diff --git a/src/relaxng/settings.rnc b/src/relaxng/settings.rnc
index 62d9451c3d..988fd0471a 100644
--- a/src/relaxng/settings.rnc
+++ b/src/relaxng/settings.rnc
@@ -1,29 +1,7 @@
 element settings {
-  element confidence_intervals { xsd:boolean }? &
+  element batches { xsd:positiveInteger }? &
 
-  (
-    element eigenvalue {
-      (element batches { xsd:positiveInteger } |
-        attribute batches { xsd:positiveInteger }) &
-      (element inactive { xsd:nonNegativeInteger } |
-        attribute inactive { xsd:nonNegativeInteger }) &
-      (element particles { xsd:positiveInteger } |
-        attribute particles { xsd:positiveInteger }) &
-      (element generations_per_batch { xsd:positiveInteger } |
-        attribute generations_per_batch { xsd:positiveInteger })? &
-      (element keff_trigger {
-        (element type { xsd:string } | attribute type { xsd:string }) &
-        (element threshold { xsd:double} | attribute threshold { xsd:double })
-        }
-      )?
-    } |
-    element fixed_source {
-      (element batches { xsd:positiveInteger } |
-        attribute batches { xsd:positiveInteger }) &
-      (element particles { xsd:positiveInteger } |
-        attribute particles { xsd:positiveInteger })
-    }
-  ) &
+  element confidence_intervals { xsd:boolean }? &
 
   element cutoff {
     (element weight { xsd:double } | attribute weight { xsd:double })? &
@@ -43,12 +21,19 @@ element settings {
       attribute upper_right { list { xsd:double+ } })
   }? &
 
+  element generations_per_batch { xsd:positiveInteger }? &
+
+  element inactive { xsd:nonNegativeInteger }? &
+
+  element keff_trigger {
+    (element type { xsd:string } | attribute type { xsd:string }) &
+    (element threshold { xsd:double} | attribute threshold { xsd:double })
+  }? &
+
   element log_grid_bins { xsd:positiveInteger }? &
 
   element max_order { xsd:nonNegativeInteger }? &
 
-  element natural_elements { xsd:string { maxLength = "20" } }? &
-
   element no_reduce { xsd:boolean }? &
 
   element output {
@@ -60,6 +45,8 @@ element settings {
 
   element output_path { xsd:string { maxLength = "255" } }? &
 
+  element particles { xsd:positiveInteger }? &
+
   element ptables { xsd:boolean }? &
 
   element run_cmfd { xsd:boolean }? &
@@ -179,5 +166,5 @@ element settings {
       (element E_max { xsd:double } |
         attribute E_max { xsd:double })?
     }*
-  }? &
+  }?
 }
diff --git a/src/relaxng/settings.rng b/src/relaxng/settings.rng
index cbeac25a51..fe0a294f42 100644
--- a/src/relaxng/settings.rng
+++ b/src/relaxng/settings.rng
@@ -1,107 +1,16 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <element name="settings" xmlns="http://relaxng.org/ns/structure/1.0" datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
   <interleave>
+    <optional>
+      <element name="batches">
+        <data type="positiveInteger"/>
+      </element>
+    </optional>
     <optional>
       <element name="confidence_intervals">
         <data type="boolean"/>
       </element>
     </optional>
-    <choice>
-      <element name="eigenvalue">
-        <interleave>
-          <choice>
-            <element name="batches">
-              <data type="positiveInteger"/>
-            </element>
-            <attribute name="batches">
-              <data type="positiveInteger"/>
-            </attribute>
-          </choice>
-          <choice>
-            <element name="inactive">
-              <data type="nonNegativeInteger"/>
-            </element>
-            <attribute name="inactive">
-              <data type="nonNegativeInteger"/>
-            </attribute>
-          </choice>
-          <choice>
-            <element name="particles">
-              <data type="positiveInteger"/>
-            </element>
-            <attribute name="particles">
-              <data type="positiveInteger"/>
-            </attribute>
-          </choice>
-          <optional>
-            <choice>
-              <element name="generations_per_batch">
-                <data type="positiveInteger"/>
-              </element>
-              <attribute name="generations_per_batch">
-                <data type="positiveInteger"/>
-              </attribute>
-            </choice>
-          </optional>
-          <optional>
-            <element name="keff_trigger">
-              <interleave>
-                <choice>
-                  <element name="type">
-                    <data type="string"/>
-                  </element>
-                  <attribute name="type">
-                    <data type="string"/>
-                  </attribute>
-                </choice>
-                <choice>
-                  <element name="threshold">
-                    <data type="double"/>
-                  </element>
-                  <attribute name="threshold">
-                    <data type="double"/>
-                  </attribute>
-                </choice>
-              </interleave>
-            </element>
-          </optional>
-        </interleave>
-      </element>
-      <element name="fixed_source">
-        <interleave>
-          <choice>
-            <element name="batches">
-              <data type="positiveInteger"/>
-            </element>
-            <attribute name="batches">
-              <data type="positiveInteger"/>
-            </attribute>
-          </choice>
-          <choice>
-            <element name="particles">
-              <data type="positiveInteger"/>
-            </element>
-            <attribute name="particles">
-              <data type="positiveInteger"/>
-            </attribute>
-          </choice>
-        </interleave>
-      </element>
-    </choice>
-    <optional>
-      <element name="cross_sections">
-        <data type="string">
-          <param name="maxLength">255</param>
-        </data>
-      </element>
-    </optional>
-    <optional>
-      <element name="multipole_library">
-        <data type="string">
-          <param name="maxLength">255</param>
-        </data>
-      </element>
-    </optional>
     <optional>
       <element name="cutoff">
         <interleave>
@@ -208,6 +117,38 @@
         </interleave>
       </element>
     </optional>
+    <optional>
+      <element name="generations_per_batch">
+        <data type="positiveInteger"/>
+      </element>
+    </optional>
+    <optional>
+      <element name="inactive">
+        <data type="nonNegativeInteger"/>
+      </element>
+    </optional>
+    <optional>
+      <element name="keff_trigger">
+        <interleave>
+          <choice>
+            <element name="type">
+              <data type="string"/>
+            </element>
+            <attribute name="type">
+              <data type="string"/>
+            </attribute>
+          </choice>
+          <choice>
+            <element name="threshold">
+              <data type="double"/>
+            </element>
+            <attribute name="threshold">
+              <data type="double"/>
+            </attribute>
+          </choice>
+        </interleave>
+      </element>
+    </optional>
     <optional>
       <element name="log_grid_bins">
         <data type="positiveInteger"/>
@@ -218,13 +159,6 @@
         <data type="nonNegativeInteger"/>
       </element>
     </optional>
-    <optional>
-      <element name="natural_elements">
-        <data type="string">
-          <param name="maxLength">20</param>
-        </data>
-      </element>
-    </optional>
     <optional>
       <element name="no_reduce">
         <data type="boolean"/>
@@ -273,6 +207,11 @@
         </data>
       </element>
     </optional>
+    <optional>
+      <element name="particles">
+        <data type="positiveInteger"/>
+      </element>
+    </optional>
     <optional>
       <element name="ptables">
         <data type="boolean"/>