A demonstration plant to vitrify radioactive waste has completed initial commissioning before deployment at the UK’s Sellafield site.
The full-scale GeoMelt In-Container Vitrification (ICV) plant is a collaboration between the UK’s National Nuclear Laboratory (NNL) and US radioactive waste management specialist Kurion.
The non-radioactive phase of the commissioning programme concluded with a demonstration on simulated Sellafield waste, showing that the system started up safely, reliably and met its design goals. The system will now be disassembled and moved to the NNL’s Central Laboratory at Sellafield, about 25 kilometres to the south of NNL’s engineering facility in Workington where the non-active testing was carried out.
The UK has over 300,000t of intermediate and low-level waste that could be suitable for treatment using GeoMelt, NNL and Kurion said. Unlike conventional vitrification technology, which requires a homogenous waste feed, GeoMelt can process various forms of waste simultaneously, and can use liabilities such as contaminated soils and inorganic ion exchange media into glass formers. It can also treat radioactive contaminated asbestos, a material found at many plants undergoing decommissioning.
The technology, initially developed by the USA’s Pacific Northwest National Laboratory, can be used to process non-radioactive hazardous wastes such as organic wastes and heavy metals, and has been used to produce a cumulative total of 26,000t of glass at various projects in Australia, Japan, the UK and the USA since the 1990s.
The system is designed to accommodate both small test melts and full-scale melts in disposal containers with a capacity of three cubic metres, providing the flexibility to demonstrate, test and process radioactively contaminated and other hazardous waste streams. Lifecycle costs for waste management are reduced by the decreased volume of waste and its conversion to a stable form with lower packaging, storage, handling, transportation and disposal costs.
NNL and Kurion plan to increase the total throughput of the system in 2016, reaching a maximum processing capacity of more than 200t a year. The companies will also evaluate the installation of additional systems.
Meanwhile, a 50t transfer tunnel has been hoisted into place at Sellafield’s Magnox Swarf Storage Silo (MSSS) building. Sellafield Limited said the tunnel is the main component of the first Silo Emptying Plant – one of three 360t machines that will scoop out the highly radioactive contents of the building as part of its decommissioning. The silo, built in the 1960s, contains legacy waste produced as part of the UK’s nuclear weapons programme and represents one of the Nuclear Decommissioning Authority’s four highest priority decommissioning jobs.
In October, a four-year study led by the Nuclear Decommissioning Authority (NDA), Sellafield Ltd and NNL, with academics from the universities of Bristol, Leeds and London South Bank, looked at the chemical behaviours of intermediate-level waste (ILW) stored at MSSS.
NDA said the scientists "have unearthed previously unknown information about the material’s long-term behaviour". According to the NDA, the discovery "points the way to a radically simplified approach to the packaging and disposal of ILW that will see significantreductions in the timescales and costs associated with decommissioning redundant nuclear facilities".
A 22-step mechanical treatment and encapsulation process had previously been thought necessary to manage and ultimately dispose of the ILW stored in the silos, built over 50 years ago. However, the study concluded that a three-step solution could be used in which "raw" waste with concrete grout is stored inside a shielded container. This waste package would be suitable for interim storage at Sellafield, the NDA said, and then for final disposal in the UK’s proposed geological repository.
The new technique will also lead to a reduction in "secondary wastes" created during the treatment process, resulting in an estimated 10% fewer waste packages being produced during the decommissioning of MSSS. According to the NDA, "Switching to this new method could speed up the decommissioning of the silo by several years and provide huge savings to the taxpayer. The technique could also be applied to other redundant nuclear facilities in the UK and around the world."
The MSSS project was built to accommodate the swarf waste produced by the decanning of Magnox fuel prior to reprocessing. The swarf was stored underwater, and the first facility of six silos began operations in 1964. By 1983 a total of 22 silos had been built, but by the early 1990s wet storage of Magnox swarf was superseded by dry storage.
Three silo emptying plants are currently being built, the first of which will be delivered to the site later this year. After undergoing testing, this should be available for solid waste retrievals in 2017. NDA strategy and technology director Adrian Simper said the research could lead to a "paradigm shift" in the management of nuclear waste.
