NSUF 21-4320: The effects of stress on void superlattice formation during Cr+ self-ion-irradiation of chromium

Chromium coating has been proposed as an accident tolerant fuel (ATF) concept to increase survivability of Zircaloy-4 fuel cladding during a loss of coolant accident. The swelling behavior of Cr is possibly critical to maintain the cladding integrity to forestall exposure of the zircalloy to steam. A previous NSUF RTE project showed that Cr indeed swells under Fe-ion irradiation but develops a void superlattice structure at relatively low dpa levels. Swelling in superlattices of other metals is known to be inherently self-limiting in volume, but it is anticipated that such self-organization may not be only stress-sensitive in its development but may lead to modified failure modes arising from crack propagation in void lattices where some planes possess a higher void fraction than others. This NSUF RTE project proposes to collect experimental data which are needed in phase field modeling of void superlattice structures in cladding under stress. We will apply a four-point bending technique during self-ion irradiation to introduce a continuous range of stresses from tensile to compressive across the thickness of one bent beam specimen, studying stress effects on both void size and superlattice constant, all systematically studied in one single ion irradiation at a given temperature. The project includes four steps: First, a four-point bending device is used to create a continuing variable stress field across the beam. Second, the cross-section of Cr under stress loading will be irradiated by Cr self-ions to induce void superlattice formation (by using 5 MeV Cr self-ions at 400°C at TAMU NSUF). Third, subsequent site-selective characterization (by using FIB and TEM at CASE NSUF) on the irradiated cross-section will be used to show the effects of stress on void swelling. Forth, nanoindentation mapping over the irradiated cross-section will be used to evaluate irradiation hardening, not only as a function of applied stress but also on grain orientation with respect to the stress state. The project will provide critical information to evaluate the overall suitability of Cr coating as an AFT concept and will provide critical data needed for developing phase field modeling of Cr swelling.

Additional Info

Field	Value
Abstract	Chromium coating has been proposed as an accident tolerant fuel (ATF) concept to increase survivability of Zircaloy-4 fuel cladding during a loss of coolant accident. The swelling behavior of Cr is possibly critical to maintain the cladding integrity to forestall exposure of the zircalloy to steam. A previous NSUF RTE project showed that Cr indeed swells under Fe-ion irradiation but develops a void superlattice structure at relatively low dpa levels. Swelling in superlattices of other metals is known to be inherently self-limiting in volume, but it is anticipated that such self-organization may not be only stress-sensitive in its development but may lead to modified failure modes arising from crack propagation in void lattices where some planes possess a higher void fraction than others. This NSUF RTE project proposes to collect experimental data which are needed in phase field modeling of void superlattice structures in cladding under stress. We will apply a four-point bending technique during self-ion irradiation to introduce a continuous range of stresses from tensile to compressive across the thickness of one bent beam specimen, studying stress effects on both void size and superlattice constant, all systematically studied in one single ion irradiation at a given temperature. The project includes four steps: First, a four-point bending device is used to create a continuing variable stress field across the beam. Second, the cross-section of Cr under stress loading will be irradiated by Cr self-ions to induce void superlattice formation (by using 5 MeV Cr self-ions at 400°C at TAMU NSUF). Third, subsequent site-selective characterization (by using FIB and TEM at CASE NSUF) on the irradiated cross-section will be used to show the effects of stress on void swelling. Forth, nanoindentation mapping over the irradiated cross-section will be used to evaluate irradiation hardening, not only as a function of applied stress but also on grain orientation with respect to the stress state. The project will provide critical information to evaluate the overall suitability of Cr coating as an AFT concept and will provide critical data needed for developing phase field modeling of Cr swelling.
Award Announced Date	2021-06-07T15:50:51.07
Awarded Institution	Idaho National Laboratory
Facility	Advanced Test Reactor
Facility Tech Lead	Alina Zackrone, Lin Shao, Yaqiao Wu
Irradiation Facility	Accelerator Laboratory
PI	Francis Garner
PI Email	[email protected]
Project Type	RTE
RTE Number	4320