NEA-0865 SCRIMP.

1. NAME OR DESIGNATION OF PROGRAM:  SCRIMP.

3. DESCRIPTION OF PROBLEM OR FUNCTION

SCRIMP is a thermal hydraulic subchannel analysis code which calculates the steady state pressure  drops, flow rates, heat transfer rates and temperatures in gas- cooled thermal reactors. It is not designed to model fast reactor conditions, but can be used if the power gradient across a fuel element is not too large.

4. METHOD OF SOLUTION

A lumped parameter type of calculation is applied using averaged values for each sub-flow-area or subsurface.  The same pressure drop is assumed to exist along each subchannel, and no net cross flow is allowed between them in any one axial step. Turbulent eddy, momentum exchange between adjacent subchannels is, however, calculated.

Four heat transfer modes are considered:
1)  Surface to coolant convection.
2)  Intersurface radiation exchange.
3)  Intersurface conduction.
4)  Surface to ambient heat loss.

Axial variation of physical properties and the redistribution of mass flow between subchannels can be accounted for by dividing the problem into a series of axial steps. The outflow properties of one  step are used to compute the inflow properties of the next.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

There is a maximum of 28 characteristic flow channels and 74 characteristic surfaces.
However, the total number of channels and surfaces is limited only by the available memory space.

6. TYPICAL RUNNING TIME

32 seconds of CP time on a CDC 6500 were required for a sample problem consisting of a 37 rod hexagonal bundle divided into 4 axial sections. 1% iteration accuracy was requested, and radiation exchange was neglected.

7. UNUSUAL FEATURES OF THE PROGRAM

SCRIMP incorporates a new sub- routine to calculate friction factors and stanton numbers in terms of subchannel boundary conditions. Thus, individual heat transfer coefficients are computed for each subsurface; the earlier SCEPTIC code calculated only one value per subchannel.

The program is suitable for a wide range of geometries.

8. RELATED AND AUXILIARY PROGRAMS

SCRIMP is an extended version of SCEPTIC, itself a modification of HECTIC-II.

10. REFERENCES:

- M. Huggenberger:
  SCRIMP: A Subchannel Analysis Code - Short Description and User's
  Guide.  TM-IN-635  September 1976.
- M. Huggenberger:
  SCRIMP: A Thermal-Hydraulic Subchannel Analysis Computer Code.
  EIR-Bericht Nr. 322  June 1977.

11. MACHINE REQUIREMENTS

140,000 octal words on a CDC 6500. In addition, one subroutine requires a buffer of 20,000 octal words of  extended core storage.

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  Standard.

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:

15. NAME AND ESTABLISHMENT OF AUTHOR

          M. Huggenberger
          Eidg. Institut fuer Reaktorforschung
          5303 Wuerenlingen
          Switzerland

File name	File description	Records
NEA0865_01.003	SCRIMP INFORMATION FILE	35
NEA0865_01.004	SCRIMP SOURCE PROGRAM (FORTRAN-4)	2076
NEA0865_01.005	SCRIMP INPUT DATA FOR TEST CASE	220
NEA0865_01.006	SCRIMP JCL FOR TEST CASE EXECUTION	14
NEA0865_01.007	SCRIMP PRINTED OUTPUT OF TEST CASE	2316