Options for the Removal of Contaminated Concrete From the Bore of the Windscale Pile Chimney

A legacy of the 1957 Windscale Pile reactor fire is the penetration of radioactive contamination into the internal surface concrete of the chimney bore. Gamma imaging of Cs-137 has shown that the contamination is widespread throughout the chimney, and core samples have shown that the contamination has penetrated to depths of around 5–25mm. The Pile chimney is 100m tall and has an internal bore diameter of 15m. It is constructed of a hard concrete comprised of Whinstone aggregate. The baseline decommissioning scheme is to remove approximately 5–25mm of the surface concrete from the entire bore of the chimney. The technology baseline in 2006 was to remove layers of contaminated concrete by mechanical means using shavers or scabblers. However, risks associated with mechanical technologies that may preclude their use include: the ability of mechanical devices to remove the hard concrete; clogging of the devices due to wet concrete; and deployment of the delivery systems. This paper discusses the options under consideration to reduce the risks associated with the removal of the contaminated concrete through application of alternative techniques. The present baseline technology is high pressure water jetting technique. Demonstrations have shown that this technology can successfully remove concrete without significant reaction forces. However, an inherent problem with this technology is the production of secondary liquid effluent waste, which would need to be treated by an appropriate conditioning process. To address the secondary effluent waste issue, technologies that produce little or no secondary waste have been considered. The technologies that have been considered are laser scabbling, microwave scabbling and nitrogen jet blasting. The paper discusses each technique in turn, highlighting their advantages and disadvantages. The results of an in-active laser scabbling and high pressure liquid nitrogen jetting trial are presented. The paper concludes with a discussion of the merits of each technology in support of the future strategy for concrete removal.

Sustainable Covers for Uranium Mill Tailings, USA: Alternative Design, Performance, and Renovation

The U.S. Department of Energy Office of Legacy Management is investigating alternatives to conventional cover designs for uranium mill tailings. A cover constructed in 2000 near Monticello, Utah, USA, was a redundant design with a conventional low-conductivity composite cover overlain with an alternative cover designed to mimic the natural soil water balance as measured in nearby undisturbed native soils and vegetation. To limit percolation, the alternative cover design relies on a 160-cm layer of sandy clay loam soil overlying a 40-cm sand capillary barrier for water storage, and a planting of native sagebrush steppe vegetation to seasonally release soil water through evapotranspiration (ET). Water balance monitoring within a 3.0-ha drainage lysimeter, embedded in the cover during construction, provided convincing evidence that the cover has performed well over a 9-year period (2000–2009). The total cumulative percolation, 4.8 mm (approximately 0.5 mm yr−1), satisfied a regulatory goal of <3.0 mm yr−1. Most percolation can be attributed to the very wet winter and spring of 2004–2005, when soil water content exceeded the storage capacity of the cover. Diversity, percent cover, and leaf area of vegetation increased over the monitoring period. Field and laboratory evaluations several years after construction show that soil structural development, changes in soil hydraulic properties, and development of vegetation patterns have not adversely impacted cover performance. A new test facility was constructed in 2008 near Grand Junction, Colorado, USA, to evaluate low-cost methods for renovating or transforming conventional covers into more sustainable ET covers.

A Systematic Planning Tool for Environmental Characterisation

Many organisations are currently dealing with long standing legacy issues in clean up, decommissioning and demolition projects. Industry is required to ensure that all bulk articles, substances and waste arisings are adequately characterised and assigned to the correct disposal routes in compliance with UK legislation and best practice. It is essential that data used to support waste sentencing is of the correct type, quality and quantity, and that it is appropriately assessed in order to support defensible, confident decisions that account for inherent uncertainties. AMEC has adopted the Data Quality Objectives (DQO) based methodology and the software package Visual Sample Plan (VSP) to provide a better, faster, and more cost effective approach to meeting regulatory and client requirements, whilst minimising the time spent gathering data and assessing the information. The DQO methodology is based on a scientific approach that requires clear objectives to be established from the outset of a project and that there is a demonstration of acceptability of the results. Through systematic planning, the team develops acceptance or performance criteria for the quality of the data collected and for the confidence in the final decision. The systematic planning process promotes communication between all departments and individuals involved in the decision-making process thus the planning phase gives an open and unambiguous method to support the decisions and enables the decision-makers (technical authorities on the materials of concern) to document all assumptions. The DQO process allows better planning, control and understanding of all the issues. All types of waste can be sentenced under one controllable system providing a more defensible position. This paper will explain that the DQO process consists of seven main steps that lead to a detailed Sampling and Analysis Plan (SAP). The process gives transparency to any assumptions made about the site or material being characterised and identifies individuals involved. The associated calculation effort is reduced using the statistically based sampling models produced with VSP. The first part of this paper explains the DQO based methodology and Visual Sample Plan and the second part shows how the DQO process has been applied in practice.

