**RSICC CODE PACKAGE PSR-579**

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**1. NAME AND TITLE**

DYN3D/M2: Reactivity Transients in Light H2O Reactors with Hexagonal Geometry.

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**2. CONTRIBUTORS**

Research Center Rossendorf Inc., DO-8051 Dresden, Germany through the Nuclear Energy Agency Data Bank, Issy-les-Moulineaux, France.

**3. CODING LANGUAGE AND
COMPUTER**

Fortran 77; IBM 3090 (P00579I309000).

**4. NATURE OF PROBLEM
SOLVED**

DYN3D/M2 is a computer code for calculating reactivity induced transients in light-water reactor cores with hexagonal fuel elements, including the initial steady state, in three-dimensional geometry. As results of the program, neutron fluxes and power distributions, thermo-hydraulics parameters of the coolant, fuel and cladding temperatures and some parameters for fuel rod failure estimation are given. Boundary conditions from the primary coolant circuit (pressure, coolant flow rate and temperature) must be given as input.

**5. METHOD OF SOLUTION**

For solving the two-group neutron diffusion equation, a nodal expansion method in hexagonal geometry is used. In the hexagonal plane, an expansion of the neutron flux in a series of Bessel functions is made. Polynomials up to the 4th order are used for the approximation of neutron flux in axial direction. An exponential transformation technique is used for the time integration of neutron kinetics equations. The thermo-hydraulic part of the code includes a one- or two-phase coolant flow model, a heat transfer regime map from liquid convection up to superheated steam, a fuel rod model including metal-water reaction as well as a simple estimation of mechanical behaviour and a lower plenum mixing model for WWER-440 type reactors. In the thermo-hydraulics model, implicit numerical solution techniques are used. A sophisticated time step control allows a wide range variation of time steps depending on the process behaviour. A restart option can be used and an off-line analysis of results from extended output data files can be accomplished.

**6. RESTRICTIONS OR
LIMITATIONS**

In the main program DYN3D/M2, three working arrays IARR, RARR and FTH are declared (two of REAL type and one of INTEGER type). The necessary lengths of these arrays are problem dependent and can be estimated by rules given in the Code Manual. If the standard lengths (IARR: 25000, RRAR: 380000, FTH: 300000) are too small for the problem considered, the DIMENSION operator in the source file has to be changed.

**7. TYPICAL RUNNING TIME**

The sample problem with 190 spatial nodes took about 340 seconds of CPU time on the IBM 3090 computer. The package was screened at the NEA/DB on a VAX 6000-510 computer under OpenVMS 6.1.

**8. COMPUTER HARDWARE
REQUIREMENTS**

The code runs on an IBM 3090 and IBM-compatible EC 1055 computer. A clock is required.

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**9. COMPUTER SOFTWARE
REQUIREMENTS**

The source files were compiled on the VAX 6000-510 under OpenVMS-6.1 using the DEC Fortran-77 compiler.

**10. REFERENCES**

U. Grundmann and U. Rohde, “The Code DYN3D/M2 for the Calculation of Reactivity Initiated Transients in Light Water Reactors with Hexagonal Fuel Elements - Code Manual and Input Data Description,” FSS-2/92 (March 1992).

**11. CONTENTS OF CODE
PACKAGE**

Included in the package is referenced document listed above along with source codes, and input/output files.

**12. DATE OF ABSTRACT**

October 2012.

**KEYWORDS:** LWR
Reactors, Fuel Rods, Heat Transfer, Hexagonal-Z, Neutron Flux, Power
Distribution, Reactivity, Reactor Cores, Reactor Kinetics, Reactor Safety,
Thermodynamics, Three-Dimensional, Transients, Two-Group Theory, Two-Phase Flow