Correction to the Potassium Cross-Section Data 
                   in the 238-Group ENDF/B-V Library
                         February 12, 2003

Introduction
------------

A minor error in the potassium cross-section data contained in the 238-
and 44-Group ENDF/B-V libraries was recently discovered. Several KENO
V.a cases involving potassium became stuck in infinite loops. The cause
was the potassium cross sections in the 238-group library were negative
in two energy groups. For systems where the potassium is not a major
component, the cross sections probably are not negative, and even if
they were, this error would affect the overall cross sections only
slightly. There are only two groups where the cross sections went
negative in the cases studied. The error in the existing set of
potassium data was identified as the inclusion of Bondarenko factors
from some other nuclide in the potassium data. Although the 44-group
library was collapsed from the 238-group library with the erroneous
data, the possibility of negative cross sections is much less likely in
the broader group structure. Thus, only an update to the 238-group 
library is being provided.

Explanation
-----------

SCALE 4.4 and 4.4a users with potassium (K) models should update the K cross-section data 
in the 238-group cross-section library using the update
file available on the SCALE Download web page. The update file is a compressed file
containing two ASCII files:

1. k-update-ascii: Corrected K data
2. potassium-update.input: SCALE input file containing input to the modules
   SHELL - Unix or DOS commands to copy k-update-ascii to unit 61 (ft61f001)
   AIM - Reads corrected 238-group K data from unit 61 and converts to binary
   AJAX - Copies the corrected K binary data and the rest of 238-group 
          library to a new library on unit 69 (ft69f001).
   SHELL - Unix or DOS commands to copy new 238-group library
           to the SCALE data subdirectory to replace the existing library.
   
Instructions to perform update
------------------------------
1. Download potassium-update.zip for PC or potassium-update.tar for Unix.

2. Unzip the PC file or untar the Unix file.

3. Edit the input file potassium-update.input
   
   IMPORTANT: THE DOS OR UNIX COMMANDS IN THE SHELL INPUT MAY REQUIRE MODIFICATION
   BY THE USER TO COPY THE NEW LIBRARIES TO THE CORRECT LOCATION. 
   Check the names of your current directories and files first.

4. If you want to keep a copy of the original libraries, copy them
   (do NOT rename them - this will cause the update to fail).

5. Change to the directory where the file potassium-update.input is located, 
   and run SCALE to execute the update.

6. Check the output file to see if everything executed normally.

7. Check the date/time and size of the 238-group libraries in the
   SCALE data subdirectory to make sure that the updated file is there.

8. Rerun your potassium validation cases.