxic are also chronic ecotoxic and the assessment of acute ecotoxicity separately is therefore not needed. The high number of HP 14 classified wastes is due to the very low limit values when stringent M factors are applied to total concentrations (worst case method). With M factor set to 1 the classification method is not sufficiently discriminating between hazardous and non-hazardous materials. The second most frequent hazard is HP 7 ‘Carcinogenic’. The third most frequent hazard is HP 10 ‘Toxic for reproduction’ and the fourth most frequent hazard is HP 4 “Irritant – skin irritation and eye damage”. In a stepwise approach, it seems relevant to assess HP 14 first, then, if the waste is not classified as hazardous, to assess subsequently HP 7, HP 10 and HP 4, and then if still not classified as hazardous, to assess the remaining properties.The elements triggering the HP 14 classification in order of importance are Zn, Cu, Pb, Cr, Cd and Hg. Progress in the speciation of Zn and Cu is essential for HP 14. Organics were quantified by the proposed method (AFNOR XP X30-489) and need no speciation. Organics can contribute significantly to intrinsic toxicity in many waste materials, but they are only of minor importance for the assessment of HP 14 as the metal concentrations are the main HP 14 classifiers. Organic compounds are however responsible for other toxicological characteristics (hormone disturbance, genotoxicity, reprotoxicity…) and shall be taken into account when the waste is not HP 14 classified.