atw 2018-04v6

atw Vol. 63 (2018) | Issue 4 ı April
OPERATION AND NEW BUILD 224
Normal operating
conditions
Steady State
LVR-15 Start up
LVR-15 Shutdown
Loops Start up
Loops Shutdown
and during Loss of Flow Accident
( LOFA) and Loss of Coolant Accident
(LOCA) accident conditions. In particular,
the structural integrity analyses
required the temperature profile
inside the Pressure Envelope (PE) as
boundary condition. For this reason
the normal operation and abnormal
operation conditions were calculated
using TRACE and ATHLET codes with
very narrow mesh nodal distribution
in the PE. For structural integrity
following criteria and limitation due
to the non-boiling condition in LVR-15
were used:
1. PE maximum temperature during
normal/abnormal transients is less
than 450 °C.
2. PE maximum temperature during
accident conditions is less than
500 °C.
3. Aluminium surface of the Receiver
maximum temperature in contact
with LVR-15 coolant less than 45 °C
during normal/abnormal conditions.
4. Aluminium surface of the Receiver
maximum temperature in contact
with LVR-15 coolant less than 60 °C
during accident conditions.
In the case of accident conditions,
both active channels of HTHL and
SCWL will have to be replaced. The
analysed scenarios are described in
the Table 1.
4 Illustrative results
The results described in the paper
refer to the simulations of SCWL and
Pressure
tests
(not simulated)
| | Tab. 1.
Operational and Accident Scenarios Description.
Abnormal
conditions
Switch off Loops Electrical
Heater for 1 min.
LVR-15 SCRAM and switch off
of Loops Electrical Heater
at t = 0 s + pump trip after 1 min.
Switch off Loops Electrical Heater
at t = 0 s + LVR15 SCRAM and
Pump Trip after 3 min.
Parameter Value Unit
Pressure 25 MPa
Inlet Flow
Temperature
Outlet Flow
Temperature
Max Flow
Temperature
Sample Area
Mass flow
| | Tab. 2.
SCWL main parameters calculated during
steady state.
HTHL during the steady state operation
with continuing in LOFA condition.
The results represent an extract
of the large number of calculations of
various combinations of operational
transients with the aim to demonstrate
the capabilities of the codes to
simulate behaviour the loops.
4.1 SCWL steady state and
LOFA analyses
The main parameters for the steady
state are shown in Table 2. The whole
steady state calculation was rather
long due to some inertia of the system.
The computer model simulated
behaviour during the transient of all
heat structures representing the
complete piping system. In the calculation
some numerical instability
complicated the steady state due to
Accident
conditions
385 ºC
406 ºC
600 ºC
35 %
By pass flow 65 %
Mass flow 200 kg/h
Loss of Flow Accident
(LOFA)
Loss of Coolant Accident
(LOCA)
small dimensions of the component
facing the deterioration flow phenomenon
during the heating up process.
For these reasons, the whole steady
state was completed in 25,000 s,
where 15,000 to 20,000 s were needed
to adjust the steady state and the
rest 5,000 s were used to verify the
steady behaviour of the main parameters.
After this period the model simulated
the accident scenario – LOFA
without the reactor SCRAM in order
to maximize the consequences and to
calculate the time to reach temperature
of PE (AC) 500 °C.
The scenario is described in the
following steps:
1. Pump stops in 1 s after the initialization
event (25,001 s)
2. Active channel internal electrical
heaters shut down to 0 % on the
nominal power in 7s (25,007 s)
3. The LVR-15 SCRAM starts at 40 s
when the maximum temperature
in the PE rises above the 500 °C.
(25,040 s)
4. The whole transient is completed
in 15,000 s (40,000 s), when the
SCWL and LVR-15 are in the
controlled cold state.
The Figure 6 and Figure 7 represent
the SCW maximum temperature
calculated in the sample area and the
outlet temperature from the active
channel, while the Figure 8 shows the
maximum temperature of the PE,
where there is the neutron flux peak
in the Boltzmann distribution.
4.2 HTHL steady state and
LOFA analyses
The design conditions calculated for
the active channel are described in
Table 3. And they are mainly summarized
as reported:
1. Mass flow rate of 0.0105 kg/s
2. Design pressure of 7 MPa
3. Design electrical heater power of
11.85 kW
4. Cold helium temperature of 210 °C
| | Fig. 6.
SCWL Coolant Maximum Temperature in LOFA.
| | Fig. 7.
SCWL Active Channel Outlet Temperature in LOFA.
Operation and New Build
Experimental and Analytical Tools for Safety Research of GEN IV Reactors ı G. Mazzini, M. Kyncl, Alis Musa and M. Ruscak