The Use of Hot-Isostatic Pressing to Process Nuclear Waste Forms

ANSTO has developed a combination of tailored nuclear waste form chemistries coupled with the use of flexible hot-isostatic pressing processing technology to enable the successful incorporation of problematic nuclear wastes into dense, durable monoliths. This combined package also enables the design of waste forms with waste loadings well in excess of those achievable via baseline melting routes using borosilicate glass, as hot-isostatic pressing is not constrained by factors such as glass viscosity, crystallisation and electrical conductivity. In this paper we will discuss some of our experiences with problematic wastes, namely plutonium wastes, sludges and HLW such as the Idaho calcines.

Increasing Operational Efficiency in a Radioactive Waste Processing Plant

The solid waste plant at Harwell in Oxfordshire, contains a purpose built facility to input, assay, visually inspect and sort remote handled intermediate level radioactive waste (RHILW). The facility includes a suite of remote handling cells, known as the head-end cells (HEC), which waste must pass through in order to be repackaged. Some newly created waste from decommissioning works on site passes through the cells, but the vast majority of waste for processing is historical waste, stored in below ground tube stores. Existing containers are not suitable for long term storage, many are already badly corroded, so the waste must be efficiently processed and repackaged in order to achieve passive safety. The Harwell site is currently being decommissioned and the land is being restored. The site is being progressively delicensed, and redeveloped as a business park, which can only be completed when all the nuclear liabilities have been removed. The recovery and processing of old waste in the solid waste plant is a key project linked to delicensing of a section of the site. Increasing the operational efficiency of the waste processing plant could shorten the time needed to clear the site and has the potential to save money for the Nuclear Decommissioning Authority (NDA). The waste processing facility was constructed in the mid 1990s, and commissioned in 1999. Since operations began, the yearly throughput of the cells has increased significantly every year. To achieve targets set out in the lifetime plan (LTP) for the site, throughput must continue to increase. The operations department has measured the overall equipment effectiveness (OEE) of the process for the last few years, and has used continuous improvement techniques to decrease the average cycle time. Philosophies from operational management practices such as ‘lean’ and ‘kaizen’ have been employed successfully to drive out losses and increase plant efficiency. This paper will describe how the solid waste plant at Harwell has continuously increased the throughput of RHILW, which should lead to significant programme savings.

Characteristics on the SAP-Based Wasteform Containing Radioactive Molten Salt Waste

This study investigated a unique wasteform containing molten salt wastes which are generated from the pyro-process for the spent fuel treatment. Using a conventional sol-gel process, SiO2-Al2O3-P2O5 (SAP) inorganic material reactive to metal chlorides were prepared. By using this inorganic composite, a monolithic wasteform were sucessfully fabricated via a simple process, reaction at 650°C and sintering at 1100°C. This unique wasteform should be qualified if it meets the requirements for final disposal. For this reasons, this paper characterized its chemical durability, physical properties, morphology and etc. In the SAP, there are three kinds of chains, Si-O-Si as a main chain, Si-O-Al as a side chain and Al-O-P/P-O-P as a reactive chain. Alkali metal chlorides were converted into metal aluminosilicate (LixAlxSi1−xO2−x) and metal phosphate (Li3PO4 and Cs2AlP3O10) while alkali earth and rare earth chlorides were changed into only metal phosphates (Sr5(PO4)3Cl and CePO4). These reaction products were compatible to borosilicate glasses which were functioned as a chemical binder for metal aluminosilicate and a physical binder for metal phosphates. By these phenomena, the wasteform was formed homogenously above μm scale. This would affect the leaching behaviors of each radionuclides or component of binder. The leach rates of Cs and Sr under the PCT-A test condition were about 10−3g/m2day. The physical properties (Cp, k, ρ, Hv, and etc) were very reasonable. Other leaching tests (ISO, MCC-1P) are on-going. From these results, it could be concluded that SAP can be considered as an effective stabilizer on metal chlorides and the method using SAP will give a chance to minimize the waste volume for the final disposal of salt wastes through further researches.

A Study on the Once-Through Back-End Fuel Cycle Scenario

There are three options for spent fuel management, recycle, once-through and wait and see. The national policy for spent fuel in Korea is “wait and see” and it has to be clearly decided for spent fuel management. The final disposal is the last stage of the fuel cycle and it is essential even though the recycling option will be chosen for spent fuel management policy. And the long-term strategy for spent fuel management considering safety and retrievability is needed. In this study, once-through fuel cycle was focused on for back-end fuel cycle. The international trend for SF management policy and the Korean situation has been investigated. The once-through back-end fuel cycle scenarios has been developed and screened in point of technical and economical aspect. The optimal scenario has been derived by relative comparison and the long-term SF management strategy has been proposed which satisfies both domestic conditions and international trends.

