Water Chemistry in Pressurized Water Reactors – A Gösgen-Specific Overview

Abstract

The three main water circuits of the Gösgen pressurized water reactor and their chemistries are described. In the primary water circuit the cooling water and its contents undergo chemical as well as radiochemical reactions. Chemical agents – such as boric acid – are used for long-term reactivity control. The boron concentration therefore is dictated by reactor physics and may not be optimal from a chemical viewpoint. Under the given circumstances the chemistry of the primary water circuit cannot be adjusted to a sole optimum covering all the tasks. Nevertheless it is possible to operate the power plant using a chemical regime that avoids excessive corrosion within the expected plant live time of 60 years. The water-steam cycle with its two phases must be conditioned chemically in a way to protect the water and steam side components from corrosion. This is done by adding hydrazine to remove oxygen and to form ammonia, which is the main contributor to water alkalinisation. The cooling water system is open to the atmosphere and supplied by river water with continually changing contents. To avoid deposits on the system surfaces an upstream water treatment plant is used to remove suspended matter and to precipitate calcium and magnesium. Thousands of tons of chemicals are needed to treat the required 20 billions of litres of water each year. Radioactive waste treatment plays an important role in the nuclear industry. Operational waste is divided into three waste streams. Only one of these waste streams (waste water) is really influenced by water chemistry.