atw 2018-02

inforum

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

| | Fig. 8.

Liquid Flow Pattern of KM100 Test Calculation

with 4 Channels Nodalization.

| | Fig. 9.

Liquid Flow Pattern of KM100 Test Calculation

with 6 Channels Nodalization.

| | Fig. 10.

Liquid Flow Pattern of KM100 Test Calculation

with 12 Channels Nodalization.

ENVIRONMENT AND SAFETY 93

| | Fig. 11.

Comparison of the Measured and Calculated ECC Bypass Fraction for Low

Steam Flow Cases.

| | Fig. 12.

Liquid Flow Pattern of KM114 Test Calculation

with 6 Channels Nodalization.

| | Fig. 13.

Vapor Flow Pattern of KM114 Test Calculation

with 6 Channels Nodalization.

fraction. The problem is aggravated

for the lower steam flow rate tests,

since the phase change effect overshadows

the convective effect. It is

hypothesized that the bypass flow

may be influenced by the interplay

between thermal and inertial effects,

particularly at the lower steam flow

rate test conditions.

5 DVI Location Effect for

the Low Steam Flow Rate

Test

As shown in the Figure 4 to Figure 6,

the DVI channels and the broken

channel share the same channel. With

this nodalization, the most of the

injected liquid flows into the control

volume directly connected to broken

cold leg. Since the steam flow for this

volume is very high, the flow regime

becomes co-current annular mist flow.

With co-current annular flow, the

injected water from the DVI swept

away to the break.

To further examine this phenomenon,

we carried out an additional

calculation. We selected the 6 channels

representation. This time, however,

the DVI-4 is connected to a

channel next to the channel where

broken cold leg is connected as shown

in the Figure 15. The DVI channels

were separated from the broken channel

(or cold leg channel), artificially.

The bypass and condensation

fraction results of the existing and new

nodalization cases with 6 channels are

compared with KM114 test conditions

in Table 4. Clearly, the new nodalization

better predicts the bypass and

condensation fraction. While the

existing nodalization predicts a bypass

fraction of 0.714, the new nodalization

predicts a bypass fraction of 0.091

with only about 16 % deviation.

| | Fig. 14.

Comparison of the Measured and Calculated Condensation Fraction.

| | Fig. 15.

New Nodalization Scheme for 6 Channels.

Test No.

Steam Flow Rate

(kg/s)

Number of Channels

4 6 12

Case

Bypass

Fraction

Condensation

Fraction

KM109 1.8086 0.029 0.036 0.052

KM100 ~ 103 ≥ 1.1 0.078 0.094 0.116

KM104 ~ 108

0.090 0.113 0.144

≤ 1.1

KM110 ~ 114 0.082 0.103 0.138

| | Tab. 3.

RMSE Calculated Results of Condensation Fraction with Measured Data.

Measured value 0.109 0.231

Existing nodalization 0.714 0.131

New nodalization 0.091 0.203

| | Tab. 4.

Bypass and Condensation Fraction Results Comparison

in Case of 6 Channels for KM114 Test.

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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