diff --git a/openmc/data/data.py b/openmc/data/data.py
index 9759411abd..14a279b408 100644
--- a/openmc/data/data.py
+++ b/openmc/data/data.py
@@ -3,78 +3,80 @@ import os
 import re
 
 
-# Isotopic abundances from M. Berglund and M. E. Wieser, "Isotopic compositions
-# of the elements 2009 (IUPAC Technical Report)", Pure. Appl. Chem. 83 (2),
-# pp. 397--410 (2011).
+# Isotopic abundances from Meija J, Coplen T B, et al, "Isotopic compositions
+# of the elements 2013 (IUPAC Technical Report)", Pure. Appl. Chem. 88 (3),
+# pp. 293-306 (2013). The "representative isotopic abundance" values from
+# column 9 are used except where an interval is given, in which case the
+# "best measurement" is used.
 NATURAL_ABUNDANCE = {
-    'H1': 0.999885, 'H2': 0.000115, 'He3': 1.34e-06,
-    'He4': 0.99999866, 'Li6': 0.0759, 'Li7': 0.9241,
-    'Be9': 1.0, 'B10': 0.199, 'B11': 0.801,
-    'C12': 0.9893, 'C13': 0.0107, 'N14': 0.99636,
-    'N15': 0.00364, 'O16': 0.99757, 'O17': 0.00038,
-    'O18': 0.00205, 'F19': 1.0, 'Ne20': 0.9048,
+    'H1': 0.99984426, 'H2': 0.00015574, 'He3': 0.000002,
+    'He4': 0.999998, 'Li6': 0.07589, 'Li7': 0.92411,
+    'Be9': 1.0, 'B10': 0.1982, 'B11': 0.8018,
+    'C12': 0.988922, 'C13': 0.011078, 'N14': 0.996337,
+    'N15': 0.003663, 'O16': 0.9976206, 'O17': 0.000379,
+    'O18': 0.0020004, 'F19': 1.0, 'Ne20': 0.9048,
     'Ne21': 0.0027, 'Ne22': 0.0925, 'Na23': 1.0,
-    'Mg24': 0.7899, 'Mg25': 0.1, 'Mg26': 0.1101,
-    'Al27': 1.0, 'Si28': 0.92223, 'Si29': 0.04685,
-    'Si30': 0.03092, 'P31': 1.0, 'S32': 0.9499,
-    'S33': 0.0075, 'S34': 0.0425, 'S36': 0.0001,
-    'Cl35': 0.7576, 'Cl37': 0.2424, 'Ar36': 0.003336,
+    'Mg24': 0.78951, 'Mg25': 0.1002, 'Mg26': 0.11029,
+    'Al27': 1.0, 'Si28': 0.9222968, 'Si29': 0.0468316,
+    'Si30': 0.0308716, 'P31': 1.0, 'S32': 0.9504074,
+    'S33': 0.0074869, 'S34': 0.0419599, 'S36': 0.0001458,
+    'Cl35': 0.757647, 'Cl37': 0.242353, 'Ar36': 0.003336,
     'Ar38': 0.000629, 'Ar40': 0.996035, 'K39': 0.932581,
     'K40': 0.000117, 'K41': 0.067302, 'Ca40': 0.96941,
     'Ca42': 0.00647, 'Ca43': 0.00135, 'Ca44': 0.02086,
-    'Ca46': 4e-05, 'Ca48': 0.00187, 'Sc45': 1.0,
+    'Ca46': 0.00004, 'Ca48': 0.00187, 'Sc45': 1.0,
     'Ti46': 0.0825, 'Ti47': 0.0744, 'Ti48': 0.7372,
     'Ti49': 0.0541, 'Ti50': 0.0518, 'V50': 0.0025,
     'V51': 0.9975, 'Cr50': 0.04345, 'Cr52': 0.83789,
     'Cr53': 0.09501, 'Cr54': 0.02365, 'Mn55': 1.0,
     'Fe54': 0.05845, 'Fe56': 0.91754, 'Fe57': 0.02119,
