  The thermal structure of accreting neutron stars is affected by the presence
of urca nuclei in the neutron star crust. Nuclear isobars harboring urca
nuclides can be produced in the ashes of Type I X-ray bursts, but the details
of their production have not yet been explored. Using the code {\tt MESA}, we
investigate urca nuclide production in a one-dimensional model of Type I X-ray
bursts using astrophysical conditions thought to resemble the source GS
1826-24. We find that high-mass ($A\geq55$) urca nuclei are primarily produced
late in the X-ray burst, during hydrogen-burning freeze-out that corresponds to
the tail of the burst light curve. The $\sim0.4$--0.6~GK temperature relevant
for nucleosynthesis of these urca nuclides is much lower than the $\sim1$~GK
temperature most relevant for X-ray burst light curve impacts by nuclear
reaction rates involving high-mass nuclides. The latter temperature is often
assumed for nuclear physics studies. Therefore, our findings alter the
excitation energy range of interest in compound nuclei for nuclear physics
studies of urca nuclide production. We demonstrate that for some cases this
will need to be considered in planning for nuclear physics experiments.
Additionally, we show that the lower temperature range for urca nuclide
production explains why variations of some nuclear reaction rates in model
calculations impacts the burst light curve but not local features of the burst
ashes.
