diff --git a/src/ace.F90 b/src/ace.F90
index 57564f0b91..45b58a8d54 100644
--- a/src/ace.F90
+++ b/src/ace.F90
@@ -19,7 +19,7 @@ module ace
   use secondary_correlated, only: CorrelatedAngleEnergy
   use secondary_kalbach, only: KalbachMann
   use secondary_uncorrelated, only: UncorrelatedAngleEnergy
-  use simple_string, only: to_str, to_lower
+  use string, only: to_str, to_lower
 
   implicit none
 
diff --git a/src/cmfd_data.F90 b/src/cmfd_data.F90
index b624e839d7..347351e318 100644
--- a/src/cmfd_data.F90
+++ b/src/cmfd_data.F90
@@ -49,17 +49,17 @@ contains
 
   subroutine compute_xs()
 
-    use constants,     only: FILTER_MESH, FILTER_ENERGYIN, FILTER_ENERGYOUT,     &
-                            FILTER_SURFACE, IN_RIGHT, OUT_RIGHT, IN_FRONT,      &
-                            OUT_FRONT, IN_TOP, OUT_TOP, CMFD_NOACCEL, ZERO,     &
-                            ONE, TINY_BIT
-    use error,         only: fatal_error
-    use global,        only: cmfd, n_cmfd_tallies, cmfd_tallies, meshes,&
-                            matching_bins
-    use mesh,          only: mesh_indices_to_bin
-    use mesh_header,   only: RegularMesh
-    use simple_string, only: to_str
-    use tally_header,  only: TallyObject
+    use constants,    only: FILTER_MESH, FILTER_ENERGYIN, FILTER_ENERGYOUT,    &
+                           FILTER_SURFACE, IN_RIGHT, OUT_RIGHT, IN_FRONT,      &
+                           OUT_FRONT, IN_TOP, OUT_TOP, CMFD_NOACCEL, ZERO,     &
+                           ONE, TINY_BIT
+    use error,        only: fatal_error
+    use global,       only: cmfd, n_cmfd_tallies, cmfd_tallies, meshes,&
+                           matching_bins
+    use mesh,         only: mesh_indices_to_bin
+    use mesh_header,  only: RegularMesh
+    use string,       only: to_str
+    use tally_header, only: TallyObject
 
     integer :: nx            ! number of mesh cells in x direction
     integer :: ny            ! number of mesh cells in y direction
@@ -625,10 +625,10 @@ contains
 
   subroutine compute_dhat()
 
-    use constants,     only: CMFD_NOACCEL, ZERO
-    use global,        only: cmfd, cmfd_coremap, dhat_reset
-    use output,        only: write_message
-    use simple_string, only: to_str
+    use constants, only: CMFD_NOACCEL, ZERO
+    use global,    only: cmfd, cmfd_coremap, dhat_reset
+    use output,    only: write_message
+    use string,    only: to_str
 
     integer :: nx             ! maximum number of cells in x direction
     integer :: ny             ! maximum number of cells in y direction
diff --git a/src/cmfd_execute.F90 b/src/cmfd_execute.F90
index af6991e47d..b7d0cc3879 100644
--- a/src/cmfd_execute.F90
+++ b/src/cmfd_execute.F90
@@ -89,9 +89,9 @@ contains
 
   subroutine calc_fission_source()
 
-    use constants,     only: CMFD_NOACCEL, ZERO, TWO
-    use global,        only: cmfd, cmfd_coremap, master, entropy_on, current_batch
-    use simple_string, only: to_str
+    use constants, only: CMFD_NOACCEL, ZERO, TWO
+    use global,    only: cmfd, cmfd_coremap, master, entropy_on, current_batch
+    use string,    only: to_str
 
 #ifdef MPI
     use global,     only: mpi_err
@@ -213,14 +213,14 @@ contains
 
   subroutine cmfd_reweight(new_weights)
 
-    use constants,     only: ZERO, ONE
-    use error,         only: warning, fatal_error
-    use global,        only: meshes, source_bank, work, n_user_meshes, cmfd, &
-                             master
-    use mesh_header,   only: RegularMesh
-    use mesh,          only: count_bank_sites, get_mesh_indices
-    use search,        only: binary_search
-    use simple_string, only: to_str
+    use constants,   only: ZERO, ONE
+    use error,       only: warning, fatal_error
+    use global,      only: meshes, source_bank, work, n_user_meshes, cmfd, &
+                           master
+    use mesh_header, only: RegularMesh
+    use mesh,        only: count_bank_sites, get_mesh_indices
+    use search,      only: binary_search
+    use string,      only: to_str
 