Geochemical Behaviour of Uranium in Sedimentary Formations: Insights From a Natural Analogue Study

Groundwater data from the natural analogue site Ruprechtov have been evaluated with special emphasis on the uranium behaviour in the so-called uranium-rich clay/lignite horizon. In this horizon in-situ Eh-values in the range of −160 to −280 mV seem to be determined by the SO42−/HS− couple. Under these conditions U(IV) is expected to be the preferential redox state in solution. However, on-site measurements in groundwater from the clay/lignite horizon show only a fraction of about 20% occurring in the reduced state U(IV). Thermodynamic calculations reveal that the high CO2 partial pressure in the clay/lignite horizon can stabilise hexavalent uranium, which explains the occurrence of U(VI). The calculations also indicate that the low uranium concentrations in the range between 0.2 and 2.1μg/l are controlled by amorphous UO2 and/or the U(IV) phosphate mineral ningyoite. This confirms the findings from previous work that the uranium (IV) mineral phases are long-term stable under the reducing conditions in the clay/lignite horizon without any signatures for uranium mobilisation. It supports the current knowledge of the geological development of the site and is also another important indication for the long-term stability of the sedimentary system itself, namely of the reducing geochemical conditions in the near-surface (30m to 60 m deep) clay/lignite horizon. Further work with respect to the impact of changes in redox conditions on the uranium speciation is on the way.

Waste Reduction by Re-Use of Low Activated Material

A multidisciplinary institute, equipped with research reactors and accelerator-driven research installations produces and, in the case of PSI, collects radioactive waste on one hand and requires material, especially for shielding purpose, on the other hand. The legislative framework for radiation protection, financial reasons and limited storage capacity strongly force Paul Scherrer Institute and comparable facilities to minimize radioactive waste. Besides free release of inactive components, recycling and re-use of low-level radioactive material in controlled areas are the best means for waste minimization. The re-use of slightly activated steel plates as a shielding material and the recycling of irradiated reactor graphite as a filling material embedded in mortar may give examples and encouragement for similar activities. Besides the advantages for radiation protection, the financial benefit can be measured in millions of dollars.

Radiological, Technical and Financial Planning for Decommissioning of Small Nuclear Facilities in Sweden

On November 1st 2008, a new ordinance came into force in Sweden. It extends the implementation of nuclear liability to all nuclear facilities and companies, regardless of size. The Government has authorized the Swedish Radiation Safety Authority (SSM) to issue further regulation as warranted and appropriate, and commissioned the same Authority to oversee the implementation. Consequently, SSM is presently conducting research in order to establish a basis for the implementation of the ordinance to smaller facilities and enterprises. The goal is to enable finance to be assured in an efficient manner so that any burden on the companies is as small as possible. Thus, “functional requirements” are identified, and used as a basis for various investigations. The aspects include technical and cost calculation prerequisites, as well as various domains of law: the environmental code, radiation and nuclear safety, financial reporting, and criminal law. It is found that the basis for the differentiation among the facility operators and owners should be the cost and the associated uncertainty. Thus, a cost calculation will have to be carried out by all. It should be based on available standards and guidance documents. It is found that this is a requirement that already exists elsewhere in the legislation, and thus no additional burden is imposed on the companies. It is found that segregated funds is the preferred option for long-term liabilities. Securities are suitable for short-term liabilities provided that the economy of the company in question is sound. Securities might also be used for long-term liabilities to cover uncertainty. It is proposed that a de minimis limit of at least kSEK 25 (about k€ 2, 4 and k$ 3, 4) is used. An important reason for this is that lower limits might be incompatible with the rules for financial reporting. It is also proposed that securities might be used also for long-term commitments if the total environmental liability does not exceed 1,00 MSEK (about k€ 96 and k$ 135). It is found that the “general advice” that must be used by smaller companies lacks proper instructions on how to account for environmental liability whilst at the same time it prohibits the use of e g the international reporting standards IFRS/IAS. It is also found that the “general advice” prohibits distribution of costs for research and development over time. This might be incompatible with a fund system where considerable research may be necessary at the early stages of the work and often many years before the actual decommissioning is to take place. The rules in the penal code require that an annual report presents an “essentially correct financial situation”. One of the interpretations to this statement is that a deviance of at most 30% might be tolerated. Although previous work has indicated that the error in cost estimates need not be higher than about 15%, even for research facilities, concealed cost raisers may from time to time lead to much larger errors, even when best practices are being used. It is therefore essential that decommissioning planning and cost predictions are made in accordance with state of the art, and that the estimating methods as well as the results are properly documented.

