Minimal Serpent Coupling Script
The Minimal Serpent Coupling Script (MSCS) is a short (< 300 lines with comments) Python program intended to give a minimal working example of a wrapper program that can communicate with Serpent in the coupled calculation mode. MSCS provides a working example of externally coupled multi-physics simulations with Serpent and may be a good starting point for the users that are interested in running such simulations with Serpent.
This page is about the really Minimal Serpent Coupling Script for steady state coupled calculations. Other MSCS versions include
NB: Serpent versions up to 2.1.26 have a small bug in the updating of the regular mesh based interface, which should be fixed before running the simulation.
Description
The coupling script communicates with Serpent using the file based communication mode.
Here, the coupling script calculates the TH-solution itself. In many cases that part of the coupling script should be replaced by writing the input for an external solver, running the external solver and reading the results from the external solver output.
The temperature treatment of the interaction physics is done on-the-fly using the TMS temperature treatment technique for the base cross sections and interpolation of thermal scattering data for the thermal scattering libraries.
The problem solved here is a 200 cm long fuel rod in infinite lattice with axially black boundary conditions. Coolant temperature and density solved by MSCS using simple correlations and assuming steady state in heat transfer.
Files
MSCS.py
#############################################################
# #
# Minimal Serpent Coupling Script v 0.3 #
# #
# Created by: Ville Valtavirta 2016/05/06 #
# Modified by: Ville Valtavirta 2020/10/26 #
# #
#############################################################
import os
import signal
import time
# Path to Serpent executable
sssexe = '/home/vvvillehe/Serpent2/2.1.31/sss2'
#######################################################
# Create the Serpent input-file for this run #
# (process id or communication file must be appended) #
#######################################################
# Open original input for reading
file_in = open('./input','r')
# Open a new input file for writing
file_out = open('./coupledinput','w')
# Write original input to new file
for line in file_in:
file_out.write(line)
# Close original input file
file_in.close()
# Append signalling mode
file_out.write('\n')
file_out.write('set comfile com.in com.out\n')
# Append interface name
file_out.write('\n')
file_out.write('ifc cool.ifc\n')
# Close new input file
file_out.close()
####################################
# Write the initial interface file #
####################################
file_out = open('./cool.ifc','w')
# Write the header line (TYPE MAT OUT)
file_out.write('2 cool 1\n')
# Write the output line (OUTFILE NZ ZMIN ZMAX NR)
file_out.write('coolifc.out 10 -100 100 1\n')
# Write the mesh type
file_out.write('1\n')
# Write the mesh size (NX XMIN XMAX NY YMIN YMAX NZ ZMIN ZMAX)
file_out.write('1 -0.75 0.75 1 -0.75 0.75 10 -100 100\n')
# Write initial coolant temperatures and densities
for i in range(10):
file_out.write('-0.99 520.0\n')
# Close interface file
file_out.close()
################################
# Start the Serpent simulation #
################################
# Create a command string that will start the Serpent simulation
runcommand = sssexe+' -omp 3 ./coupledinput &'
# Execute the command string
os.system(runcommand)
#########################
# Picard iteration loop #
#########################
iterating = 1
while iterating == 1:
###################
# Wait for signal #
###################
sleeping = 1
while sleeping == 1:
# Sleep for two seconds
time.sleep(2)
# Open file to check if we got a signal
fin = open('./com.out','r')
# Read line
line = fin.readline()
# Close file
fin.close()
# Check signal
if int(line) != -1:
if int(line) == signal.SIGUSR1.value:
# Got the signal to resume
sleeping = 0
elif int(line) == signal.SIGUSR2.value:
# Got the signal to move to next time point
iterating = 0
sleeping = 0
elif int(line) == signal.SIGTERM.value:
# Got the signal to end the calculation
iterating = 0
sleeping = 0
else:
# Unknown signal
print("\nUnknown signal read from file, exiting\n")
# Exit
quit()
# Reset the signal in the file
file_out = open('./com.out','w')
file_out.write('-1')
file_out.close()
# Check if iteration has finished
if (iterating == 0):
