  The Jiangmen Underground Neutrino Observatory (JUNO) is an experiment
proposed to determine the neutrino mass hierarchy and probe the fundamental
properties of neutrino oscillation. The JUNO central detector is a spherical
liquid scintillator detector with 20 kton fiducial mass. It is required to
achieve a $3\%/\sqrt{E(MeV)}$ energy resolution with very low radioactive
background, which is a big challenge to the detector design. In order to ensure
the detector performance can meet the physics requirements, reliable detector
simulation is necessary to provide useful information for detector design. A
simulation study of natural radioactivity backgrounds in the JUNO central
detector has been performed to guide the detector design and set requirements
to the radiopurity of detector materials.
