Seismic behaviour of a degraded advanced gas cooled reactor core model

Abstract

Advanced Gas Cooled Reactors provide the backbone of stable low carbon nuclear energy within the United Kingdom. However, accumulation of radiation damage over time leads to a degradation of their graphite cores and a phenomenon known as keyway root cracking. In the event of an earthquake these reactors must be able to shut down safely through the insertion of
control rods down core channels. The seismic safety case for these reactors is currently provided through numerical modelling using the GCORE finite element software that uses the explicit dynamic solver LS-DYNA (later ABAQUS). In order to validate the results from GCORE an experimental model was produced at the University of Bristol. This dissertation analyses the key results from the experimental configurations to probe the reactor behaviour under an
earthquake scenario. Techniques are also developed to acquire detailed responses of the core, including the key behaviour, from videos taken during the tests. These methodologies are used to investigate the behaviour of a bearing key in a cracked core channel. A numerical model of the experiment, using the discrete element software 3DEC, is used to probe the physics of the
core such as forces and allows rapid changes of configurations that are not practical to physically test. Advanced visualisation of the large datasets produced by the experiment is explored using virtual reality modelling language. The control column displacements are then studied for the intact core and for 9 other configurations with damage going up to levels where 50% of the
fuel bricks are cracked in layers 4-7 for an 8 layer model. From this analysis the main drivers for worsening core seismic performance are seen to be increased global cracking percentage, increased seismic amplitude and broken layer spanning keys. These results may be used to direct the configurations that GCORE explores for a conservative safety case.

Date of Award	21 Jun 2022
Original language	English
Awarding Institution	University of Bristol
Sponsors	Edf Energy Nuclear Generation Limited
Supervisor	Adam J Crewe (Supervisor) & Dawei Han (Supervisor)