Natural Circulation (Interruption) Analysis with MELCOR 2.2 during Asymmetric Cooldown Transients(NUREG/IA-0507)

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Publication Information

Manuscript Completed: September 2018
Date Published: March 2019

Prepared by:
Martina Adorni, Anis Bousbia Salah, and Jacques Vlassenbroeck

Bel V
Rue Walcourt 148 Walcourtstraat
1070 Brussels, Belgium

Hossein Esmaili, NRC Project Manager

Division of Systems Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
Under the Cooperative Severe Accident Research Program (CSARP)

Published by:
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice


This document describes the analysis carried out with MELCOR 2.2 computer code of the natural circulation (interruption) phenomena during asymmetric cooldown transients in a 3-loop nuclear power plant (NPP) configuration. Indeed, thermal-hydraulic analysis is an important issue for severe accident codes, it constitutes the starting point of the analysis before the occurrence of the core degradation.

The considered accident scenario consists in a feedwater line break (FWLB) combined with loss of offsite power (LOOP) in a generic 1000 MWe 3-loop pressurized water reactor (PWR).

For this study, a Bel V MELCOR 3-loop PWR model has been developed. The main goal is to verify the capabilities of the MELCOR code in predicting the establishment of the natural circulation flow regime, the eventual occurrence of the natural circulation interruption (NCI) phenomena and to compare to the results from an equivalent analysis performed using the thermal-hydraulic system code CATHARE. The activity is completed by carrying out sensitivity analyses in order to identify the key MELCOR modeling parameters.

The calculation results confirm the Bel V MELCOR 3-loop plant model capability and suitability for its intended purpose in support of regulatory activities.

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