Nuclear Research: Water Radiolysis and Corrosion Science

Reactors 25 August 2017

The most common type of nuclear reactor worldwide is the pressurised water reactor (PWR).[1]  This design uses two discrete water coolant systems, termed the primary and secondary coolant loop. The primary coolant passes through the reactor core where nuclear fission takes place, ultimately transferring heat to the secondary coolant loop for thermal energy conversion to generate electricity.

Conditions in the primary coolant are extremely harsh; the temperature is around 300 °C and the radiation produced from nuclear fission is intense. A host of chemical reactions can occur in water when it is exposed to radiation, making what at first seems like a simple system into something quite complex and corrosive. The general term for all interactions between water and radiation is ‘water radiolysis’.

The hostile conditions of a nuclear reactor core make it difficult to monitor changes in the chemistry of the primary coolant. A key objective in the field of radiation chemistry is to develop a complete model of water radiolysis at high temperatures. This model can be used to accurately predict the primary water chemistry in a given nuclear reactor, which will ultimately lead to better control of corrosion in the reactor core, and even the extension of reactor lifetimes. However, the water radiolysis model currently has some gaps; this is where my research comes in.

The general approach to completing the model is to study the changes in water chemistry caused by each type of radiation separately, as the effects can vary significantly depending on the type of radiation. As things stand, there is a limited understanding of the way in which neutron radiation affects water chemistry. The main reason for this is that neutron radiation of high energy and intensity is extremely difficult to produce in a laboratory setting. In my research, a proton beam is used as an alternative, as protons and neutrons are expected to have a similar effect on water, yet protons are much easier to produce in the lab. This data collection will improve the reliability of the water radiolysis model by providing a comparative resource for performance analysis.

My research can be put under the general heading of ‘corrosion science’ which is a big topic in nuclear engineering at the moment (and rightly so). Poor control of primary coolant chemistry could potentially lead to the catastrophic failure of a nuclear reactor. Indeed, such a case was only narrowly avoided at the Davis-Besse nuclear power plant in Ohio, USA in 2002. Despite the PWR design being extremely popular worldwide, the UK only has one PWR which is situated at Sizewell on the east coast of England.  However, the entire fleet of the UK’s new-build nuclear reactors will be advanced variants of the PWR design, and so all of them will be water cooled. The field of corrosion science research now stands the nuclear industry in good stead for the next generation of power plants when they roll out in 2025.