Linking Microstructure to Neutron Irradiation Defects in Advanced Manufacture of Steels

Lead Research Organisation: University of Oxford
Department Name: Materials

Abstract

The UK plans to build a new fleet of nuclear power plants starting with two units at Hinkley Point in Somerset. The UK government has also recently announced in the autumn 2015 statement that £250M will be set aside for in innovative nuclear technologies. More specifically it has stated that the UK will invest in small modular reactor designs. The large reactors and many small modular reactor designs are based around a reactor type called a pressurised water reactor. These reactor designs have a steel reactor pressure vessel to enclose the nuclear fuel and act as a key barrier to the release of radiotoxic materials to the environment. The integrity of the vessels is paramount to the safety and continued operation of the reactor. Unfortunately, neutron irradiation from the nuclear fuel damages the steels over their 40-60 year design life. Understanding the role of neutron damage to these steels is therefore key to continued operation beyond the design life.

This programme of work will study commonly used reactor pressure vessel forging grade steels (A508 class 3), under neutron irradiation damage, at the OPAL test reactor, at Lucas Heights in Australia. The steels will be manufactured by processes not commonly used in nuclear reactors i.e. hot isostatic pressing (HIP) of powdered material and then welded using electron beams (EB). These new manufacturing processes could potentially be used to manufacture parts for the reactor pressure vessels of future small reactor designs. As yet there is no information on how changing the manufacturing routes from arc welding of forged material to EB welding of HIPed material will change the neutron irradiation response of the material. In this case the chemistry of the material remains unchanged so the key variable is the so-called "microstructure" of the material.

It is planned to irradiate samples, at the OPAL reactor, for up to 1 year, to achieve doses of neutron embrittlement equivalent to 40-60 years reactor operation. The irradiated material will then be mechanically tested, in hot cells, at the Australian Nuclear Science and Technology Organisation before material is shipped to the new Materials Research Faclility at UKAEA Culham site in the UK. Here, it will be prepared for state-of-the-art characterisation, by atom probe tomography on the new LEAP 5000 atom probe recently installed at Oxford University, Chemi-STEM transmission electron microscopy at Manchester University, together with atomic scale models developed at Imperial College London and Manchester University. The project will also have management and input from the National Nuclear Laboratory and Rolls-Royce and international links to the University of New South Wales, University of California Santa Barbara and Oak Ridge National Laboratory.

The overall output from this work will be much improved mechanistic understanding and models of how neutron irradiation effects steels manufactured by HIP and EB welding, lead to a new generation of engineers in the UK who can perform work on irradiated materials and help direct the use of such technologies for the building of future small reactor designs. It will also be a crucial driver in the effort to rebuild the physical and knowledge based infrastructure, for dealing with neutron irradiated steels, that has been missing for a generation in the UK.

Publications

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Description The project has started well, although is in the early stages of the research. Preliminary findings in this project include - collaborators at Manchester using electron microscopy imaging have shown that the RPV steel manufactured using the HIPed processing route have a very different microstructure in comparison to the forged materials. In particular in the HIPed samples there are large ferrite grains not conventionally seen in these bainitic steels. It offers the opportuinity to investigate the effects of irradiation (neutron, ion, proton) on ferrite and bainite in the same sample. We have shown that it is possible to combine Transmission Kikuchi Diffraction (TKD) techniques with FIB specimen preparation for atom probe in these materials to enable a holistic characterisation of grain boundary in terms chemistry and crystallographic structure. Hence we can investigate specific grain boundary types pre-/post-irradiation treatment. We also have preliminary data on the micrstructural changes to the E-beam weld materials showing segragtion of molybdenum to dislocations previously only decorated by carbon before heat treatment. Irradiation of these specimen will be instructive.
Exploitation Route The characterisation techniques developed to enbale APT analyses can be readily taken up by users of this mnicroscopy on a very wide range of other materials research investigations.
Sectors Aerospace, Defence and Marine,Construction,Electronics,Energy,Manufacturing, including Industrial Biotechology

 
Description A LEAP 5000 XS for the UK National Atom Probe Facility
Amount £2,914,083 (GBP)
Funding ID EP/S021663/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2019 
End 01/2021
 
Description An Atomic-Scale Characterisation Facility for Active Nuclear Materials
Amount £3,822,136 (GBP)
Funding ID EP/T011505/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 11/2019 
End 03/2023
 
Description EPSRC Case Incentivisation - Pryzemslaw Klups
Amount £59,500 (GBP)
Organisation Rolls Royce Group Plc 
Sector Private
Country United Kingdom
Start 10/2018 
End 05/2022
 
Description Ni-based ODS alloys for Molten Salt Reactors
Amount £499,728 (GBP)
Funding ID EP/T002441/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 08/2019 
End 08/2022
 
Description Simultaneous Corrosion/Irradiation Testing in Lead and Lead-Bismuth Eutectic: The Radiation Decelerated Corrosion Hypothesis (RC-3)
Amount £543,314 (GBP)
Funding ID EP/T002808/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 09/2019 
End 09/2022
 
Description G. Robert Odette UCSB 
Organisation University of California, Santa Barbara
Country United States 
Sector Academic/University 
PI Contribution Specimen preparation an APT analysis of neutron irradiated RPV steels, undertaken at Idaho National Laboratory
Collaborator Contribution Provision of a matrix of neutron irradiated RPV steels from the ATR-2 test reactor. Consultation on the metallurgical interpretation of the APT analyses.
Impact Articles in preparation. Presentation at Atom Probe Tomography & Microscopy Conference at NIST (Washington) 2018
Start Year 2017