Top plot: star temperature vs. radius profiles. Bottom plot: mass fraction of the Urca species vs. radius. The gray curves represent the initial state of the simulations in B2025, the blue curves the initial state of the FN1 and NB1 simulations, and the green curves the initial state of the FN2 simulation. The dashed curves represent the ²³Ne and the solid ones the ²³Na. The vertical red line indicates the position of the Urca shell.