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EDF Energy Fuel Building – 150t Nuclear Crane Upgrade

When nuclear cranes and handling systems are designed, they often have an expected working life of 20, 30, 40 years, sometimes more. During that time, operational requirements change, and the all-important safety landscape shifts, often making older equipment redundant. However, it doesn’t always have to be the case that older equipment must be decommissioned and replaced. Expert analysis and assessment of mechanical handling equipment that is reaching the end of its design life can pave the way for an EC&I-led solution, where control, safety and motive systems can be comprehensively overhauled and upgraded.

The Challenge

The reactor at EDF Energy’s Sizewell B plant is more than capable of generating electricity beyond its original design life. However, its existing fuel storage pond was approaching full capacity and an alternative means of storing spent fuel was therefore required.

EDF’s Dry Fuel Store project would achieve this – however, the safe lifting, transportation and final positioning of the new, specialised dry fuel casks was a complete change of use for the original 28-year-old, 152-tonne fuel building crane.

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The Solution

SCX was commissioned to perform a complete overhaul and upgrade of the original crane’s control and protection systems. This required an extensive design, testing, installation and commissioning programme, for one of the most complex contracts that SCX has ever undertaken.

The Safety Case for handling the fuel casks introduced a number of new Safety Functional Requirements (SFRs) into the crane’s new specification. These were met by a three-tiered Nuclear Protection System, where the crane’s new control system, plus two independent and diverse layers of hard-wired protection, all contributed to achieving the specified nuclear safety targets.

Technical Details

A complex EC&I challenge
  • The fuel crane overhaul and upgrade required an in-depth analysis of all electrical and mechanical systems
  • Safety-critical elements of the new EC&I system were recreated at SCX’s Barrow Road facility, in order to simulate crane operations before installation on-site at Sizewell B
  • This was central to de-risking the retrofitted EC&I solution and included: modes of operation; tiered safety systems; operator interfaces; key locks; crane displays; and sensor inputs
Diverse nuclear protection
  • Achieving the specified SFR targets for the dual-layered hard-wired protection systems required very careful selection of crane equipment
  • Diverse sensor technologies and manufacturers were selected to remove potential common mode failures
  • Non-intelligent type B sensors are used across all NPS systems to ensure failure modes are well understood, avoiding the possibility of dangerous undetected faults compromising the integrity of individual SFR circuits
Handling things together
  • The main 152-tonne overhead travelling crane runs on a double-girder bridge, with the 5-tonne auxiliary hoist running on a C-shaped monorail attached to one of the main girders
  • The main hoist has a twin rope with 16 falls, the auxiliary hoist has a single rope with 4 falls
  • The height of lift for the main hoist is 25m, and 22m for the auxiliary, with hoisting speeds of 1.2m/min and 5.8m/min respectively
Measured moves
  • A SCADA-based interface provides real-time crane status information, fed directly from sensors around the crane and its operating zones
  • Alarm logging, sensor trending and data logging provide a full audit trail of every operator action and crane event, enabling detailed scrutiny of individual operations and fault investigations
  • Movement interlocks ensure only one axis can be operated at any one time
Testing is key
  • A fundamental part of achieving the target PFDs is the  requirement to periodically test each independent nuclear protection system circuit every 12 months
  • This is achieved by having separate NPS1 & NPS2 testing stations, using different manufacturers of safety key equipment for the testing and resetting of each NPS circuit
  • All safety keys and test/reset circuits have the same high level of reliability as the primary NPS trip circuits
Operational integrity
  • Primary operation is via a high-integrity customised Cattron wireless pendant, designed to comply with EDF’s human factors requirements
  • The pendant maximises operator functionality, critical information visibility and operational safety
  • Backup crane operation is via a suite of control desks comprising secondary controls, a full SCADA-based graphical interface and two diverse sets of safety key systems for testing and resetting the tiered Nuclear Protection Systems
Functional safety by design
  • An overall ‘probability of failure on demand’ (PFD) of 1×10-4 for each individual SFR was achieved
  • The SFRs are hoist height, travel corridor collisions, overload, main and auxiliary clash protection and travel overspeeds
  • A diverse, hard-wired, dual-layered Nuclear Protection System (NPS1 & NPS2) was designed for each SFR, which – together with the primary PLC-based crane control system, operating independently of the hard-wired SFRs – delivers the specified target PFDs
  • SCX delivers world-class, safety-critical EC&I services with a BS EN ISO 12100 compliant Design Risk Assessment driving the design process
  • Comprehensive documentation with designs compliant and validated against standards including Machinery Safety EN ISO 13849 and Functional Safety Standards IEC 61508
  • SCX uses the ‘V Model’ full life cycle approach to ensure that testing, implementation and validation phases are in line with approved designs
Maximum visibility
  • A large high-visibility display is fitted to the underside of the crane to ensure all critical operating parameters can be seen clearly during flask movements
  • These are: long and cross travel speeds and positions; active hoist (main or auxiliary) load and height; and main hoist rotational position
  • Active Hoist and travel axis selection is done using either the Cattron controller or from the Operator Control Desk

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