BREDA-RPV

Irradiation induced ageing of the weld material of the reactor pressure vessel (RPV) is a limiting factor from a long-term operation perspective. The closed Barsebäck 2 reactor gives an opportunity to harvest samples from the RPV, which was manufactured and welded with the same technique and high amounts of nickel and manganese as most Nordic RPVs. A test program to analyze the as-aged material properties has been prepared within the NKS-R activity BREDA-RPV.

In 2016 base line testing was performed at VTT on un-irradiated material retrieved from the original testing of the reactor pressure vessel. In addition, a feasibility study on harvesting of material from the reactor pressure vessel at Barsebäck was presented in the end of 2016 as a collaboration between the present project group and Ringhals AB, who will act as contact point for the trepan extraction. The microstructural features of un-irradiated material was mapped for several specimens laying the foundation for continued studies on irradiated materials.

The activity in 2018 started by studies of the mechanical properties of an accelerated surveillance capsule as well as material from a standard surveillance capsule from the RPV of Barsebäck 2. The main deliverable was a literature review on the feasibility to utilize specimens with high degree of constrain, i.e. very small test specimen, to study the effects of irradiation on the mechanical properties. This was a preparation for testing of material from the reactor pressure vessel itself, which was made available in the end of 2018. It further contained an enhanced microstructural evolution of RPV weld materials containing high levels of nickel and manganese to study the build-up of agglomerates that are in part responsible for irradiation hardening of these alloys. This study included Light Optical, Scanning Electron, Transmission Electron and Atom Probe Microscopy at CTH and VTT. The issue is also relevant to the Finnish new-build project in Hanhikivi since the base metal in that RPV has a similar composition.

During 2019, further microscopy work will be performed to map the microstructure of the reactor vessel material as well as the samples retrieved from the surveillance program of Barsebäck 2. This work will be performed at VTT and CTH encompassing methods from Light Optical Microscopy, LOM, to high resolution nanoscopic analysis with Atom Probe Tomography, APT. Mechanical testing of small sized speciemens will commence at VTT of the material retrieved from the accelerated surveillance capsule. In addition to this, development of the test methods applied in BREDA will contiue at VTT.

The trepan cut-outs will be transported to VTT for further machining in order to prepare samples for mechanical and microstructural testing. Finite Element models allowing for parametrical studies of samples and test methods to support the mechanical testing will continue at KTH. Testing of material with the objective to study the influence of constraint of the aged material will start during the next program year.

In 2020, further microscopy work will be performed to map the microstructure of the reactor vessel belt-line material. This work will be performed at VTT and Chalmers encompassing methods from Light Optical Microscopy, LOM, to high resolution nanoscopic analysis with Atom Probe Tomography, APT. Mechanical testing of small sized speciments will commence at VTT of the material retrieved from the accelerated surveillance capsule. In addition to this, development of the test methods applied in BREDA will continue at VTT. The trepan cut-outs from the beltine region will be transported to VTT for further machining in order to prepare samples for mechanical and microstructural testing. Finite Element models allowing for parametrical studies of samples and test methods to support the mechanical testing will continue at KTH. Testing of material with the objective to study the influence of constraint of the aged material will start during the next program year. It is foreseen that the second student from the program will defend his thesis at KTH before the summer of 2020. A follow up program has been started at KTH to allow for a fourth Ph.D. student to work within the program and to continue the effort.

A workshop to present the results up to 2020 is proposed to be held as part of the NKS program. The timing for the workshop is still pending but it will be an important mean to discuss and disseminate the results from the program so far and to guide the future work.