Nuclear Diving at Sellafield

Working safely in a nuclear pond

Diving in nuclear ponds, while novel at Sellafield, is a widely accepted and mature technique for conducting this type of work worldwide and is a recommended technique within the International Atomic Energy Authority (IAEA) guide to pond decommissioning. After a fact-finding mission to Sizewell was undertaken a trial of nuclear diving on the Sellafield Site has been conducted and has proven that the use of commercial divers in a nuclear pond is a viable option for decommissioning.

The trial was performed in a pond that had already undergone a significant amount of clean up works using ROV’s and other methods, and several hundred tonnes of waste material had already been successfully exported from the pond. The major challenge for achieving the best possible clean-up of the ponds is that there are many integral structures on the floor of ponds which cannot be easily accessed.

The photo above shows a typical uncleaned pond floor.

The image below shows the floor layout which has proved difficult to clean using conventional techniques.

The scope of the Nuclear Diving Project was to prove that commercial nuclear diving reduces time at the work face and gives an overall reduced dose uptake, as well as a cleaner state, to base future decisions on. Extensive optioneering was undertaken on possible methods to clean up the pond. Internal and external professionals with backgrounds in sludge and debris retrieval, various industries, and ponds decommissioning were involved in this exercise. This concluded that divers provided a potentially game-changing opportunity to expediate pond floor clean up. An ALARP (As Low As Reasonably Practicable) assessment confirmed that diving represents the most effective overall option to further remediate the bays. A detailed safety assessment has been completed to confirm this can be achieved safely. The project team have designed and installed new equipment to facilitate the divers, modified plant infrastructure, undertaken a HARR (Hazardous Activity Readiness Review) and worked with a plethora of stakeholders to get to where they are today.

The trial work involved removing the remaining residual sludge and debris from areas which have been difficult to reach using the many tools developed to clear the bays to date. This material is in troughs, around encast steelwork and at the pond edges which make it very difficult and time consuming to deploy remotely operated equipment. Diving is the deployment of divers has confirmed that divers offer much greater working efficiency compared to other available techniques, due to their:

• Versatility to perform multiple operations during a single dive.

• Ability to improvise, problem solve and apply their experience to deal with the different scenarios.

• Ability to operate in a low visibility environment (e.g. algal blooms).

• Greater dexterity when deploying equipment.

• Ability to offer a platform for deployment of a range of tooling rather than the design, development, manufacture and installation of numerous separate machines, most of which can only be operated in isolation.

In December 2022, the divers were successfully deployed following the facility being granted the licence instrument. The diving project has provided invaluable learning to shape the future remediation strategy of the site facilities and to ponds across the site. This pilot project has:

• Significantly accelerated the remediation schedule. The increased effectiveness can undoubtedly reduce the overall schedule for remediating the pond. Evidence from other nuclear dives in the UK suggests two years were saved from their baseline plans.

• it is clear that a different approach to traditional decommissioning is required to remove lower hazard inventory and commercial diving is a valid method of performing this work.

• Minimised the risk associated with pond side operations. While the risks associated with diving in a nuclear pond are obvious, the alternatives are far from risk free. The majority of operations carried out to date have been done by operators standing at the pond side manipulating pond tools on 5m long poles. These operations are time consuming and physically demanding and by their nature have to be carried out in higher dose areas. Even working with Remotely Operated Vehicles requires significant time to be spent local to the workface to allow deployment, commissioning, maintenance and removal which can take more time than the operation due to each job having unique requirements, requiring bespoke solutions.

The radiation dose uptake from the diver’s project is significantly less than estimated for continued use of existing techniques and this could be amplified across future remediation projects. There are also wider benefits, as divers could enable other programmes across UK nuclear sites to reduce their dose uptake impact, costs and schedule accordingly.

This pilot project has successfully demonstrated that we can deploy nuclear divers in a facility to rapidly accelerate decommissioning and remediation. This not only allows for tasks to be accomplished that couldn’t before but also changes the thinking for future projects and the wider site approach to decommissioning with this new capability. Putting a human at the workface, is an overall ALARP solution recommended within the International Atomic Energy Authority guide to pond decommissioning. It provides greater dexterity and, therefore, quicker operations allowing us to make decommissioned nuclear facilities safer sooner.