-    'Fe58': 0.00282, 'Co59': 1.0, 'Ni58': 0.68077,
-    'Ni60': 0.26223, 'Ni61': 0.011399, 'Ni62': 0.036346,
-    'Ni64': 0.009255, 'Cu63': 0.6915, 'Cu65': 0.3085,
+    'Fe58': 0.00282, 'Co59': 1.0, 'Ni58': 0.680769,
+    'Ni60': 0.262231, 'Ni61': 0.011399, 'Ni62': 0.036345,
+    'Ni64': 0.009256, 'Cu63': 0.6915, 'Cu65': 0.3085,
     'Zn64': 0.4917, 'Zn66': 0.2773, 'Zn67': 0.0404,
     'Zn68': 0.1845, 'Zn70': 0.0061, 'Ga69': 0.60108,
-    'Ga71': 0.39892, 'Ge70': 0.2057, 'Ge72': 0.2745,
-    'Ge73': 0.0775, 'Ge74': 0.365, 'Ge76': 0.0773,
-    'As75': 1.0, 'Se74': 0.0089, 'Se76': 0.0937,
-    'Se77': 0.0763, 'Se78': 0.2377, 'Se80': 0.4961,
-    'Se82': 0.0873, 'Br79': 0.5069, 'Br81': 0.4931,
+    'Ga71': 0.39892, 'Ge70': 0.2052, 'Ge72': 0.2745,
+    'Ge73': 0.0776, 'Ge74': 0.3652, 'Ge76': 0.0775,
+    'As75': 1.0, 'Se74': 0.0086, 'Se76': 0.0923,
+    'Se77': 0.076, 'Se78': 0.2369, 'Se80': 0.498,
+    'Se82': 0.0882, 'Br79': 0.50686, 'Br81': 0.49314,
     'Kr78': 0.00355, 'Kr80': 0.02286, 'Kr82': 0.11593,
     'Kr83': 0.115, 'Kr84': 0.56987, 'Kr86': 0.17279,
     'Rb85': 0.7217, 'Rb87': 0.2783, 'Sr84': 0.0056,
     'Sr86': 0.0986, 'Sr87': 0.07, 'Sr88': 0.8258,
     'Y89': 1.0, 'Zr90': 0.5145, 'Zr91': 0.1122,
     'Zr92': 0.1715, 'Zr94': 0.1738, 'Zr96': 0.028,
-    'Nb93': 1.0, 'Mo92': 0.1453, 'Mo94': 0.0915,
-    'Mo95': 0.1584, 'Mo96': 0.1667, 'Mo97': 0.096,
-    'Mo98': 0.2439, 'Mo100': 0.0982, 'Ru96': 0.0554,
+    'Nb93': 1.0, 'Mo92': 0.14649, 'Mo94': 0.09187,
+    'Mo95': 0.15873, 'Mo96': 0.16673, 'Mo97': 0.09582,
+    'Mo98': 0.24292, 'Mo100': 0.09744, 'Ru96': 0.0554,
     'Ru98': 0.0187, 'Ru99': 0.1276, 'Ru100': 0.126,
     'Ru101': 0.1706, 'Ru102': 0.3155, 'Ru104': 0.1862,
     'Rh103': 1.0, 'Pd102': 0.0102, 'Pd104': 0.1114,
     'Pd105': 0.2233, 'Pd106': 0.2733, 'Pd108': 0.2646,
     'Pd110': 0.1172, 'Ag107': 0.51839, 'Ag109': 0.48161,
-    'Cd106': 0.0125, 'Cd108': 0.0089, 'Cd110': 0.1249,
-    'Cd111': 0.128, 'Cd112': 0.2413, 'Cd113': 0.1222,
-    'Cd114': 0.2873, 'Cd116': 0.0749, 'In113': 0.0429,
-    'In115': 0.9571, 'Sn112': 0.0097, 'Sn114': 0.0066,
+    'Cd106': 0.01245, 'Cd108': 0.00888, 'Cd110': 0.1247,
+    'Cd111': 0.12795, 'Cd112': 0.24109, 'Cd113': 0.12227,
+    'Cd114': 0.28754, 'Cd116': 0.07512, 'In113': 0.04281,
+    'In115': 0.95719, 'Sn112': 0.0097, 'Sn114': 0.0066,
     'Sn115': 0.0034, 'Sn116': 0.1454, 'Sn117': 0.0768,
     'Sn118': 0.2422, 'Sn119': 0.0859, 'Sn120': 0.3258,
     'Sn122': 0.0463, 'Sn124': 0.0579, 'Sb121': 0.5721,
     'Sb123': 0.4279, 'Te120': 0.0009, 'Te122': 0.0255,