 #ifdef MPI
     use global,      only: mpi_err
diff --git a/src/cmfd_input.F90 b/src/cmfd_input.F90
index 5e22d38559..2d9df4182c 100644
--- a/src/cmfd_input.F90
+++ b/src/cmfd_input.F90
@@ -45,10 +45,10 @@ contains
   subroutine read_cmfd_xml()
 
     use constants, only: ZERO, ONE
-    use error,         only: fatal_error, warning
+    use error,     only: fatal_error, warning
     use global
-    use output,        only: write_message
-    use simple_string, only: to_lower
+    use output,    only: write_message
+    use string,    only: to_lower
     use xml_interface
     use, intrinsic :: ISO_FORTRAN_ENV
 
diff --git a/src/distribution_univariate.F90 b/src/distribution_univariate.F90
index 274c6b1155..0ec2959c3b 100644
--- a/src/distribution_univariate.F90
+++ b/src/distribution_univariate.F90
@@ -1,11 +1,11 @@
 module distribution_univariate
 
-  use constants,     only: ZERO, ONE, HALF, HISTOGRAM, LINEAR_LINEAR, &
+  use constants,  only: ZERO, ONE, HALF, HISTOGRAM, LINEAR_LINEAR, &
        MAX_LINE_LEN, MAX_WORD_LEN
-  use error,         only: fatal_error
-  use random_lcg,    only: prn
-  use spectra,       only: maxwell_spectrum, watt_spectrum
-  use simple_string, only: to_lower
+  use error,      only: fatal_error
+  use random_lcg, only: prn
+  use spectra,    only: maxwell_spectrum, watt_spectrum
+  use string,     only: to_lower
   use xml_interface
 
   implicit none
diff --git a/src/eigenvalue.F90 b/src/eigenvalue.F90
index 7ed6c34f01..e735bc8d8a 100644
--- a/src/eigenvalue.F90
+++ b/src/eigenvalue.F90
@@ -4,15 +4,15 @@ module eigenvalue
   use message_passing
 #endif
 
-  use constants,     only: ZERO
-  use error,         only: fatal_error, warning
+  use constants,   only: ZERO
+  use error,       only: fatal_error, warning
   use global
-  use math,          only: t_percentile
-  use mesh,          only: count_bank_sites
-  use mesh_header,   only: RegularMesh
-  use random_lcg,    only: prn, set_particle_seed, prn_skip
-  use search,        only: binary_search
-  use simple_string, only: to_str
+  use math,        only: t_percentile
+  use mesh,        only: count_bank_sites
+  use mesh_header, only: RegularMesh
+  use random_lcg,  only: prn, set_particle_seed, prn_skip
+  use search,      only: binary_search
+  use string,      only: to_str
 
   implicit none
 
diff --git a/src/endf.F90 b/src/endf.F90
index 0539e8b9d2..64f26539a9 100644
--- a/src/endf.F90
+++ b/src/endf.F90
@@ -1,7 +1,7 @@
 module endf
 
   use constants
-  use simple_string, only: to_str
+  use string, only: to_str
 
   implicit none
 
diff --git a/src/geometry.F90 b/src/geometry.F90
index 53e2f29fc2..8a38f982b5 100644
--- a/src/geometry.F90
+++ b/src/geometry.F90
@@ -10,7 +10,7 @@ module geometry
   use particle_restart_write, only: write_particle_restart
   use surface_header
   use stl_vector,             only: VectorInt
-  use simple_string,          only: to_str
+  use string,                 only: to_str
   use tally,                  only: score_surface_current
 
   implicit none
diff --git a/src/initialize.F90 b/src/initialize.F90
index 00e5bab443..74bba03e72 100644
--- a/src/initialize.F90
+++ b/src/initialize.F90
@@ -1,32 +1,31 @@
 module initialize
 
-  use ace,              only: read_ace_xs, same_nuclide_list
-  use bank_header,      only: Bank
+  use ace,             only: read_ace_xs, same_nuclide_list
+  use bank_header,     only: Bank
   use constants
-  use dict_header,      only: DictIntInt, ElemKeyValueII
-  use set_header,       only: SetInt
-  use energy_grid,      only: logarithmic_grid, grid_method, unionized_grid
-  use error,            only: fatal_error, warning
-  use geometry,         only: neighbor_lists, count_instance, calc_offsets,    &
-                              maximum_levels
-  use geometry_header,  only: Cell, Universe, Lattice, RectLattice, HexLattice,&
-                              &BASE_UNIVERSE
+  use dict_header,     only: DictIntInt, ElemKeyValueII
+  use set_header,      only: SetInt
+  use energy_grid,     only: logarithmic_grid, grid_method, unionized_grid
+  use error,           only: fatal_error, warning
+  use geometry,        only: neighbor_lists, count_instance, calc_offsets,    &
+                             maximum_levels
+  use geometry_header, only: Cell, Universe, Lattice, RectLattice, HexLattice,&
+                             &BASE_UNIVERSE
   use global
-  use hdf5_interface,   only: file_open, read_dataset, file_close, hdf5_bank_t,&
-                              hdf5_tallyresult_t, hdf5_integer8_t
-  use input_xml,        only: read_input_xml, cells_in_univ_dict, read_plots_xml
-  use material_header,  only: Material
-  use mgxs_data,        only: read_mgxs, same_nuclide_mg_list, create_macro_xs
-  use output,           only: title, header, print_version, write_message,     &
-                              print_usage, write_xs_summary, print_plot
-  use random_lcg,       only: initialize_prng
-  use state_point,      only: load_state_point
-  use simple_string,    only: to_str, starts_with, ends_with
-  use string,           only: str_to_int
-  use summary,          only: write_summary
-  use tally_header,     only: TallyObject, TallyResult, TallyFilter
-  use tally_initialize, only: configure_tallies
-  use tally,            only: init_tally_routines
+  use hdf5_interface,  only: file_open, read_dataset, file_close, hdf5_bank_t,&
+                             hdf5_tallyresult_t, hdf5_integer8_t
+  use input_xml,       only: read_input_xml, cells_in_univ_dict, read_plots_xml
+  use material_header, only: Material
+  use mgxs_data,       only: read_mgxs, same_nuclide_mg_list, create_macro_xs
+  use output,          only: title, header, print_version, write_message,     &
+                             print_usage, write_xs_summary, print_plot
+  use random_lcg,      only: initialize_prng
+  use state_point,     only: load_state_point
+  use string,          only: to_str, starts_with, ends_with, str_to_int
+  use summary,         only: write_summary
+  use tally_header,    only: TallyObject, TallyResult, TallyFilter
+  use tally_initialize,only: configure_tallies
+  use tally,           only: init_tally_routines
 
