|
Studies of mechanical and microstructural properties of Irradiated Low Alloy Steel
trepan samples from the Reactor pressure vessel wall of Barsebäck 2 (BREDA-RPV).
Irradiation induced ageing of the reactor pressure vessel (RPV) steel is closely
monitored in specified ageing management programs called surveillance programs.
These consist of a number of capsules positioned inside the RPV to allow for accelerated irradiation of the RPV material to predict the evolution of the mechanical
properties of the material as a function of neutron dose. The closed Barsebäck 2 reactor gives an opportunity to harvest samples from the aged reactor pressure vessel (RPV). The RPV was manufactured and welded with the same technique and high amounts of Nickel and Manganese as most Nordic RPVs. The weld material is now a limiting factor from a Long term operation, LTO, perspective as shown with studies at the PWR-plants Ringhals 3 and 4. By studying the evolution of the mechanical properties om both unirraidated samples and materials harvested from the reactor pressure vessel itself, it is possible to verify the validity of the surveillance specimen used for the monitoring of the RPV status. An example is if the (often separately performed) heat treatment of the surveillance samples gives representative values as compared to the real RPV. Another example is
the analysis of the degradation gradient through the depth of the RPV thickness due to irradiation, as the embrittlement properties at a ¼ of the wall thickness is used in the reporting to the radiation safety authority (SSM). A possibility to acquire for example three or four trepan samples from locations at different axial positions would make it possible to study the metallurgic variability and different ageing phenomena from thermal and radiation induced degradation: the core region has substantial neutron flux, while the RPV top lid has a substantial thermal component while the neutron flux is orders of magnitude lower. The study will be carried out as parts of as PhD studies performed at KTH, in strong collaboration with Chalmers on micro-structural analysis, and VTT for mechanical testing.
|
