ELGA Process Water equipment helps to keep a nuclear power station safe

A nuclear power station is, perhaps, not the first place most scientists would expect to find ultrapure water, but water that feeds the high pressure steam generators is of the highest purity, with a maximum dissolved solids concentration of 0.5µg/l. As steam leaves under pressure to drive the turbines the water remaining in the steam generator becomes more concentrated in contaminants, and the chemistry has to be closely controlled to prevent scale and corrosion. After passing through the turbines, the steam is condensed and may pick up contamination from corrosion or leakage in the condenser, so the condensed water has to be re-purified by a condensate polishing plant before it is returned to the steam generator.

Maintaining the feed water quality to the steam generators is of paramount importance since they have to last the life of the station. This means a lot of analytical work for Power Station Chemists like Jon Clack, who is responsible for the analytical laboratory at British Energy’s Hartlepool Nuclear Power Station. “We use a Dionex Ion Chromatograph to analyse for trace contaminants at µg/l and even ng/l levels,” says Jon, “When you are working at this level you have make up standards for calibration using water which is even purer than that in the samples you are analysing, so we use an ELGA LabWater PURELAB Ultra Ionic.”

The Hartlepool lab’s Dionex calibration rig is the heart of the analytical equipment. Feed water from the station’s condensate polishing plant is fed into a PURELAB Ultra Ionic laboratory water purifier which polishes it, using a combination of ion exchange, UV photo-oxidation and microfiltration, to ultrapure water standards: 18.2MΩ.cm resistivity, <5µg/l TOC and <1cfu/ml bacteria count. “This quality is absolutely critical because we’re working to an estimated limit of detection for the critical chloride and sulphate anions of 0.02µg/l,” says Jon, “We inject a known concentration of reagent into the flowing water so that we get in-line dilution to whatever standard calibration strength we need – it’s much more accurate than batch mixing in a flask and much more convenient because the Dionex has to run continuously,” he says. The unit has a DV35 Docking Vessel which holds 35 litres of ultrapure water and it is continuously recirculated through the purification cartridges, out to the injection point and then to the Dionex calibration pot. Unused water from the calibration pot is returned to the Ultra Ionic’s Docking Vessel as the flow diagram shows.

It was the Ultra Ionic’s water quality and recirculation capability, as well as a compact design that minimises bench space that convinced Jon that the PURELAB system was the best option for his application. In fact he was so pleased with the unit that he bought a second Ultra Ionic for general laboratory use. That and the fact that ELGA Process Water provide a 24/7 helpline to assist with troubleshooting and the most comprehensive service support network in the UK.