 #ifdef MPI
   use message_passing
diff --git a/src/input_xml.F90 b/src/input_xml.F90
index fde77f498e..e726b6f403 100644
--- a/src/input_xml.F90
+++ b/src/input_xml.F90
@@ -17,8 +17,8 @@ module input_xml
   use random_lcg,       only: prn, seed
   use surface_header
   use stl_vector,       only: VectorInt
-  use simple_string,    only: to_lower, to_str, starts_with, ends_with
-  use string,           only: str_to_int, str_to_real, tokenize
+  use string,           only: str_to_int, str_to_real, tokenize, &
+                              to_lower, to_str, starts_with, ends_with
   use tally_header,     only: TallyObject, TallyFilter
   use tally_initialize, only: add_tallies
   use xml_interface
diff --git a/src/interpolation.F90 b/src/interpolation.F90
index 49d3de7fe8..5f87870677 100644
--- a/src/interpolation.F90
+++ b/src/interpolation.F90
@@ -1,9 +1,9 @@
 module interpolation
 
   use constants
-  use endf_header,   only: Tab1
-  use search,        only: binary_search
-  use simple_string, only: to_str
+  use endf_header, only: Tab1
+  use search,      only: binary_search
+  use string,      only: to_str
 
   implicit none
 
diff --git a/src/mgxs_data.F90 b/src/mgxs_data.F90
index f48238afa9..880764edad 100644
--- a/src/mgxs_data.F90
+++ b/src/mgxs_data.F90
@@ -1,14 +1,14 @@
 module mgxs_data
 
 use constants
-  use error,            only: fatal_error
+  use error,           only: fatal_error
   use global
   use macroxs_header
-  use material_header,  only: Material
+  use material_header, only: Material
   use nuclide_header
-  use output,           only: write_message
-  use set_header,       only: SetChar
-  use simple_string,    only: to_lower
+  use output,          only: write_message
+  use set_header,      only: SetChar
+  use string,          only: to_lower
   use xml_interface
 
   implicit none
diff --git a/src/nuclide_header.F90 b/src/nuclide_header.F90
index 72e1a4dc66..398e91eb20 100644
--- a/src/nuclide_header.F90
+++ b/src/nuclide_header.F90
@@ -7,8 +7,7 @@ module nuclide_header
   use endf,        only: reaction_name
   use list_header, only: ListInt
   use math,        only: evaluate_legendre
-  !use scattdata_header
-  use simple_string
+  use string
 
   implicit none
 
diff --git a/src/output.F90 b/src/output.F90
index 5379555ff0..29844076e6 100644
--- a/src/output.F90
+++ b/src/output.F90
@@ -16,7 +16,7 @@ module output
   use particle_header, only: LocalCoord, Particle
   use plot_header
   use sab_header,      only: SAlphaBeta
-  use simple_string,   only: to_upper, to_str
+  use string,          only: to_upper, to_str
   use tally_header,    only: TallyObject
 
   implicit none
diff --git a/src/particle_restart_write.F90 b/src/particle_restart_write.F90
index 324e96bc7a..e1a280e9fa 100644
--- a/src/particle_restart_write.F90
+++ b/src/particle_restart_write.F90
@@ -1,10 +1,10 @@
 module particle_restart_write
 
