1. Introduction

W. A. Wieselquist

The SCALE code system includes verified and validated tools for criticality safety, reactor physics, radiation shielding, radioactive source characterization, and sensitivity and uncertainty analysis. SCALE is developed, maintained, tested, and managed by Oak Ridge National Laboratory (ORNL) and may be obtained through the Radiation Safety Information Computational Center (RSICC).

This manual documents version 6.3 of the SCALE code system, with initial release of 6.3.0 in 2022. The previous 6.2 series had its last maintenance release, 6.2.4, in 2020. This section describes the key features in 6.3 relative to 6.2 and details on how to run SCALE.

Maintenance releases of SCALE 6.3 (6.3.1, 6.3.2, etc.) will be made as needed to fix any issues discovered. Historically, there has been approximately one maintenance release per year. Note that once users have been granted a license from RSICC, any subsequent maintenance releases may be obtained free of charge directly from the SCALE team by sending an email to scalehelp@ornl.gov.

The next major release of SCALE with additional features will be SCALE 7.0 in ~2025.

The SCALE manual is included with installation; however, an online version is also available. The online version is new as of SCALE 6.3 and is in a convenient format for users, containing detailed lists of changes as well as any issues discovered in a particular version, starting with SCALE 6.3.0.

Instructions on installing or building SCALE, testing the configuration with the sample problems are available in Sect. 12.

1.1. Organization

SCALE’s top-level applications have been historically called “sequences” because of their original design, which called specific modules in sequence to solve specific problems. With the development of SCALE 6.3, we have found it more useful to think of SCALE as a set of products. A product is potentially more than one sequence and attempts to logically group capabilities around a particular application area. This is useful both from the standpoint of helping a user identify which sequences they should use and from a development point of view, as domain experts are assigned to each product. See Table 1.1.1 for the relationships between end user applications, SCALE products, and sequences.

Table 1.1.1 Relationship between end-user applications, SCALE products, and sequences

End user Application Area


Example Sequences

Reactor Physics








Criticality Safety






Spent Fuel Inventory






Activation and Decay




Radiation Shielding



Sensitivity and Uncertainty











The reconceptualization of sequences as products also facilitates management and discussion of certain key SCALE components, such as nuclear data. Table 1.1.2 briefly describes each product and contains links to the relevant section(s) in the manual.

Table 1.1.2 SCALE Products





SCALE Graphical User Interface

Sect. 12.3.1


Solve Monte-Carlo (and deterministic) criticality problems

Sect. 2.1


Solve Monte-Carlo fixed source radiation transport with automatic variance reduction for difficult shielding tallies

Sect. 4.1


Generate fast LWR spent fuel inventory predictions

Sect. 5.4


General depletion

Sect. 5.1.5


Easy-to-use lattice physics

Sect. 3.2


General Uncertainty Propagation

Sect. 6.4


Sensitivity and experiment selection analysis

Sect. 6.1, Sect. 6.2


Trending analysis

Sect. 6.5


Solve coupled neutron transport and depletion problems for nuclear reactor systems

Sect. 3.1


Accurate multi-group cross section self-shielding methods

Sect. 7.1


Verified and validated SCALE fundamental nuclear data

Sect. 10.1


Transform ENDF-formatted data into SCALE libraries



Flexible user interface for HPC Applications


1.2. SCALE 6.3 Updates by Product

The new features relative to SCALE 6.2 are described below, organized in terms of products as shown in Table 1.1.2.

1.2.1. Fulcrum

The major new feature in Fulcrum is the 3D visualization of geometry, including results overlay capability.


Fig. 1.2.1 Fulcrum visualization of geometry including new 3D.


Fig. 1.2.2 Fulcrum visualization of 3D reactor geometry with flux overlay.

1.2.2. CSAS

The key new CSAS feature in 6.3 is the ability to call Shift for neutron transport. The same CSAS user interface is available for both CSAS-KENO and CSAS-Shift, and the majority of KENO features are supported by Shift. See Sect. 2.2 for details.

  • CSAS-KENO now allows specification of the upper thermal scattering cutoff energy. A value above the default 10 eV may be necessary for high-temperature graphite–moderated systems. See Sect. for details.

  • CSAS now supports reusable energy and spatial grid definitions in the definitions block, especially useful for producing *.3dmap files for visualization in Fulcrum. See Sect. for details.

  • Shift can randomly place spheres within volumes, also useful for tristructural isotropic (TRISO) packing in pebbles. See Sect. for details.

