**
1. NAME AND TITLE**

BUCORST: A Code to Prepare Burnup-Dependent Multigroup Nuclear Reactor Source Terms.

**2. CONTRIBUTOR**

National Accelerator Center, Faure, South Africa.

**3. CODING LANGUAGE AND COMPUTER**

Fortran 77 and MathCad 3.1 for MS Windows 3.1; IBM PC's and compatibles with a 80386 or better processor (P00339PC38600).

**4. NATURE OF PROBLEM SOLVED**

Prompt fission neutrons constitute the most important component of the neutral-particle source term of an operating nuclear reactor. The three isotopes 235U, 238U, and 239Pu make the major contribution to fission in a typical power reactor. Their prompt fission neutron spectra differ; and their relative contributions to fission is a function of burnup, which is, in turn, a time-dependent function of the spatial position in the reactor core. BUCORST uses a rigorous source term model that takes the above factors into consideration, to produce a multigroup source term for reactor shielding calculations in one-dimensional cylindrical geometry. Tabular prompt fission neutron spectra for the above three isotopes, derived from a sophisticated microscopic model calculation, are used. An approximate prompt and delayed fission gamma-ray model is also included. Output is written in a format suitable for direct importation into ANISN or XSDRNPM input data sets.

**5. METHOD OF SOLUTION**

A rigorous, burnup-dependent expression for the continuous prompt fission
neutron source-term function, *Q(E,x) N(E,x)P(x)*, is numerically integrated between the
neutron energy group boundaries and evaluated at the midpoints *xi*, of every spatial
interval. The spatial power distribution function *P(x)* is formed by cubic spline
interpolation between relative power values specified at certain locations inside the source
region. For prompt and delayed fission gamma-rays, it is assumed that the energy and
spatial dependence of the source term is separable, i.e. *Q(E,x) N(E)*. The 1-D volume-
distributed fixed gamma-ray source term is then *Qgi = NgP(xi)*, where *Ng* is the multigroup
energy spectrum (obtained by numerical integration), and *xi* is the midpoint of the *i*'th
spatial interval. The code consists of two modules - a MathCad main module which
performs the source term calculation in a coarse spatial mesh and a Fortran postprocessor
which interpolates to a finer spatial mesh writing output in FIDO format.

**6. RESTRICTIONS OR LIMITATIONS**

Maximum number of energy groups: 150.

Maximum number of coarse-mesh spatial intervals (used in MathCad): 150.

Maximum number of fine-mesh spatial intervals (used in the transport calculation): 1000.

All spatial intervals have the same dimension. This restriction is not inherent in the code and may be easily removed by additional programming.

**7. TYPICAL RUNNING TIME**

The sample problem executes in 15 minutes on a 33 MHZ 80486 PC.

**8. COMPUTER HARDWARE REQUIREMENTS**

An 80386 (or better) IBM-compatible PC and at least 4 MB of RAM. Execution will be very slow on PC's not fitted with floating-point coprocessors, so that the latter is strongly recommended.

**
9. COMPUTER SOFTWARE REQUIREMENTS**

Microsoft Windows 3.1 and MathCad 3.1 are required.

BUCORST was developed using Salford Software's FTN77/484 compiler. This compiler uses the DBOS DOS extender. No special compiler features were used. Adaptation to other Fortran compilers with DOS extenders is possible. RSIC used Lahey F77L/EM32 v5.1 making minor modifications to the source to allow for CHARACTER to INTEGER equivalencies in the FFPUN subroutine. RSIC has also included an executable created with the Lahey compiler that does not require the Lahey software. The original executable is not bound with the DBOS DOS extender and requires the Salford Software Fortran package for execution.

**10. REFERENCES**

T. J. van Rooyen, "Bucorst, a Code to Prepare Burnup-Dependent Multigroup Nuclear Reactor Source Terms," NAC/93-01 (June 1993).

T. J. van Rooyen, G. P. de Beer, "A Burnup-Compensated Madland-Nix Prompt Fission Neutron Source Term for Multigroup Nuclear Reactor Shielding Calculations," Nucl. Sci. & Eng., 114, 87-101 (June 1993). (Copyright 1993 by the American Nuclear Society, La Grange Park, Illinois.)

**
11. CONTENTS OF CODE PACKAGE**

The referenced documents and 1 DS/HD 3.5" (1.44 MB) diskette in self-extracting compressed DOS files are included. The diskette contains Fortran 77 source files, executables, MathCad scripts, sample input/output, and an information file.

**12. DATE OF ABSTRACT**

March 1994.

** KEYWORDS**: NEUTRON; SOURCE STRENGTH; BURNUP; MICROCOMPUTER