-  use bank_header,      only: Bank
+  use bank_header,     only: Bank
   use global
   use hdf5_interface
-  use particle_header,  only: Particle
-  use simple_string,    only: to_str
+  use particle_header, only: Particle
+  use string,          only: to_str
 
   use hdf5
 
diff --git a/src/physics.F90 b/src/physics.F90
index 2212269209..cb216467cd 100644
--- a/src/physics.F90
+++ b/src/physics.F90
@@ -18,7 +18,7 @@ module physics
   use random_lcg,             only: prn
   use search,                 only: binary_search
   use secondary_uncorrelated, only: UncorrelatedAngleEnergy
-  use simple_string,          only: to_str
+  use string,                 only: to_str
   use spectra
 
   implicit none
diff --git a/src/physics_mg.F90 b/src/physics_mg.F90
index a5272e1f47..a8a9084171 100644
--- a/src/physics_mg.F90
+++ b/src/physics_mg.F90
@@ -15,7 +15,7 @@ module physics_mg
   use physics_common
   use random_lcg,             only: prn
   use scattdata_header
-  use simple_string,          only: to_str
+  use string,                 only: to_str
   use spectra,                only: rotate_angle
 
   implicit none
diff --git a/src/plot.F90 b/src/plot.F90
index cdddc6d706..796cce6afa 100644
--- a/src/plot.F90
+++ b/src/plot.F90
@@ -14,7 +14,7 @@ module plot
   use ppmlib,          only: Image, init_image, allocate_image, &
                              deallocate_image, set_pixel
   use progress_header, only: ProgressBar
-  use simple_string,   only: to_str
+  use string,          only: to_str
 
   use hdf5
 
diff --git a/src/sab_header.F90 b/src/sab_header.F90
index a2d70d4f21..56617dd01d 100644
--- a/src/sab_header.F90
+++ b/src/sab_header.F90
@@ -3,7 +3,7 @@ module sab_header
   use, intrinsic :: ISO_FORTRAN_ENV
 