     'Te123': 0.0089, 'Te124': 0.0474, 'Te125': 0.0707,
     'Te126': 0.1884, 'Te128': 0.3174, 'Te130': 0.3408,
-    'I127': 1.0, 'Xe124': 0.000952, 'Xe126': 0.00089,
-    'Xe128': 0.019102, 'Xe129': 0.264006, 'Xe130': 0.04071,
-    'Xe131': 0.212324, 'Xe132': 0.269086, 'Xe134': 0.104357,
-    'Xe136': 0.088573, 'Cs133': 1.0, 'Ba130': 0.00106,
-    'Ba132': 0.00101, 'Ba134': 0.02417, 'Ba135': 0.06592,
-    'Ba136': 0.07854, 'Ba137': 0.11232, 'Ba138': 0.71698,
-    'La138': 0.0008881, 'La139': 0.9991119, 'Ce136': 0.00185,
-    'Ce138': 0.00251, 'Ce140': 0.8845, 'Ce142': 0.11114,
-    'Pr141': 1.0, 'Nd142': 0.27152, 'Nd143': 0.12174,
+    'I127': 1.0, 'Xe124': 0.00095, 'Xe126': 0.00089,
+    'Xe128': 0.0191, 'Xe129': 0.26401, 'Xe130': 0.04071,
+    'Xe131': 0.21232, 'Xe132': 0.26909, 'Xe134': 0.10436,
+    'Xe136': 0.08857, 'Cs133': 1.0, 'Ba130': 0.0011,
+    'Ba132': 0.001, 'Ba134': 0.0242, 'Ba135': 0.0659,
+    'Ba136': 0.0785, 'Ba137': 0.1123, 'Ba138': 0.717,
+    'La138': 0.0008881, 'La139': 0.9991119, 'Ce136': 0.00186,
+    'Ce138': 0.00251, 'Ce140': 0.88449, 'Ce142': 0.11114,
+    'Pr141': 1.0, 'Nd142': 0.27153, 'Nd143': 0.12173,
     'Nd144': 0.23798, 'Nd145': 0.08293, 'Nd146': 0.17189,
-    'Nd148': 0.05756, 'Nd150': 0.05638, 'Sm144': 0.0307,
-    'Sm147': 0.1499, 'Sm148': 0.1124, 'Sm149': 0.1382,
-    'Sm150': 0.0738, 'Sm152': 0.2675, 'Sm154': 0.2275,
+    'Nd148': 0.05756, 'Nd150': 0.05638, 'Sm144': 0.0308,
+    'Sm147': 0.15, 'Sm148': 0.1125, 'Sm149': 0.1382,
+    'Sm150': 0.0737, 'Sm152': 0.2674, 'Sm154': 0.2274,
     'Eu151': 0.4781, 'Eu153': 0.5219, 'Gd152': 0.002,
     'Gd154': 0.0218, 'Gd155': 0.148, 'Gd156': 0.2047,
     'Gd157': 0.1565, 'Gd158': 0.2484, 'Gd160': 0.2186,
@@ -84,8 +86,8 @@ NATURAL_ABUNDANCE = {
     'Er162': 0.00139, 'Er164': 0.01601, 'Er166': 0.33503,
     'Er167': 0.22869, 'Er168': 0.26978, 'Er170': 0.1491,
     'Tm169': 1.0, 'Yb168': 0.00123, 'Yb170': 0.02982,
-    'Yb171': 0.1409, 'Yb172': 0.2168, 'Yb173': 0.16103,
-    'Yb174': 0.32026, 'Yb176': 0.12996, 'Lu175': 0.97401,
+    'Yb171': 0.14086, 'Yb172': 0.21686, 'Yb173': 0.16103,
+    'Yb174': 0.32025, 'Yb176': 0.12995, 'Lu175': 0.97401,
     'Lu176': 0.02599, 'Hf174': 0.0016, 'Hf176': 0.0526,
     'Hf177': 0.186, 'Hf178': 0.2728, 'Hf179': 0.1362,
     'Hf180': 0.3508, 'Ta180': 0.0001201, 'Ta181': 0.9998799,
@@ -95,14 +97,15 @@ NATURAL_ABUNDANCE = {
     'Os187': 0.0196, 'Os188': 0.1324, 'Os189': 0.1615,
     'Os190': 0.2626, 'Os192': 0.4078, 'Ir191': 0.373,
