Science and Technology of Nuclear Installations 
Volume 2008 (2008), Article ID 423175, 16 pages
doi:10.1155/2008/423175
Research Article

Analyses of Instability Events in the Peach Bottom-2 BWR Using Thermal-Hydraulic and 3D Neutron Kinetic Coupled Codes Technique

Antonella Lombardi Costa,1 Alessandro Petruzzi,2 Francesco D'Auria,2 and Walter Ambrosini2

 1Departamento de Engenharia Nuclear, Universidade Federal de Minas Gerais, Avenida Antônio Carlos 6627, Campus UFMG, PCA1—Anexo Engenharia, Pampulha, Belo Horizonte 31270-90, MG, Brazil
2Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione, Università di Pisa, Via Diotisalvi 2, Pisa 56126, Italy
Received 17 May 2007; Accepted 25 October 2007

Recommended by John Cleveland

Abstract

Boiling water reactor (BWR) instabilities may occur when, starting from a stable operating condition, changes in system parameters bring the reactor towards an unstable region. In order to design more stable and safer core configurations, experimental and theoretical studies about BWR stability have been performed to characterise the phenomenon and to predict the conditions for its occurrence. In this work, contributions to the study of BWR instability phenomena are presented. The RELAP5/MOD3.3 thermal-hydraulic (TH) system code and the PARCS-2.4 3D neutron kinetic (NK) code were coupled to simulate BWR transients. Different algorithms were used to calculate the decay ratio (DR) and the natural frequency (NF) from the power oscillation predicted by the transient calculations as two typical parameters used to provide a quantitative description of instabilities. The validation of the code model set up for the Peach Bottom Unit 2 BWR plant is performed against low-flow stability tests (LFSTs). The four series of LFST have been performed during the first quarter of 1977 at the end of cycle 2 in Pennsylvania. The tests were intended to measure the reactor core stability margins at the limiting conditions used in design and safety analyses.