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Numerical Investigations of the Effect of Radial Power Distribution and Inlet Orifice on the Stability Behavior of Parallel Multichannel Type Natural Circulation Boiling Water Reactor

[+] Author and Article Information
Sapna Singh

Homi Bhabha National Institute,
Anushakti Nagar,
Mumbai 400094, India
e-mail: sapna.nst@gmail.com

Garima Singal

Reactor Engineering Division,
Bhabha Atomic Research Centre,
Trombay,
Mumbai 400085, India

A. K. Nayak

Homi Bhabha National Institute,
Anushakti Nagar,
Mumbai 400094, India;
Reactor Engineering Division,
Bhabha Atomic Research Centre,
Trombay,
Mumbai 400085, India

Umasankari Kannan

Homi Bhabha National Institute,
Anushakti Nagar,
Mumbai 400094, India;
Reactor Physics Design Division,
Bhabha Atomic Research Centre,
Trombay,
Mumbai 400085, India

1Corresponding author.

Manuscript received August 10, 2017; final manuscript received March 5, 2018; published online May 16, 2018. Assoc. Editor: Xiaojing Liu.

ASME J of Nuclear Rad Sci 4(3), 031002 (May 16, 2018) (24 pages) Paper No: NERS-17-1075; doi: 10.1115/1.4039594 History: Received August 10, 2017; Revised March 05, 2018

In a natural circulation boiling water reactor (BWR), the core power varies in both axial and radial directions inside the reactor core. The variation along the axial direction is more or less constant throughout the reactor; however, there exists variation of reactor power in the radial direction. The channels located at the periphery have low power compared to the center of the core and are equipped with orifices at their inlet. This creates nonuniformity in the radial direction in the core. This study has been performed in order to understand the effect of this radial variation of power on the stability characteristics of the reactor. Four channels of a pressure tube type natural circulation BWR have been considered. The reactor has been modeled using RELAP5/MOD3.2. Before using the model, it was first benchmarked with experimental measurements and then the characteristics of both low power and high power oscillations, respectively, known as type-I and type-II instability, have been investigated. It was observed that the type-I instability shows slight destabilizing effect of increase in power variation among different channels. However, in the case of type-II instability, it was found out that the oscillations get damped with an increase in power variation among the channels. A similar effect was found for the presence of orifices at the inlet in different channels. However, the increase in number of orificed channels showed stabilizing effect for both type-I and type-II instabilities.

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References

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Kumar, A. , and Srivenkatesan, R. , 1984, “ Nodal Expansion Method for Reactor Core Calculations,” Bhabha Atomic Research Centre, Bombay, India, Report No. BARC-1249 https://inis.iaea.org/search/search.aspx?orig_q=RN:16064505.
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The RELAP5 Code Development Team, 1995, “ RELAP5/MOD3 Code Manual Volume II: User's Guide and Input Requirements,” Idaho National Engineering Laboratory, Idaho Falls, ID, Report, No. INEL-95/0174. https://www.nrc.gov/docs/ML1103/ML110330252.pdf
Jain, V. , Nayak, A. K. , Vijayan, P. K. , Saha, D. , and Sinha, R. K. , 2010, “ Experimental Investigation on the Flow Instability Behavior of a Multi-Channel Boiling Natural Circulation Loop at Low-Pressures,” Exp. Therm. Fluid Sci., 34(6), pp. 776–787. [CrossRef]
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Figures

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Fig. 1

Schematic of a main heat transport loop of AHWR

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Fig. 2

Power distribution in the quarter equilibrium core of AHWR

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Fig. 3

Nodalization scheme used in RELAP5

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Fig. 5

Single phase flow measured during the experiment

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Fig. 6

Single phase flow as predicted by RELAP5

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Fig. 7

Boiling induced type-I oscillations as measured during the experiment

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Fig. 8

Boiling induced type-I oscillations as predicted by RELAP5

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Fig. 9

Stable two-phase flow as measured during the experiment

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Fig. 10

Stable two-phase as predicted by RELAP5

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Fig. 11

Type-II oscillations as observed during the experiment

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Fig. 12

Type-II oscillations as predicted by RELAP5

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Fig. 13

Onset of type-I oscillations (case-A)

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Fig. 14

Mixed mode of oscillations as observed in identical channel case (case-A)

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Fig. 15

The phase shift of 90 deg among the four channels (case-A)

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Fig. 16

Damping of type-I oscillations with mixed mode (case-A)

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Fig. 17

Stable two-phase flow with increase in power at a constant subcooling (case-A)

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Fig. 18

Initiation of type-II oscillations (case-A)

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Fig. 19

Fully developed type-II oscillations (case-A)

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Fig. 20

Predicted stability map for four identical channels case (case-A)

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Fig. 21

Single phase flow in all four channels when the highest channel power was 0.3 MW (case-B1)

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Fig. 22

Onset of two-phase flow oscillations in two higher powered channels (case-B1)

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Fig. 23

Behavior of lower power channels with respect to high power channels (case-B1)

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Fig. 24

Behavior of low power channel with that of high powered channel during decay of type-I oscillations (case-B1)

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Fig. 25

Stable two-phase flow with the highest power rated channel at 0.8 MW (case-B1)

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Fig. 26

Initiation of type-II oscillations (case-B1)

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Fig. 27

Fully developed type-II oscillations (case-B1)

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Fig. 28

Single phase flow in all four channels (case-B2)

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Fig. 29

Onset of two-phase flow oscillations in two higher powered channels (case-B2)

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Fig. 30

Behavior of lower power channels with respect to high power channels (case-B2)

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Fig. 31

Decay of type-I oscillations in channel-1 (case-B2)

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Fig. 32

Damping of type-I oscillations (case-B2)

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Fig. 33

Stable two-phase flow (case-B2)

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Fig. 34

Initiation of type-II oscillations (case-B2)

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Fig. 35

Fully developed type-II oscillations (case-B2)

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Fig. 36

Stability boundary for four unequal powered AHWR channels with that of four identical powered channels (case-B)

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Fig. 37

Onset of type-I oscillation in orifice channel (case-C1)

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Fig. 38

Oscillation behavior of highest power channel and orifice channel (case-C1)

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Fig. 39

Damping of type-I oscillations in orifice channel (case-C1)

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Fig. 40

Damping of type-I oscillation in highest power channel (case-C1)

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Fig. 41

Stable two phase flow in all channels (case-C1)

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Fig. 42

Initiation of type-II oscillations in the highest powered channel (case-C1)

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Fig. 43

Spread of type-II instability in Ch-2 and -3 (case-C1)

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Fig. 44

Stability boundary for case-C in comparison with that of case-A (case-C)

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Fig. 45

Initiation of type-I instability first in Ch-3 (highest powered orifice channel) (case-D1)

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Fig. 46

Spreading of the oscillation to Ch-4 and Ch-1 (case-D1)

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Fig. 47

Stable flow in orifice channels and oscillations in nonorifice channel (case-D1)

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Fig. 48

Initiation of type-II oscillation in Ch-1 and -2 (nonorifice channel) (case-D1)

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Fig. 49

Fully developed type-II oscillations (case-D1)

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Fig. 50

Onset of the type-I oscillations in highest powered channel (case-D3)

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Fig. 51

Damping of type-I oscillations in channel 1 and oscillations in other channels (case-D3)

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Fig. 52

Damping of type-I oscillations in all the channels (case-D3)

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Fig. 53

Type-II oscillations (case-D3)

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Fig. 54

Stability boundaries (all orificed channels) in comparison to case-A (identical powered nonorificed channels) (case-D)

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