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# International Comparative Assessment Study of Pressurized Thermal Shock in Reactor Pressure Vessels (NUREG/CR-6651)

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## Publication Information

**Manuscript Completed:** November 1999**Date Published:** December 1999

**Prepared by:**B.R. Bass, C.E. Pugh, Oak Ridge National LaboratoryJ. Sievers, H. Schulz, Gesellschaft für Anlagen-und Reaktorsicherheit (GRS)

Oak Ridge National LaboratoryManaged by Lockheed Martin Energy Research CorporationOak Ridge, TN 37831-6370

Gesellschaft für Anlagen-und Reaktorsicherheit (GRS) Koln, Germany

C.G. Santos, NRC Project Manager

**Prepared for:**Division of Engineering TechnologyOffice of Nuclear Regulatory ResearchU.S. Nuclear Regulatory CommissionWashington, DC 20555-0001

NRC Job Code W6631

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## Abstract

A summary of the recently completed International Comparative Assessment Study of PressurizedThermal-Shock in Reactor Pressure Vessels (ICAS PTS RPV) is presented to record the results in actual and comparative fashions. The ICAS Project brought together an international group of experts from research, utility and regulatory organizations to perform a comparative evaluation of analysis methodologies employed in the assessment of RPV integrity under PTS loading conditions. The Project was sponsored jointly by Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), Köln, Germany, and Oak Ridge National Laboratory (ORNL), with assistance from the Organization for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA)/Committee on the Safety of Nuclear Installations (CSNI)/Principal Working Group (PWG) No. 3 (Integrity of Components and Structures). The ICAS Project grew out of a strong interest expressed by participants in the previous FALSIRE II Project to proceed with further evaluations of analysis methods used in RPV integrity assessment. Also, a Problem Statement was drafted to define a Western type four-loop RPV with cladding on the inner surface, and a detailed task matrix was defined that included a set of transient thermal-mechanical loading conditions postulated to result from loss-of-coolant accidents. The analytical assessment activities, which focused on the behavior of shallow cracks, were based on the Problem Statement and divided under three tasks: deterministic fracture mechanics (DFM), probabilistic fracture mechanics (PFM) and thermal-hydraulic mixing (THM). Researchers representing 25 organizations in 13 countries participated in ICAS, and approximately 145 comparative plots were generated from an electronic data base of results to focus on the predictive capabilities of the analysis methods applied to the different tasks. Selected plots are presented and discussed in this report. The results show that a best-estimate methodology for RPV integrity assessment can benefit from a reduction of the uncertainties in each phase of the process. ICAS participants drafted a list of topics where future work concerning further refinement of RPV integrity assessment methodology would be beneficial.

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