Design Improvements and ALARA at U.S. Uranium In Situ Recovery Facilities

In the last few years, there has been a significant increase in the demand for Uranium as historical inventories have been consumed and new reactor orders are being placed. Numerous mineralized properties around the world are being evaluated for Uranium recovery and new mining / milling projects are being evaluated and developed. Ore bodies which are considered uneconomical to mine by conventional methods such as tunneling or open pits, can be candidates for non-conventional recovery techniques, involving considerably less capital expenditure. Technologies such as Uranium In Situ Leaching / In Situ Recovery (ISL / ISR - also refered to as “solution mining”), have enabled commercial scale mining and milling of relatively small ore pockets of lower grade, and are expected to make a significant contribution to overall world wide uranium supplies over the next ten years. Commercial size solution mining production facilities have operated in the US since the mid 1970’s. However, current designs are expected to result in less radiological wastes and emissions relative to these “first” generation plants (which were designed, constructed and operated through the 1980s). These early designs typically used alkaline leach chemistries in situ including use of ammonium carbonate which resulted in groundwater restoration challenges, open to air recovery vessels and high temperature calcining systems for final product drying vs the “zero emmisions” vaccum dryers as typically used today. Improved containment, automation and instrumentation control and use of vacuum dryers in the design of current generation plants are expected to reduce production of secondary waste byproduct material, reduce Radon emisions and reduce potential for employee exposure to uranium concentrate aerosols at the back end of the milling process. In Situ Recovery in the U.S. typically involves the circulation of groundwater, fortified with oxidizing (gaseous oxygen e.g) and complexing agents (carbon dioxide, e.g) into an ore body, solubilizing the uranium in situ, and then pumping the solutions to the surface where they are fed to a processing plant (mill). Processing involves ion exchange and may also include precipitation, drying or calcining and packaging operations depending on facility specifics. This paper presents an overview of the ISR process and the health physics monitoring programs developed at a number of commercial scale ISL / ISR Uranium recovery and production facillities as a result of the radiological character of these processes. Although many radiological aspects of the process are similar to that of conventional mills, conventional-type tailings as such are not generated. However, liquid and solid byproduct materials may be generated and impounded. The quantity and radiological character of these by products are related to facility specifics. Some special monitoring considerations are presented which are required due to the manner in which radon gas is evolved in the process and the unique aspects of controlling solution flow patterns underground. The radiological character of these procesess are described using empirical data collected from many operating facilities. Additionally, the major aspects of the health physics and radiation protection programs that were developed at these first generation facilities are discussed and contrasted to circumstances of the current generation and state of the art of uranium ISR technologies and facilities.

A Successful Remediation Project

As part of a program to visit formerly licensed sites to determine if they meet current uncontrolled release conditions, a United States Nuclear Regulatory Commission (USNRC) inspection was conducted in the fall of 1993 at a site that had possessed a radioactive material license from about 1955 to 1970. While the license was in force, the plant processed magnesium scrap containing up to 4 percent thorium. The source of the scrap is believed to be the aircraft manufacturing industry. The scrap was placed in furnaces and heated to the melting point of magnesium, and the molten magnesium was drawn off, leaving the thorium with the residue (dross). Under the regulation in existence at that time, the thorium dross was buried on site in an approximate 14 acre field. In 1993 the inspector found readings up to 900uR/h. Early in 1994 an informal grid survey of most of the 14 acre site was conducted. Based on that survey, it was concluded that the thorium was widespread and extended beyond the property lines. The preliminary findings were reported to the USNRC, and in 1994 the site was designated as a Site Decommissioning Management Plan (SMPD) site. A remediation team was formed which included the following disciplines: remediation health physics, geology, hydrology, engineering, law, public relations, and project management. This remediation team planned, participated in selecting vendors, and provided project over site for all activities from site characterization through the final status survey. In 2006 the site was released for uncontrolled access. A chronology of activities with lessons learned will be presented.

