TMI-2 accident: core heat-up analysis

Abstract

ORDERING INFORMATION Copies of this report may be ordered from Research Reports Center (RRC), Box 50490, Palo Alto, CA 94303, (415) 965-4081 There is no charge to NSAC member utilities and certain other nonprofit organizations. Keywords TMI-2, Core Damage Assessment, Heat-Up Transient anifttfiimiirinimwuiqufiij i%iiiijiiiii fiiimn NSAC authorizes the reproduction and distribution of all or any portion of this report and the preparation of any derivative work based on this report, in each case on the condition that any such reproduction, distribution, and preparation shall acknowledge this report and NSAC as the source NOTICE This report was prepared by the Nuclear Safety Analysis Center (NSAC) operated by the Electric Power Research Institute, Inc (EPRI) Neither NSAC, EPRI, members of EPRI, other persons contnbuting to or assisting in the preparation of the report, nor any person acting on the behalf of any of these parties (a) makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights, or (b) assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method, or process disclosed in this report FOREWORD PROJECT DESCRIPTION Much of what happened at TMI-2 is known from parameters that were monitored and recorded. However, there are aspects for which direct indications of plant conditions were fragmentary or unavailable. This is the case for the reactor core conditions, e.g., coolant levels, flows, and fuel temperatures. Although the damage sustained by the core will become known during plant recovery, analysis is required to establish the thermal path by which this condition might have been reached. This report presents results of an analysis to determine what happened in the reactor core during the critical phase of the accident between 113 and 208 minutes after the reactor tripped. It is during this period that most of the fuel damage is believed to have occurred. Much of the present work is the product of in-house NSAC efforts that are based on a comprehensive study of the TMI-2 accident. Substantial contributions to the analysis were made by contractors assigned to specific problem areas (see references). PROJECT OBJECTIVES The objective of this effort was to develop a "best-estimate" thermal-hydraulic analysis of the TMI-2 core heat-up transient. This analysis made use of known boundary conditions, indirect supporting information, and gross indicators of core damage (such as hydrogen production and fission-product release). Many boundary conditions used in the analysis themselves bear uncertainties and require some measure of interpretation. Nevertheless, an effort was made to include all relevant information and subject it to technical evaluations to achieve a consistent whole. PROJECT RESULTS A good characterization o...