   use constants
-  use simple_string, only: to_str
+  use string, only: to_str
 
   implicit none
 
diff --git a/src/simple_string.F90 b/src/simple_string.F90
deleted file mode 100644
index 65eb58ac0b..0000000000
--- a/src/simple_string.F90
+++ /dev/null
@@ -1,308 +0,0 @@
-module simple_string
-
-  use constants, only: ERROR_REAL, ERROR_INT, MAX_LINE_LEN
-
-  implicit none
-
-  interface to_str
-    module procedure int4_to_str, int8_to_str, real_to_str
-  end interface
-
-contains
-
-!===============================================================================
-! TO_LOWER converts a string to all lower case characters
-!===============================================================================
-
-  pure function to_lower(word) result(word_lower)
-    character(*), intent(in) :: word
-    character(len=len(word)) :: word_lower
-
-    integer :: i
-    integer :: ic
-
-    do i = 1, len(word)
-      ic = ichar(word(i:i))
-      if (ic >= 65 .and. ic <= 90) then
-        word_lower(i:i) = char(ic+32)
-      else
-        word_lower(i:i) = word(i:i)
-      end if
-    end do
-
-  end function to_lower
-
-!===============================================================================
-! TO_UPPER converts a string to all upper case characters
-!===============================================================================
-
-  pure function to_upper(word) result(word_upper)
-    character(*), intent(in) :: word
-    character(len=len(word)) :: word_upper
-
-    integer :: i
-    integer :: ic
-
-    do i = 1, len(word)
-      ic = ichar(word(i:i))
-      if (ic >= 97 .and. ic <= 122) then
-        word_upper(i:i) = char(ic-32)
-      else
-        word_upper(i:i) = word(i:i)
-      end if
-    end do
-
-  end function to_upper
-
-!===============================================================================
-! IS_NUMBER determines whether a string of characters is all 0-9 characters
-!===============================================================================
-
-  pure function is_number(word) result(number)
-    character(*), intent(in) :: word
-    logical                  :: number
-
-    integer :: i
-    integer :: ic
-
-    number = .true.
-    do i = 1, len_trim(word)
-      ic = ichar(word(i:i))
-      if (ic < 48 .or. ic >= 58) number = .false.
-    end do
-
-  end function is_number
-
-!===============================================================================
-! STARTS_WITH determines whether a string starts with a certain
-! sequence of characters
-!===============================================================================
-
-  pure logical function starts_with(str, seq)
-    character(*), intent(in) :: str ! string to check
-    character(*), intent(in) :: seq ! sequence of characters
-
-    integer :: i
-    integer :: i_start
-    integer :: str_len
-    integer :: seq_len
-
-    str_len = len_trim(str)
-    seq_len = len_trim(seq)
-
-    ! determine how many spaces are at beginning of string
-    i_start = 0
-    do i = 1, str_len
-      if (str(i:i) == ' ' .or. str(i:i) == achar(9)) cycle
-      i_start = i
-      exit
-    end do
-
-    ! Check if string starts with sequence using INDEX intrinsic
-    if (index(str(1:str_len), seq(1:seq_len)) == i_start) then
-      starts_with = .true.
-    else
-      starts_with = .false.
-    end if
-
-  end function starts_with
-
-!===============================================================================
-! ENDS_WITH determines whether a string ends with a certain sequence
-! of characters
-!===============================================================================
-
-  pure logical function ends_with(str, seq)
-    character(*), intent(in) :: str ! string to check
-    character(*), intent(in) :: seq ! sequence of characters
-
-    integer :: i_start
-    integer :: str_len
-    integer :: seq_len
-
-    str_len = len_trim(str)
-    seq_len = len_trim(seq)
-
-    ! determine how many spaces are at beginning of string
-    i_start = str_len - seq_len + 1
-
-    ! Check if string starts with sequence using INDEX intrinsic
-    if (index(str(1:str_len), seq(1:seq_len), .true.) == i_start) then
-      ends_with = .true.
-    else
-      ends_with = .false.
-    end if
-
-  end function ends_with
-
-!===============================================================================
-! COUNT_DIGITS returns the number of digits needed to represent the input
-! integer.
-!===============================================================================
-
-  pure function count_digits(num) result(n_digits)
-    integer, intent(in) :: num
-    integer             :: n_digits
-
-    n_digits = 1
-    do while (num / 10**(n_digits) /= 0 .and. abs(num / 10 **(n_digits-1)) /= 1&
-              &.and. n_digits /= 10)
-      ! Note that 10 digits is the maximum needed to represent an integer(4) so
-      ! the loop automatically exits when n_digits = 10.
-      n_digits = n_digits + 1
-    end do
-
-  end function count_digits
-
-!===============================================================================
-! INT4_TO_STR converts an integer(4) to a string.
-!===============================================================================
-
-  pure function int4_to_str(num) result(str)
-
-    integer, intent(in) :: num
-    character(11) :: str
-
-    write (str, '(I11)') num
-    str = adjustl(str)
-
-  end function int4_to_str
-
-!===============================================================================
-! INT8_TO_STR converts an integer(8) to a string.
-!===============================================================================
-
-  pure function int8_to_str(num) result(str)
-
-    integer(8), intent(in) :: num
-    character(21) :: str
-
-    write (str, '(I21)') num
-    str = adjustl(str)
-
-  end function int8_to_str
-
-!===============================================================================
-! REAL_TO_STR converts a real(8) to a string based on how large the value is and
-! how many significant digits are desired. By default, six significants digits
-! are used.
-!===============================================================================
-
-  pure function real_to_str(num, sig_digits) result(string)
-
-    real(8),           intent(in) :: num        ! number to convert
-    integer, optional, intent(in) :: sig_digits ! # of significant digits
-    character(15)                 :: string     ! string returned
-
-    integer      :: decimal ! number of places after decimal
-    integer      :: width   ! total field width
-    real(8)      :: num2    ! absolute value of number
-    character(9) :: fmt     ! format specifier for writing number
-
-    ! set default field width
-    width = 15
-
-    ! set number of places after decimal
-    if (present(sig_digits)) then
-      decimal = sig_digits
-    else
-      decimal = 6
-    end if
-
-    ! Create format specifier for writing character
-    num2 = abs(num)
-    if (num2 == 0.0_8) then
-      write(fmt, '("(F",I2,".",I2,")")') width, 1
-    elseif (num2 < 1.0e-1_8) then
-      write(fmt, '("(ES",I2,".",I2,")")') width, decimal - 1
-    elseif (num2 >= 1.0e-1_8 .and. num2 < 1.0_8) then
-      write(fmt, '("(F",I2,".",I2,")")') width, decimal
-    elseif (num2 >= 1.0_8 .and. num2 < 10.0_8) then
-      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-1, 0)
-    elseif (num2 >= 10.0_8 .and. num2 < 100.0_8) then
-      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-2, 0)
-    elseif (num2 >= 100.0_8 .and. num2 < 1000.0_8) then
-      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-3, 0)
-    elseif (num2 >= 100.0_8 .and. num2 < 10000.0_8) then
-      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-4, 0)
-    elseif (num2 >= 10000.0_8 .and. num2 < 100000.0_8) then
-      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-5, 0)
-    else
-      write(fmt, '("(ES",I2,".",I2,")")') width, decimal - 1
-    end if
-
-    ! Write string and left adjust
-    write(string, fmt) num
-    string = adjustl(string)
-
-  end function real_to_str
-
-!===============================================================================
-! STR_TO_INT converts a string to an integer.
-!===============================================================================
-
-  pure function str_to_int(str) result(num)
-
-    character(*), intent(in) :: str
-    integer(8) :: num
-
-    character(5) :: fmt
-    integer      :: w
-    integer      :: ioError
-
-    ! Determine width of string
-    w = len_trim(str)
-
-    ! Create format specifier for reading string
-    write(UNIT=fmt, FMT='("(I",I2,")")') w
-
-    ! read string into integer
-    read(UNIT=str, FMT=fmt, IOSTAT=ioError) num
-    if (ioError > 0) num = ERROR_INT
-
-  end function str_to_int
-
-!===============================================================================
-! STR_TO_REAL converts an arbitrary string to a real(8)
-!===============================================================================
-
-  pure function str_to_real(string) result(num)
-
-    character(*), intent(in) :: string
-    real(8)                  :: num
-
-    integer :: ioError
-
-    ! Read string
-    read(UNIT=string, FMT=*, IOSTAT=ioError) num
-    if (ioError > 0) num = ERROR_REAL
-
-  end function str_to_real
-
-!===============================================================================
-! CONCATENATE takes an array of words and concatenates them together in one
-! string with a single space between words
-!
-! Arguments:
-!   words   = array of words
-!   n_words = total number of words
-!   string  = concatenated string
-!===============================================================================
-
-  pure function concatenate(words, n_words) result(string)
-
-    integer,        intent(in)  :: n_words
-    character(*),   intent(in)  :: words(n_words)
-    character(MAX_LINE_LEN)     :: string
-
-    integer :: i ! index
-
-    string = words(1)
-    if (n_words == 1) return
-    do i = 2, n_words
-      string = trim(string) // ' ' // words(i)
-    end do
-
-  end function concatenate
-
-end module simple_string
\ No newline at end of file
diff --git a/src/simulation.F90 b/src/simulation.F90
index d1b96d8b08..4a419df906 100644
--- a/src/simulation.F90
+++ b/src/simulation.F90
@@ -19,7 +19,7 @@ module simulation
   use random_lcg,      only: set_particle_seed
   use source,          only: initialize_source
   use state_point,     only: write_state_point, write_source_point
-  use simple_string,   only: to_str
+  use string,          only: to_str
   use tally,           only: synchronize_tallies, setup_active_usertallies, &
                              reset_result
   use trigger,         only: check_triggers
diff --git a/src/source.F90 b/src/source.F90
index 7f56b240b7..601232192a 100644
--- a/src/source.F90
+++ b/src/source.F90
@@ -13,7 +13,7 @@ module source
   use particle_header,  only: Particle
   use random_lcg,       only: prn, set_particle_seed, prn_set_stream
   use search,           only: binary_search
-  use simple_string,    only: to_str
+  use string,           only: to_str
   use spectra
   use state_point,      only: read_source_bank, write_source_bank
 
