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Licensed Unlicensed Requires Authentication Published by De Gruyter May 6, 2013

Simulation of the neutronic-thermal hydraulic stability behaviour of boiling water reactors

Simulation des nuklear-thermohydraulischen Stabilitätsverhaltens von Siedewasserreaktionen
  • A. H. Gorzel , M. W. Henschel , E. M. Mrosk and W. E. Scheerer
From the journal Kerntechnik

Abstract

Neutronic-thermal hydraulic oscillations are a well known phenomenon in the operation of boiling water reactors. Despite the progresses that have been made concerning their simulation, the computational determination of the stability threshold in the power-flow map still suffers from inaccuracies. In this work, the decay ratio of neutronic-thermal hydraulic oscillations and hence the stability threshold was calculated with the SIMULATE-3K code developed by Studsvik Scandpower. It is known from experience that there is a higher probability for a less stable reactor operation in the case of one or more pumps tripped while the remaining pumps run at minimum speed. For the analysis of this state, the characteristics of the pump system were modelled carefully. It is shown that the stability behaviour is determined by the axial and radial power profile due to control rod manoeuvring and fuel burn-up and by the number of pumps running. Furthermore the calculations reveal the impacts of the insertion of shallow rods and of the control-rod group insertion on the decay ratio. A comparison of the calculations with experimental results of stability measurements shows that by a thorough analysis and proper modelling of the plant characteristics the decay ratios can be calculated with the SIMULATE-3K code.

Kurzfassung

Nuklear-thermohydraulische Schwingungen sind ein bekanntes Phänomen beim Betrieb von Siedewasserreaktionen. Trotz der Fortschritte, die es hinsichtlich ihrer Simulation gab, ist die theoretische Bestimmung der Stabilitätsgrenze im Betriebskennfeld mit Unsicherheiten verknüpft. In dieser Arbeit wurde das Abklingverhältnis nuklear-thermohydraulischer Schwingungen und damit auch die Stabilitätsgrenze mithilfe des Programms SIMULATE-3K der Firma Studsvik Scanpower ermittelt. Aus früheren Messungen und analytischen Untersuchungen ist bekannt, dass sich zwischen den Betriebspunkten Naturumlauf und Mindestdrehzahl aller Zwangsumwälzpumpen ein minimaler Abstand zwischen der Stabilitätsgrenze und der Umwälzregelkennlinie einstellt. Für die theoretische Beschreibung dieses Zustands wurde das Pumpenkennfeld als mittleres Pumpenkennfeld – entsprechend den Anforderungen des Programms – sorgfälltig modelliert. Es werden die Auswirkungen sowohl von Änderungen des axialen unnd radialen Leistungsprofils aufgrund von Steuerstabbewegungen und fortschreitendem Abbrand als auch von der Anzahl der laufenden Pumpen auf das Stabilitätsverhalten dargestellt. Darüber hinaus demonstrieren die Berechnungen die Einflüsse von „Shallow Rods“ und des Pulkeinfahrens von Steuerstäben auf das Abklingverhältnis. Ein Vergleich der Berechnungen mit Stabilitätsmessungen zeigt – bei hinreichend genauer Modellierung der Anlage – die Anwendbarkeit des Programms SIMULATE-3K für Stabilitätsberechnungen.


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Received: 2005-2-8
Published Online: 2013-05-06
Published in Print: 2005-08-01

© 2005, Carl Hanser Verlag, München

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