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Status of the LAHETT" Code System *

Laurie Waters, Richard E. Prael Group XTM, Theoretical and Computational Physics Division

Los Alamos National Laboratory 505-665-4127

Abstract The LAHET Code System (LCS) is extensively used for medium energy accelerator applications, including spallation target design and deep penetration shield- ing problems. Current applications include Accelera- tor Production of Tritium (APT), Accelerator Driven Transmutation Technologies (ADTT), LANSCE and WNR spallation target upgrades, as well as various medical projects. We will discuss recent upgrades to the MCNP and LAHET components of LCS, and re- view the work in progress now funded under the APT program.

1 Introduction The Los Alamos High Energy Transport (LAHET)

Code System [l] consists of two monte carlo codes, LAHETTM and MCNPTM, both of which use the same geometry package. LAHET transports charged and neutral hadrons and mesons down to user defined cutoff energies, while neutrons below the cutoff are passed to the MCNP code. LCS offers a variety of analysis meth- ods, standard tallies and user defined histogramming capability. This paper will review recent advances in the codes, user interfaces, and data libraries, particu- larly as they relate to medium energy accelerator ap- plications. Further information may be found on the LCS Web page: http://www-xdiv.lanl.gov/XTM/lcs/lcs-dir.htm1

2 MCNP The Monte Carlo N Particle (MCNP) version 4a

[2] was released to RSIC on October 4, 1993. Improve- ments to the code include the following [3]:

0 PVM Multiprocessing [4]

0 X window and color graphics display

0 10 statistical tests for assessing convergence [5]

0 Repeated structures tallies

0 Dynamic memory allocation on UNIX systems

0 MS-DOS compatibility

* LAHET, MCNP, Justine, AVATAR and THREEDANT are trademarks of the Regents of the University of California, Los Alamos National Laboratory

0 PTRAK data output files [6]

The estimated release date for MCNP version 4b is October, 1996, and will include the following improve- ments:

PVM load balancing/fault protection

Postscript graphics files on all systems

Online cross section plotting

Multigroup adjoint improvements [7]

Perturbation capability [8]

ITS3 electron/photon physics [9]

In addition, work is being done on formalizing source biasing techniques, as well as user interfaces to do cus- tomized data analysis and histogramming online as a compliment to the current tally procedure [lo].

A variety of classes for MCNP are now available, and are listed on the Web site: http://www-xdiv.lanl.gov/XTM/mcnp/mcnp.html A newsletter is available, along with an internet dis- cussion group, which may be joined by sending email to listserv@pss0l8.psi.ch, and including the message: subscribe mcnp-1 [first name, last name]

MCNP complies with a Software Quality Assurance plan that is consistent with both IEEE and ISO-9000 guidelines for SQA.

Data Of particular interest t o accelerator applications are the high energy libraries now available for MCNP. ENDF/B-VI libraries for MCNP were released in the Fall of 1994 [ll]. Within this release are several nu- clides with data above the traditional 20 MeV limit:

0 lH to 100 MeV

0 notC t o 32 MeV

0 1271 to 30 MeV

e 1 6 5 H ~ to 30 MeV

0 lg7Au to 30 MeV

0 241Am to 30 MeV

A new MCKP data library known as IOOXS [12, 131 contains continuous energy neutron cross sections up to 100 MeV for the following materials: “e, lZC, l60, 27A1, Si, “Ca, Fe, 1%’ Multigroup neutron and/or proton cross sections may also be used for these materials to 100 MeV in MCNP versions having multigroup and BFP capability. A ma- jor effort to upgrade libraries to 150 MeV is now under- way for the APT project, and will be described below.

Photon and electron data are available from 1 keV to 100 GeV (photons), and 1 GeV (electrons).

4 JustineT“ Demand has been growing for a graphical user interface for MCNP and other codes maintained by the Trans- port Group at Los Alamos. Justine [14] is such a GUI, which allows the user to define geometries via construc- tive solid geometric operations on three dimensional objects. Through menu driven options the user can also input all parameters needed to build an MCNP output file. MCNP itself can be run through the Jus- tine interface, and output displayed.

