Papers by Author: Robert Moskovic

Abstract: The formation of fracture process zones in polygranular reactor core moderator graphites subjected to four-point bending has been investigated. The three-dimensional digital image correlation technique has been combined with resistance strain gauge measurements to evaluate, both the localised and the global displacements during testing. The non-linear load-displacement characteristics prior to peak load are correlated with the localised displacements which can extend up to ~3mm (process zone) from the tensile surface of the specimen. At peak load a macro-crack propagates rapidly along an irregular path controlled by the direction of the applied tensile load and the microstructure of the graphite. These cracks arrest prior to complete separation of the specimen. Localised tensile process zones extend for distances of up to ~3mm ahead of the tips of these cracks.

Abstract: As part of the requirement to demonstrate safe operation of the steel reactor pressure vessels for the UK Magnox fleet, surveillance samples were installed at the time of construction. These were representative of the steels and weld metals used for the manufacture of the vessels. The history of sample removal and mechanical property testing is briefly reviewed. The factors leading to changes in the fracture resistance and tensile properties will be discussed. The link is described between the mechanisms leading to changes in mechanical properties and the statistically based approach adopted to predict values of fracture toughness for the neutron dose and temperatures at key vessel locations. Predictions are compared with test results obtained from samples removed from a decommissioned reactor and also surveillance and accelerated radiation samples removed towards the end of reactor life.