UK supplier Nuclear Engineering Services has finished building two mobile shielded cells (caves) to retrieve stored Sellafield fuel debris after a marathon 18-year build.
The intermediate-level waste comprising Magnox swarf (external cooling fins) and other materials is stored under water in 22 vertical silos. Over time, Magnox waste stored in water tends to corrode into sludge.
The caves, operating on a rail system, weigh about 400t each and contain more than 13,500 parts. They remove waste with a hydraulic grab and tooling system through a tunnel mounted on top of the waste silos.
The first of two contracts for the Silo Emptying Plant (SEP) project was originally won by Rolls Royce NES in 1996, according to a 2004 article in NEI magazine; NES separated from Rolls Royce in 2003.
The complex project has experienced many delays. Testing of the first unit, SEP 2, in the 2000s lead to design changes for SEP 1, according to the article.
Design and build of SEP 2 was completed in November 2012 and it is now in commissioning for operation in 2015. SEP 1 was finished in February 2014, and work will now move to preparation for test and commissioning, maintenance demonstrations and integration of off-board equipment.
"The teams from Sellafield Ltd and NES have worked together to address the challenges of accelerated and compressed design, procurement and assembly phases, with frequent and consistent communication lines for project reporting," NES said.
NES said it had to be flexible in its manufacturing processes, it said: "NES adopted a flexible working regime that included working around the clock, where necessary, to ensure that quality and programme standards were maintained at all times. The strategy driving this was to ensure areas of the build were not left for long periods of time awaiting issue resolution or clarifications, mitigating potential schedule delay."
Compared to construction of SEP 2, NES made process improvements:
- Parallel purchasing of critical and long lead items in the supply chain together with early engagement of the supply chain during design reviews, particularly on large subcontract orders.
- NES introduced an improved on-site document control system (drawings, installation and termination sheets) to ensure control of drawing issue on both the cabling and pipe work systems and employed a more rigorous tracking of outstanding document operations.
- Patrol inspectors were used during the build phase leading to improved quality assurance.
- Waste caused during terminations was captured by a bagging system to alleviate foreign material being introduced.
- Increased visual management such as outstanding items, health and safety awareness and quality management contributed to improve quality issues.
Photo: Silo Emptying Plants 1 and 2 pictured in January 2014 (Source: NES)