The new automatic variance reduction program AVATARTM [15] is also implemented through Justine. Weight windows are an important variance reduction technique which involve setting upper and lower par- ticle weight limits within a cell, and a particle will be split or Russian Rouletted if its weight is out- side the limits. This weight function is continually modified as the problem proceeds, and thus is par- ticularly sensitive to the initial function input by the user. The procedure is meant to direct particles to- ward the most probably phase space path from the source to a tally. AVATAR (Automatic Variance And Time of Analysis Reduction) uses an approximate ad- joint solution from a three-dimensional deterministic code calculation (THREEDANTTM) to design the ini- tial weight function. The forward calculation then pro- ceeds as usual with MCNP, which continually modifies the weight function via fhe standard weight window generator. Justine prepares the THREEDANT spatial grid, converts results to MCNP weight windows, and runs both codes without any intervention of the user. The user need only set up the forward MCNP problem.

5 LAHET The current version of LAHET is 2.81, which will be considered frozen (except for correction of obvious er- rors) until the work described in the next section is completed. We anticipate the full release of LAHET to RSIC in 1996.

The following improvements have been included in latest version of the code [la]:

1. Variance Reduction: Cell-wise importances, as used in MCNP, have been adapted for LA-

2.

HET. Separate importances can be implemrntfri ‘ for muons, if desired. Roulette/splitting has long been present in LX- HET for neutrons written to the file which is passed to MCNP, controlled by the user de- fined variable SWTM (neutrons with weight less than SWTM are killed with probability (1- weight/SWTM), all others are kept and given weight SWTM). The new scheme further weights the neutrons written to the interim file by the in- verse of the importance of the cell. Similar mod- ifications have been made to the weight controls already present for decaying pions and emerging muons.

Nucleon-Nucleus Elastic Scattering [16]: A new elastic scattering model has been imple- mented in LAHET for neutrons above 15 MeV and protons above 50 MeV. Previously elastic scattering was limited to neutrons below 100 MeV with the Bechetti-Greenlees potential. The new model is a modification of the HERMES code [17]. It includes a complete rewrite of the sampling algorithm for the center-of-mass scat- tering angle, and the elastic cross section data has been replaced from 50 to 400 MeV with a global medium-energy nucleon-nucIeus phenomenologi- cal optical model potential. HERMES data has been kept above 400 MeV. Below 50 MeV there is no elastic scattering implementation for protons. and HERMES data is used for neutrons. The optical potential is based on a relativistic Schrodinger representation using the proton op- tical potential of Schwant et. al. as a starting point. Cross sections for 9 mass values and 20 energies are tabulated in LAHET, and interpola- tions made to other masses.

3. Secondary Multiple Scattering: A user de- fined parameter now controls whether multiple scattering is applied to all particle, or just pri- maries.

4. User Hook A set of user routines is now avail- able which links to the standard LAHET code. These may be used for online data analysis and histogramming techniques not available in the current HTAPE analysis routines.

5. HMCNP: A new code, TRANSM, may be used to process LAHET output into MCNP ”surface source read (SSR)” RSSA files. Such files may be read by any recent version of MCNP, thereby eliminating the need for the special HMCNP ver- sion.

6. New Tally Options Two new edits have been added to the LAHET analysis routine H’TAPE. A collision rate edit will tabulate all collisions,

* neutron elastic scattering, or non-elastic events. 7 References This edit may also be used to generate a CIN- DER90 removal rate input file.

The second new edit produces spectra of to- tal recoil energy, neutron elastic recoil energy,

REFERENCES [I] Richard E. Prael and Henry Lichtenstein, ‘User Guide

to LCS: The LAHET Code System’, Los Aiamos Na- total damage energy and neutron elastic dam- age energy’ The mean weight Of frag- merits, damage energy, and energy per fragment

tional Lab, LA-UR-89-3014, September, 1989. [2] Judith F. Briesmeister, Ed., ‘MCNP-A General Monte

Carlo N-Particle Transport Code, ver 4a’, Los Alamos is also produced. The damage energy U comes National Lab, LA-12625-M, November, 1993. from a parameterization Of the Lindhard func-

energy. This [3] John S. Hendficks, ‘MCNP-Recent Developments~,

ANS Transactions vol 71, 1994 Winter Meeting, Wash- U=E*L(E), where E is edit is primarily used for materials damage stud- ies.

ington, DC, November 13-17, 1994, ~396-397. [4] Gregg W. McKinney, ‘Parallel Processing with Monte

Carlo Radiation Transport Codes’, Proceedings, 8th In- ternational Conference on Radiation Shielding, April

[5] S. P. Pederson, R. A. Forster, T. E. Booth, ‘Confidence Interval Procedures for Monte Carlo Transport Simula-

