diff --git a/src/ace.F90 b/src/ace.F90
index 32894116c3..85f91a8495 100644
--- a/src/ace.F90
+++ b/src/ace.F90
@@ -212,9 +212,9 @@ contains
   end subroutine read_xs
 
 !===============================================================================
-! READ_ACE_BINARY reads a single cross section table in binary format. This
-! routine reads the header data for each table and then calls appropriate
-! subroutines to parse the actual data.
+! READ_ACE_TABLE reads a single cross section table in either ASCII or binary
+! format. This routine reads the header data for each table and then calls
+! appropriate subroutines to parse the actual data.
 !===============================================================================
 
   subroutine read_ace_table(index_table, index_list)
diff --git a/src/ace_header.F90 b/src/ace_header.F90
index 0c14a1ca5f..3caa5eb563 100644
--- a/src/ace_header.F90
+++ b/src/ace_header.F90
@@ -194,6 +194,9 @@ module ace_header
      ! Information for S(a,b) use
      logical :: use_sab     ! in S(a,b) energy range?
      real(8) :: elastic_sab ! microscopic elastic scattering on S(a,b) table
+
+     ! Information for URR probability table use
+     logical :: use_ptable  ! in URR range with probability tables?
   end type NuclideMicroXS
 
 !===============================================================================
diff --git a/src/cross_section.F90 b/src/cross_section.F90
index 367d277cf5..ae58618c5a 100644
--- a/src/cross_section.F90
+++ b/src/cross_section.F90
@@ -129,6 +129,7 @@ contains
     ! Initialize sab treatment to false
     micro_xs(index_nuclide) % use_sab     = .false.
     micro_xs(index_nuclide) % elastic_sab = ZERO
+    micro_xs(index_nuclide) % use_ptable  = .false.
 
     ! Initialize nuclide cross-sections to zero
     micro_xs(index_nuclide) % fission    = ZERO
@@ -284,6 +285,8 @@ contains
     type(Nuclide),  pointer :: nuc => null()
     type(Reaction), pointer :: rxn => null()
 
+    micro_xs(index_nuclide) % use_ptable = .true.
+
     ! copy cross-sections already calculated
     elastic    = micro_xs(index_nuclide) % elastic
     absorption = micro_xs(index_nuclide) % absorption
diff --git a/src/physics.F90 b/src/physics.F90
index 869acc367a..fb35d53d0f 100644
--- a/src/physics.F90
+++ b/src/physics.F90
@@ -331,28 +331,42 @@ contains
           ! just like any other reaction. Here we loop through the fission
           ! reactions for the nuclide and see if any of them occur
           
-          do i = 1, nuc % n_fission
-             rxn => nuc % reactions(nuc % index_fission(i))
+          if (micro_xs(index_nuclide) % use_ptable) then
 
-             ! if energy is below threshold for this reaction, skip it
-             if (IE < rxn%IE) cycle
-
-             ! add to cumulative probability
-             if (nuc % has_partial_fission) then
-                prob = prob + ((ONE-f)*rxn%sigma(IE-rxn%IE+1) & 
-                     + f*(rxn%sigma(IE-rxn%IE+2)))
-             else
-                prob = prob + micro_xs(index_nuclide) % fission
-             end if
-
-             ! Create fission bank sites if fission occus
+             prob = prob + micro_xs(index_nuclide) % fission
              if (prob > cutoff) then
+                rxn => nuc % reactions(nuc % index_fission(1))
                 call create_fission_sites(p, index_nuclide, rxn, .true.)
                 p % alive = .false.
                 MT = rxn % MT
                 return
              end if
-          end do
+          else
+
+             do i = 1, nuc % n_fission
+                rxn => nuc % reactions(nuc % index_fission(i))
+
+                ! if energy is below threshold for this reaction, skip it
+                if (IE < rxn%IE) cycle
+
+                ! add to cumulative probability
+                if (nuc % has_partial_fission) then
+                   prob = prob + ((ONE-f)*rxn%sigma(IE-rxn%IE+1) & 
+                        + f*(rxn%sigma(IE-rxn%IE+2)))
+                else
+                   prob = prob + micro_xs(index_nuclide) % fission
+                end if
+
+                ! Create fission bank sites if fission occus
+                if (prob > cutoff) then
+                   call create_fission_sites(p, index_nuclide, rxn, .true.)
+                   p % alive = .false.
+                   MT = rxn % MT
+                   return
+                end if
+             end do
+
+          end if
        end if
 
     end if