Description of output files

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Default output files

The following output files are always produced.

Main output file

The main output file contains all results calculated by default during the transport cycle. The file is written in Matlab-readable format in file:



[input]  : is the name of the input file

In calculations involving multiple transport cycles (such burnup calculation) the file is appended after each cycle. When the file is read into Matlab, each parameter is read into a variable (scalar or vector). A run index “idx” is assigned to each block of results, and the output data from different cycles are read into different rows (turning scalar variables into vectors and vector variables into matrices).

The list of parameters is provided separately here.

Nuclide and material data

Nuclear and material data is collected in in file:



[input]  : is the name of the input file

Basically the file lists all nuclides and their reactions as they are read from the nuclear data libraries. The material data includes isotopic compositions and densities, as well as volumes and masses if available. The format is self-explanatory.

Burnup calculation output

Output from burnup calculations is printed in file:


This file contains Matlab format data in several variables of form:



[material]  : is the name of a material in the calculation
[data]  : is the data type

Every variable is a matrix with rows corresponding to the nuclides requested in the set inventory option and colums corresponding to different burnup steps. The data types are:

ADENS : Atom density in b-1 cm-1
MDENS : mass density in g/cm3
A : Activity in becquerels
H : Decay heat in Watts
SF : Spontaneous fission rate in fissions per second
GSRC : Photon emission rate in photons per second
ING_TOX : Ingestion toxicity in sieverts
INH_TOX : Inhalation toxicity in sieverts
VOLUME : Material volume in cm3
BURNUP : Burnup in MWd/kgU


  • For 2D geometries, values are on a per axial length basis.
  • To additional rows are printed for each data array: data for lost nuclides (reaction products without nuclide data) and total.

Additional output files

The following output files are produced by invoking various input options.

Group constant output

Group constant data is printed separately in file:



[input]  : is the name of the input file

The file is designed to be read by post-processing scripts, and the format is described together with the automated burnup sequence.

Reaction rate output

Calculation of analog reaction rates by counting the number of sampled interactions is invoked using the set arr option. The output is printed in file:



[input]  : is the name of the input file
[n]  : is the burnup index (zero for first step or if no burnup calculation is run)

The data is printed in Matlab format in two variables: string array "nuc", which contains the nuclide identifiers (, and table "rr", consisting one row for each reaction and 7 columns:


where the values are:

IDX : Nuclide index corresponding to the entries in the nuc array
ZAI : Nuclide ZAI
MT : ENDF reaction MT
EMIN : Minimum energy of the reaction mode
EMAX : Maximum energy of the reaction mode
RR : Reaction rate
ERR : Relative statistical error


  • The values are normalized microscopic reaction rates integrated over all materials and energies.
  • Neutron transport mode includes either reactions that affect neutron balance (absorption, fission, neutron-multiplying scattering) or all reactions, depending on the value of the input option.
  • All reaction modes are included in photon transport mode.

Micro depletion output

Microscopic few-group cross sections calculated for the purpose of micro-depletion (set mdep) option are printed in file:



[input]  : is the name of the input file
[n]  : is the burnup index (zero for first step or if no burnup calculation is run)

or in branch calculation:



[input]  : is the name of the input file
[i]  : is the burnup index
[j]  : is the branch index

Cross sections

The data includes few-group cross sections printed in table XS_[u], where [u] is the universe for which the calculation is carried out. The columns are:


where the values are:

ZAI : Nuclide identifier (ZAI)
MT : ENDF reaction MT
I : Special flag (isomeric state or fission yield distribution number)
N : Nuclide density smeared to homogenized volume
ERRN : Associated relative statistical error
XSg : Microscopic cross section
ERRg : Associated relative statistical error
RR : Reaction rate
ERR : Relative statistical error

Fission yields

Actinide fission yields are additionally printed in variables NFY_[ZAI]_[n], where [ZAI] is the nuclide identifier and [n] is the yield distribution number. Each yield corresponds to an energy, printed in variable NFY_[ZAI]_[n]E. The columns in the fission yield distribution are:


where the values are:

ZAI : Product identifier
FI : Independent yield
FC : Cumulative yield

Decay data

Decay data of decaying nuclides are additionally printed in variable dec. The columns in the decay data table are:

1. ZAI
2. decay constant (1/s)
3. specific decay energy (J)
4. reaction type
5. branch fraction
6. product ZAI


  • For fission reactions the special flag corresponds to a fission product yield distribution, which are tabulated for different energies.
  • For transmutation reactions the special flag indicates the isomeric state of the product nuclide (0 = ground state, 1 = isomeric state).
  • Nuclide densities were not present before 2.1.32.
  • Additional product nuclides (e.g. H-1) can be determined from the reaction type. Each number in the reaction type corresponds to one simultaneous reaction.

History output

Certain cycle-wise results are stored when the the set his option is invoked. The results are printed in file:



[input]  : is the name of the input file
[n]  : is the burnup index (zero for first step or if no burnup calculation is run)

The output consists of tables corresponding to different parameters. The first column lists the cycle index, which is then followed by the results grouped in three columns that provide the cycle-wise value, the cumulative mean and the corresponding relative statistical error. If the parameter has two values, the number of columns is 7 (cycle index + two groups of three columns of results), and so on.

By default the output includes the following variables:

Parameter Description
HIS_IMP_KEFF Implicit estimator of keff
HIS_ANA_KEFF Analog estimator of keff (total, prompt and delayed)
HIS_COL_KEFF Collision estimator of keff
HIS_MEAN_POP_SIZE Mean simulated population size
HIS_MEAN_POP_WGT Mean simulated population weight
HIS_TRANSPORT_RUNTIME Transport cycle running time (wall-clock and CPU time)
HIS_TRANSPORT_CPU_USAGE Mean CPU usage (ratio of CPU and wall-clock time)
HIS_ENTR_SPT Shannon entropy of source point distribution (total, x, y and z)
HIS_ENTR_SWG Shannon entropy of source weight distribution (total, x, y and z)

Burned material output

Burned materials' isotopic compositions and densities at each burnup step can be printed using the set printm option. The output will be in files of the form:



[input]  : is the name of the input file
[n]  : is the burnup index (zero for first step or if no burnup calculation is run)

The data will be printed in a serpent-compatible material definition format.