atw Vol. 63 (2018) | Issue 2 ı February
ENVIRONMENT AND SAFETY 94
| | 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.
In this paper, a nodalization sensitivity
analysis for the MIDAS test was
performed using the SPACE code.
Three cases were modeled: 4, 6, and
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
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.
This research was supported by the
2017 Research Fund of the KINGS
(KEPCO International Nuclear
Graduate School), Republic of Korea.
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Professor Dr. Seung-Jong Oh
Professor Dr. Aya Diab
Department of NPP Engineering
KEPCO International Nuclear
Graduate School (KINGS)
Environment and Safety
Sensitivity Analysis of MIDAS Tests Using SPACE Code: Effect of Nodalization ı Shin Eom, Seung-Jong Oh and Aya Diab