|Project:||Heysham 2, Reactor Sea Water Cooling Pipeline System|
As part of the replacement of Reactor Sea Water (RSW) cooling pipeline system for use at EDF Heysham 2 Nuclear Power Station, Boulting and its partners developed a metal-free Polyethylene (PE) piping solution. This provided wide-ranging safety, cost, reliability and longevity benefits.
Growing increasingly frustrated by the frequency with which traditional Vylastic coated carbon steel RSW cooling water pipework required replacement, Heysham 2’s System Health Engineer together with Boulting and its partners, embarked on an investigation into establishing a more effective means of cooling water transportation.
Following a highly satisfactory small-scale test, involving the replacement of some pipework at Heysham 2, the client was sufficiently confident to proceed with the use of polyethylene. Boulting was awarded the contract to replace the coated steel pipework.
Working to a comprehensive design brief, Boulting and its partners was tasked with ensuring that:
All wetted parts manufactured from polyethylene
Neoprene used as an effective gasket material
Valves fitted should be easily removed to assist maintenance procedures
Couplings should be flexible to assist maintenance and serviceability
With safety a paramount, the Heysham 2 team also stipulated the use of PE100 SDR 11 piping in order to achieve a pressure rating of 16 barg.
• Geometrical considerations
• Thermal characteristics of PE
• Necessary seismic likelihoods
• hydraulic constraints to ensure the resultant system would not be hydraulically compromised
At this stage the existing pipework was mimicked and the mechanical properties of the PE material was analysed. Compensation for the difference in characteristics between the existing metal piping and the proposed PE was achieved by enhancing the frequency of pipe support and correctly evaluating such issues as allowable nozzle loads and imposed pipework stresses.
With all design criteria established, elaborate modelling tools were used to build a ‘walkthrough’ 3-D model of the installation. At the same time, stress models were produced and the whole design was stress analysed using the Caesar II stress analysis package.
A primary Nuclear Safety issue is the loss of cooling and a subsequent reactor trip. Boulting maintained a total commitment to safety by investigating dynamic effects (such as the effect of seismic activity) and operational scenarios. Various potential stresses, displacements and forces to pipeline supports and other tie-ins were fully considered.
During the stress analysis stages a source of neoprene bellows was identified that when strategically placed in the design, facilitated the easy removal of existing inline equipment.
The use of the bellows, in some instances, was unrestrained to aid thermal growth. This resulted in the development of considerable static thrusts which, when combined with innovative anchor designs, not only contained the pipeline pressure, but managed the thermal growth.
As part of their design brief all the supports were designed for the PE piping in order to comply with the laid down stress/force parameters and to accommodate the necessary supporting requirements of the material.
In accordance with recognised codes and standards, detailed construction drawings were then produced for approval by EDF, after which procurement, fabrication and installation took place with all work successfully completed within the statutory outage period, as stipulated by EDF.
The installed system has proved itself to be wholly reliable and robust
EDF believes it to be the first of its kind in the world. “Polyethylene offers strength, flexibility and erosion resistance. It won’t corrode and even the sea life which previously attached itself to the old pipeline doesn’t like it. There’s also the added advantage of consistently better sea water flow.”
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