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Research Papers: Nuclear Power

# The Application of System CFD to the Design and Optimization of High-Temperature Gas-Cooled Nuclear Power Plants

[+] Author and Article Information
Gideon P. Greyvenstein

Postgraduate School of Nuclear Science and Engineering, The North-West University, Private Bag X6001, Potchefstroom 2520, South Africagpg@mtechindustrial.com

Engineering Equation Solver (www.fChart.com).

J. Eng. Gas Turbines Power 130(3), 032901 (Mar 28, 2008) (11 pages) doi:10.1115/1.2835057 History: Received January 07, 2007; Revised October 30, 2007; Published March 28, 2008

## Abstract

The objective of this paper is to model the steady-state and dynamic operation of a pebble-bed-type high temperature gas-cooled reactor power plant using a system computational fluid dynamics (CFD) approach. System CFD codes are 1D network codes with embedded 2D or even 3D discretized component models that provide a good balance between accuracy and speed. In the method presented in this paper, valves, orifices, compressors, and turbines are modeled as lumped or 0D components, whereas pipes and heat exchangers are modeled as 1D discretized components. The reactor is modeled as 2D discretized system. A point kinetics neutronic model will predict the heat release in the reactor. Firstly, the layout of the power conversion system is discussed together with the major plant parameters. This is followed by a high level description of the system CFD approach together with a description of the various component models. The code is used to model the steady-state operation of the system. The results are verified by comparing them with detailed cycle analysis calculations performed with another code. The model is then used to predict the net power delivered to the shaft over a wide range of speeds from zero to full speed. This information is used to specify parameters for a proportional-integral-derivative controller that senses the speed of the power turbine and adjusts the generator power during the startup of the plant. The generator initially acts as a motor that drives the shaft and then changes over to a generator load that approaches the design point value as the speed of the shaft approaches the design speed. A full startup simulation is done to demonstrate the behavior of the plant during startup. This example demonstrates the application of a system CFD code to test control strategies. A load rejection example is considered where the generator load is suddenly dropped to zero from a full load condition. A controller senses the speed of the low pressure compressor/low pressure turbine shaft and then adjusts the opening of a bypass valve to keep the speed of the shaft constant at $60rps$. The example demonstrates how detailed information on critical parameters such as turbine and reactor inlet temperatures, maximum fuel temperature, and compressor surge margin can be obtained during operating transients. System CFD codes is a powerful design tool that is indispensable in the design of complex power systems such as gas-cooled nuclear power plants.

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## Figures

Figure 2

Discretization of a thermal-fluid system into a network of nodes and elements

Figure 1

Schematic layout of a two-shaft power conversion unit (PCU) for a pebble-bed-type HTR

Figure 15

Flownex network of the direct two-shaft closed intercooled recuperated Brayton cycle PBMR power plant

Figure 17

Variation of temperatures during startup

Figure 18

Variation of mass flows during startup (E=element)

Figure 19

Variation of shaft speeds during startup (E=element)

Figure 20

Variation of generator power during startup

Figure 22

Locus plot of HPC operating point during startup

Figure 23

Locus plot of LPC operating point during startup

Figure 24

Variation of pressures during load rejection

Figure 25

Variation of temperatures during load rejection

Figure 26

Variation of mass flows during load rejection

Figure 27

Variation of shaft speeds during load rejection

Figure 28

Variation of valve opening during load rejection

Figure 3

General node with neighboring nodes connected through branch elements

Figure 10

LPT PR characteristics

Figure 11

LPT efficiency characteristics

Figure 12

Staggered CFD grid of the flow domain inside the reactor

Figure 13

FLOWNEX network representation of the staggered CFD grid

Figure 14

Network for calculating heat transfer inside the pebbles, between pebbles, and between pebbles and gas

Figure 16

Variation of pressures during startup (N=node)

Figure 21

Maximum fuel temperature during startup

Figure 4

Flownex’s FTX

Figure 5

Discretization of FTX

Figure 6

Notation used to describe heat transfer in a heat exchanger element

Figure 7

Discretization of counter/parallel flow heat exchanger

Figure 8

LPC PR characteristics

Figure 9

LPC efficiency characteristics

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