1.2.3. VADER

VADER is the modernization of the trending analysis code USLStats previously externally distributed with SCALE. VADER uses the SON input format introduced in SCALE 6.2. See Sect. 6.5 for details.

1.2.4. MAVRIC

The key new MAVRIC feature in 6.3 is the ability to call Shift for neutron and gamma transport. Append -shift to the sequence name to use Shift as in the example below.

Leakage spectrum of Cf-252 through a heavy water sphere

read composition
    d2o          1 0.99286 293.0 end
    h2o          1 0.00714 293.0 end
    polyethylene 2 0.882   293.0 end
    boron        2 0.118   293.0 end
    iron         3 1.0     293.0 end
    orconcrete   4 1.0     293.0 end
end composition

' Geometry Block
read geometry
    global unit 1
        sphere    10   0.5
        sphere    11  15.0
        sphere    21   2.0  origin x=75.0
        cuboid    41  650.0 -650  500 -500   2300 -200
        cuboid    42  750.0 -750  600 -600   2400 -300
        media  0 1   10
        media  1 1   11 -10
        media  0 1   21          vol=33.510322
        media  0 1   41 -11 -21
        media  4 1   42 -41
    boundary 42
end geometry

' Definitions Block
read definitions
    distribution 1
        title="Cf-252 neutrons, Watt spectrum a=1.025 MeV and  b=2.926/MeV"
        parameters 1.025 2.926 end
    end distribution
end definitions

' Sources Block
'   Cf-252 neutrons, Watt fission spectrum model
'   strength set so that total unattenuated flux at detector would be 1
'      strength = 4*pi*(75)^2
read sources
    src 1
        title="Cf-252 neutrons, Watt fission spectrum, using a=1.025 and b=2.926"
        neutrons  strength=70685.834704
        sphere 0.1
    end src
end sources

' Tallies Block
read tallies
    regionTally 3
        title="example region tally"
        unit=1 region=3
    end regionTally
end tallies

' Parameters Block
read parameters
    neutrons  noPhotons
    fissionMult=0  secondaryMult=0

'   speed things up for the sample problem
end parameters

end data


Some features in MAVRIC using the default Monaco transport engine are not yet available in Shift.

1.2.5. TRITON

TRITON was updated with a host of new capabilities in SCALE 6.3.

  • TRITON can now call the new Shift Monte Carlo code instead of KENO. Shift was designed with parallelism and robustness as the highest priorities. With Shift enabled, few-group macroscopic cross sections on 3D hex and Cartesian meshes can be generated, similar to but more general than existing capabilities in TRITON-NEWT and Polaris. See Sect. for details.

  • Shift can randomly place spheres within volumes, which is available in both CSAS-Shift and TRITON-Shift. See Sect. for details.

  • A new flow block has been added to the TRITON timetable, intended for simulating molten salt reactors. See Sect. for details.

1.2.6. Polaris

The main Polaris improvement for 6.3 is a noticeable decrease in runtime, by a factor of 3 to 5 for almost all use cases. This was enabled through numerous performance-related refactors of the geometry, transport, and self-shielding components.

In addition, the following updates were made.

  • Additional accident-tolerant fuel compositions (see Sect. and new dopant properties (see Sect.

  • Polaris can now generate ORIGEN library files (*.f33) (see Sect.

  • Gamma detector modeling was added.

  • Output file was improved.

See Sect. 3.2.2 for details on the updates.

1.2.7. ORIGEN

Extensive improvements to ORIGEN were made for SCALE 6.3, including the following.

  • Modernized library construction integrated into the ORIGEN sequence instead of external the COUPLE sequence (see Sect. for details).

  • Sensitivity analysis capability (see Sect. for details).

  • OBIWAN command line utility (see Sect. 5.2 for details).

1.2.8. ORIGAMI

There were minimal changes to ORIGAMI for SCALE 6.3; however, the ORIGEN reactor library data has been refreshed and includes higher burnups and enrichments (see Sect. 5.3 for details).

1.2.9. XSProc

The main changes to XSProc for SCALE 6.3 comprise adjustments to the default self-shielding parameters to reduce biases at high temperature and high burnup, as well as to improve the Bondarenko method accuracy for fuel models with multiple radial temperature zones. The input below demonstrates a lattice cell with multiple temperature rings using the fast Bondarenko-based self-shielding method (Bonami).

