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
Fig. 1. Modeling diagram of ATLAS and SGTR simulation pipe using SPACE code.
2.3 SGTR simulation facility
The geometry of the ATLAS facility, which
was composed of a SGTR simulation pipe
and connected with a PAFS facility, was
modeled as shown in F i g u r e 1. In the AT-
LAS facility with the SGTR simulation pipe,
the primary system inventory was discharged
from the hot side of the lower plenum
to the upper location of the SG-1 secondary
hot-side to simulate a MSGTR accident.
It is composed of a break simulation
valve, an orifice flow meter, an orifice, and
break nozzles. The ‘PIPE’ component option
of SPACE code was used to model the
upstream pipe, which was part of the SGTR
simulation pipe; this pipe section was geometrically
divided into 10 nodes. The break
nozzle was installed to simulate a five-tube
rupture with a non-choking orifice. This
tube section is modeled using the ‘CELL’
component option of SPACE code. The input
of the inner diameter is 1.756 mm and
the total flow area is the summation of the
five-tube area. An orifice with a 1.68 mm
hole was installed at the end of the break
nozzles to simulate the choking flow condition
at tube rupture, and the break nozzles
were designed to maintain the equivalent
pressure drop in the case of the non-choking
flow condition. The mass flow rate
through the SGTR simulation pipe was
measured using an orifice flow meter.
These orifice and orifice flow meter sections
were modeled using the ‘FACE’ component
option of SPACE code. The experiment
began by opening an initiation valve
to simulate a MSGTR on the SG-1. This
valve was modeled as the ‘TRIP VALV’ component
option of SPACE code, and it was
opened at the start of the transient calculation.
The MSGTR occurs on the tubes of
SG-1, which are connected to the SGTR
simulation pipe; five break nozzles are
opened in total [4].
2.4 Passive Auxiliary Feedwater
System (PAFS)
The steam supply and return water line
connected the PCHX to the SG-2 of the AT-
LAS [12]. Therefore, as shown in F i g -
u r e 2 , the PAFS was modeled by adding
junctions at the main steam line and at the
economizer nozzle as the inlet and outlet
of the PAFS, respectively. The steam supply
line and the return water line were divided
into 24 nodes and 31 nodes, respectively.
The diameters of the steam supply line and
the return water line were about 0.04 m
and 0.03 m, respectively. The PAFS operation
valve was connected to the return water
line and the feed water line, and it was
modeled as a trip valve. This valve open
signal was synchronized to the instant that
the collapsed water level in the steam generator
reached the set point of the low
steam generator level. Once the valve was
open, the latched option made it impossible
for the valve to close again. The end of
the return line was connected to the bottom
nozzle of the steam generator economizer
volume. The PCHX was the most important
component of PAFS, and it was
filled with condensate water and the return
water line on steady state condition. The
condensation tube of PCHX was modeled
with 24 nodes as shown in F i g u r e 3 . The
length of the horizontal nodes was about
0.23 m and the horizontal part of the PCHX
was modeled as 1.806 m. An inclination of
3 ° was applied to the horizontal tube region
while an inclination of 41.2 ° was applied
to one inlet node and one outlet node
to simulate a U-shaped bend. These design
values were determined to prevent the condensation-induced
water hammer inside
the tube of PCHX [13]. The area of the
PCHX pipe component was about
22.35 cm 2 , which equals the summation of
the three-tube area. The connected heat
structures were modeled as a cylindrical
shape. The inner and outer coordinates
were the inner and outer radii of the tube,
respectively. The number of tubes was used
as an input for equivalent heat transferring
area. The top and bottom headers of PCHX,
which both play roles in preventing the vibration
of the PCHX tube in the PCCT, were
modeled as cell components. The Passive
Condensate Cooling Tank (PCCT) of PAFS
was designed as a rectangular pool. Whenthe
PAFS was actuated, the heat transfer
from the PCHX caused the pool water in
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