Neutronics design of VVER-1000 fuel assembly with burnable poison particles

Study on Transmutation of Minor Actinides as Burnable Poison in VVER-1000 Fuel Assembly

“…Also, the role of MAs as burnable absorbers in partial replacement to the gadolinium and boric acid in the VVER-1000 reactor was confirmed and in line with recent publications for PWRs [19,20]. It is worth noting that the reduction of the boron concentration not only could help attain a more negative moderator temperature coefficient during the core lifetime but also could allow minimizing the operation of a complicated chemical control system as well as reducing the corrosion of structural materials [26]. Furthermore, the reduced gadolinium content could help improve the thermal conductivity and melting point of the UGD pins [28].…”

“…It was found that the MAs can be loaded up to 10 wt.% into the UGD pins and the combined reduction in the gadolinium content and boron concentration could help facilitate the excess reactivity control at the beginning of the fuel cycle without significant effect on the cycle length. As in the current practice the MA content in MA bearing fuels should be limited to a few percent (up to 5 wt.%) for the homogeneous case [2], the limitations regarding the relatively high MA content from 6 wt.% to 10 wt.% can be possibly overcome by increasing the number of the UGD pins (up to 36 pins) in the VVER-1000 fuel assembly [26,27]. Increasing the number of the UGD pins could reduce the MA content in the UGD pins less than 5 wt.% while allowing a high total MA loading amount in the whole assembly and thus avoid serious shielding issues in the fabrication, transport, and handling of MA bearing fuels.…”

“…Although in the current practice the MA content in MA bearing fuels should be limited to a few percent (up to 5 wt.%) for the homogeneous case [2], the relatively high MA content from 6 wt.% to 10 wt.% was selected in this investigation to allow high MA loading amount so as to demonstrate a considerable MA transmutation rate from neutronic viewpoint. As the VVER-1000 LEU fuel assembly used in this study has 12 UGD pins, its configuration can be redesigned to accommodate more UGD pins (up to 36 pins) [26,27]. With a larger number of the UGD pins, equivalent or even higher MA loading amount in the UGD pins as compared with this study can be easily obtained with the MA content not higher than 5 wt.%.…”

In-Reactor Behaviour and Economic Assessment of Enriched Gadolinia Burnable Absorbers

“…Since the gadolinium (Gd) isotopes in the outer layers of the fuel pellet capture the neutrons that moderated by the cooling water, the BA isotopes in the inner layers are depleted later (Franceschini and Petrović, 2009). The self-shielding effect results in a suppression of reactivity, but as the Gd isotopes become depleted, the reactivity increases and ultimately reaches the level of reactivity of fuel without the presence of Gd isotopes when the Gd isotopes are almost completely depleted (Tran et al, 2019).…”