Spotlight on Springfields9 July 2015
Springfields in the UK has been producing nuclear fuel for nearly 70 years. Bob McKenzie and Brian Armer give an overview of recent upgrades at the site.
The Springfields nuclear fuel manufacturing site in the UK is now operated by Westinghouse Electric Company, following an agreement with the UK's Nuclear Decommissioning Authority in 2010 for the company to operate and develop the site under a 150-year lease.
Today the site's main products are advanced gas-cooled reactor (AGR) fuel for EDF Energy's UK reactors; light water reactor (LWR) fuel for export; intermediate products such as uranium dioxide, pellets and granules; and uranium recovery services.
In the 1990s, a new plant, the Oxide Fuels Complex (OFC), consolidated fuel manufacturing operations for UO2 powder, pellets and finished fuel. The plant was commissioned in 1996 and remains one of the world's most modern commercial nuclear fuel facilities. It uses automation and control at all stages of manufacture, which delivers significant production economies. For example, the uranium pellet soft-handling process, developed in the 1980s, uses cushion transfer to move pellets around the production line and avoid pellet damage.
The highly automated plant minimises operator involvement, which results in low operator doses, so the plant is suitable for off-specification products and manufacture of fuel from reprocessed uranium.
The plant feed is enriched uranium hexafluoride (UF6) which is converted into ceramic grade UO2 powder in a kiln in a single stage process developed at Springfields in the 1960s. The UO2 powder is processed into pellets and loaded into stainless steel fuel tubes (for AGR fuel) or zirconium alloy tubes (for LWR fuel).
Since its startup, there have been no manufacturing defects in fuel rods from the Oxide Fuels Complex plant that have caused leaks.
There have been a number of developments in fuel manufacture. After eight years of collaborative development work with EDF Energy, Springfields began delivering an improved robust AGR fuel design in 2010, to improve in-reactor safety and reliability, and support reactor life extensions and higher burnup.
The most significant improvement from a fuel manufacturing perspective was the development of a machined support brace made from a single piece of steel using laser cutting and milling technologies. Previously, braces were fabricated from strips formed into individual cells, one for each fuel pin, joined together with more than 600 spot welds. Machining provides benefits of greater dimensional accuracy and the machined brace also contains less steel, which reduces in-reactor neutron absorption.
LWR fuel production
Westinghouse's substantial investment in the LWR fuel production facilities in the Oxide Fuels Complex ensured the re-qualification of the facility. PWR fuel deliveries from Springfields halted in 1999 after supply of the initial core and three reloads to the UK's only PWR, Sizewell B. After a hiatus of 10 years, in one year 28 refurbishment projects were completed to bring the plant up to the latest safety and operational standards, as well as incorporating best practice.
Springfields used proven designs from Westinghouse's production facilities in the USA and Sweden. For example, the soft-handling process has been enhanced using laser technology to perform a 100 percent measurement check and automatic sensing of pellet diameter.
Throughout the upgrade, emphasis was placed on improving accuracy and repeatability of tasks by means of sturdy mechanical design and specifically designed computer-controlled systems. This was used to good effect on the bulge rig, by positioning the tool cluster at each grid position using a servomotor and verifying the precise location using linear encoder technology. Outward expansion of the bulge tools is controlled by motorised actuators, which are controlled via touchscreen panels that can transfer data to the plant management information system. The equipment can automatically create the sample pieces required for product verification. A light curtain extends the entire length of the rig, and will shut down the process if encroachment occurs.
Similar HMI and light curtain technology has been used on the new rod puller, but the most significant enhancement to improve product quality is the use of a servomotor-driven lead screw instead of a chain drive to pull the rods into the skeleton. This minimises distortion of the grids and maintains individual cell sizes, which reduces the risk of envelope alignment and channel spacing check deviations. The accuracy of these checks, which are done after the top and bottom nozzles have been attached, has also been improved by compensating for thermal distortion of the measurement rig due to ambient temperature variations. This is achieved through laser mapping of the support column.
In addition to advanced technologies, production practices also evolved, for example excluding foreign materials - crucial in maintaining fuel reliability.
The upgraded facility is now a qualified supplier of Westinghouse 12ft (17x17) PWR fuel, and can produce finished PWR and AGR fuel. Qualification to produce Westinghouse 14ft (extra-long) 17x17 PWR fuel is expected by 2016.
The first PWR fuel off the refurbished production line was delivered to EDF's reactors at Gravelines in France during March 2013 and so far it has performed flawlessly.
Looking ahead, the Springfields Oxide Fuels Complex is expected to provide fuel for three AP1000® reactors that the NuGen consortium (a joint venture between Toshiba and GDF Suez) aims to build in the UK and for AP1000 reactors built elsewhere in Europe.
About the authors
Bob McKenzie, Chief Technical Officer at Westinghouse Springfields, and Brian Armer, Oxide Programme Manager, Westinghouse Springfields