=csas6 parm=(bonami)
mg-keno with bonami for nonuniform temperature
read comp
   uo2  1  den=10.97  1.0 1200.0  92235 5.0  92238 95.0 end
   uo2  2  den=10.97  1.0 1100.0  92235 5.0  92238 95.0 end
   uo2  3  den=10.97  1.0 1000.0  92235 5.0  92238 95.0 end
   uo2  4  den=10.97  1.0  900.0  92235 5.0  92238 95.0 end
   uo2  5  den=10.97  1.0  800.0  92235 5.0  92238 95.0 end
   uo2  6  den=10.97  1.0  700.0  92235 5.0  92238 95.0 end
   uo2  7  den=10.97  1.0  600.0  92235 5.0  92238 95.0 end
helium  8   1.0 600.0 end
 zirc4  9   1.0 600.0 end
   h2o 10  den=0.661  1.0  600.0 end
end comp

read celldata
latticecell squarepitch
  pitch=1.4427  10
  fuelr=0.177473 1
  fuelr=0.250985 2
  fuelr=0.307393 3
  fuelr=0.354946 4
  fuelr=0.396842 5
  fuelr=0.434719 6
  fuelr=0.469550 7
  gapr=0.479100  8
  cladr=0.546400 9 end
end celldata

read param
end param

read geometry
global unit 1
  cylinder 1 0.177473 1.0 -1.0
  cylinder 2 0.250985 1.0 -1.0
  cylinder 3 0.307393 1.0 -1.0
  cylinder 4 0.354946 1.0 -1.0
  cylinder 5 0.396842 1.0 -1.0
  cylinder 6 0.434719 1.0 -1.0
  cylinder 7 0.469550 1.0 -1.0
  cylinder 8 0.479100 1.0 -1.0
  cylinder 9 0.546400 1.0 -1.0
  cuboid  10 6p0.72135
  media   1  1  1
  media   2  1  2 -1
  media   3  1  3 -2
  media   4  1  4 -3
  media   5  1  5 -4
  media   6  1  6 -5
  media   7  1  7 -6
  media   8  1  8 -7
  media   9  1  9 -8
  media  10  1 10 -9
  boundary 10
end geometry

read bounds
end bounds

end data

1.2.10. DATA

One of the main data updates for SCALE 6.3 is the inclusion of additional ENDF/B-VIII.0 data resources and the removal of ENDF/B-VII.0 data. New data resources include the following:

  • New ice and other compounds such as reactor-grade graphite present in ENDF/B-VIII.0.

  • Continuous-energy (CE) cross section data based on ENDF/B-VII.1 and ENDF/B-VIII.0.

  • New multigroup (MG) libraries for fast-spectrum and thermal-spectrum systems (reactivity and depletion results closer to higher fidelity CE results).

See Sect. 10.1 for details.

Note that all 3D Monte Carlo codes in SCALE (TRITON, CSAS, MAVRIC) support both CE and MG methods. MG data and methods are faster but more approximate solutions.

1.2.11. Sampler

Sampler includes considerable updates to help users understand the causes of uncertainty in their simulations. Updates include the following:

  • New sensitivity metrics for understanding nuclear data responsible for the majority of uncertainty (see Sect. for details).

  • Ability to analyze uncertainty due to delayed neutron data using the new perturb_kinetics option.

  • A new analysis block which includes ability to calculate correlation coefficients between arbitrary outputs (see Sect. for details).

1.2.12. TSUNAMI

For SCALE 6.3, the following enhancements were made to TSUNAMI.

  • New Shift-based iterated fission probability (IFP) method with better performance than previous KENO-based IFP and Clutch methods.

  • Improved performance of TSUNAMI-IP similarity and uncertainty calculations.

  • New general HDF5 format for the sensitivity coefficients (see Sect. for details).

1.2.13. AMPX

AMPX continues to be included in SCALE 6.3 and has been used exclusively to generate all libraries described in Sect. 10.1. The major enhancements were modernization related—to increase robustness of generated CE and MG libraries and to enable reading the new international GNDS data format. AMPX is now an open-source code system; the newest features are available by contacting the AMPX team.

1.2.14. Omnibus

Omnibus is the new frontend for the high-performance Shift Monte Carlo and Denovo deterministic transport codes that enables cutting-edge execution of Shift on GPU and Hybrid GPU/CPU platforms. As this capability evolves rapidly, please contact the authors of [IntroPJE+16] for details on getting the latest version of this frontend and manual [IntroJED+20].

1.3. Removed Components in SCALE 6.3

Three SCALE sequences have been removed in SCALE 6.3,


  • STARBUCS`, and

  • CSAS5S`.