An Overview of US EPA’s Current Radioactive Waste Management and General Radiation Protection Efforts

The United States Environmental Protection Agency’s (EPA) Radiation Protection Division is the portion of EPA (or the Agency) that develops environmental standards for radioactive waste disposal in the United States. One current issue of concern is the disposal of low activity radioactive waste (LAW), including wastes that would be produced by a radiological dispersal device (RDD), for which current disposal options may be either inconsistent with the hazard presented by the material or logistically problematic. Another major issue is related to the resurgence in uranium mining. Over the past several years, demand for uranium for nuclear power plant fuel has increased as has the price. The increase in price has made uranium mining potentially profitable in the US. EPA is reviewing its relevant regulations, developed primarily in the 1980s, for potential revisions. For example, in-situ leaching (also known as in-situ recovery) is now the technology of choice where applicable, yet our current environmental standards are focused on conventional uranium milling. EPA has two actions in process, one related to the Clean Air Act, the other related to revising the environmental standards that implement the Uranium Mill Tailings Radiation Control Act of 1978 (UMTRCA). Separately, but related, EPA has developed over the last several years uranium mining documents that address technologically enhanced natural occurring radioactive materials (TENORM) from abandoned uranium mines, and wastes generated by active uranium extraction facilities. Lastly, in 1977 EPA developed environmental standards that address nuclear energy, fuel fabrication, reprocessing, and other aspects of the uranium fuel cycle. In light of the increased interest in nuclear power and the potential implementation of advanced fuel cycle technologies, the Agency is now reviewing the standards to determine their continued applicability for the twenty-first century.

Measurement of Solid-Liquid Mixtures Using Electrical Tomography Measurement Techniques

Electrical Impedance Tomography measurement techniques have been applied to a variety of solid-liquid processes in the laboratory and on industrial plant. This paper reviews the advances in the measurement techniques to determine key process information in solid-liquid systems such as concentration mapping, mixture homogeneity, interface detection and suspension velocity. A number of applications to solid-liquid flow applications are presented. The use of the technology for improved design and operation is highlighted, as are the opportunities for on-line sensing for flow measurement, fault detection and process control. A recent development in high-speed electrical imaging has allowed velocity maps to be calculated for fast flowing suspensions (up to 10 ms−1). The methodology for determining mixture homogeneity in both pipeline flows and agitated tanks are summarized. Finally the application of a linear ERT electrode array to identify interfaces during the settling of solid-liquid mixtures is presented.

Designing a New Highly Active Liquid Evaporator

The Highly Active Liquid Effluent Storage (HALES) plant stores, concentrates and conditions Highly Active Liquor (HAL) in evaporators for buffer storage in Highly Active Storage Tanks (HAST). Highly Active (HA) evaporators play a pivotal role in the delivery of reprocessing, historic clean up and hazard reduction missions across the Sellafield site. In addition to the engineering projects implemented to extend the life expectation of the current evaporator fleet, the UK Nuclear Decommissioning Agency (NDA) is sponsoring the construction of a new HA evaporator (Evaporator D) on the Sellafield site. The design and operation of the new HA evaporator is based on existing/recent HA evaporator technology but learning from past operational experience. Operational experience has been a key area where the existing plant operators have influenced both the new design itself and the requirements for commissioning and training. Many of the learning experiences require relatively simple engineering design modifications such as a new internal washing provision and transfer line blockage recovery systems, they are never-the-less expected to significantly improve the flexibility and operational capability of the new evaporator. Issues that the project delivery team has addressed as part of the development of the design and construction have included: • Minimising interruptions and/or changes to the normal operations of interfacing plants during construction, commissioning and operation of the new facility. • Modularisation of the plant, enabling fabrication of the majority of the plant equipment off-site within a workshop (as opposed to on-site) environment improving Quality Assurance and reducing on-Site testing needs. • Drawing out the balance between operational and corrosion resistance improvements with actual design and delivery needs. • Provision of a new facility reliant on the infrastructure of an existing and ageing facility and the competing demands of the related safety cases.

Research Reactor Spent Nuclear Fuel Shipment From the Czech Republic to the Russian Federation

In May 2004, the Global Threat Reduction Initiative agreement was signed by the governments of the United States and the Russian Federation. The goal of this initiative is to minimize, in cooperation with the International Atomic Energy Agency (IAEA) in Vienna, the existing threat of misuse of nuclear and radioactive materials for terrorist purposes, particularly highly enriched uranium (HEU), fresh and spent nuclear fuel (SNF), and plutonium, which have been stored in a number of countries. Within the framework of the initiative, HEU materials and SNF from research reactors of Russian origin will be transported back to the Russian Federation for reprocessing/liquidation. The program is designated as the Russian Research Reactor Fuel Return (RRRFR) Program and is similar to the U.S. Foreign Research Reactor Spent Nuclear Fuel Acceptance Program, which is underway for nuclear materials of United States origin. These RRRFR activities are carried out under the responsibilities of the respective ministries (i.e., U.S. Department of Energy (DOE) and Russian Federation Rosatom). The Czech Republic and the Nuclear Research Institute Rez, plc (NRI) joined Global Threat Reduction Initiative in 2004. During NRI’s more than 50 years of existence, radioactive and nuclear materials had accumulated and had been safely stored on its grounds. In 1995, the Czech regulatory body, State Office for Nuclear Safety (SONS), instructed NRI that all ecological burdens from its past activities must be addressed and that the SNF from the research reactor LVR-15 had to be transported for reprocessing. At the end of November 2007, all these activities culminated with the unique shipment to the Russian Federation of 527 fuel assemblies of SNF type EK-10 (enrichment 10% U235) and IRT-M (enrichment 36% and 80% U235) and 657 irradiated fuel rods of EK-10 fuel, which were used in LVR-15 reactor.

