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1-D steady-state neutronics thermal-hydraulics model of a SBWR.

Jakob Christensen

Copyright © 1995 Jakob Christensen
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of the author.

Typeset by the author with the LATEX Documentation System.


This work was done for the fulfillment of the MSc degree at the Technical University of Denmark (DTU).

The work which lasted for a year was completed in co-operation with the Department of Fluid Mechanics and the Institute of Mathematical Modeling both at DTU.

Furthermore, assistance in regard to the reactor physical model especially for the generation of homogenized cross sections was provided by the Department of Nuclear Safety at RISØ1.

The purpose of the work was to present a 1-D steady-state physical model of both the neutronics (reactor physics) of the reactor core and the thermal-hydraulics of the primary coolant system. With the theoretical foundation of the two models established the objective was to implement a computer code which solves the coupled neutronics thermal-hydraulics model by means of suitable numerical methods.

The results of the project consist chiefly of a computer code for the solution of the coupled neutronics thermal-hydraulics model. The key features of the implementation are listed below

  • 1-D axial multi-group treatment.
  • Variable number of energy groups.
  • Feedback from both void fraction and fuel temperature.
  • Intelligent grid generation to ensure optimal control of discretization errors.
  • Both the power method and inverse power method are available to ensure fast computation.
  • Modeling of the major flow paths within the reactor pressure vessel: lower plenum, core, riser, steam separator and downcomer with feedwater inlet.
  • Core is modeled by a number of identical fuel channels (bypass flow neglected).
  • Core flow model: 1-D partial equilibrium2 drift-flux mixture formulation of the two-phase flow.
  • Subcooled boiling model is based on a profile fit law.
  • Intelligent grid generation to ensure optimal accuracy.
  • Flexible treatment of grid spacers in regard to placement and loss coefficient.
Thermal design:
  • All heat transfer regions are treated, ie single-phase, subcooled boiling and saturated boiling heat transfer.
  • Fuel-Clad gap modeled by a constant user specified conductance.
  • Flux depression is accounted for through a parabolic power profile.
  • User friendly input/output interface through input files with flexible comment statements and the use of ${\mbox{MATLAB}}^{\mbox{\protect\scriptsize tm}}$ mat-files for output.
  • Dynamic memory allocation.

The text is divided up into the four parts below

Part I: The neutronics model.

Part II: The hydraulics model.

Part III: The core thermal analysis model.

Part IV: The coupled model with applications.

The author would like to thank V.A. Barker at the Institute of Mathematical Modeling, DTU and P.S. Larsen at the Department of Fluid Mechanics, DTU for good advice and support.

Finally, I would like to thank E. Nonbøl and C.F. Højerup both at the Department of Nuclear Safety, RISØ for assistance in regard to the neutronics model. Their support is gratefully acknowledged.

August, 1995

$\textstyle \parbox{3cm}{Jakob Christensen \\

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