diff --git a/src/state_point.F90 b/src/state_point.F90
index a46450fc5a..2249e3d45e 100644
--- a/src/state_point.F90
+++ b/src/state_point.F90
@@ -18,8 +18,7 @@ module state_point
   use global
   use hdf5_interface
   use output,             only: write_message, time_stamp
-  use simple_string,      only: to_str, count_digits
-  use string,             only: zero_padded
+  use string,             only: to_str, count_digits, zero_padded
   use tally_header,       only: TallyObject
   use mesh_header,        only: RegularMesh
   use dict_header,        only: ElemKeyValueII, ElemKeyValueCI
diff --git a/src/string.F90 b/src/string.F90
index e5f09a50d4..b51763a611 100644
--- a/src/string.F90
+++ b/src/string.F90
@@ -1,13 +1,16 @@
 module string
 
-  use constants,     only: MAX_WORDS, MAX_LINE_LEN, ERROR_INT, ERROR_REAL, &
+  use constants, only: MAX_WORDS, MAX_LINE_LEN, ERROR_INT, ERROR_REAL, &
        OP_LEFT_PAREN, OP_RIGHT_PAREN, OP_COMPLEMENT, OP_INTERSECTION, OP_UNION
-  use error,         only: fatal_error, warning
-  use simple_string, only: str_to_int, str_to_real
-  use stl_vector,    only: VectorInt
+  use error,     only: fatal_error, warning
+  use stl_vector, only: VectorInt
 
   implicit none
 
+  interface to_str
+    module procedure int4_to_str, int8_to_str, real_to_str
+  end interface
+
 contains
 
 !===============================================================================
@@ -151,6 +154,75 @@ contains
     end if
   end subroutine tokenize
 
+!===============================================================================
+! CONCATENATE takes an array of words and concatenates them together in one
+! string with a single space between words
+!
+! Arguments:
+!   words   = array of words
+!   n_words = total number of words
+!   string  = concatenated string
+!===============================================================================
+
+  pure function concatenate(words, n_words) result(string)
+
+    integer,        intent(in)  :: n_words
+    character(*),   intent(in)  :: words(n_words)
+    character(MAX_LINE_LEN)     :: string
+
+    integer :: i ! index
+
+    string = words(1)
+    if (n_words == 1) return
+    do i = 2, n_words
+      string = trim(string) // ' ' // words(i)
+    end do
+
+  end function concatenate
+
+!===============================================================================
+! TO_LOWER converts a string to all lower case characters
+!===============================================================================
+
+  pure function to_lower(word) result(word_lower)
+    character(*), intent(in) :: word
+    character(len=len(word)) :: word_lower
+
+    integer :: i
+    integer :: ic
+
+    do i = 1, len(word)
+      ic = ichar(word(i:i))
+      if (ic >= 65 .and. ic <= 90) then
+        word_lower(i:i) = char(ic+32)
+      else
+        word_lower(i:i) = word(i:i)
+      end if
+    end do
+
+  end function to_lower
+
+!===============================================================================
+! TO_UPPER converts a string to all upper case characters
+!===============================================================================
+
+  pure function to_upper(word) result(word_upper)
+    character(*), intent(in) :: word
+    character(len=len(word)) :: word_upper
+
+    integer :: i
+    integer :: ic
+
+    do i = 1, len(word)
+      ic = ichar(word(i:i))
+      if (ic >= 97 .and. ic <= 122) then
+        word_upper(i:i) = char(ic-32)
+      else
+        word_upper(i:i) = word(i:i)
+      end if
+    end do
+
+  end function to_upper
 
