Radioactive waste handling and storage poses challenges due to the inherent chemical and physical hazards of the waste. The wastes from decommissioning range from wet, mobile slurries and sludges to large heavy pieces of plant and building structures.
Individually these wastes may be problematic due to radiological and chemotoxic hazards that may preclude direct man access to facilities in order to deploy equipment. The facilities containing waste do not have man-access. Further waste arising from decommissioning may be mixed and potentially need further segregation, for example pieces of plant such as tanks and vessels may still contain residual liquors, slurries or deposits.
Innovative tools and techniques for the remote handling of waste are required to work alongside or replace baseline technologies so that waste handling is more efficient.
An established business with a global customer base in the oil and gas sector, Rawwater Engineering Company Limited provides materials science and engineering solutions to oil and gas operators and service companies.
Rawwater Engineering’s innovative Bismuth Plug was developed as a superior option to cement for sealing onshore and offshore oil and gas wells during decommissioning.
The Bismuth Plug, formed using Rawwater Engineering’s Molten Metal Manipulation (M3) technology, comprises a suite of metal alloys with compositions that are tailored to expand when they solidify, according to need.
The metal can seal large openings, or fill small cracks or pores, preventing leakage of fluids in a wide range of applications and offering extreme length of service. The sealing process is reversible and the alloys are recyclable.
In 2016, Rawwater Engineering identified a potential opportunity for this same molten metal alloy technology to be deployed in nuclear decommissioning.
Bismuth has the unusual property of expanding upon freezing, similar to water becoming ice. It can be combined with various other metals to produce a wide range of fusible (low melting temperature) alloys.
Once molten these alloys have a very low viscosity, allowing them to conform to the profile of any surface they come into contact with.
When expanding bismuth comes into contact with the casing ID, a large contact load is generated; this leads to an ultra high integrity metal-to-metal seal being formed.
The bismuth casting process is a matter of hours, as opposed to days, as it is for cement setting.
A 910mm bismuth plug can readily outperform a conventional cement seal, which may be up to 15,200mm in length.
Rawwater Engineering’s background in expanding metal technology spans more than two decades with the Bismuth Plug making its debut in 2003. News of the prototype was picked up by the Museum of Science and Industry in Manchester and used as an exemplar of innovative businesses in the North West UK.
Full scale well abandonment Bismuth Plugs were deployed in Alberta, Canada, in late 2010. This was a world first for metal-to-metal plugging technology and underpinned the launch of Rawwater’s joint industry project to develop offshore plugging and abandonment tools.
This was supported by the UK Government and an international consortium of oil operators.
Rawwater are currently designing and qualifying large diameter offshore plugs deployable using electric as well as pyrotechnic heaters. As if the rigours of new technology qualification are not enough, the project sponsors set a target life expectancy of ‘in perpetuity’.
Rawwater began engagement with Sellafield Ltd through the Game Changers Innovation Programme, which provided invaluable access to Sellafield and the National Nuclear Laboratory’s (NNL) technical experts.
This resulted in Rawwater Engineering securing Game Changers proof-of-concept project funding to assess the feasibility of deploying the M3 technology for sealing cracked walls underwater in nuclear decommissioning programmes.
During the proof-of-concept project, Rawwater Engineering made significant progress on technical development of the M3 system for the underwater crack sealing, and the system was showcased directly to Sellafield and NNL staff in well-received demonstrations.
Bob Eden, Managing Director of Rawwater Engineering, said: “It was encouraging to find that our Bismuth Plug technology was exactly the type of innovation that Sellafield was looking for through the Game Changers initiative.
“With our experience in the oil and gas industry, and deep understanding of bismuth alloy properties, we were able to give Sellafield confidence that the technology had been proven in another field with similarly high standards of health and safety and quality.
“Engaging with the Game Changers initiative has enabled our innovative technology to gain an accelerated level of interest across the Sellafield site and the funding awarded has given us confidence that there is a potential significant new market for our technology.”
As a result of the development work and engagement with Sellafield and NNL during the proof of concept project, the versatility of the molten metal alloy technology was highlighted, with a number of new avenues opening up for Rawwater Engineering to deliver a viable solution to specific industry challenges.
While the primary application showcased in the proof of concept project was for underwater deployment of the molten metal alloy, Rawwater Engineering also developed and tested their unique metal spraying system in air, resulting in a technology suitable for producing robust, uniform surface coatings with the potential to seal cracks or to provide full encapsulation of complex shapes.
The alloy can be deployed at low temperature, and is therefore easy and fast to deploy in a range of situations, such as an emergency repair kit for cracks or holes, or for encapsulation.
As a result of contacts made through the Game Changers Innovation Programme, Rawwater Engineering was also able to work with another SME, collaborating with Dr Ron Jones of Cryoroc, to very quickly produce a prototype encapsulated freeze-cast ceramic block, within 24 hours of discussing the possibility.
This example of rapid collaboration between two SMEs could potentially provide additional options for the encapsulation of Intermediate Level Waste in nuclear decommissioning, using Rawwater Engineering’s molten metal manipulation technology as part of the solution.
A number of other innovative applications for the M3 technology are currently being explored.
Rawwater Engineering has been approached by Sellafield in relation to the use of the M3 technology for underwater repairs to sluice gate seals.
Rawwater Engineering was able to respond quickly and propose a potential solution. Discussions are in progress on the use of Rawwater Engineering’s M3 as a secondary seal in conjunction with the field-proven EPDM rubber seals.
Rawwater are also exploring the opportunity of applying their M3 technology to both fill a crack, whilst at the same time act as a counter electrode for impressed current protection of rebar in reinforced concrete.