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Research Papers: Nuclear Power

Mixing Conditions in the Lower Plenum and Core Inlet of a Boiling Water Reactor

[+] Author and Article Information
Hernan Tinoco1

 Forsmarks Kraftgrupp AB, SE-742 03 Östhammar, Swedenhtb@forsmark.vattenfall.se

Stefan Ahlinder2

 Forsmarks Kraftgrupp AB, SE-742 03 Östhammar, Swedenahl@forsmark.vattenfall.se

1

Corresponding author.

2

Present address: AREVA NP GmbH, Abteilung NEPR-G, Paul-Gossen-Strasse 100, 91052 Erlangen, Germany.

J. Eng. Gas Turbines Power 131(6), 062903 (Jul 17, 2009) (12 pages) doi:10.1115/1.3097130 History: Received October 31, 2008; Revised November 10, 2008; Published July 17, 2009

A thermal mixing analysis of the downcomer, main recirculation pumps (MRPs) and lower plenum of Forsmark’s Unit 3 has been carried out with three separate computational fluid dynamics models. Several difficulties with the boundary conditions have been encountered, particularly with the MRP model. The results obtained predict stable temperature differences of around 8 K at the core inlet. Such large temperature differences have never been observed at Forsmark nuclear power plant (NPP). Temperature measurements at four positions above the reactor pressure vessel (RPV) bottom give the mean value used as the core inlet temperature for core analyses. Even if the temperature transmitters used are rather slow and inaccurate, they should be able to detect such large temperature differences that may lead to fuel damage. The only damage reported at Forsmark NPP since the implementation of liner cladding in fuel design is that caused by mechanically induced debris fretting (threadlike particles). Also, the difficulties with the connection of the models throw some doubt on the accuracy of these predictions. A completely connected model of the same RPV volume covered by the separate models predicts temperature differences at core inlet that are almost one-fourth of those mentioned above, i.e., approximately 2.5 K. Most of the mixing occurs downstream of the MRP diffusers, at the lower plenum “inlet.” This prediction divergence seems to arise from an impossibility of a correct transfer of complete three-dimensional flow field properties by means of boundary conditions defined at a two-dimensional inlet section.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Temperature (in kelvin) at the downcomer center

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Figure 6

Temperature distribution (in kelvin) at the MRP inlet at a level close to the pump deck

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Figure 7

Diffuser outlet temperature (in kelvin) for MR pump test flow (upper view) and streamlines through the pump

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Figure 8

Comparison of mixing in a MR pump with MRF (left) and SMM (right) approaches (impeller blades)

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Figure 9

Comparison of mixing in a MR pump with MRF (left) and SMM (right) approaches (pump outlet)

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Figure 10

Geometry of CFD model of lower plenum

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Figure 11

CR guide tube holes constituting the core bypass inlet (left) and corresponding grid (right)

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Figure 12

View of inlet temperature distribution (in kelvin) for lower plenum test flow

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Figure 13

Temperature distribution (in kelvin) at the bottom inner wall of the reactor vessel

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Figure 14

Water temperature (in kelvin) at a horizontal plane 1.58 m above the bottom of the RPV

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Figure 15

Water temperature (in kelvin) at a horizontal plane 4.08 m above the bottom of the RPV

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Figure 22

Water temperature distribution (in kelvin) at the core inlet

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Figure 23

Turbulent kinetic energy (in m2/s2) in a vertical radial plane at 22.5 deg in lower plenum inlet (LPM)

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Figure 24

Turbulent kinetic energy (in m2/s2) in a vertical radial plane at 22.5 deg in lower plenum inlet (CCM)

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Figure 25

Turbulent kinetic energy (in m2/s2) in a vertical radial plane at 45 deg in lower plenum inlet (LPM)

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Figure 26

Turbulent kinetic energy (in m2/s2) in a vertical radial plane at 45 deg in lower plenum inlet (CCM)

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Figure 27

Turbulent kinetic energy (in m2/s2) at the plane in Fig. 1, left LPM and right CCM

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Figure 28

Turbulent viscosity (in kg/m s) at the plane in Fig. 1, left LPM and right CCM

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Figure 29

Taylor macroscale (in meters) at the plane in Fig. 1, left LPM and right CCM

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Figure 30

Temperature (in kelvin) at the plane in Fig. 1, left LPM and right CCM

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Figure 21

Temperature distribution (in kelvin) at the bottom inner wall of the reactor vessel

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Figure 20

Temperature distribution (in kelvin) at MRP diffuser outlets

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Figure 19

Temperature distribution (in kelvin) at the MRP inlets at a level close to the pump deck

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Figure 18

Temperature distribution (in kelvin) along a vertical cylindrical surface at the center of the downcomer

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Figure 17

Frontal view of the simplified geometry of the completely connected CFD model

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Figure 16

Core inlet temperature distribution (in kelvin)

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Figure 5

View of downcomer temperature boundary conditions (in kelvin) for MR pump test flow

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Figure 4

Simplified geometry of CFD model MR pump

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Figure 3

Velocity distribution (in m/s) at the downcomer center (left view) and streamlines (right view)

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Figure 2

Temperature distribution (in kelvin) at the MPR inlets at a level close to the pump deck

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