     'Ir193': 0.627, 'Pt190': 0.00012, 'Pt192': 0.00782,
-    'Pt194': 0.3286, 'Pt195': 0.3378, 'Pt196': 0.2521,
+    'Pt194': 0.32864, 'Pt195': 0.33775, 'Pt196': 0.25211,
     'Pt198': 0.07356, 'Au197': 1.0, 'Hg196': 0.0015,
-    'Hg198': 0.0997, 'Hg199': 0.1687, 'Hg200': 0.231,
-    'Hg201': 0.1318, 'Hg202': 0.2986, 'Hg204': 0.0687,
-    'Tl203': 0.2952, 'Tl205': 0.7048, 'Pb204': 0.014,
+    'Hg198': 0.1004, 'Hg199': 0.1694, 'Hg200': 0.2314,
+    'Hg201': 0.1317, 'Hg202': 0.2974, 'Hg204': 0.0682,
+    'Tl203': 0.29524, 'Tl205': 0.70476, 'Pb204': 0.014,
     'Pb206': 0.241, 'Pb207': 0.221, 'Pb208': 0.524,
-    'Bi209': 1.0, 'Th232': 1.0, 'Pa231': 1.0,
-    'U234': 5.4e-05, 'U235': 0.007204, 'U238': 0.992742
+    'Bi209': 1.0, 'Th230': 0.0002, 'Th232': 0.9998,
+    'Pa231': 1.0, 'U234': 0.000054, 'U235': 0.007204,
+    'U238': 0.992742
 }
 
 ATOMIC_SYMBOL = {0: 'n', 1: 'H', 2: 'He', 3: 'Li', 4: 'Be', 5: 'B', 6: 'C',
diff --git a/openmc/material.py b/openmc/material.py
index 73329a5320..f276f0f1ab 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -663,7 +663,7 @@ class Material(object):
         if not percent_in_atom:
             for n, nuc in enumerate(nucs):
                 nuc_densities[n] *= self.average_molar_mass / \
-                                    openmc.data.atomic_mass(nuc)
+                                    openmc.data.atomic_mass(nuc.name)
 
         # Now that we have the atomic amounts, lets finish calculating densities
         sum_percent = np.sum(nuc_densities)
diff --git a/tests/test_triso/inputs_true.dat b/tests/test_triso/inputs_true.dat
index 424af7fd56..be6d2d0eae 100644
--- a/tests/test_triso/inputs_true.dat
+++ b/tests/test_triso/inputs_true.dat
@@ -413,9 +413,9 @@
     <material id="10003">
         <density units="g/cm3" value="3.2" />
         <nuclide ao="1.0" name="C0" />
-        <nuclide ao="0.92223" name="Si28" />
-        <nuclide ao="0.04685" name="Si29" />
-        <nuclide ao="0.03092" name="Si30" />
+        <nuclide ao="0.9222968" name="Si28" />
+        <nuclide ao="0.0468316" name="Si29" />
+        <nuclide ao="0.0308716" name="Si30" />
     </material>
     <material id="10004">
         <density units="g/cm3" value="1.87" />
diff --git a/tests/test_triso/results_true.dat b/tests/test_triso/results_true.dat
index 43aef9276a..4942024dd4 100644
--- a/tests/test_triso/results_true.dat
+++ b/tests/test_triso/results_true.dat
@@ -1,2 +1,2 @@
 k-combined:
-1.587300E+00 9.381519E-02
+1.620345E+00 6.133879E-02