NEA-0615 RELOSS.

1. NAME OR DESIGNATION OF PROGRAM:  RELOSS (RELiability Of Safety Systems).

3. DESCRIPTION OF PROBLEM OR FUNCTION

Program RELOSS is used in the reliability/safety assessment of any complex system with predetermined operational logic in qualitative and (if required) quantitative terms. The program calculates the possible system outcomes following an abnormal operating condition and the probability of occurrence, if required. Furthermore, the program deduces the minimal cut or tie sets of the system outcomes and identifies the potential common mode failures.

4. METHOD OF SOLUTION

The reliability analysis performed by the program is based on the event tree methodology. Using this methodology, the program develops the event tree of a system or a module of that system and relates each path of this tree to its qualitative and/or quantitative impact on specified system or module outcomes. If the system being analysed is subdivided into modules the program assesses each module in turn as described previously and then combines the module information to obtain results for the overall system.

Having developed the event tree of a module or a system, the program identifies which paths lead or do not lead to various outcomes depending on whether the cut or the tie sets of the outcomes are required and deduces the corresponding sets.

Furthermore the program identifies for a specific system outcome, the potential common mode failures and the cut or tie sets containing potential dependent failures of some components.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

The present dimensions of the program are as follows. They can however be easily modified:

Maximum number of modules (equivalent components):  25
Maximum number of components in a module:  15
Maximum number of levels of parentheses in a logical statement:  10
Maximum number of system outcomes:  3
Maximum number of module outcomes:  2
Maximum number of points in time for which quantitative analysis is     required:  5
Maximum order of any cut or tie set:  10
Maximum order of a cut or tie of any module outcome:  3
Maximum order of a cut or tie set of any system outcome in terms of     (equivalent) components:  5
Maximum order of a cut or tie set of any system outcome in terms of   individual components (used only if the system is divided into    modules):  5
Maximum number of special conditions considered for a common mode    failure analysis:  5
Maximum number of probability laws:  30
Maximum number of pairs of modules sharing components:  10

6. TYPICAL RUNNING TIME

Typical CPU time for a system with 4 objectives and 17 modules (qualitative and quantitative analysis, cut/tie sets and common mode failure analysis) on a CDC 7600 computer was less than 6 seconds.

7. UNUSUAL FEATURES OF THE PROGRAM

Program RELOSS relates qualitatively and quantitatively a single initiating event to various system outcomes using the event tree methodology. The necessary input information being deduced from line diagrams of the  system, engineering description of its operational logic and general design information, makes the program very versatile because it can  be used to relate directly to engineering design without recourse to an intermediate reliability appreciation of the system. It can be also used to identify the critical failure modes of complex systems  by deducing the minimal cut or tie sets of the various system outcomes of interest.

8. RELATED AND AUXILIARY PROGRAMS

RELOSS does not supersede a previous version and does not require auxiliary programs.

10. REFERENCES

- R.N. Allan, I.L. Rondiris, D.M. Fryer, C. Tye:
  Computational Development of Event Trees in Nuclear Reactor
  Systems
  Second National Reliability Conference (March 1979), Birmingham
  (available from Institute of Quality Assurance, London).
- I.L. Rondiris:
  Reliability Evaluation of Nuclear Power Plants,
  PhD Thesis, University of Manchester (1978).

- R.N. Allan and I.L. Rondiris:
  Users Manual for RELOSS (Reliability of Safety Systems)
  PhD Thesis, University of Manchester (April 1979)

11. MACHINE REQUIREMENTS

No additional requirements other than the usual input and output tapes.

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

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

If
found necessary, the following overlay structure can be used:

Root segment:        Main program
Primary Overlay 1:   RDATA, CPREV, TIMEPR, FNLWE, FNL, PROBDF,
                     CONVRT, SIMPLE
Primary Overlay 2:   CMFSUB, REVISE, BACK
Primary Overlay 3:   MCUT2, RENUB, CMSC
Primary Overlay 4:   COMROW, SYSTEM, MODULE, PROB, CUT, COMCUT,
                     NEWCUT, MINCUT, EVMAP, CHECK, PROBCUT, CTEST,
                     TEST, SPLIT

The above overlay structure gives a storage saving of 14.5%.

15. NAME AND ESTABLISHMENT OF AUTHOR

          R. N. Allan, I. L. Rondiris, A. Adraktas
          Power Systems Research Group
          Department of Electrical Engineering and Electronics
          UMIST, Manchester, M60 1QD
          United Kingdom.

File name	File description	Records
NEA0615_01.001	INFORMATION FILE	13
NEA0615_01.002	INFORMATION FILE	13
NEA0615_01.003	SOURCE	4853
NEA0615_01.004	S.P. INPUT	109
NEA0615_01.005	S.P. OUTPUT	1176