Calculations are made to investigate sensitivities of the central NISUS spectrum and reaction-rate ratios to uncertainties in the macroscopic configuration. These uncertainties include density (of graphite, borone carbide and natural uranium), impurity (moisture and 10B in graphite), abundance ( 10B natural abundance) and tolerance (in Al cladding and B 4C shell). The sensitivities to the variations in the fission cross section of 235U and 238U are also studied. In these calculations the ANISN one-dimensional transport code is used with a 37 group data set derived from the UKAEA Nuclear Data Library by the GALAXY processing code. The effects of uncertainties are studied in detail and a comparison is made between the NISUS and MOL-ΣΣ standard neutron fields.