  The chemical element nickel is of particular interest in stellar physics. In
the layers in which the Fe-peak elements dominate the mean opacity (the
so-called Z-bump), Ni is the second contributor to the Rosseland opacity after
iron, according to the Opacity Project data. Reliable nickel cross sections are
therefore mandatory for building realistic stellar models, especially for
main-sequence pulsators such as $\beta$ Cep and slowly pulsating B stars, whose
oscillations are triggered by the $\kappa$-mechanism of the Fe-peak elements.
Unfortunately, the Opacity Project data for Ni were extrapolated from those of
Fe, and previous studies have shown that they were underestimated in comparison
to detailed calculations. We investigate the impact of newly computed
monochromatic cross sections on the Rosseland mean opacity of Ni and on the
structure of main-sequence massive pulsators. We compare our results with the
widely used Opacity Project and OPAL data. Monochromatic cross sections for Ni
were obtained with the SCO-RCG code. The Toulouse-Geneva evolution code was
used to build the stellar models. With the new data, the Rosseland opacities of
Ni are roughly the same as those of the Opacity Project or OPAL at high
temperatures ($\log\ T>6$). At lower temperatures, significant departures are
observed; the ratios are up to six times higher with SCO-RCG. These
discrepancies span a wider temperature range in the comparison with OPAL than
in comparison with the Opacity Project. For massive star models, the results of
the comparison with a structure computed with Opacity Project data show that
the Rosseland mean of the global stellar mixture is only marginally altered in
the Z-bump. The maximum opacity is shifted towards slightly more superficial
layers. A new maximum appears in the temperature derivative of the mean
opacity, and the driving of the pulsations should be affected.
