**MCNP/X Merger**

John S. Hendricks

H. Grady Hughes

Gregg W. McKinney

Richard E. Prael

John T. Goorley

*Los Alamos National Laborator,MS A143, Los Alamos NM 87545*
<jxh@lanl.gov>

MCNP \[1\] and MCNPX \[2\] are being merged into a single Monte Carlo
radiation transport code, eventually to be released as "MCNP6." We
present here the background, description of merger work, and results.

# **BACKGROUND**

MCNP is heir to the original development of Monte Carlo radiation
transport during the Manhattan Project at Los Alamos during World War
II. Over the years the Monte Carlo method has become increasingly
popular due to improvements in the method and computers. Codes such as
MCNP have become the repository of physics knowledge representing
hundreds of person-years of development. MCNP is perhaps the most widely
used physics software in the world. It is used for a wide variety of
radiation simulation applications, ranging from outer space to oil well
logging deep underground, from defense and homeland security to health
physics and medical therapy applications, from nuclear safety to nuclear
safeguards.

Over the years MCNP has been developed by making stand-alone codes which
then are integrated into the main code only after achieving robustness
and acceptance. Examples include merging MCN (neutrons) \[3\], MCG
(gammas), and MCP (photons) \[4\] to make the original MCNP. Later
mergers include nuclear criticality (KCODE), multigroup / adjoint (MCMG)
\[5\], electron physics (MCNPE), and tally plotting (MCPLOT.) In 1992
MCNPX development commenced to merge MCNP4B \[6\] and LAHET \[7\] (built
upon HETC \[8\], Bertini \[9\], ISABEL \[10\], FLUKA \[11\], and CEM
\[12\]) into a high-energy many-particle MCNP superset \[13\]. Within a
decade MCNPX could do everything MCNP could do and could transport 34
nuclear particles and light ions up to TeV energies \[14\]. Soon MCNPX
was based upon MCNP4C \[15\], adding new capabilities for accelerator
applications, nuclear safeguards, space applications, and homeland
security \[16\]. Meanwhile, MCNP5 \[17-19\] was released with a more
modern architecture, new electron \[20\], and new criticality
capabilities \[21\].

Beginning October 2006 a two-year project was initiated to merge MCNP5
and MCNPX to halt divergence, end duplication of effort, and provide a
unified tool for a wider variety of applications.

# **MERGER WORK AND STATUS**

The MCNP/X merger project is scheduled for two years. MCNP5 consists of
450 subroutines of which 150 are significantly different than MCNPX and
several dozen are unique to MCNP. MCNPX has about 1200 additional
subroutines independent of MCNP. The capabilities of MCNPX26B \[22\] are
being integrated into a preliminary MCNP6 which already had a proton
transport capability and features developed especially for proton
radiography \[23\]. MCNP has about 400 subroutines. MCNPX has 500
subroutines for various physics models and other capabilities in
addition to 400 subroutines related to MCNP4C. Of these, 55 are new, 200
are nearly the same as MCNP5, and 150 are significantly different
requiring careful merging.

The integration of MCNPX into MCNP is being done subroutine by
subroutine in 9 phases. In each phase the integrity of MCNP6 is
maintained and passes the MCNP test sets while additional MCNPX
capabilities are added. The phases are:

1.  Move MCNPX variables to MCNP6 and reconcile particles;

2.  Read MCNPX input;

3.  Process MCNPX input (geometry, tallies, materials, new capabilities
    -- finish IMCN);

4.  Process MCNPX data libraries, proton libraries, heating and other
    material capabilities (XACT);

5.  Run particles;

6.  Enable MCNPX extended transport capabilities such as tallies,
    special sources, variance reduction, burnup, ion recoil, fission
    multiplicity, etc.;

7.  Enable geometry and tally plotting;

8.  Reconcile mesh tallies and other advanced plotting capabilities;

9.  Update to all recent MCNP5 and MCNPX (versions 26c, d, e, f)
    advances (delayed neutron and gamma models, activation neutrons and
    gammas, heavy ion \[2000+ particles\] transport with LAQGSM, muon
    capture physics, energy-time coupled weight windows, spherical
    windows and mesh tallies, etc.\[24\])

As of the January 2008 paper deadline Phase 6 was nearing completion.
The 90-problem MCNP regression test set runs correctly and most of the
65-problem MCNPX regression test set runs.

# **RESULTS**

During the past two years the MCNP and MCNPX Teams have integrated key
personnel and have released MCNP and MCNPX upgrades/versions and data
libraries together through the Radiation Safety Information
Computational Center (RSICC) in Oak Ridge, TN. Classes have been
coordinated and starting June 2008 consolidated. Separate versions of
MCNP and MCNPX will continue to be released until the merged code has
all the functionality and backwards compatibility of both.

A preliminary merged code version, MCNP6, is expected by the June 2008
ANS Anaheim meeting with an internal LANL release target date of
October, 2008.