The immediate task of the Accelerator Production of tions’, ANS Transactions ~ 0 1 73, 1995 Winter Meeting, Tritium program is to design, build and test criti- San Francisco, Oct 29-Nov 2, 1995, ~202-204. cal components of the Proposed accelerator. hsel ine [6] K. A. Van Riper, G. W. McKinney and T. J. Urbatsch, parameters currently are 1000 MeV 200 mAmp ma- ‘The Use of Particle Tracks in Problem Analysis’, LOS chine, where beam is incident on a lead-Tungsten tar- Alamos National Lab, LA-UR-95-129, Fifth Interna- get. Neutrons provided by this source will be moder- tional Conference on Nuclear Criticality Safety, Sept ated in DzO, and capture on 3He to produce tritium. 17-22, 1995- A machine of this intensity makes severe demands on [7] Kenneth J. Adams, Michelle Hart, ‘Multigroup the accuracy of simulation codes involved in its design, Boltzmann-Fokker-Planck Electron-Photon Transport and a program to upgrade the LAHET Code System Capability in MCNP’ ANS Transactions V O ~ 73, 1995 is now underway. I t is estimated that it will take three Winter Meeting, San Francisco, Oct 29-Nov 2, 1995, years t o complete the major components of this effort. P334-337.

the Monte Carlo Differential Operator Technique for LAHET with MCNP. This will enable the user to take MCNP’, Los Alamos National Lab, LA 13098, Decem- advantage of the extensive MCNP variance reduction ber, 1995. techniques, source description, and convergence tests.

[9] H. G. Hughes ‘Status of Electron Transport in MCNP’, It also eliminates the need for large interim files now ANS Transactions vol 73, 1995 Winter Meeting, San Franscisco, Oct 29-Nov 2, 1995, p333-334.

present in LCS. Where library data is not present the LAHET physics routines will be substituted. The code will be highly modular so that new routines can be [lo] Laurie S. Waters, ‘Data Analysis and Visualization in

MCNP’, ANS Transactions vol 71, 1994 Winter Meet- easily implemented, and the whole will be controlled ing, Washington, DC, November 13-17, 1994, p401-402. through the Justine GUI.

[ll] J. S. Hendricks, S. C. Frankle and J. D. Court, Another element of the program is the generation ‘ENDF/B-VI data for MCNP’, Los Alamos National of continuous energy data libraries for neutrons and Lab, LA-^^^^^, 1994. protons up to the pion threshold (about 150 MeV).

[12] Robert C. Little, ‘Summary Documentation for the 100XS Neutron cross Section Library’, Los Alamos Na- Data for all isotopes of approximately 26 elements will

be generated using FKK-GNASH formalism, and the tional Lab, LA-UR-96-24, January, 1996.

[13] P. G. Young, et. al., ‘Transport Data Libraries for In- merged MCNP/LAHET code modified to read new data formats and perform charged particle transport. cident Proton and Neutron Energies to 100 MeV’, Los The present physics contained in LAHET is not ade- Alaos National Lab, LA-11753-MS, 1990. quate for energies below 150 MeV, and the develop-

[14] s. R. Lee, et. al., ‘Unified GUI for the Los Alamos Ra- ment of the libraries is given high priority. diation Transport Code System’, ANS Transactions vol

Improvement of Physics in LAHET is also anti& 71, 1994 Winter Meeting, Washington, DC, November pated, primarily through the continuation of the Opti- 13-17, 1994, p402-403. cal Model work discussed above. This work will affect 1151 Kenneth A. Van Riper, et. al., ‘Generation of a Monte items such carlo variance Reduction M~~ from a Deterministic well as the independent library generation. Improved Transport Calculation’, LOS A l a o s National Lab, LA- nuclear masses will also be added to the code. Other UR-95-747, submitted t o Nuclear Science and Engineer- improvements will take place as funding allows. ing, July, 1995.

24-28, 1994, ~391-397. 6 APT

One element of the program is a complete merger of 181 Gregg We McKinneY and Jess Iverson, ‘Verification of

total cross section in the LAHET code,

, i * ,,

r : I . [I61 Richard E. Prael .LAHET Code System Modifications

for LAHET ’?.8’, Los Xlamos National Laboratory, LX- UR-95-3605, September 30, 1995.

[17] P. Cloth et. al., ‘HERMES - A Monte Carlo Program System for Beam-Materials Interaction Studies’, Kern- forschungsanlage Julich GmbH, Jul-2203, May, 1988.