From an engineering design standpoint, the merit of elaborate analyses has to be judged in the light of the presence of scatter in material data and difficulties in obtaining suitable constitutive relationships, especially when material degradation occurs through cycling, ageing, embrittlement and other environmental interactions. It is desirable to minimize the duration of a plant shutdown and to have the ability to make critical modifications and replacements so that future plant integrity is assumed.

Contrary to the expectation that widespread use of FEM would displace approximate method of analysis, the need for the latter has actually increased. The main reason for this trend is that the results of FEM often need reinterpretation through appropriate post-processing in order to make rational engineering assessments.

One of the most important attributes of approximate methods, that can be used in conjunction with NDE, is the ability to capture their conceptual essence for the purpose of making "robust" assessments. Robustness is the ability of an approximate method to provide acceptable results for a wide range of component geometry and loading conditions on the basis of a less-than-ideal input together with conceptual insight and economy of computational effort. Robust methods of analysis form the basis of a number of simplified assessment methods employed by ASME [1], RCC-MR [2] and Nuclear Electric [3, 4].

The concept of local region constraint is central to assessments involving multiaxial stress-relaxation, creep-damage, low-cycle fatigue, creep crack-growth and elastic-plastic fracture toughness. The local region constraint parameter, , can be obtained by the GLOSS method [5] on the basis of two linear finite element analysis.

The GLOSS R-Node method [6] enables the determination of the "combined r-node strain ( n )" which is related to the so-called reference stress. The r-node strain can be used in the determination plastic collapse loads, evaluation of J and C*, and overall component integrity.

In this paper, the GLOSS and GLOSS R-Node methods are used to provide a comprehensive framework for robust plant integrity assessment that can be used in conjunction with non-destructive methods of measuring damage. REFERENCES

1. Criteria of the ASME Boiler and Pressure Vessel Code for Design by Analysis in Sections III and VIII, Division 2, "Pressure Vessels and Piping: Design and Analysis", Vol. 1, ASME, 1972
2. RCC-MR, Design and Construction Rules for Mechanical Components of FBR Nuclear Islands, Section I, Sub-section B, AFCEN, Paris, 1985
3. R5, Assessment Procedure for High Temperature Response of Structures, Nuclear Electric, Berkeley Nuclear Laboratories, 1990
4. R6, Assessment of the Integrity of Structures Containing Defects, Nuclear Electric, Berkeley Nuclear Laboratories, 1990
5. R. Seshadri, "The Effect of Multiaxiality and Follow-up on Creep Damage", Transactions of the ASME: Journal of Pressure Vessel Technology, Vol. 112, pp. 378-385, 1990
6. R. Seshadri and C. P. D. Fernando, "Limit Loads of Mechanical Components and Structures Using the GLOSS R-Node Method", Transactions of the ASME: Journal of Pressure Vessel Technology, Vol. 114, 1992.