NESC1115 VISA2.

1. NAME OR DESIGNATION OF PROGRAM:  VISA2.

3. DESCRIPTION OF PROGRAM OR FUNCTION

VISA2 (Vessel Integrity Simulation Analysis) was developed to estimate the failure probability of nuclear reactor pressure vessels under pressurized thermal shock conditions. The deterministic portion of the code performs heat transfer, stress, and fracture mechanics calculations  for a vessel subjected to a user-specified temperature and pressure  transient. The probabilistic analysis performs a Monte Carlo simulation to estimate the probability of vessel failure. Parameters such as initial crack size and position, copper and nickel content,  fluence, and the fracture toughness values for crack initiation and  arrest are treated as random variables. Linear elastic fracture mechanics methods are used to model crack initiation and growth. This includes cladding effects in the heat transfer, stress, and fracture mechanics calculations. The simulation procedure treats an  entire vessel and recognizes that more than one flaw can exist in a  given vessel. The flaw model allows random positioning of the flaw within the vessel wall thickness, and the user can specify either flaw length or length-to-depth aspect ratio for crack initiation and arrest predictions. The flaw size distribution can be adjust on the  basis of different inservice inspection techniques and inspection conditions. The toughness simulation model includes a menu of alternative equations for predicting the shift in the reference temperature of the nil-ductility transition.

4. METHOD OF SOLUTION

The solution method uses closed form equations  for temperatures, stresses, and stress intensity factors. A polynomial fitting procedure approximates the specified pressure and temperature transient. Failure probabilities are calculated by a Monte Carlo simulation.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

Maxima of -
   30 welds
VISA2 models only the beltline (cylindrical) region of a reactor vessel. The stresses are a function of the radial (through-wall) coordinate only and are independent of the axial and circumferential coordinates. The polynomial approximation of pressure-temperature transients requires the user to avoid (or smooth) transients with pressure spikes and other discontinuities.

6. TYPICAL RUNNING TIME

Typical problems require five minutes on a DEC VAX11/780 and one hour on an IBM PC. NESC executed the sample problem in 50 seconds on a DEC VAX6220 and in 3 minutes on an IBM PS/2 Model 70 with math coprocessor.

7. UNUSUAL FEATURES OF THE PROGRAM:

8. RELATED AND AUXILIARY PROGRAMS

VISA2 is an upgrated release of the original VISA program developed by U.S. Nuclear Regulatory Commission staff. Improvements include a treatment of cladding effects; a more general simulation of flaw size, shape and location; a simulation of inservice inspection; a revised simulation of the reference temperature of the nil-ductility transition; and treatment of vessels with multiple welds and initial flaws.

10. REFERENCES

- D.L. Stevens and al.:
  VISA - A Computer Code for Predicting the Probability of Reactor
  Pressure-Vessel Failure
  NUREG/CR-3884 (PNL-4774) (September 1983).
- E.P. Simonen and al.:
Vessel Integrity Simulation Analysis (VISA) Code Sensitivity Study    NUREG/CR-4267 (PNL-5469) (December 1985).

- F.A. Simonen and al.:
  VISA-II A Computer Code for Predicting the Probability of Reactor
  Pressure Vessel Failure
  NUREG/CR-4486 (PNL-5775) (March 1986) with Corrections.
- L. Eyberger:
  VISA2 IBM PC Version Flexible Disk Cartridge Description and
  Implementation Information
  NESC Note 89-97 (September 29, 1989).

11. MACHINE REQUIREMENTS

The sample problem required 61 Kbytes of memory on a DEC VAX6220 and 113 Kbytes on an IBM PS/2 Model 70.

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  VMS (DEC VAX), DOS 2.10, 4.0 (IBM PC).

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:

15. NAME AND ESTABLISHMENT OF AUTHORS

         F. Simonen and K. Johnson
         Pacific Northwest Laboratory

File name	File description	Records
NESC1115_02.001	Information file	47
NESC1115_02.002	batch file to compile and link VISA2	2
NESC1115_02.003	Sample input file	25
NESC1115_02.004	VISA2PC1 Fortran 77 source file	1350
NESC1115_02.005	VISA2PC2 Fortran 77 source file	1535
NESC1115_02.006	Sample output file	1150
NESC1115_02.007	Executable	0
NESC1115_02.008	DOS file-names	7