  Three-dimensional hydrodynamic simulations exploring the first 18 hours of
the 2010 January 28 outburst of the recurrent nova U Scorpii have been
performed. Special emphasis was placed on capturing the enormous range in
spatial scales in the blast. The pre-explosion system conditions included the
secondary star and a flared accretion disk. These conditions can have a
profound influence on the evolving blast wave. The blast itself is shadowed by
the secondary star, which itself gives rise to a low-temperature bow-shock. The
accretion disk is completely destroyed in the explosion. A model with a disk
gas density of 10^{15} cm^{-3} produced a blast wave that is collimated and
with clear bipolar structures, including a bipolar X-ray emitting shell. The
degree of collimation depends on the initial mass of ejecta, energy of
explosion, and circumstellar gas density distribution. It is most pronounced
for a model with the lowest explosion energy (10^{43} erg) and mass of ejecta
(10^{-8} M_{\odot}). The X-ray luminosities of three of six models computed are
close to, but consistent with, an upper limit to the early blast X-ray emission
obtained by the Swift satellite, the X-ray luminosity being larger for higher
circumstellar gas density and higher ejecta mass. The latter consideration,
together with estimates of the blast energy from previous outbursts, suggests
that the mass of ejecta in the 2010 outburst was not larger than 10^{-7}
M_{\odot}.