Evaluation and Potential Remediation of the Industrial Norm Legacy in Liverpool

Sefton, on the north side of Liverpool, holds a radioactive legacy from its industrial past. This legacy is in the form of Tin slag buried in sub-surface seams. Located near the docks and adjacent to the rich Lancashire coal seams, Sefton became one of the main production centres of Tin plate in Britain. A consequence of this industrial process is the production of mildly radioactive waste slag. Tin rich ores are heated under reducing conditions to produce a molten metal stream This is then separated into the component metal streams. Solid wastes produced by this process are known as slag and were usually stored on site in spoil heaps. Because this slag is a very hard, glassy material it has been historically used as aggregate in underlying roads and rail way sleepers. Many of these sites pre-date the introduction of the regulation of radioactive substances in the UK and have never been under legislative control under the Radioactive Substances Act, RSA93. There is a risk that the existence may not be known of some of these sites. U-238 and Th-232 and their associated decay chains, are the major contributors to the radionuclide inventory of the slags, levels of these radionuclides being in the range 1–10Bq/g. A series of alpha and beta decays for both chains leads eventually to the generation of a stable isotope of lead. Radiologically, the main area of concern is with the potential inhalation or ingestion of contaminated dusts. There is also a potential for Ra-226 to leach out into groundwater. AMEC has worked for Sefton Metropolitan Council and various developers, to carry out specialist, non intrusive gamma radiation surveys of numerous sites in Sefton. This is the first stage in carrying out a radiological risk review of a given site. What often then follows is an intrusive, geo-technical survey, with trial pitting and radiological sampling for later sensitive lab based radiochemical analysis. Radiological supervision is also required at this time to ensure that the radiological exposure of the Contractors carrying the survey is restricted and ensure that plant dose not become contaminated with radionuclides. These surveys are the preliminary stage for redevelopment works with new housing replacing antiquated commercial premises. By bringing together expertise in sensitive gamma surveying, radiochemical analysis and a detailed understanding of the regulatory framework, AMEC is able to support the borough of Sefton in its re-development programme ensuring safe compliant development of an area with an historic radiological legacy.

Cone Penetration Testing of Radiologically Contaminated Burial Trenches

Golder Associates (UK) Ltd, in partnership with Serco Assurance (Serco), undertook targeted cone penetration testing (CPT) of a series of six parallel on-site burial trenches on a nuclear licensed site in the UK. The form and concentration of radioactive and chemical material within the trenches is unknown. CPT was used to confirm the location of the bund walls and to characterise the material within the trenches. The CPT technique involves hydraulically pushing rods fitted with specialist characterisation “cones” into the ground. CPT generates no solid or liquid waste, and allowed rapid investigation of the trenches and bunds while ensuring exposure of radiation and contamination to workers was kept to a minimum, or removed in entirety. As a result of the unknown nature of radiological contamination within the trenches and the potential of introducing contamination into the inside of the CPT truck, a purpose-built extraction rig was constructed to withdraw the CPT equipment from the ground. Extraction of the equipment assumed airborne radioactive contamination was a potential hazard. The CPT locations selected for the investigation were based on non-intrusive geophysical survey work and a radiation survey, which identified the approximate location of the trenches, anomalies within the material (e.g. metallic objects), and radiation hotspots. The results of the geophysical surveys were overlaid with the original as-built drawings of the trenches. During the investigation the following investigation cones were deployed: • Resistance/friction cone, which determines geology through measurement of the friction on the sleeve of the cone and resistance on the tip of the cone; this was used to investigate the geology of the bunds. • Total gamma cone, which was used to obtain total gamma radiation results (in counts per second); • Groundwater sampler (BAT Sampler™), which was used to obtain a water sample from beneath the trenches; • Video cone, which was used to obtain a visual recording of the material within the trenches; and • Conductivity cone, which was used to investigate the presence of and depth to bodies of water below ground level (e.g. perched water, regional groundwater). The investigation collected essential data from an area of the site that had not previously been investigated, while minimising potential radiological exposure to all workers, and producing no investigation-derived waste. The investigation therefore confirmed the efficacy of cone penetration testing as a valid site investigation technique in a high hazard area. The data acquired from the CPT investigation and geophysical investigation also allowed boreholes to be sited in the bund walls between the trenches. Siting of the boreholes was a major risk for the project and presented a significant potential hazard. Golder has successfully used CPT on nuclear sites in the UK: as an innovative site investigation technique to facilitate radiological characterisation of an area with variable ground conditions; to investigate organic solvent plumes; and for the installation of blind tubes as a way of conducting subsurface radiation surveys and as part of a leak detection system (work in progress in partnership with Serco).