Effects of process-generated hydrogen on RPV walls

Master of Science in Nuclear Engineering

Thesis Summary Page

Name of the student:

Kristof Dockx

Title:

Potential effects of process-generated hydrogen on RPV walls during thermal gradients.

Abstract:

The reactor pressure vessel (RPV) is an important component in the safety system of a pressurized water reactor. In 2012, several flaws have been detected in the RPVs of Doel 3 and Tihange 2 in Belgium. These flaws were identified as hydrogen flakes and are concentrated in the upper and lower core shells of the RPV. As these flaws originate from the presence of hydrogen, this work focusses on the evolution of hydrogen gas and atoms in the RPV both during normal operation as for accidental conditions. Three different sources of hydrogen are identified, i.e. hydrogen dissolved in the primary water, corrosion generated hydrogen and radiolysis of the primary water. These hydrogen sources are quantified using literature and a chemical modelling code. After quantification, one can calculate the corresponding hydrogen pressure in the RPV wall for different operating conditions. During hot in-service conditions, according to the model, the radiolysis generated hydrogen corresponds to a mechanical hydrogen pressure of 1.5 10 5 atm, while the effect of corrosion might be limited to 3.62 Pa. However, d uring a cold shutdown, the mechanical hydrogen pressure increases up to 1.7 10 5 atm and between 166 - 1.3 10 5 Pa for radiolysis and corrosion, respectively. Finally a pressurized thermal shock is considered as an accidental operating condition. During a PTS, the hydrogen pressure is found to be 1.6 10 5 atm for radiolysis and up to 4.7 10 4 Pa due to corrosion. It has been found that these mechanical pressures are in the same order of magnitude as the required pressure for cracks to grow in a steel material. Therefore, these simulations and models can not assure the stability of the hydrogen flakes in the RPV.

Promotor:

Prof. dr. ir. Walter Bogaerts

Approval for submission by promotor:

Assessors:

Prof. dr. ir. Jacqueline Lecomte-Beckers Prof. dr. Digby D. Macdonald Prof. dr. ir. Pierre Van Iseghem

Academic Year 2016-2017

Belgian Nuclear higher Education Network, c/o SCK  CEN, Boeretang 200, BE-2400 Mol, Belgium

i