atw 2018-02


atw Vol. 63 (2018) | Issue 2 ı February


| | Fig. 16.

Liquid Flow Pattern of KM114 Test Calculation

with 6 Channels of New Nodalization.

Similarly, while the existing nodalization

predicts a condensation fraction

of 0.131, the new nodalization predicts

a condensation fraction of 0.203 with

only about 12 % deviation.

The liquid and vapor flow pattern

diagrams of the 6 channels case for

the KM114 test are presented in

Figure 16 and Figure 17 for the new

nodalization, respectively. The liquid

flow issuing from DVI-4 becomes

continuous downward flow as shown

in Figure 16. This shows the importance

of proper representation of the

flow regime. Given that the new

nodalization does not strictly reflect

the actual experimental arrangement,

the proper nodalization scheme needs

to be further developed.

6 Conclusions

In this paper, a nodalization sensitivity

analysis for the MIDAS test was

performed using the SPACE code.

Three cases were modeled: 4, 6, and

12 channels.

In the case of high steam flow rate

with DVI injection from both sides

tests (KM100 ~ KM103) and DVI-2

injection test (KM109), the SPACE

code estimated the bypass fraction

relatively accurately and the nodalization

scheme does not affect

the code results much. From the

efficiency, 4 channel representation

is recommended for SPACE code


Similar to RELAP5 calculation, the

SPACE code was unable to accurately

predict the bypass fraction for the low

steam flow rate MIDAS tests (KM104

~ 108 and KM 110 ~ 114) regardless

of the nodalization used. From a

safety perspective, over-prediction of

the bypass flow is conservative for a

LOCA simulation.

The over-prediction at low steam

flow may be attributed to the difficulty

to correctly represent the flow regime

in the vicinity of the broken cold leg.

This led to under-prediction of

| | Fig. 17.

Vapor Flow Pattern of KM114 Test Calculation

with 6 Channels of New Nodalization.

condensation rate and over-prediction

of interfacial shear. When the DVI

channels were horizontally shifted

with respect to the break channel, the

SPACE better predicted the bypass

fraction for the lowest steam flow rate

MIDAS test (KM114). This fictitious fix

proves the hypothesis but the result

should be treated with discretion.

7 Acknowledgments

This research was supported by the

2017 Research Fund of the KINGS

(KEPCO International Nuclear

Graduate School), Republic of Korea.


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code for Nuclear Power Plant Design,

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[7] ***, KAERI, Direct Vessel Injection Test

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[8] W.A. Carbiener and R.A. Cudnik,

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Shin Eom

Graduate Student

Professor Dr. Seung-Jong Oh

Professor Dr. Aya Diab

Department of NPP Engineering

KEPCO International Nuclear

Graduate School (KINGS)

Ulsan, Korea

Environment and Safety

Sensitivity Analysis of MIDAS Tests Using SPACE Code: Effect of Nodalization ı Shin Eom, Seung-Jong Oh and Aya Diab

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