Powerful actions this summer at Ringhals 4

This year’s outage at Ringhals 4  is a long one – about 100 days – but it does include an unusually large number of major activities and replacements of components. Never before has so much been planned to take place during a single shutdown. The aim is even higher safety and future electricity production.

How hard can it be to get three steam generators similar in height to a seven-storey house through an opening in the wall of the reactor containment, put three new ones in place and get the reactor up and running at full power – and all this in a three months´ outage?

Sven-Erik Rosén, who is project manager for this summer’s steam generator replacement at Ringhals 4, knows how hard it is because he has done it before. At Ringhals 2 in 1989, Sven-Erik Rosén was in charge of the tenth replacement of steam generators in the world, which was done in record time. And in 1995, it was time for Ringhals 3.

”It is not easier this time”, he admits. ”During the planned outage, we are not only replacing the three steam generators but also the pressurizer, a procedure which has never previously been carried out in a European nuclear power plant.

Almost as new
Ringhals 4 will be upgraded with new steam generators and new pressurizer, new high pressure turbines, low pressure preheaters and main steam reheaters as well as the upgrading of the turbine with new instrumentation and control equipment.

”When the work is completed, Ringhals 4 will be almost as good as new. We are making significant investments in safety, availability and future production capability,” says Christian Lundqvist, customer representative of Ringhals 4’s renewal program.”

In total the outage will involve some 2,150 people, around 1,700 of whom are contracted from 80 different companies.

Modern steam generators
The steam generators have been the source of some concern down through the years at Ringhals, while Ringhals 4 has managed well by avoiding the same extensive problems with corrosion and vibrations which have affected Ringhals 2 and Ringhals 3. Thanks to good steam generator chemistry, Ringhals 4 has been able to operate its original steam generators for 28 years.

The new steam generators are of the same type as those installed in new nuclear power plants, for instance in Olkiluoto 3. They are of an economizer model with axial preheating, which offers higher steam pressure and thereby better turbine efficiency. The replacement facilitates an increase in Ringhals 4’s thermal output from 2,783 MW to 3,300 MW, that is 118.6 percent.

The power uprate will however not be implemented at the time of the replacement. As long as Ringhals is obliged to comply with specific surveillance conditions drawn up by the Swedish Radiation Safety Authority (SSM), the application from Ringhals 4 regarding the increase of thermal output will not be processed. All technological conditions for the power uprate at Ringhals 4 are being prepared, but implementation will be put on hold.

Lifting in the components
In order to get the old components out and new ones in, a temporary transport opening about 6.2 x 7.6 metres will be made in the containment wall. The opening is made by the contractor, NCC, using so-called seam drilling. More than 100 drill cores are removed from each side of the tightness barrier (steel plate) inside the about 1.1 metre thick wall which is reinforced and fitted with horizontal and vertical pre-stressed tendons.

A gigantic crane will be used for the outdoor lifting. The crane is about 50 metres tall and can provide a maximum lifting capacity of 660 tonnes. The space to manoeuvre in the reactor containment is limited for the 21 metre long and 334 tonne heavy steam generators, and displacement has to take place with great precision using two temporary lifting devices installed on top of the existing polar crane beams.

“It is not primarily the technology that has become more complex”, Sven-Erik Rosén says.

The procedure for the steam generator replacement is mainly the same as before, and there is excellent and proven experience to fall back on. But it is fifteen years since the last replacement, and since then many new demands have been put in place and certain expertise and experience is hard to find. The way to approach this is with good planning and a plan of action to tackle the unexpected that may occur during the duration of the project.

New control systems
Big things are also happening on the turbine side. At the outage, we are replacing the high pressure turbines and main steam reheaters as well as modifying the feedwater pumps and installing two new low pressure preheaters. The contractor is Alstom, which is also responsible for replacement of the turbines' protection and control system including new screen-based supervision in the control room.

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Ringhals outages 2011