NSUF 19-1683: Resolving the Puzzle of Flux Effects on High Fluence Precipitation and Embrittlement of RPV Steels

This proposal covers characterization 5 alloys by Atom Probe Tomography (APT) and making FIB liftouts (LO) from 15 ATR-2 irradiated alloys including a set of split melt core alloys with systematic variations in Cu, Ni, Mn and Si and 5 surveillance steel alloys representing a range of compositions, as shown in Table 1 of the proposal narrative. The steels were primarily irradiated to a fluence of ≈ 1.4x1020 n/cm2 at Ti ≈ 290°C in the ATR-2 experiment. Recently, extensive post-irradiation examination results from ATR-2 and other irradiated RPV steel databases has led to the development of both detailed and simpler reduced order microstructurally based physical models to accurately predict high fluence embrittlement at end of life 80-year fluences. Most recently a model of steel composition dependence (Cu, Ni, Mn, Si, P) of embrittlement was derived for the ATR irradiation conditions. Thus there is a need to determine the effect of the higher flux in ATR-2 compared to actual low flux service conditions. We propose to establish a rigorous basis to deal with flux effects, by carefully characterizing the evolution of the precipitates and for the first time, tiny dislocation loops with fluence. The loops act as defect sinks and have a dominant effect of flux effects which are very different at high versus low fluence. While measuring 3 nm solute shielded loops is not easy, it is possible using modern STEM weak beam diffraction techniques to be carried out on other LOs by leading experts at our institution and other TEM facilities.

Additional Info

Field	Value
Abstract	This proposal covers characterization 5 alloys by Atom Probe Tomography (APT) and making FIB liftouts (LO) from 15 ATR-2 irradiated alloys including a set of split melt core alloys with systematic variations in Cu, Ni, Mn and Si and 5 surveillance steel alloys representing a range of compositions, as shown in Table 1 of the proposal narrative. The steels were primarily irradiated to a fluence of ≈ 1.4x1020 n/cm2 at Ti ≈ 290°C in the ATR-2 experiment. Recently, extensive post-irradiation examination results from ATR-2 and other irradiated RPV steel databases has led to the development of both detailed and simpler reduced order microstructurally based physical models to accurately predict high fluence embrittlement at end of life 80-year fluences. Most recently a model of steel composition dependence (Cu, Ni, Mn, Si, P) of embrittlement was derived for the ATR irradiation conditions. Thus there is a need to determine the effect of the higher flux in ATR-2 compared to actual low flux service conditions. We propose to establish a rigorous basis to deal with flux effects, by carefully characterizing the evolution of the precipitates and for the first time, tiny dislocation loops with fluence. The loops act as defect sinks and have a dominant effect of flux effects which are very different at high versus low fluence. While measuring 3 nm solute shielded loops is not easy, it is possible using modern STEM weak beam diffraction techniques to be carried out on other LOs by leading experts at our institution and other TEM facilities.
Award Announced Date	2019-02-08T00:00:00
Awarded Institution	None
Facility	None
Facility Tech Lead	Yaqiao Wu
Irradiation Facility	None
PI	Nathan Almirall
PI Email	[email protected]
Project Type	RTE
RTE Number	1683