Motor specifications for nuclear engineering
04 September 2017
Maintenance and repair procedures in most industries require specific standards to be met when repairing or replacing equipment.
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When these tasks are being carried out in a nuclear power plant, the specifications can be quite unique and demand an altogether higher level of expertise.
Lammers Exico Sales Director, Lucie Hodkova, looks at considerations for the specification of electric motors for applications in nuclear power plants.
In 2016 the UK government approved the building of a new £18bn nuclear power station at Hinkley Point in Somerset, signalling a new era of power generation for the country. Nuclear is now expected to be the second biggest contributor to the grid after renewables by 2025. With coal powered stations expected to be phased out by the mid-2020s and reliance on gas fired power stations greatly diminished, there is much riding on the success of nuclear.
Several additional nuclear power plants are also in the planning stages, with the UK’s existing reactors getting towards the end of their operational lives and all but one scheduled to be retired by 2030. In the meantime there is an ongoing requirement to upgrade the likes of steam turbines, valves, coolant pipes and control systems in the existing reactors to ensure their continued safe operation. In an industry where safety is critical, correctly specified components are a key focus.
Component specification, of course, follows stringent regulations, regardless of whether they will be employed in nuclear or non-nuclear duties within the power plant. In both areas, electric motors play critical roles, including actuator and valve control in containment rooms, various pumping, ventilation, filtering and hoisting applications, low head safety injection pumping systems, emergency feed water system pumps, and containment heat removal system pumps.
So what sort of specification criteria should engineers consider when looking at electric motors, either as part of a new reactor design or as part of ongoing maintenance procedures and upgrade processes? Clearly motors should be designated as Nuclear Class, and rated as seismically safe, but what does this mean and how is it assured?
To provide the highest levels of specification of motors for the nuclear industry, Lammers Exico works with nuclear class motor specialist Obeki. Certified to UNE 73401:1995 GES/ UNES for Quality Assurance in Nuclear Facilities by Spain’s Asociacion Espanola de Normalizacion, the company’s motors are relied upon across the globe in a host of nuclear power industry applications, both for the replacement of existing motors and for new developments or new plants under construction. It has a better understanding than many of the key requirements for motor specification within the industry.
The first point to be considered is what safety class the motor needs to meet, according to whether the motor is within the conventional island or the nuclear island. Systems that are important to safety are classified in the UK as Class 1, Class 2, and Class 3. Within this classification, Class 1 systems are specific to safety, while Class 2 and Class 3 are designated as safety-related. Under-specifying could have significant safety implications, while over-specifying for a given application represents additional cost.
Lammers Exico supplies seismic class motors for all systems important to safety, as well as standard class motors for those systems either designated as not important to safety or non-classified. For motors used in safety classified areas, quality control is paramount, and suppliers should be able to demonstrate that specific key tests have been performed, not only to the finished motor but also to almost every component during the manufacturing process.
Seismic class motors should carry a range of approvals, including manufacture to client-approved procedures. Seismic testing should be fully detailed, with notes on how seismic resistance has been determined by analysis, by testing on a vibration table and by comparison with previously-qualified motors according to procedures accepted by the end user. For Class 1 motors, users should expect a detailed final report.
Suppliers should also have a good understanding of radiation and its impact on the materials of construction within electric motors. As a matter of course, they should be able to demonstrate full traceability of materials sources and specifications, with certification as required. Any special radiation requirements – such as resistance to radiation through the use of special insulation or copper rotors – should be noted by the supplier.
Further, suppliers should also be able to provide details of painting following client-approved procedures. This might include initial cleaning and sand-blasting of surfaces, specified numbers of layers of paint, with details on the paint material, the thickness of each layer and its drying time.
Taking all these considerations into account, users should have the confidence – backed up by full certification – that electric motors meet requirements for thermal ageing, mechanical ageing, irradiation ageing, electromagnetic compatibility and seismic/vibration conditions.
Working closely with Obeki as well as with nuclear industry customers, Lammers Exico is able to deliver the highest level of assurances that motors supplied for nuclear reactor applications will meet all safety and reliability requirements. The motors meet all of the upgrade requirements of systems integrators tasked with keeping the UK’s existing nuclear power plants safe and efficient right to the end of their operational lives, while meeting the highest specifications for new developments and new power plants under construction.
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