The Nuclear Research and Consultancy Group (NRG) has announced the successful completion of a program for EDF Energy to study the effects of irradiation creep on graphite. Over a period of four years, four consecutive irradiation stages were performed on loaded graphite specimens in the High Flux Reactor in Petten, the Netherlands.
The ACCENT program was established in 2012 to generate data on graphite irradiation creep - a mechanism by which graphite changes in dimensions and properties when it is irradiated and subjected to a load at high temperature.
EDF Energy launched a new graphite irradiation research program in support of ageing management of Advanced Gas-Cooled Reactors (AGRs) in the UK, in February last year, following its announcement of new scheduled closure dates for four of its UK AGR nuclear power plants.
AGR reactors feature a graphite moderator and are cooled using carbon dioxide. The graphite blocks cannot be replaced or repaired during the operating life of the reactors. However, radiation damage changes the shape and size of the crystallites that comprise graphite, a process known as dimensional change, which in turn degrades the mechanical properties of the graphite. For continued operation, it is therefore necessary to demonstrate that the graphite can still perform its intended role irrespective of the degradation.
NRG said yesterday that, before and after each irradiation stage, all graphite specimens are characterised by their physical and structural properties in NRG's Hot Cell Laboratories. The data that has been generated shows how graphite properties change from the earliest onset of irradiation to high doses at end-of-life conditions for AGRs.
The graphite creep program called ACCENT is one of the activities that NRG performs in support of the operation and extension of the operating periods of AGRs in the UK.
"The effort of NRG's staff in collaboration with EDF Energy and other suppliers has enabled the program to be completed to the highest standards on quality, time and budget," NRG said.
"Knowledge of this phenomenon is essential to determine the time to which graphite moderated reactors can be operated safely and economically," it added.
It added that the irradiation rig designed to contain the specimens allows "excellent control" of both temperature and load on the specimens.
NRG will this year continue an irradiation program for EDF Energy that will study the effect of graphite property changes with irradiation and radiolytic oxidation. Alongside the work for AGR reactors, more irradiations will be performed in support of graphite moderated High Temperature Reactors, it added.
Researched and written
by World Nuclear News