SCALE 5.1 BONAMIST Update                 4 January 2007
                                         Updated: 25 June 2007

This update corrects a minor error in BONAMIST, which is used with the
TSUNAMI-1D and TSUNAMI-3D sensitivity and uncertainty analysis sequences
to perform resonance self-shielding calculations. The error is
undetectable in most problems but resulted in an 0.3% bias in k-eff in
one particular case. 

The error results in the calculation of incorrect background cross
sections for reactions other than the total cross section. The incorrect
background cross section led to incorrect resonance self-shielding in
the unresolved resonance region. For most cases examined, the impact is
minimal, on the order of 0.01% delta-k. For an extreme case where most
of the reactivity occurs in unresolved resonances (an intermediate
spectra MOX fuel with depleted uranium reflector), the impact was a 0.3%
delta-k bias.

Installation of the updated BONAMIST is highly recommended for users of
SCALE 5.1 who intend to use TSUNAMI. The error was introduced in
updating BONAMIST from SCALE 5.0 to 5.1. This error is not present
in the SCALE 5.0 version of BONAMIST.


Installation instructions 
------------------------- 

The updates are now included with the MIPLIB Dancoff factor correction update
on www.ornl.gov/sci/scale/miplib_update.htm. See the README file there for 
instructions to download and install.