diff --git a/openmc/deplete/integrator/cecm.py b/openmc/deplete/integrator/cecm.py
index ac519cf878..4554a3f226 100644
--- a/openmc/deplete/integrator/cecm.py
+++ b/openmc/deplete/integrator/cecm.py
@@ -95,10 +95,10 @@ def cecm(operator, timesteps, power=None, power_density=None, print_out=True):
                 # Scale reaction rates by ratio of powers
                 power_res = operator.prev_res[-1].power
                 ratio_power = p / power_res
-                op_results[0].rates[0] *= ratio_power[0]
+                op_results[0].rates *= ratio_power[0]
 
             # Deplete for first half of timestep
-            x_middle = deplete(chain, x[0], op_results[0], dt/2, print_out)
+            x_middle = deplete(chain, x[0], op_results[0].rates, dt/2, print_out)
 
             # Get middle-of-timestep reaction rates
             x.append(x_middle)
@@ -106,7 +106,7 @@ def cecm(operator, timesteps, power=None, power_density=None, print_out=True):
 
             # Deplete for full timestep using beginning-of-step materials
             # and middle-of-timestep reaction rates
-            x_end = deplete(chain, x[0], op_results[1], dt, print_out)
+            x_end = deplete(chain, x[0], op_results[1].rates, dt, print_out)
 
             # Create results, write to disk
             Results.save(operator, x, op_results, [t, t + dt], p, i_res + i)
diff --git a/openmc/deplete/integrator/cram.py b/openmc/deplete/integrator/cram.py
index 85954603a1..ea2d55b7de 100644
--- a/openmc/deplete/integrator/cram.py
+++ b/openmc/deplete/integrator/cram.py
@@ -14,7 +14,7 @@ import scipy.sparse.linalg as sla
 from .. import comm
 
 
-def deplete(chain, x, op_result, dt, print_out):
+def deplete(chain, x, rates, dt, print_out):
     """Deplete materials using given reaction rates for a specified time
 
     Parameters
@@ -23,8 +23,8 @@ def deplete(chain, x, op_result, dt, print_out):
         Depletion chain
     x : list of numpy.ndarray
         Atom number vectors for each material
-    op_result : openmc.deplete.OperatorResult
-        Result of applying transport operator (contains reaction rates)
+    rates : openmc.deplete.ReactionRates
+        Reaction rates (from transport operator)
     dt : float
         Time in [s] to deplete for
     print_out : bool
@@ -38,16 +38,9 @@ def deplete(chain, x, op_result, dt, print_out):
     """
     t_start = time.time()
 
-    # Set up iterators
-    n_mats = len(x)
-    chains = repeat(chain, n_mats)
-    vecs = (x[i] for i in range(n_mats))
-    rates = (op_result.rates[i, :, :] for i in range(n_mats))
-    dts = repeat(dt, n_mats)
-
     # Use multiprocessing pool to distribute work
     with Pool() as pool:
-        iters = zip(chains, vecs, rates, dts)
+        iters = zip(repeat(chain), x, rates, repeat(dt))
         x_result = list(pool.starmap(_cram_wrapper, iters))
 
     t_end = time.time()
@@ -63,7 +56,7 @@ def _cram_wrapper(chain, n0, rates, dt):
 
     Parameters
     ----------
-    chain : DepletionChain
+    chain : openmc.deplete.Chain
         Depletion chain used to construct the burnup matrix
     n0 : numpy.array
         Vector to operate a matrix exponent on.
diff --git a/openmc/deplete/integrator/predictor.py b/openmc/deplete/integrator/predictor.py
index 969144f68f..f480f55fb8 100644
--- a/openmc/deplete/integrator/predictor.py
+++ b/openmc/deplete/integrator/predictor.py
@@ -90,10 +90,10 @@ def predictor(operator, timesteps, power=None, power_density=None,
                 # Scale reaction rates by ratio of powers
                 power_res = operator.prev_res[-1].power
                 ratio_power = p / power_res
-                op_results[0].rates[0] *= ratio_power[0]
+                op_results[0].rates *= ratio_power[0]
 
             # Deplete for full timestep
-            x_end = deplete(chain, x[0], op_results[0], dt, print_out)
+            x_end = deplete(chain, x[0], op_results[0].rates, dt, print_out)
 
             # Advance time, update vector
             t += dt