A new graphite irradiation research program has been launched in support of ageing management of Advanced Gas-Cooled Reactors (AGRs) in the UK. Last week, EDF Energy announced 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.
EDF Energy - together with Atkins, Frazer Nash and NRG - launched the Blackstone project in 2006. The project aims to simulate accelerated aging of reactor graphite. This involves neutron irradiation at the right temperature combined with simultaneous radiolytic oxidation.
Phase 1 aimed to show that graphite samples could be irradiated in the Materials Test Reactor - operated by NRG at Petten, the Netherlands - and then subjected to non-destructive and destructive post-irradiation examination. A database of the results was compiled. Phase 2, started in August 2011, further developed and expanded that database by obtaining end of lifetime data for graphite cores.
The research partners have now announced the start of Phase 3 of Project Blackstone, which will run for five years and will focus on the graphite from the Heysham B and Torness AGR reactors. During Phases 1 and 2 of the project, graphite from other AGRs was successfully characterized to support life-time extension. Phase 1 looked at graphite samples from Hinkley Point B and Hunterston B, while Phase 2 studied specimens from Hartlepool and Heysham 1.
NRG said on 18 February, as part of the project, graphite material extracted from AGRs will be irradiated in the High Flux Reactor operated by NRG at Petten. During the irradiation, both the in-core neutron and oxidation damage mechanisms that take place in an AGR are simulated and accelerated under representative conditions. Following irradiation, the graphite samples are characterized in the NRG hot cell laboratories to provide material behaviour data, providing input to graphite property models which are used to assess the future structural integrity of AGR cores.
On 16 February, EDF Energy announced that the scheduled closure dates for its Heysham 1 and Hartlepool plants had been extended by five years to 2024, while those of Heysham 2 and Torness had been extended by seven years to 2030. The announcement followed life extensions at EDF Energy's other AGR power plants.
Researched and written
by World Nuclear News