diff --git a/armi/reactor/parameters/parameterCollections.py b/armi/reactor/parameters/parameterCollections.py
index 44cc06d30..2c6af073e 100644
--- a/armi/reactor/parameters/parameterCollections.py
+++ b/armi/reactor/parameters/parameterCollections.py
@@ -146,6 +146,8 @@ def __init__(self, _state: Optional[List[Any]] = None):
             should come from a call to __getstate__(). This should only be used
             internally to this model.
         """
+        self._slots.add("readOnly")
+        self.readOnly = False
         if self.pDefs is None or not self.pDefs.locked:
             type(self).applyParameters()
 
@@ -275,7 +277,13 @@ def __setattr__(self, key, value):
             "Trying to set undefined attribute `{}` on "
             "a ParameterCollection!".format(key)
         )
-
+        if getattr(self, "readOnly", False):
+            if key == "readOnly":
+                raise RuntimeError(
+                    "Parameter Collections cannot be made writeable after being set to read only."
+                )
+            else:
+                raise RuntimeError(f"Cannot set read-only parameter {key}")
         object.__setattr__(self, key, value)
 
     def __deepcopy__(self, memo):
diff --git a/armi/reactor/parameters/parameterDefinitions.py b/armi/reactor/parameters/parameterDefinitions.py
index a953ed377..c993a8bf5 100644
--- a/armi/reactor/parameters/parameterDefinitions.py
+++ b/armi/reactor/parameters/parameterDefinitions.py
@@ -283,7 +283,6 @@ def __init__(
         self.categories = categories
         self.assigned = NEVER
         self._backup = None
-        self.readOnly = False
 
         if self.default is not NoDefault:
 
@@ -331,9 +330,6 @@ def __setstate__(self, state):
 
     def __set__(self, obj, val):
         """This is a property setter, see Python documentation for "descriptor"."""
-        if self.readOnly:
-            raise RuntimeError(f"Cannot set read-only parameter {self.name}.")
-
         self._setter(obj, val)
 
     def __get__(self, obj, cls=None):
diff --git a/armi/reactor/reactorParameters.py b/armi/reactor/reactorParameters.py
index ad67a20bb..9997c3d7c 100644
--- a/armi/reactor/reactorParameters.py
+++ b/armi/reactor/reactorParameters.py
@@ -791,17 +791,12 @@ def makeParametersReadOnly(r, readOnly=True):
     ARMI. So if you run this function once with `readOnly=True`, and you want to move on to other
     things, run this method on your reactor again with `readOnly=False` to unclock ARMI.
     """
-    for pdef0 in r.p.paramDefs:
-        pdef0.readOnly = readOnly
-        for system in r.getChildren():
-            for pdef1 in system.p.paramDefs:
-                pdef1.readOnly = readOnly
-            for a in system.getChildren():
-                for pdef2 in a.p.paramDefs:
-                    pdef2.readOnly = readOnly
-                for b in a.getChildren():
-                    for pdef3 in b.p.paramDefs:
-                        pdef3.readOnly = readOnly
-                    for c in b.getChildren():
-                        for pdef4 in c.p.paramDefs:
-                            pdef4.readOnly = readOnly
+    r.p.readOnly = readOnly
+    for system in r.getChildren():
+        system.p.readOnly = readOnly
+        for a in system.getChildren():
+            a.p.readOnly = readOnly
+            for b in a.getChildren():
+                b.p.readOnly = readOnly
+                for c in b.getChildren():
+                    c.p.readOnly = readOnly