International Standard Problems and Small Break Loss-of-Coolant Accident (SBLOCA)

Abstract

Best-estimate thermal-hydraulic system codes are widely used to perform safety and licensing analyses of nuclear power plants and also used in the design of advance reactors. Evaluation of the capabilities and the performance of these codes can be accomplished by comparing the code predictions with measured experimental data obtained on different test facilities. OECD/NEA Committee on the Safety of Nuclear Installations (CSNI) has promoted, over the last twenty-nine years, some forty-eight international standard problems (ISPs). These ISPs were performed in different fields as in-vessel thermal-hydraulic behaviour, fuel behaviour under accident conditions, fission product release and transport, core/concrete interactions, hydrogen distribution and mixing, containment thermal-hydraulic behaviour. 80% of these ISPs were related to the working domain of principal working group no.2 on coolant system behaviour (PWG2) and were one of the major PWG2 activities for many years. A global review and synthesis on the contribution that ISPs have made to address nuclear reactor safety issues was initiated by CSNI-PWG2 and an overview on the subject of small break LOCA ISPs is given in this paper based on a report prepared by a writing group. In addition, the relevance of small break LOCA in a PWR with relation to nuclear reactor safety and the reorientation of the reactor safety program after TMI-2 accident are shortly summarized. The experiments in four integral test facilities, LOBI, SPES, BETHSY, ROSA IV/LSTF and the recorded data during a steam generator tube rupture transient in the DOEL-2 PWR (Belgium) were the basis of the five small break LOCA related ISP exercises, which deal with the phenomenon typical of small break LOCAs in Western design PWRs. Some lessons learned from these small break LOCA ISPs are identified in relation to code deficiencies and capabilities, progress in the code capabilities, possibility of scaling, and various additional aspects. ISPs are providing unique material and benefits for some safety-related issues.

Thermal-Hydraulic System Codes in Nulcear Reactor Safety and Qualification Procedures

“…Counter-part tests and similar tests in differently scaled facilities are considered highly important for code validation and therefore they were included in the tables of ITF selected experiments. Moreover, over the last twenty-nine years, CSNI has promoted 48 ISPs [18]. The main objectives of the ISPs are as follows: to contribute to better understanding of postulated events, to compare and evaluate the capability of codes (mainly best estimate codes), to suggest improvements to the code developers, to improve the ability of code users and to address the so-called scaling effect.…”

ASTEC–MAAP Comparison of a 2 Inch Cold Leg LOCA until RPV Failure

“…Since the standard reference SBLOCA experiments were conducted with break sizes ranging between 0.5% and 5% [34], the present 6%-equivalent break LOCA is expected to behave between an SBLOCA and MBLOCA in terms of primary system depressurization and accumulator discharge rate. The reactor thermal-hydraulic response to breaks of this size as initiating event has shown large sensitivity to the initial and plant-specific conditions.…”

Computer analyses on loop seal clearing experiment at PWR PACTEL

“…It can occur in a U-leg part (i.e., in the loop seal) in a cold leg during a small or an intermediate break loss-of-coolant accident (LOCA). Small and intermediate break LOCA and water seal formation and clearing in the loop seal have been investigated previously in several studies (e.g., Lee and Kim, 1992;Liebert and Emmerling, 1998;and Osakabe et al, 1988) and with different test facilities such as BETHSY and LSTF (Aksan, 2008).…”