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UNCERTAINTY iuncer {0} <path_floor {0.005} loop_floor {0.01} max_depth {10} iuncer >

This keyword allows user control of the uncertainty estimates and pathway information that are calculated and output for each time interval. This is primarily specified by the parameter iuncer {0}. The allowed values are:

-1 resets default values for a particular run and permits other values to be specified by the following parameters, which can be present only for this value of iuncer;
0 no pathways or estimates of uncertainty are calculated or output;
1 only estimates of uncertainty are output (although all the pathway information is calculated);
2 both estimates of uncertainty and the pathway information are output;
3 only the pathway information is output;
4 now generates a fatal error message.

path floor {0.005} All pathways contributing more than the path floor fraction of the inventory of the final (target) nuclide are retained.

loop floor {0.01} All loops that increase the inventory contribution of the path they are on by a fraction greater than the loop floor are retained.

max depth {10} is the maximum number of links in a path from a source nuclide to a target nuclide.

iuncer following all the other parameters allows values 0, 1, 2 or 3 to be input again so that after resetting the default values an actual calculation with the new values can be done.

Note any use of the keyword UNCERTAINTY to change the default settings for the pathways calculation must precede the first occurrence of the keywords ATOMS or SPECTRUM.

Note that if no uncertainty data exist in the cross-section library then the valid values of iuncer are only −1, 0 or 3.

Omitting the keyword will ensure that only inventory calculations are carried out, and should be done if a fast scoping run is required.

The most common usage of 'UNCERTAINTY, which also generates and output pathway information, is:

< -- Control phase -- >
* Title of the simulation
< -- Initial phase -- > 
< -- Inventory phase -- > 

To change the parameters of the uncertainty run, the following example could be used:

UNCERTAINTY -1 0.001 0.005 10 2