In a corner of northwest England’s Sellafield – one of the most complex and dense nuclear sites in the world – a team of engineers is proving just that. After years of collaboration, designs and painstaking rehearsals, a Bechtel-Cavendish Nuclear joint venture, under the aegis of Sellafield Ltd, has achieved a major milestone.
The Pile Fuel Cladding Silo (PFCS) is a 29m long, 10m wide, 18m high structure dating back to the early 1950s, which was built to store waste resulting from removing the metal cladding (so-called ‘de-canning’ operations’) from nuclear fuels used in the Windscale piles and later Magnox plants. The structure was modelled on a farm grain silo, with six-chambers, but it has far exceeded its expected lifecycle and must be emptied as part of Sellafield’s overall environmental cleanup plan.
Nearly 70 years after PFCS was built, Bechtel-Cavendish Nuclear Solutions (BCNS) is celebrating cutting the third of six holes to clean out the waste. Cutting each hole involved the removing a 4.5t concrete monolith and installing an airtight door that will be used to retrieve radioactive waste that has been sitting in the locked vault for over 65 years. The waste, once retrieved, will be repackaged for safe, secure, long-term disposal.
Project manager Jim Delaney said: “It’s a detailed and patiently deliberate process – but through significant pre-planning activities and a fit-for-purpose philosophy, a lot of great work has been invested to allow timely project delivery, with all working as one team, and with top marks for safety and quality.”
None of this happened by chance. Since 2011, BCNS has worked through a three-strand plan to design, construct and install all the retrieval equipment needed to safely remove waste from the silos. This included modelling and building six 12t steel silo doors to slide over the six silo holes to provide radiological shielding, and a retrievals access penetration rig with a 39t undercarriage and 36t monolith removal frame.
The team of engineers created a replica silo at the manufacturing base in Rosyth, Scotland, for several practice runs, which were carried out in full breathing air apparatus to protect the operators from argon gas, which is pumped into the silo to prevent a fire.
Early on, BCNS and Sellafield management recognised that an environment that encouraged ideas and challenges and allowing for flexibility at every stage was key to a successful outcome. The team continuously carries out joint design reviews to scrutinise every aspect of the design and identify ways to accelerate the work before construction starts.
The logistics on PFCS are tough, located as it is in a congested space bordered by other nuclear waste silos, active pipe bridges and immediately adjacent facilities containing highly active waste and residual fuel from the UK’s commercial and military nuclear programmes. With three separate companies, each bringing a range of skill sets, experiences and cultures, this effort involves many organisational meetings. BCNS is in continuous communication internally and with its supply chain companies as part of an integrated team. Together they collaborate with Sellafield Ltd, as the customer, and the Nuclear Decommissioning Authority. The Integrated Project Team is currently pursuing certification to the international Collaborative Working standard.
Collaborating with Sellafield, BCNS was encouraged to innovate, to resolve technical challenges and cost and schedule risks: it simplified the scope, reduced costs, offset delays and improved commercial terms.
For example, it modified the sequence and methods of door and equipment installations, eliminating a lifting platform and reducing regulatory constraints to save over £12 million and eight months of project time.
BCNS simplified the design for waste retrieval and handling equipment and operations, further shortening the schedule.
These cost and schedule efficiencies were largely the result of innovations in construction, design, manufacturing and equipment. Design simplification reduced the retrievals housing from 535m2 to 432m2 and correspondingly reduced the amount of machinery needed to maintain it. This measure alone reduced the cost of the housing and the construction schedule, and off-site equipment fabrication and testing led to further efficiencies. Savings totalled £40 million and 18 months.
Another design innovation replaced a centralised control scheme with independent controls for each plant system, allowing the use of commercial-off-the-shelf components and saving £2.5 million. Innovations, such as the use of mockups, 3D and virtual reality modelling, and mazel shielding, have achieved additional savings in money, time and risk.
This ‘lead and learn’ approach – set out by Sellafield in a formal strategy to share best practice and de-risk overall delivery – also resulted in a new, less complex design for the waste retrievals. It meant shifting emphasis to one silo at a time, rather than targeting all six with a brand new methodology and at high risk.
The BCNS construction team successfully completed over 150 lifting operations using 300t and 100t cranes. Of these, 40 were highly complex and involved items including the giant doors and 40t door installation frame. Although many activities involved working at height, and hands- on heavy mechanical installation, over 2.3 million person-hours were achieved without a lost time accident or recordable injury.
“The project harnesses the engineering expertise and ingenuity of two companies with global reach to provide Sellafield with the tools it needs to deliver hazard reduction on a truly epic scale,” said Paul Smith, managing director of UK Projects at Cavendish Nuclear.
“Both companies have drawn upon the depth and diversity of their talents to knit together a seamless project team, capable of integrating with the customer and supply chain to meet the most demanding specification.”
BCNS’s solutions right across the project had dramatic cost and schedule impacts. An early estimate of initial waste retrievals by 2023 was brought forward to 2020, and now there are hopes it could begin as early as 2019, with savings of more than £111 million. These solutions were rewarded with official recognition at the 2016 Sellafield Business Excellence Awards.
Steven Carroll, head of PFCS programme delivery, said: “The level of challenge involved with PFCS is unparalleled considering the age of the facility, the lack of historical information about the waste itself, the argon atmospherics, and its existence on one of the most congested footprints of any site, anywhere in the world. Despite this melting
pot of complexity, the teams have worked together to identify and implement opportunities to accelerate and simplify our approach to getting the waste out and into safer storage – yielding significant cost and schedule benefits. We’re increasingly confident that we may be able to begin retrievals ahead of the November 2020 schedule date.”
What next? Cutting the six holes is the final major enabling activity for the Early Retrievals Project, and provides essential access for the waste retrievals equipment. It is anticipated this will be completed by the end of this year. The project will continue to prepare for the installation of retrievals equipment and tooling for the start of operations to safely store the waste.