Determination of Trace Elements and Isotope Ratios in Borated Cooling Water of a Nuclear Power Plant Application Note · PlasmaQuant MS

Introduction

Nuclear power plants are an important and efficient source of electrical energy, supplying over 12% of the world’s electricity. Many modern plants use a pressurized water reactor (PWR) due to their improved safety and self-regulating capability. The reactor coolant plays a very important role in the process. In a PWR, the primary coolant (water) is pumped under high pressure to the reactor core where it is heated by the energy generated by the fission of atoms. The higher water pressure enables more heat to be carried from the reactor and the heated, radioactive water then flows to a steam generator where it transfers its thermal energy to a secondary system. Here, non-radioactive steam is generated which drives the turbines for the electric generator.

Like all thermal reactor designs, PWR require the fast fission neutrons to be slowed down in a process called ‘moderation’ in order to interact with the nuclear fuel and sustain the chain reaction.

In PWRs, the coolant water is also used as a moderator by letting the neutrons undergo multiple collisions with light hydrogen atoms in the water, losing speed in the process.

Boron is often added in the form of boric acid to the reactor coolant as a neutron absorber to control the nuclear reactivity in the primary reactor. The neutron absorption cross-section, reported in the unit ‘barns’ is a measure of how likely a neutron will react with the nucleus. 10B isotope is known for being a strong neutron absorber and has a much higher neutron absorption cross section than 11B.

The pH of the coolant is also crucial in maintaining the system as a pH lower than 6.9 at elevated temperatures of 300 °C can cause accelerated corrosion of the fuel rod cladding. As boric acid is weakly acidic, lithium hydroxide is regularly added to the coolant to achieve the desired pH.