diff --git a/src/openmc_plasma_source/fuel_types.py b/src/openmc_plasma_source/fuel_types.py
index e270446..1ca478a 100644
--- a/src/openmc_plasma_source/fuel_types.py
+++ b/src/openmc_plasma_source/fuel_types.py
@@ -93,18 +93,18 @@ def neutron_energy_std_dev(ion_temperature: float, reaction: str) -> float:
     return std_dev
 
 
-
 def get_reactions_from_fuel(fuel):
     if ["D", "T"] == sorted(set(fuel.keys())):
-        return ['DT', 'DD', 'TT']
+        return ["DT", "DD", "TT"]
     elif ["D"] == sorted(set(fuel.keys())):
-        return ['DD']
+        return ["DD"]
     elif ["T"] == sorted(set(fuel.keys())):
-        return ['TT']
+        return ["TT"]
     else:
         msg = 'reactions of fuel {fuel} could not be found. Supported fuel keys are "T" and "D"'
         raise ValueError(msg)
 
+
 def get_neutron_energy_distribution(
     ion_temperature: float,
     fuel: dict,
@@ -160,7 +160,7 @@ def get_neutron_energy_distribution(
 
     reactions = get_reactions_from_fuel(fuel)
 
-    if reactions == ['TT']:
+    if reactions == ["TT"]:
         strength_TT = 1.0
         dNdE_TT = strength_TT * nst.dNdE_TT(E_pspec, ion_temperature)
         tt_source = openmc.stats.Tabular(E_pspec * 1e6, dNdE_TT)
@@ -186,9 +186,9 @@ def get_neutron_energy_distribution(
         dNdE_TT = strength_TT * nst.dNdE_TT(E_pspec, ion_temperature)
 
         # removing any zeros from the end of the array
-        dNdE_TT = np.trim_zeros(dNdE_TT, 'b')
+        dNdE_TT = np.trim_zeros(dNdE_TT, "b")
         # making array lengths match
-        E_pspec = E_pspec[:len(dNdE_TT)]
+        E_pspec = E_pspec[: len(dNdE_TT)]
 
         tt_source = openmc.stats.Tabular(E_pspec, dNdE_TT)
 
diff --git a/src/openmc_plasma_source/tokamak_source.py b/src/openmc_plasma_source/tokamak_source.py
index 338b121..033a2b8 100644
--- a/src/openmc_plasma_source/tokamak_source.py
+++ b/src/openmc_plasma_source/tokamak_source.py
@@ -132,7 +132,7 @@ def tokamak_source(
 
     fuel_densities = {}
     for key, value in fuel.items():
-        fuel_densities[key] = densities*value
+        fuel_densities[key] = densities * value
 
     # compute temperatures
     temperatures = tokamak_ion_temperature(
@@ -158,11 +158,12 @@ def tokamak_source(
         elongation=elongation,
     )
 
-    neutron_source_density = tokamak_neutron_source_density(fuel_densities, temperatures, reaction)
+    neutron_source_density = tokamak_neutron_source_density(
+        fuel_densities, temperatures, reaction
+    )
 
     strengths = neutron_source_density / sum(neutron_source_density)
 
-
     sources = tokamak_make_openmc_sources(
         strengths=strengths,
         angles=angles,
@@ -380,18 +381,20 @@ def tokamak_neutron_source_density(ion_density, ion_temperature, reaction):
         float, ndarray: Neutron source density (neutron/s/m3)
     """
 
-    ion_density = np.asarray(ion_density[reaction[0]]) * np.asarray(ion_density[reaction[1]])
+    ion_density = np.asarray(ion_density[reaction[0]]) * np.asarray(
+        ion_density[reaction[1]]
+    )
     ion_temperature = np.asarray(ion_temperature)
 
-    if reaction == 'DT':
-        return ion_density * nst.reac_DT(ion_temperature) # could use _DT_xs instead
-    if reaction == 'DD':
+    if reaction == "DT":
+        return ion_density * nst.reac_DT(ion_temperature)  # could use _DT_xs instead
+    if reaction == "DD":
         return ion_density * nst.reac_DD(ion_temperature)
-    if reaction == 'TT':
+    if reaction == "TT":
         return ion_density * nst.reac_TT(ion_temperature)
 
 
-#TODO consider replace with NeSST or getting DD version as well
+# TODO consider replace with NeSST or getting DD version as well
 def _DT_xs(ion_temperature):
     """Sadler–Van Belle formula
     Ref : https://doi.org/10.1016/j.fusengdes.2012.02.025
@@ -400,7 +403,7 @@ def _DT_xs(ion_temperature):
     Returns:
         float, ndarray: the DT cross section at the given temperature
     """
-    ion_temperature_kev = np.asarray(ion_temperature/1e3)
+    ion_temperature_kev = np.asarray(ion_temperature / 1e3)
     c = [
         2.5663271e-18,
         19.983026,