**REFERENCES**

1.  <http://mcnp-green.lanl.gov/>

2.  <http://mcnpx.lanl.gov/>

3.  E. D. Cashwell, J. R. Neergaard, W. M. Taylor, and G. D. Turner,
    "MCN: A Neutron Monte Carlo Code," *Los Alamos National Laboratory
    Report,* LA-4751 (January 1972)

4.  E. D. Cashwell, J. R. Neergaard, C. J. Everett, R. G.
    Schrandt, W. M. Taylor, and G. D. Turner, "Monte Carlo Photon Codes:
    MCG and MCP," *Los Alamos National Laboratory Report,* LA-5157
    (March 1973)

5.  John C. Wagner, Everett L. Redmond II, Scott P. Palmtag, and John S.
    Hendricks, "MCNP: Multigroup/Adjoint Capabilities." *Los Alamos
    National Laboratory Report,* LA-12704 (April 1994)

6.  R. E. Prael and H.Lichtenstein, "*User Guide to LCS: The LAHET Code
    System*," *Los Alamos National Laboratory Report* LA-UR-89-3014,
    Revised (September 15, 1989)

7.  J. F. Briesmeister, Ed., "MCNP - A General Monte Carlo N-Particle
    Transport Code \-\-- Version 4B," *Los Alamos National Laboratory
    Report,* LA-12625-M (March 1997)

8.  Radiation Shielding Information Center, "HETC Monte Carlo
    High-Energy Nucleon-Meson Transport Code," *Oak Ridge National
    Laboratory Report* CCC-178, (August 1977)

9.  H. W. Bertini, *Physics Review* **188** 1711 (1969)

10. Y. Yarviv and Z. Fraenkel, *Physics Review C* **24** 488 (1981)

11. P. A. Aarnio, J. Lindgren, A. Fasso, J. Ranft and G. R. Stevenson,
    "FLUKA-87," CERN-TISRP/190 (1987)

12. S. G. Mashnik, A. J. Sierk, O. Bersillon, and T. A. Gabriel,
    "Cascade-Exciton Model Detailed Analysis of Proton Spallation at
    Energies from 10 MeV to 5 GeV", *Nucl. Instr. Meth.* **A414** (1998)
    and *Los Alamos National Laboratory Report* LA-UR-97-2905 (1997)

13. H. G. Hughes, et. al., "Status of the MCNP/LCS Merger Project,"
    American Nuclear Society Radiation Protection and Shielding Topical
    Conference, Nashville, TN (April 19-23, 1998)

14. Laurie S. Waters, Ed., "MCNPX User's Manual -- Version 2.3.0," *Los
    Alamos National Laboratory Report,* LA-UR-02-2607 (April 2002)

15. J. F. Briesmeister, Ed., "MCNP - A General Monte Carlo N-Particle
    Transport Code \-\-- Version 4C, *Los Alamos National Laboratory
    Report,* LA-13709-M (March 2000)

16. Denise B. Pelowitz, ed., "MCNPX User's Manual, Version 2.5.0," *Los
    Alamos National Laboratory Report,* LA-CP-05-0369 (April 2005)

17. X-5 Monte Carlo Team, "MCNP --- A General Monte Carlo N-Particle
    Transport Code, Version 5, Volume I, MCNP Overview and Theory," *Los
    Alamos National Laboratory Report,* LA-UR-03-1987, April 24, 2003
    (Revised 10/3/05)

18. X-5 Monte Carlo Team, "MCNP --- A General Monte Carlo N-Particle
    Transport Code, Version 5, Volume II: MCNP User's Guide," *Los
    Alamos National Laboratory Report,* LA-CP-03-0245, April 24, 2003
    (Revised 10/3/05)

19. X-5 Monte Carlo Team, "MCNP --- A General Monte Carlo N-Particle
    Transport Code, Version 5, Volume III, MCNP Developer's Guide," *Los
    Alamos National Laboratory Report,* LA-CP-03-0284, April 24, 2003
    (Revised 10/3/05)

20. H. Grady Hughes, "Improved Logic for Sampling Landau Straggling in
    MCNP5," *Los Alamos National Laboratory Report* LA-UR-05-4404, M&C
    2005, ANS Mathematics and Computation Topical Meeting, Avignon,
    France (September 12-15, 2005)

21. F. Brown, B. Nease, J. Cheatham, "Convergence Testing for MCNP5
    Monte Carlo Eigenvalue Calculations," Joint International Topical
    Meeting on Mathematics and Computations and Supercomputing for
    Nuclear Applications, (Monterey, CA, April 15-19, 2007)

22. John S. Hendricks, Gregg W. McKinney, Holly R. Trellue, Joe W.
    Durkee, Joshua P. Finch, Michael L. Fensin, Michael R. James,
    Denise B. Pelowitz, Laurie S. Waters, Franz X. Gallmeier,
    Jean-Christophe David, "MCNPX Version 26B" *Los Alamos National
    Laboratory Report* LA-UR-06-3248 (June 2006)

23. H. Grady Hughes, et. al., \"MCNP5 for Proton Radiography,\" *Los
    Alamos National Laboratory Report* LA-UR-04-8760,
    ISBN:0-89448-695-0, ANS Order No. 700321, Monte Carlo 2005,
    Chattanooga, TN (April 17-21, 2005)

24. John S. Hendricks, Gregg W. McKinney, Michael L. Fensin, Michael R.
    James, Russell C. Johns , Joe W. Durkee, Joshua P. Finch, Denise B.
    Pelowitz, Laurie S. Waters, Franz X. Gallmeier, "MCNPX Version 26E"
    *Los Alamos National Laboratory Report* LA-UR-07-6632 (October 2007)