Delivering Step Change Improvements to UK Low Level Waste Strategy

The UK Nuclear Industry continues to produce significant quantities of Low Level Waste (LLW) as decommissioning projects generating waste become more prevalent. Current infrastructure and projected increasing waste volumes will deliver a volumetric shortfall of storage capacity in the near future. Recently established as a stand alone site licence company, the Low Level Waste Repository (LLWR) near Drigg, in West Cumbria (formerly operated and owned by British Nuclear Group) is tasked with managing the safe treatment and disposal of LLW in the UK, on behalf of the Nuclear Decommissioning Authority (NDA). The problem is complex involving many stakeholders with potentially different priorities. Previously, most nuclear waste generators operated independently with limited integration with other similar organisations. However, the current financial, programme and technical pressures require collaborative working to facilitate a step-change improvement in LLW management. Achieving this quickly is as much of a challenge as delivering robust cost effective technical solutions. NDA is working in partnership with LLWR to develop a LLW Strategy for the Nuclear Industry and has in parallel commissioned a number of studies by the National Nuclear Laboratory (NNL), looking at opportunities to share best practice. A National Strategy Group has been established to develop a working partnership between the Nuclear Decommissioning Authority, LLW Repository Ltd, Regulators, Stakeholders and LLW Consignors, promoting innovation, value for money, and robust implementation of the waste hierarchy (avoid-reduce-re-use-recycle). Additionally the LLWR supported by the NNL have undertaken a comprehensive strategic review of the UK’s LLW management activities. Initial collaborative work has provided for the first time a detailed picture of the existing strategic baseline and identified significant national benefits from improving the way LLW is forecasted, characterised, segregated, and treated in line with the waste hierarchy. Implementation of volume reduction technologies, such as incineration and metal treatment, is critical to mitigate the LLWR capacity gap and reduce NDA’s liabilities. The cumulative effect of these solutions has the potential to reduce lifetime costs by several £billion and extend the life of the existing LLWR site to 2070 and possibly beyond. This work has informed the NDA’s UK Nuclear Industry LLW Strategy, published for consultation in June 2009 and the Draft UK LLW Management Plan which sets out how the strategy will be implemented. Technical and infrastructure solutions have been found to exist via the supply chain supporting deliver of the necessary step changes in the near future. Work continues to reduce the LLW inventory forecast uncertainties and evaluate strategic implementation options in more detail, e.g. benefits of national vs. local treatment and disposal solutions, plus on gaining the corresponding stakeholder acceptance and operational authorisations.

Hydraulic Behaviour of Nuclear Waste Flows

A great deal of existing nuclear waste is stored as a solid-liquid slurry, and the effective transportation of such systems is an essential element in the successful implementation of almost all waste treatment strategies involving particulate wastes within the nuclear industry. A detailed knowledge of turbulent, particle-laden liquid flow behaviour is therefore obviously important. However, systematic and detailed studies of solid-liquid flows by experimental investigation are still limited for pipe flows, contrary to the significant amount of work available for channel flows. Research is therefore required to understand the effects of physical parameters, such as particle shape, size and size distribution, and solids concentration, on the properties of solid-liquid systems, particularly in horizontal pipe flows where particles may settle out of the flow and form solid beds which can potentially lead to pipe blockages. The presence of particles in a turbulent pipe flow also modifies the characteristics of the flow, thereby changing its ability to maintain particles in suspension. The work described concerns pipe flows over a Reynolds number range of 1,000–10,000, with varying levels of solids concentration within the flow. Measurements of the flow and particle characteristics have been gathered using particle image velocimetry (PIV) and, for high solids concentrations, ultrasound Doppler velocity profiling (UDVP) techniques. This work has demonstrated that the intensity of turbulence within such flows can be significantly affected by the presence of solid particles, with small particles generally attenuating turbulence levels, while large particles often augment turbulence levels from the pipe centre-line to the near-wall region. In addition, the coagulation of particles into larger agglomerates is also of importance, with data demonstrating that whilst turbulence levels are influenced and augmented by such agglomerates at low Reynolds numbers, high turbulence levels at high Reynolds numbers can destroy the agglomerates and reduce their effect on the carrier fluid. Work has also been undertaken to examine the effect of particle size and Reynolds number on particle deposition within the flows, and also to establish the minimum transport velocity required to re-suspend particles from solid beds. All these findings are of importance in enhancing our understanding of flows of particles in pipes which in turn is of value in enabling the design of cost effective and efficient waste treatment processes.