Effects of process-generated hydrogen on RPV walls

Chapter 7 Hydrogen pressure in PWR

7.1 Introduction The increased hydrogen concentration in the RPV wall will have its influence on the mechanical properties of the material. Due to phenomena like hydrogen embrittlement and others, the material will have a decreased toughness. Apart from the effect on the mechanical properties, this investigation focuses on the possibility for the hydrogen flakes to grow due to in-service generated hydrogen. When the internal pressure in the hydrogen flakes increases, local stresses at the crack tip might overcome the fracture toughness of the material, resulting in crack growth. The internal hydrogen pressure in the material is calculated using Sieverts’ law. This is done for normal operating conditions and accidental conditions, like a pressurized thermal shock. 7.2 Pressure during normal operating conditions Two normal operating conditions can be differentiated. The first is the hot in-service condition. This is the normal condition during power production. The second normal operating condition is a cold shutdown. This occurs at the end of a cycle when the fuel has to be replaced. The reactor is slowly cooled down and the internal pressure decreased. 7.2.1 Hot in-service condition The first of two normal operating conditions is the hot in-service condition. The reactor is operating at full power and the typical operating conditions considered before are valid. The temperature of the primary water is 300 ◦ C and the pressure in the primary system is 150 bar. The O 2 and H 2 O 2 concentration in the primary water are close to 0.01 ppm. Depending on the moment in the fuel cycle, the boron concentration will be between 2400 and 0 ppm, while the lithium concentration is between 5 and 0.5 ppm. These operating conditions have been considered before. The corresponding maximum atomic H concentration in the RPV wall ferritic steel due corrosion varies between 0.010 and 0.271 ppm, depending on the absorption 77