1.3.1. SOURCERER Alternatives

SOURCERER was designed as a sequence that wraps a CSAS calculation with a starting source from a Denovo deterministic calculation. The hope was that this would accelerate convergence, however the utility for practical applications has been questionable. For SCALE 7.0, additional source convergence diagnostics are being developed and it is the intention that any techniques for starting sources would become part of the CSAS starting source specification, not their own sequence, and apply to both KENO and Shift.

1.3.2. STARBUCS Alternatives

STARBUCS is to a certain extent superseded by the UNF Standards system for generating spent fuel inventory and generating dry storage and transportation casks for criticality and shielding calculations. Although it is not a 1-to-1 replacement, as STARBUCS is designed specifically for burnup credit applications, the usership of STARBUCS appears to be quite low in recent years and there was little sponsor interest in funding the modernization. For SCALE 7.0, we are entertaining the idea that a burnup credit application could be built using functionality in Sampler and ORIGAMI and some of the key enhancements needed for this application would be useful in other areas as well. Those include the following.

  • Refocusing ORIGAMI on simply generating high-quality, annotated F71s. Annotated means that there is information about burnup, operating history, assembly type, and other data that can be used by downstream codes, e.g. ORIGAMI-generated axial zone-wise data can easily be translated to a 3D model

  • Develop tools to effectively translate that inventory to CSAS and MAVRIC models
    • Populating any SCALE mixture with data from an F71

    • Generating composition blocks from an F71

  • Add additional search capabilities to Sampler.

1.3.3. CSAS5S Alternatives

The parametric study option in Sampler is the clear successor to CSAS5S search capability. With the parametric study, users are able to construct \(k_{eff}\) curves as a function of any parameters in the model. SCALE 7.0 Sampler enhancements will enable surface reconstruction and some search capability which can be used in any sequence.

1.4. Deprecated Components in SCALE 6.3

The following components are deprecated in SCALE 6.3 and are slated for removal in SCALE 7.0.

  • COUPLE: the FIDO-based ORIGEN library manipulator is currently superseded by the

    capabilities in the new ORIGEN build_lib block. Additional manipulation will be available using the OBIWAN command line utility.

  • ARP: the ORIGEN library interpolator will be removed in SCALE 7.0 in favor of inline interpolation methods used within ORIGEN and ORIGAMI.

The following default changes will occur in SCALE 7.0.

  • ORIGEN’s CRAM solver will become the default instead of MATREX for ORIGEN and all other transport plus depletion sequences like Polaris and TRITON.

  • All ORIGEN libraries will be written in HDF5 format.

1.5. Using SCALE

SCALE sequences have been incrementally developed over several decades, with the primary goals of robustness, accuracy, and ease-of-use. One side effect of this evolution can be seen in our user interfaces: the text-based input that drives a calculation. There is no standard SCALE input. For example, TRITON, CSAS, and MAVRIC are similar in their style, which predates SCALE 6.2, when numerous new user interfaces were introduced.

For example:

  • The Polaris sequence for lattice physics was modeled after the brevity and conciseness of CASMO and has a distinct syntax and output.

  • The ORIGEN code for general depletion and decay uses the SON syntax introduced in SCALE 6.2 as a significant upgrade from FIDO, but it keeps the same basic input structure and has a more general feel compared to Polaris.

  • The Sampler code for uncertainty propagation was created with a syntax originally intended to be the upgrade to the TRITON, CSAS, and MAVRIC style, but it was superseded by SON.

  • The shell sequence, which can perform a limited set of common file system operations across platforms.

The SCALE input file is quite flexible in that it can contain numerous sequence inputs executed sequentially. For example, in the input below, we irradiate a milligram of iron in a beginning-of-life pressurized water reactor spectrum for one day and then decay for nine days.

cp ${DATA}/arplibs/w17_e50.f33 f33

  lib{ file=f33 pos=1 }
  mat{ iso=[Fe=0.001] units=GRAMS }
  flux=[1e14  0] %neutrons/cm^2-s
  time=[   1 10] %days

The first =shell sequence copies a specific ORIGEN library from the SCALE data directory to the temporary working directory. ORIGEN can then find this file to load one-group cross sections for this test irradiation.

1.5.1. Running SCALE from Fulcrum

The most convenient way to run SCALE from a desktop is by launching Fulcrum. The Fulcrum executable is provided in the bin directory where SCALE was installed (e.g., C:\SCALE-6.3.0\bin\Fulcrum.exe). Fulcrum includes an online help document to assist users with its many features, and it includes links to the user manual and primers.