 !===============================================================================
 ! ZERO_PADDED returns a string of the input integer padded with zeros to the
@@ -185,4 +257,229 @@ contains
     write(str, zp_form) num
   end function zero_padded
 
+!===============================================================================
+! IS_NUMBER determines whether a string of characters is all 0-9 characters
+!===============================================================================
+
+  pure function is_number(word) result(number)
+    character(*), intent(in) :: word
+    logical                  :: number
+
+    integer :: i
+    integer :: ic
+
+    number = .true.
+    do i = 1, len_trim(word)
+      ic = ichar(word(i:i))
+      if (ic < 48 .or. ic >= 58) number = .false.
+    end do
+
+  end function is_number
+
+!===============================================================================
+! STARTS_WITH determines whether a string starts with a certain
+! sequence of characters
+!===============================================================================
+
+  pure logical function starts_with(str, seq)
+    character(*), intent(in) :: str ! string to check
+    character(*), intent(in) :: seq ! sequence of characters
+
+    integer :: i
+    integer :: i_start
+    integer :: str_len
+    integer :: seq_len
+
+    str_len = len_trim(str)
+    seq_len = len_trim(seq)
+
+    ! determine how many spaces are at beginning of string
+    i_start = 0
+    do i = 1, str_len
+      if (str(i:i) == ' ' .or. str(i:i) == achar(9)) cycle
+      i_start = i
+      exit
+    end do
+
+    ! Check if string starts with sequence using INDEX intrinsic
+    if (index(str(1:str_len), seq(1:seq_len)) == i_start) then
+      starts_with = .true.
+    else
+      starts_with = .false.
+    end if
+
+  end function starts_with
+
+!===============================================================================
+! ENDS_WITH determines whether a string ends with a certain sequence
+! of characters
+!===============================================================================
+
+  pure logical function ends_with(str, seq)
+    character(*), intent(in) :: str ! string to check
+    character(*), intent(in) :: seq ! sequence of characters
+
+    integer :: i_start
+    integer :: str_len
+    integer :: seq_len
+
+    str_len = len_trim(str)
+    seq_len = len_trim(seq)
+
+    ! determine how many spaces are at beginning of string
+    i_start = str_len - seq_len + 1
+
+    ! Check if string starts with sequence using INDEX intrinsic
+    if (index(str(1:str_len), seq(1:seq_len), .true.) == i_start) then
+      ends_with = .true.
+    else
+      ends_with = .false.
+    end if
+
+  end function ends_with
+
+!===============================================================================
+! COUNT_DIGITS returns the number of digits needed to represent the input
+! integer.
+!===============================================================================
+
+  pure function count_digits(num) result(n_digits)
+    integer, intent(in) :: num
+    integer             :: n_digits
+
+    n_digits = 1
+    do while (num / 10**(n_digits) /= 0 .and. abs(num / 10 **(n_digits-1)) /= 1&
+              &.and. n_digits /= 10)
+      ! Note that 10 digits is the maximum needed to represent an integer(4) so
+      ! the loop automatically exits when n_digits = 10.
+      n_digits = n_digits + 1
+    end do
+
+  end function count_digits
+
+!===============================================================================
+! INT4_TO_STR converts an integer(4) to a string.
+!===============================================================================
+
+  pure function int4_to_str(num) result(str)
+
+    integer, intent(in) :: num
+    character(11) :: str
+
+    write (str, '(I11)') num
+    str = adjustl(str)
+
+  end function int4_to_str
+
+!===============================================================================
+! INT8_TO_STR converts an integer(8) to a string.
+!===============================================================================
+
+  pure function int8_to_str(num) result(str)
+
+    integer(8), intent(in) :: num
+    character(21) :: str
+
+    write (str, '(I21)') num
+    str = adjustl(str)
+
+  end function int8_to_str
+
+!===============================================================================
+! STR_TO_INT converts a string to an integer.
+!===============================================================================
+
+  pure function str_to_int(str) result(num)
+
+    character(*), intent(in) :: str
+    integer(8) :: num
+
+    character(5) :: fmt
+    integer      :: w
+    integer      :: ioError
+
+    ! Determine width of string
+    w = len_trim(str)
+
+    ! Create format specifier for reading string
+    write(UNIT=fmt, FMT='("(I",I2,")")') w
+
+    ! read string into integer
+    read(UNIT=str, FMT=fmt, IOSTAT=ioError) num
+    if (ioError > 0) num = ERROR_INT
+
+  end function str_to_int
+
+!===============================================================================
+! STR_TO_REAL converts an arbitrary string to a real(8)
+!===============================================================================
+
+  pure function str_to_real(string) result(num)
+
+    character(*), intent(in) :: string
+    real(8)                  :: num
+
+    integer :: ioError
+
+    ! Read string
+    read(UNIT=string, FMT=*, IOSTAT=ioError) num
+    if (ioError > 0) num = ERROR_REAL
+
+  end function str_to_real
+
+!===============================================================================
+! REAL_TO_STR converts a real(8) to a string based on how large the value is and
+! how many significant digits are desired. By default, six significants digits
+! are used.
+!===============================================================================
+
+  pure function real_to_str(num, sig_digits) result(string)
+
+    real(8),           intent(in) :: num        ! number to convert
+    integer, optional, intent(in) :: sig_digits ! # of significant digits
+    character(15)                 :: string     ! string returned
+
+    integer      :: decimal ! number of places after decimal
+    integer      :: width   ! total field width
+    real(8)      :: num2    ! absolute value of number
+    character(9) :: fmt     ! format specifier for writing number
+
+    ! set default field width
+    width = 15
+
+    ! set number of places after decimal
+    if (present(sig_digits)) then
+      decimal = sig_digits
+    else
+      decimal = 6
+    end if
+
+    ! Create format specifier for writing character
+    num2 = abs(num)
+    if (num2 == 0.0_8) then
+      write(fmt, '("(F",I2,".",I2,")")') width, 1
+    elseif (num2 < 1.0e-1_8) then
+      write(fmt, '("(ES",I2,".",I2,")")') width, decimal - 1
+    elseif (num2 >= 1.0e-1_8 .and. num2 < 1.0_8) then
+      write(fmt, '("(F",I2,".",I2,")")') width, decimal
+    elseif (num2 >= 1.0_8 .and. num2 < 10.0_8) then
+      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-1, 0)
+    elseif (num2 >= 10.0_8 .and. num2 < 100.0_8) then
+      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-2, 0)
+    elseif (num2 >= 100.0_8 .and. num2 < 1000.0_8) then
+      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-3, 0)
+    elseif (num2 >= 100.0_8 .and. num2 < 10000.0_8) then
+      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-4, 0)
+    elseif (num2 >= 10000.0_8 .and. num2 < 100000.0_8) then
+      write(fmt, '("(F",I2,".",I2,")")') width, max(decimal-5, 0)
+    else
+      write(fmt, '("(ES",I2,".",I2,")")') width, decimal - 1
+    end if
+
+    ! Write string and left adjust
+    write(string, fmt) num
+    string = adjustl(string)
+
+  end function real_to_str
+
 end module string
diff --git a/src/summary.F90 b/src/summary.F90
index 2f255a4fc5..e662aa473b 100644
--- a/src/summary.F90
+++ b/src/summary.F90
@@ -12,7 +12,7 @@ module summary
   use nuclide_header
   use output,          only: time_stamp
   use surface_header
-  use simple_string,   only: to_str
+  use string,          only: to_str
   use tally_header,    only: TallyObject
 
