# Infinite homogeneous LWR-like reactor transient example

From Serpent Wiki

**Note:** For transient simulations, the initial system needs to be as close to criticality as possible. The exact multiplication factor of the system may vary if different cross section libraries is used. In that case, adjust the boron content in the `fuel` material to achieve criticality.

## Generating the steady state source distributions

set title "Creating source for a time dependent simulation" % --- Geometry is just a cube surf 2 cuboid -100.0 100.0 -100.0 100.0 -100.0 100.0 % --- Cell definitions: cell 3 0 fuel -2 cell 99 0 outside 2 % Outside world % --- Fuel material is a homogenized LWR material: mat fuel sum vol 8.0000E+06 moder lwtr 1001 8016.03c 0.316667 1001.03c 0.633333 92235.03c 0.0015 92238.03c 0.0485 5010.03c 0.000115793 % --- Thermal scattering data for hydrogen in light water (294 K) therm lwtr lwj3.00t % --- Reflective boundary condition: set bc 2 2 2 % --- Set power level set power 1.0 % --- Neutron population: % --- Large population size: (produced approx. 60M neutron and 40M precursor source points) set pop 80000 80000 200 1.0 100 % --- Save neutron and precursor source to "./source"-files set savesrc "./source" % --- Do not generate group constants set gcu -1 % --- Do not use implicit capture, nxn, or fission set impl 0 0 0

## Time dependent simulation (no reactivity insertion)

set title "Time dependent simulation, zero reactivity insertion" % --- Geometry is just a cube surf 2 cuboid -100.0 100.0 -100.0 100.0 -100.0 100.0 % --- Cell definitions: cell 3 0 fuel -2 cell 99 0 outside 2 % Outside world % --- Fuel material is a homogenized LWR material: mat fuel sum vol 8.0000E+06 moder lwtr 1001 8016.03c 0.316667 1001.03c 0.633333 92235.03c 0.0015 92238.03c 0.0485 5010.03c 0.000115793 % 0$ reactivity insertion % --- Thermal scattering data for hydrogen in light water (294 K) therm lwtr lwj3.00t % --- Reflective boundary condition: set bc 2 2 2 % --- Set up time structures for simulation and detectors: % --- 30 time bins for detector tme dettime 2 30 0 3e-3 % --- 1 time interval for simulation (no population control) tme simutime 2 1 0 3e-3 % --- Increase the size of neutron buffer since there is no pop. control set nbuf 10 % --- Neutron population: % --- 60M neutrons in 6k batches (1k neutrons per batch) set nps 60000000 6000 simutime % --- Link source (use point-wise precursor tracking) set dynsrc "./source" 1 % --- Set up detectors: % --- Tally neutron population as a function of time det 1 dr -15 void di dettime % --- Tally fission energy deposition as a function of time det 2 dr -8 void di dettime % --- Save neutron and precursor source to "./source_end"-files set savesrc "./source_end" % --- Do not generate group constants set gcu -1 % --- Do not use implicit capture, nxn, or fission set impl 0 0 0

## Time dependent simulation (0.85$ reactivity insertion)

set title "Time dependent simulation, 0.85$ reactivity insertion" % --- Geometry is just a cube surf 2 cuboid -100.0 100.0 -100.0 100.0 -100.0 100.0 % --- Cell definitions: cell 3 0 fuel -2 cell 99 0 outside 2 % Outside world % --- Fuel material is a homogenized LWR material: mat fuel sum vol 8.0000E+06 moder lwtr 1001 8016.03c 0.316667 1001.03c 0.633333 92235.03c 0.0015 92238.03c 0.0485 5010.03c 0.000113 % 0.85$ reactivity insertion % --- Thermal scattering data for hydrogen in light water (294 K) therm lwtr lwj3.00t % --- Reflective boundary condition: set bc 2 2 2 % --- Set up time structures for simulation and detectors: % --- 30 time bins for detector tme dettime 2 30 0 3e-3 % --- 1 time interval for simulation (no population control) tme simutime 2 1 0 3e-3 % --- Increase the size of neutron buffer since there is no pop. control set nbuf 10 % --- Neutron population: % --- 60M neutrons in 6k batches (10k neutrons per batch) set nps 60000000 6000 simutime % --- Link source (use point-wise precursor tracking) set dynsrc "./source" 1 % --- Set up detectors: % --- Tally neutron population as a function of time det 1 dr -15 void di dettime % --- Tally fission energy deposition as a function of time det 2 dr -8 void di dettime % --- Save neutron and precursor source to "./source_end"-files set savesrc "./source_end" % --- Do not generate group constants set gcu -1 % --- Do not use implicit capture, nxn, or fission set impl 0 0 0