break
###########################
# Read power distribution #
###########################
# Reset power distribution
P = []
# Open output file
file_in = open('./coolifc.out','r')
# Loop over output file to read power distribution
for line in file_in:
# Split line to values
strtuple = line.split()
# Store power
P.append(float(strtuple[8]))
file_in.close()
###########################
# Calculate TH-solution #
###########################
# Reset TH-solution
T = []
rho = []
# Coolant specific heat capacity
cp = 4900 # J/(kg*K)
# Coolant mass flow rate
w = 0.3 # kg/s
# Put inlet temperature
T.append(520)
# Put inlet density
rho.append(0.813)
# Calculate temperatures at (nz+1) axial nodes
for i in range(10):
# Calculate next temperature
# T(i+1) = T(i) + P(i)/(w*cp)
Tnext = T[i] + P[i]/(w*cp)
# Store new temperature
T.append(Tnext)
# Calculate next density based on temperature
# Linear interpolation between
# T0 = 520, rho0 = 0.813
# T1 = 600, rho1 = 0.653
rhonext = 0.813 + (0.653 - 0.813)/(600.0 - 520.0)*(Tnext - 520.0)
# Store new density
rho.append(rhonext)
###########################
# Update interface #
###########################
file_out = open('./cool.ifc','w')
# Write the header line (TYPE MAT OUT)
file_out.write('2 cool 1\n')
# Write the output line (OUTFILE NZ ZMIN ZMAX NR)
file_out.write('coolifc.out 10 -100 100 1\n')
# Write the mesh type
file_out.write('1\n')
# Write the mesh size (NX XMIN XMAX NY YMIN YMAX NZ ZMIN ZMAX)
file_out.write('1 -0.75 0.75 1 -0.75 0.75 10 -100 100\n')
# Write updated coolant temperatures and densities
for i in range(10):
# Calculate density and temperature at this layer as an average
# of layer bottom and top values
Tnext = (T[i]+T[i+1])/2.0
rhonext = (rho[i]+rho[i+1])/2.0
# Write density and temperature at this layer
file_out.write('{} {}\n'.format(-rhonext, Tnext))
file_out.close()
############################
# Signal Serpent (SIGUSR1) #
############################
file_out = open('./com.in','w')
file_out.write("{}".format(int(signal.SIGUSR1.value)))
file_out.close()
input
% --- Input for MSCS testing set title "Serpent-MSCS externally coupled calculation" % --- Fuel Pin definition: pin 1 fuel 0.4335 gas 0.442000 clad 0.502500 cool % --- Lattice (type = 1, pin pitch = 1.5): lat 10 1 0.0 0.0 1 1 1.5 1 % --- Boundary of the geometry (200 cm active length) surf 2 cuboid -0.75 0.75 -0.75 0.75 -100 100 % --- Cell definitions: cell 3 0 fill 10 -2 % Pin-cell cell 99 0 outside 2 % Outside world % --- Fuel material: mat fuel -10.424 tmp 1200.0 rgb 100 160 140 92235.03c -0.015867 92238.03c -0.86563 8016.03c -0.1185 % --- Cladding material: mat clad -6.55 rgb 200 200 200 40090.03c -0.98135 24052.03c -0.00100 26056.03c -0.00135 28058.03c -0.00055 50120.03c -0.01450 8016.03c -0.00125 % --- Gas gap: mat gas -1E-4 rgb 255 255 255 2004.06c 1.0 % --- Coolant (majorant density and TMS-limits for temperature): mat cool -0.990 tft 520 624 moder lwtr 1001 rgb 150 160 240 1001.03c 0.66667 8016.03c 0.33333 % --- Thermal scattering data for light water: % On-the-fly treatment for SAB-data between 474 K -- 624 K therm lwtr 0 lwj3.07t lwj3.09t lwj3.11t lwj3.13t % --- Reflective boundary conditions in XY set bc 3 3 1 % --- Neutron population and criticality cycles: set pop 10000 50 50 % --- Use fission source passing with 20 inactive cycles on % later iterations set fsp 1 20 % --- Maximum number of coupled calculation iterations set to 2 set ccmaxiter 2 % --- Total power for normalization (600 W/cm, unrealistically high): set power 120000.00 % --- Disable group constant generation set gcu -1
Setup
MSCS has been tested with Python 3.8.13 and Serpent 2.2.0.
- Save the contents of the MSCS.py file (above) to a file of the same name.
- Replace the absolute path to the Serpent executable on line 16 of MSCS.py.
- Save the contents of the input file to a file called input in the same directory where the MSCS.py file is located.
- Add some cross section libraries to the input-file using the set acelib input option.
- The test case is now ready to run.
Running
Note: Before running the MSCS you should familiarize yourself with finding and killing background processes in your operating system. Since MSCS runs Serpent as a background process, killing MSCS will not kill the Serpent process automatically.
Run the simulation from the folder containing both files using the command python MSCS.py
The output of the Serpent run will be printed to the terminal.
