NEA-0437 RELAP-UK.

1. NAME OR DESIGNATION OF PROGRAM:  RELAP-UK.

3. NATURE OF PHYSICAL PROBLEM SOLVED

The program calculates thermal- hydraulic transients in water-cooled nuclear reactors by solving approximations to the one-dimensional equations of hydraulics in an  arbitrarily connected system of nodes. A one-dimensional fuel pin heat conduction model is incorporated, and pumps, heat exchangers, valves, fill systems and leaks may be represented. A point neutron kinetics model, with Doppler and void feedback, is included. A steady state option is available.

RELAP-UK/MK4 is the latest UK code in the RELAP series. It is the first version with full capability for PWR blowdown. The major im- provements over earlier versions are a drift flux model, the Bryce flow-dependent slip correlation, a revised bubble rise model and a generalised "heat slab" option. Other developments include a simple  rewetting model, Fanning friction factor and change of area pressure drop models, time-dependent boundary nodes and an option to input pump speed history.

4. METHOD OF SOLUTION

The fluid mass and energy conservation equations are advanced explicitly, while the momentum equation is partially implicit. Other items are treated explicitly.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

No restriction on number of nodes and connections other than size of core store available. A 44 node and 48 connection problem requires 483k bytes,  the minimum program size being 449k bytes. The use of explicit advancement in time means that the maximum stable time step is limited by the speed of sound in the fluid, and is proportional to the size of the smallest node. The user is required to choose the time step size, and to check that his choice gives a 'converged' result.

6. TYPICAL RUNNING TIME

The 44 node and 48 connection problem requires 1.64 minutes CPU time on the IBM 370 for 0.2 seconds of real time (1000 time steps). The restriction in '5' above means that the running time on a given problem is roughly proportional to the square of the number of nodes. However, the maximum stable time step will be problem dependent.

7. UNUSUAL FEATURES OF THE PROGRAM

Program is different from other versions of RELAP and most other blowdown codes in having a steady state option.

8. RELATED AND AUXILIARY PROGRAMS:  Based on the ANC code RELAP-3.

- I. Brittain and F.J. Fayers:
  Some Aspects of Model Improvements in RELAP-UK
  AEEW - M 1253 (March 1974).
- NEA CPL:
  RELAP-3 Testing Notes
  (Sept. 1972).
- W.H. Rettig et al:
  RELAP3 - A Computer Program for Reactor Blowdown Analysis
  IN-1321 (June 1970).
- Errata Refer to Manual IN-1321 as Corrected by Revision 5/71
  (August 18, 1971).
- Development of the Optional Two-Phase Frictional Pressure Drop
  Correlation for use in RELAP3
  (August 18, 1971).
- M.A. Lintner:
  PLOTR3, A Plotting Routine for RELAP Data Tapes
  (January 1970).
- Walter H. Rettig:
  VDRELAP3 - A Program to Redimension RELAP3
- I. Brittain et al:
  The Status of RELAP-UK MKIII at July 1976 - A program for
  Transient Thermal-Hydraulic Analysis
  AEEW-R 1083 (May 1977).
- I. Brittain et al:
  The RELAP-UK MK IV Transient Thermal-Hydraulic Code Summaty and
  Input Data Description
  AEEW-R 1196 (Aug 1978).
- M. Heitsch and H. Wand:
  Pre- and Post-Test Calculations with RELAP-UK/MK4 for a Small Brea
  LOCA Experiment.
  Reprint from "Kernenergie", 30(1987)9, 351-357

11. MACHINE REQUIREMENTS

449k bytes to 690k bytes of fast core. Up to 2 tape/disk units for restart option. A clock is required only for output of CPU time used.

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

14. ANY OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

To run either very small problems efficiently, or very large problems,  a small change is required in one dimension statement in the main program.

15. NAME AND ESTABLISHMENT OF AUTHOR

    I. Brittain and C. Green
    United Kingdom Atomic Energy Authority
    Winfrith, Dorchester, Dorset
    England.

File name	File description	Records
NEA0437_01.001	SOURCE PROGRAM (F4) EBCDIC	14968
NEA0437_01.002	ASSEMBLER SUBROUTINES	718
NEA0437_01.003	OVERLAY CARDS	13
NEA0437_01.004	SAMPLE PROBLEM DATA	156
NEA0437_01.005	SAMPLE PROBLEM PRINTED OUTPUT	6276

File name	File description	Records
NEA0437_02.001	INFORMATION	13
NEA0437_02.002	ASSEMBLER (BUFOUT)	202
NEA0437_02.003	ASSEMBLER (DATE)	92
NEA0437_02.004	ASSEMBLER (KB10AS)	368
NEA0437_02.005	ASSEMBLER (TIMSET)	31
NEA0437_02.006	ASSEMBLER (ZA19AS)	91
NEA0437_02.007	SOURCE	28686
NEA0437_02.008	'REEDIT' ROUTINE	173
NEA0437_02.009	JCL	126
NEA0437_02.010	OVERLAY CARDS	31
NEA0437_02.011	INPUT DATA FOR SAMPLE PROBLEM	403
NEA0437_02.012	OUTPUT OF SAMPLE PROBLEM	2560