Abstract
Decommissioning of the damaged Chernobyl nuclear reactor Unit 4 is a top priority for the global community. Before such operations begin, it is crucial to understand the behaviour of the hazardous materials formed during the accident. Since those materials formed under extreme and mostly unquantified conditions, modelling alone is insufficient to accurately predict their physical, chemical and, predominantly, mechanical behaviour. Meanwhile, knowledge of the mechanical characteristics of those materials, such as their strength, is a priority before robotic systems are employed for retrieval and the force expected from them to be exerted is one of the key design questions. In this paper we target to measurement of the standard mechanical properties of the materials formed during the accident by testing small-scale, low radioactivity simulants. A combined methodology using Hertzian indentation, synchrotron X-ray tomography and digital volume correlation (DVC), was adopted to estimate the mechanical properties. Displacement fields around the Hertzian indentation, performed in-situ in a synchrotron, were measured by analysing tomograms with DVC. The load applied during the indentation, combined with full-field displacement measured by DVC was used to estimate the mechanical properties, such as Young's modulus and Poisson's ratio of these hazardous materials.
Highlights
On 26th April 1986, a severe nuclear accident occurred at Unit 4 of the Chernobyl nuclear reactor during an experimental power failure test
Performing indentation loading with successive X-ray computed tomography (XCT) and digital volume correlation (DVC) on the samples tested on a synchrotron beamline is an effective method to determine the mechanical behaviour and the microstructure of materials
The methodology included a series of stepwise Hertzian indentation loading performed on surrogate materials, coupled with successive synchrotron XCT, and subsequently analysed using DVC
Summary
On 26th April 1986, a severe nuclear accident occurred at Unit 4 of the Chernobyl nuclear reactor during an experimental power failure test. The fuel-cladding melt further interacted with neighbouring reactor components, including stainless steel and construction materials (concrete, sand and serpentinite) [2]. These molten materials formed a “lava-like” mixture, which dispersed within the reactor, penetrating premises of the structure, eventually solidifying in the basement levels. After the accident occurred, a massive steel and concrete structure was assembled to cover the building where the Unit 4 ruined reactor was located. This structure, known as the Chernobyl nuclear power plant sarcophagus, was designed to limit the post-accident radioactive contamination. Further complications arise from their complex and heterogeneous microstructures that makes single measurements of properties carried out on safe, small-scale specimen testing nonrepresentative of the bulk properties
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