  In the field of nuclear reactor physics, transient phenomena are usually
studied using deterministic or hybrids methods. These methods require many
approximations, such as: geometry, time and energy discretizations, material
homogenization and assumption of diffusion conditions, among others. In this
context, Monte Carlo simulations are specially adequate to study these
problems. Challenges presented when using Monte Carlo simulations in space-time
kinetics in fissile systems are the different time-scales involved in prompt
and delayed neutron emission, which implies that results obtained have a large
variance associated if an analog Monte Carlo simulation is utilized.
Furthermore, in both deterministic and Monte Carlo simulations delayed neutron
precursors are grouped in a $6$- or $8$- group structure, but nowadays there is
not a solid reason to keep this aggregation. In this work, and for the first
time, individual precursor data is implemented in a Monte Carlo simulation,
explicitly including the time dependence related to the $\beta$-delayed neutron
emission. This was accomplished by modifying the open source Monte Carlo code
OpenMC. In the modified code -- Time Dependent OpenMC or OpenMC(TD) -- time
dependency related to delayed neutron emission originated from $\beta$-decay
was addressed. Continuous energy neutron cross-sections data used comes from
JEFF-$3$.$1$.$1$ library. Individual precursor data was taken from
JEFF-$3$.$1$.$1$ (cumulative yields) and ENDF-B/VIII.$0$ (delayed neutron
emission probabilities and delayed neutron energy spectra). OpenMC(TD) was
tested in: i) a monoenergetic system; ii) an energy dependent unmoderated
system where the precursors were taken individually or in a group structure;
and finally iii) a light-water moderated energy dependent system, using
$6$-groups, $50$ and $40$ individual precursors.