1.5.2. Running SCALE from the Command Line

Using the command line, SCALE can be executed using the scalerte command from the bin directory inside the SCALE installation (e.g., C:\SCALE-6.3.0\bin\scalerte). Your directory may differ based on the installation. Assuming the location of scalerte is known, a SCALE input can be run simply as

scalerte -m my.inp

with the -m option requesting SCALE to output status updates to the terminal. See Sect. 12 for details.

1.6. User Guidance and Technical Assistance

This SCALE manual serves as the primary reference for SCALE users. The fundamental theory and all code options are documented herein. Several SCALE primers are available to serve as step-by-step guides for new users performing common calculations using the GUIs. SCALE training courses are presented several weeks each year, during which users can interact directly with the software developers and expert users from ORNL. Additional technical information on SCALE can be found at http://scale.ornl.gov—including training course schedules, a link to an online user forum, newsletters, benchmark reports, and downloads. Technical assistance is also provided via email at scalehelp@ornl.gov.

1.7. Code Availability

The SCALE code system is packaged and distributed by the RSICC and is also distributed through the Organization for Economic Cooperation and Development (OECD) Nuclear Energy Agency (NEA) Data Bank in France and the Research Organization for Information Science and Technology (RIST) in Japan.

1.8. History

The SCALE code system dates back to 1969, when ORNL began providing the transportation package certification staff at the US Atomic Energy Commission (AEC) with computational support in the use of the new KENO code. KENO was used to perform criticality safety assessments with the statistical Monte Carlo method. From 1969 to 1976, the AEC certification staff relied on ORNL personnel to assist them in the correct use of codes and data for criticality, shielding, and heat transfer analyses of transportation packages. However, the certification staff learned that occasional users had difficulty becoming proficient in performing the calculations often needed for an independent safety review. Thus, shortly after the certification staff was moved to the US Nuclear Regulatory Commission (NRC), the NRC proposed development of an easy-to-use analysis system that provided the technical capabilities of the individual modules with which they were familiar. With this proposal, the concept of SCALE as a comprehensive modeling and simulation suite for nuclear safety analysis and design was born. The NRC staff provided ORNL with some general development criteria for SCALE: (1) focus on applications related to nuclear fuel facilities and package designs, (2) use well-established computer codes and data libraries, (3) design an input format for the occasional or novice user, (4) prepare standard analysis sequences (control modules) to automate the use of multiple codes (functional modules) and data to perform a system analysis, and (5) provide complete documentation and public availability. With these criteria, the ORNL staff laid out the framework for the SCALE system and began development efforts. The initial version of SCALE (Version 0) was distributed in July 1980. Although the capabilities of the system continue to evolve, the philosophy established with the initial release still serves as the foundation of SCALE 6.3, more than 40 years later. In July 1980, the initial version of SCALE was made available to the Radiation Safety Information Computational Center (RSICC) at ORNL. This system was packaged and released by RSICC as CCC-288/SCALE 0. Subsequent additions and modifications resulted in the following releases: CCC-424/SCALE1 in 1981; CCC-450/SCALE 2 in 1983; CCC-466/SCALE 3 in 1985; CCC-545/SCALE 4.0 in 1990; SCALE 4.1 in 1992; SCALE 4.2 in 1994; SCALE 4.3 in 1995; SCALE 4.4 in 1998; SCALE 4.4a in 2000; CCC-725/SCALE 5 in 2004; CCC-732/SCALE 5.1 in 2006; CCC-750/SCALE 6.0 in 2009; CCC-785/SCALE 6.1 in 2011; CCC-834/SCALE 6.2 in 2016.

1.9. Acknowledgements

Most team members are credited for their authorship of the sections in this manual that correspond to their work. A few individuals have been essential to the development and maintenance of SCALE but are not credited by authorship. These individuals include B. Taylor, J. Batson, M. Henley, S. Poarch, B. Bevard, L. Aloisi, D. Bowen, and R. Grove.

We also acknowledge the support of Dr. A. Chambers and the DOE/NCSP and D. Algama, D. Barto, L. Kyriazidis, and H. Esmaili of the NRC.



Seth R. Johnson, Thomas M. Evans, Gregory G. Davidson, Steven P. Hamilton, Tara M. Pandya, Katherine E. Royston, and Elliott D. Biondo. Omnibus User Manual. Technical Report ORNL/TM-2018/1073, Oak Ridge National Laboratory, Oak Ridge, TN (USA), 2020.


T. M. Pandya, S. R. Johnson, Evans, T.M., G. G. Davidson, S. P. Hamilton, and A. T. Godfrey. Implementation, capabilities, and benchmarking of shift, a massively parallel monte carlo radiation transport code. Journal of Computational Physics, 308:239–272, 2016. Publisher: Elsevier.