How I stared into the heart of a nuclear reactor

  • 20 May 2011

In the wake of the Fukushima plant disaster in Japan, it's not surprising that nuclear reactors have been having a bit of a tough time, PR-wise.

We've been bombarded with scaremongered snippets about the 19-mile exclusion zone, Chernobyl parallels, food contamination and radiation suits.

Despite all of this, last week I donned the sort of overall one might wear for a school art class and peered down at the mesmerising underwater blue glow of a nuclear reactor (the glow is caused by the Cherenkov radiation, created when electrons emitted by the fission process move faster than the speed of light in water). The Geiger meter I was carrying to detect any radiation barely wavered.

The reactor is situated in a huge pressurised chamber (so that if there were to be a radiation leak, the radiation would be pulled inwards rather than pushed outwards) at the Institut Laue-Langevin (ILL), a centre of neutron science in Grenoble, France. It generates around 58 megawatts of power -- 25 times less than any commercial reactors. Despite this, our guide

Robert Cubitt

is skittish as I lean over to gaze into the pool, fearing that my glasses might fall into the water. I ask him what the consequence of this would be. His answer? "Big trouble."

The reactor's role is to produce free neutrons through nuclear fission. ILL's reactor -- celebrating its 40th anniversary this year -- is the most intense neutron source in the world. It performs the same process as used in nuclear power generation, but at a lower temperature. The neutrons are then cooled into useful wavelengths and directed to a whole host of instruments to be used like super X-rays to understand the world at the atomic level.

The reactor provides a beam of neutrons over a wide energy range, from hot (high-energy or fast), thermal (medium-energy), cold (low-energy or slow) and ultra-cold (very slow). The lower energy neutrons are used for precise experiments on gravity and to understand the properties of neutrons themselves.

Neutrons are particularly useful because they can penetrate deep into matter, while remaining non-destructive. They have a magnetic moment, called a spin, that can interact with the electron spins in magnetic materials. Polarised neutron beams provide a unique tool for characterising exotic materials with complicated magnetic structures. They are also very sensitive to hydrogen atoms (which are almost invisible to X-rays) and as such can probe the locations of water molecules in a sample.

These various beams have a wide range of applications in areas including magnetism, superconductivity, materials engineering and

biological substances. Researchers from all over Europe convene at ILL to use the facility and grab themselves some "beam time", as it's described.

The reason why it was perfectly safe to lean over the reactor is because water makes an excellent radiation shield -- specifically the heavy water that the core is contained in, which prevents neutron and gamma radiation from escaping.

It's encouraging to know that the alarms have not been triggered since the Fukushima radiation drifted over from Japan. Unless, of course, the Geiger meters were rigged... So far I haven't developed any super powers, but watch this space.