Bel v Subsidiary of the Belgian Federal Agency for Nuclear Control

Brussels, Belgium

Bel v Subsidiary of the Belgian Federal Agency for Nuclear Control

Brussels, Belgium

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Vlassenbroeck J.,Bel V Subsidiary of the Belgian Federal Agency for Nuclear Control | Salah A.B.,Bel V Subsidiary of the Belgian Federal Agency for Nuclear Control | Bucalossi A.,European Commission
Nuclear Technology | Year: 2010

This paper presents assessment results for the natural circulation interruption (NCI) phenomenon during the cooldown phase in a nuclear pressurized water reactor. This phenomenon could take place because of several circumstances, such as an asymmetric cooldown after the loss of the forced primary flow. Under NCI conditions, the homogeneous boration of the reactor coolant system (RCS) and the connection of the RCS to the residual heat removal system could be hindered. Moreover, at very low or no primary flow rates and an operating safety injection system, a pressurized thermal shock could occur in the reactor vessel due to cold fluid stratification in the loops. It is therefore important to understand the cause of loop flow stagnation and to derive accordingly the appropriate operator actions to avoid such a phenomenon. The main goal of the current study is to assess the effect of a cooldown strategy upon the single-phase NCI occurrence. For this purpose, two scenarios with asymmetric cooling between the reactor cooling loops were investigated: The first one concerns afeedwater line break combined with a loss of off site power (LOOP), while the second one is limited to the LOOP (or any other transient leading to the loss of the forced primary flow). The analyses were carried out using the best-estimate thermalhydraulic system code CATHARE 2/V2.5-lmod8.1, developed by Commissariat à l'Energie Atomique, Electricité de France, AREVA, and Institut de Radioprotection et de SÛreté Nucléaire. The calculation results mainly emphasize the effect of the cooldown rate and the opening strategy of the main steam atmospheric discharge valve upon the occurrence of the NCI phenomenon.


Bousbia Salah A.,Bel V Subsidiary of the Belgian Federal Agency for Nuclear Control | Vlassenbroeck J.,Bel V Subsidiary of the Belgian Federal Agency for Nuclear Control | Austregesilo H.,GRS Society for plants and Reactor Safety
Nuclear Technology | Year: 2015

Following an accidental event in a nuclear pressurized water reactor, involving the loss of primaiy-side forced coolant flow, the core decay heat is generally removed through a natural circulation convection process. The cooldown of the reactor coolant system is carried out through the secondary-side heat sink following prescribed guidelines. However, under asymmetric primaiy-side cooling conditions, natural circulation interruption (NCI) in the loops with an inactive steam generator may take place. Under such conditions, the cooldown of the primary side may be hindered and the transient may evolve toward a degraded state. The NCI issue was recently addressed within the thermal-hydraulic experimental projects ROSA-2 and PKL-2 of the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development. The objective was to identify the conditions that may lead to the occurrence of NCI, to develop cooldown procedures that prevent the occurrence of NCI, and to assess the thermal-hydraulic code capabilities in predicting this phenomenon. In the current study, NCI experimental tests carried out in the LSTF (Large Scale Test Facility) and PKL (Primaer-KreisLauf) facilities are assessed using the best-estimate thermal-hydraulic system codes CATHARE and ATHLET. The simulation results are presented and conclusions are derived accordingly.


Bousbia Salah A.,Bel v Subsidiary of the Belgian Federal Agency for Nuclear Control | Vlassenbroeck J.,Bel v Subsidiary of the Belgian Federal Agency for Nuclear Control
Nuclear Engineering and Design | Year: 2013

Coolant mixing in the reactor vessel of a pressurized water reactor constitutes a key parameter for predicting the core behaviour under abnormal asymmetric cooling conditions. This issue was recently investigated within the experimental framework of the OECD/PKL-2 project. The aim was twofold: to assess the coolant mixing in the vessel downcomer and the core lower plenum under buoyant asymmetric cooling loops, as well as to evaluate the capabilities of computer codes in simulating such phenomenon. It is commonly known that CFD codes are applied for this objective using millions of nodes and large computer resources. However, thermal-hydraulic system codes having the 3D vessel models could also be considered for such purpose. Indeed, these codes benefit from large validation background, require less computational resources and include 3D capabilities that are up to now not fully exploited. In this framework the CATHARE 3D models are assessed against two asymmetrical buoyant mixing experimental tests performed at the ROCOM facility. The outcomes of the current study show good prediction potentialities of the 3D thermal-hydraulic system codes. However their applicability to NPP scale has to be further investigated experimentally and analytically as well. © 2013 Elsevier B.V. All rights reserved.


Bousbia Salah A.,Bel v Subsidiary of the Belgian Federal Agency for Nuclear Control | Vlassenbroeck J.,Bel v Subsidiary of the Belgian Federal Agency for Nuclear Control
Science and Technology of Nuclear Installations | Year: 2012

Results of the CATHARE code calculations related to asymmetric cooldown tests in the PKL facility are presented. The test under consideration is the G2.1 experiment performed within the OECD/NEA PKL-2 project. It consists of carrying out a cooldown under natural circulation conditions in presence of two (out of four) emptied Steam Generators (SGs) and isolated on their secondary sides. The main goal of the current study is to assess the impact of a chosen cooldown strategy upon the occurrence of a Natural Circulation Interruption (NCI) in the inactive (i.e., noncooling) loops. For this purpose, three G2.1 test runs were investigated. The calculation results emphasize, mainly, the effect of the cooldown strategy, and the conditions that could lead to the occurrence of the NCI phenomenon.

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