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Ågesta, hoses and sieves

I was recently at Ågesta which was the first commercial nuclear power plant in Sweden, it was a small reactor (10 MWe) which was on the edge of Stockholm. It also was used to provide heat to the district heating system.

The plant was a bit like a CANDU, it ran on natural uranium and used heavy water as the moderator and heat transfer fluid. When I visited Ågesta I was taken into the controlled area and shown around part of the reactor hall.

The reactor is inside a steel tank which in turn is inside a concrete shield, from the concrete shield pipes bring the heated pressurized heavy water to the steam generators. Two of the steam generators have been taken away. Between the steam generator and a spiral staircase was a chain link fence. This was using extra large chains which are about double the size of a normal chain link fence hole.

The fence intrigued me, I thought for a moment it was to try to keep people from wandering into what can be a high radiation area. I know that steam turbines of BWRs have a lot of nitrogen-16 in them during normal operation. This is caused by a n,p reaction of oxygen-16 inside the core. The nitrogen-16 is a very short-lived and high energy gamma emitter. It decays by the emission of an electron (beta decay) back to oxygen-16.

But then one of my fellow guests pointed out why, he commented that the fence is a sieve which is designed to break up a water jet. I then choose to try and experiment at home. I went to my sink and turned on a tap. With a digital camera I took a flash photograph so that you can see a jet of water from a tap.

Kitchen tap photographed using a flash

I then grabbed by sieve and placed this under the tap before taking another photo.

The same tap now with a sieve added under the outlet

I am sure that you can now see that the jet of water has been broken up. Further experiments may be done later with sieves and water jets to show you this effect in greater clarity.


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