VGB POWERTECH 7 (2021) - International Journal for Generation and Storage of Electricity and Heat

VGB PowerTech 7 l 2021
Verification of SPACE code based on an MSGTR experiment at the ATLAS-PAFS facility
C883
F884 ~ 896
C882
97.1 kW based on the information of the
initial experiment condition. During the
initial conditions, the major thermal hydraulic
parameters, including the system
pressure, fluid temperature, and mass
flow rate, were reasonably consistent with
the experiment condition. The calculation
time started from -1000.0 s to 0.0 s and
all design parameters converged after
-500.0 s. After checking the steady
1 2 11 12 13
NX = 1
Fig. 4. Nodding diagram of PCCT using ‘3D’ option of SPACE code.
NY = 13
NZ = 14
Tab. 1. Comparison results between initial condition of experiment and steady state results of
SPACE code.
Parameter Experiment SPACE code Difference (%)
Primary system
Core power (MW) 1.627 1.627 0.00
Heat loss (kW) 97.1 97.2 0.40
Pressurizer (PZR) pressure (MPa) 15.52 15.50 0.13
PZR level (m) 3.71 3.71 0.00
Cold leg flow rate (kg/s) 1.9728 1.941 1.61
Core inlet temp. (°C) 292.0 289.4 0.89
Core outlet temp. (°C) 327.5 325.2 0.70
Secondary system
Steam flow rate (kg/s) 0.4019 0.4153 3.33
Feed water flow rate (kg/s) 0.4209 0.4194 0.36
Feed water temp. (°C) 233.3 233.3 0.00
Steam dome pressure (MPa) 7.83 7.81 0.20
Steam temp. (°C) 295.7 294.2 0.51
SG collapsed water level (m) 4.97 4.97 0.00
Passive Auxiliary Feedwater System (PAFS)
Initial PCCT level (m) 3.8 3.8 0.00
Initial PCCT temp. (°C) 28.8 28.8 0.00
state condition, the transient calculation
started at 0.0 s of the steady state condition.
3.2 Transient analysis results
According to the agreement of the ATLAS
Domestic Standard Problem-05, the experimental
data should be confidential. Therefore,
all of the experiment results in this
paper including the time frame (t*) were
divided by an arbitrary value and plotted
on the non-dimensional axis.
3.2.1 Sequence of transient calculation
result
Ta b l e 2 summarizes the measured and
calculated sequences of a MSGTR-PAFS
test. The transient was initiated with the
MSGTR in normal condition. To initiate the
MSGTR transient, the break valve was
opened at 0.0 s with the pressurizer heater
off according to the experiment scenario.
The break flow contributed to the steam
generator overfill, and the collapsed water
level of the SG-1 reached a set point of
HSGL signal, leading to the generation of
the HSGL signal. This signal was generated
at a later time in the calculation case than
it was in the experiment case. The reactor
trip occurred simultaneously due to the
HSGL signal, and the MSIVs and MFIVs
were also closed after their respective delay
times. After the MSIVs were closed, the
pressure in steam generator was controlled
by the cyclic operation of MSSVs. According
to the experimental assumptions, the
heater power which simulates the decay
power had the ANS-73 decay curve applied
for the experimental condition, and the
heater power started after the reactor trip.
For the calculation, time verse decay power
data was applied in accordance with the
experiment information [4]. The time at
which the MSSVs first opened in the experiment
and the calculation results were
the same after the HSGL signal was triggered.
During this steam generator overfill
period, the pressure in the primary system
decreased substantially. As a result, when
the primary system pressure decreased to
the set point of the LPP trip, the LPP signal
was triggered, and the SIP injection was
initiated after the delay time. The collapsed
water level of SG-2 decreased due to
the decay power, then reached a set point
of PAFS operation. Finally, the PAFS operation
valve automatically opened and passive
cooling using PAFS was initiated.
3.2.2 Primary system behaviors
The decay power was one of the important
factors in this analysis, and the calculation
results were consistent with the experimental
result, as shown in F i g u r e 5 .
F i g u r e 6 shows the measured and calculated
break flow, which were normalized
by the maximum value of the experiment.
The break flow rate largely depended on
the pressure difference between the primary
and the secondary systems. Therefore,
as shown in F i g u r e 6 , the peak flow
rate occurred at the beginning of transient.
After the occurrence of peak flow, the
break flow in the experiment case oscillated
and gradually decreased. On the other
hand, the calculation result shows that the
break flow was maintained constantly. The
break flow was deeply related to the difference
between the pressures of the primary
and secondary systems. After the pressure
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