   use hdf5
diff --git a/src/tally.F90 b/src/tally.F90
index 842b7644ea..bbe099c3e4 100644
--- a/src/tally.F90
+++ b/src/tally.F90
@@ -13,7 +13,7 @@ module tally
   use output,           only: header
   use particle_header,  only: LocalCoord, Particle
   use search,           only: binary_search
-  use simple_string,    only: to_str
+  use string,           only: to_str
   use tally_header,     only: TallyResult, TallyMapItem, TallyMapElement
   use fission,          only: nu_total, nu_delayed, yield_delayed
   use interpolation,    only: interpolate_tab1
diff --git a/src/track_output.F90 b/src/track_output.F90
index 87dbfbfa44..1411738622 100644
--- a/src/track_output.F90
+++ b/src/track_output.F90
@@ -7,8 +7,8 @@ module track_output
 
   use global
   use hdf5_interface
-  use particle_header,   only: Particle
-  use simple_string,     only: to_str
+  use particle_header, only: Particle
+  use string,          only: to_str
 
   use hdf5
 
diff --git a/src/tracking.F90 b/src/tracking.F90
index 992cc2ca95..0b2719ef5d 100644
--- a/src/tracking.F90
+++ b/src/tracking.F90
@@ -13,7 +13,7 @@ module tracking
   use physics,         only: collision
   use physics_mg,      only: collision_mg
   use random_lcg,      only: prn
-  use simple_string,   only: to_str
+  use string,          only: to_str
   use tally,           only: score_analog_tally, score_tracklength_tally, &
                              score_collision_tally, score_surface_current
   use track_output,    only: initialize_particle_track, write_particle_track, &
diff --git a/src/trigger.F90 b/src/trigger.F90
index 967d74b14e..ed362154b4 100644
--- a/src/trigger.F90
+++ b/src/trigger.F90
@@ -6,12 +6,12 @@ module trigger
 
   use constants
   use global
-  use simple_string,    only: to_str
-  use output,           only: warning, write_message
-  use mesh,             only: mesh_indices_to_bin
-  use mesh_header,      only: RegularMesh
-  use trigger_header,   only: TriggerObject
-  use tally,            only: TallyObject
+  use string,         only: to_str
+  use output,         only: warning, write_message
+  use mesh,           only: mesh_indices_to_bin
+  use mesh_header,    only: RegularMesh
+  use trigger_header, only: TriggerObject
+  use tally,          only: TallyObject
 
   implicit none