diff --git a/openmc/config.py b/openmc/config.py
index 08b8c3cb64..fe7c5aa06e 100644
--- a/openmc/config.py
+++ b/openmc/config.py
@@ -33,6 +33,7 @@ class _Config(MutableMapping):
             os.environ['OPENMC_MG_CROSS_SECTIONS'] = str(value)
         elif key == 'chain_file':
             self._set_path(key, value)
+            os.environ['OPENMC_CHAIN_FILE'] = str(value)
         else:
             raise KeyError(f'Unrecognized config key: {key}')
 
@@ -62,7 +63,7 @@ def _default_config():
         config['mg_cross_sections'] = os.environ["OPENMC_MG_CROSS_SECTIONS"]
 
     # Set depletion chain
-    chain_file = os.environ.get("OPENMC_DEPLETE_CHAIN")
+    chain_file = os.environ.get("OPENMC_CHAIN_FILE")
     if (chain_file is None and
         config['cross_sections'] is not None and
         config['cross_sections'].exists()
diff --git a/tests/unit_tests/test_config.py b/tests/unit_tests/test_config.py
new file mode 100644
index 0000000000..1d3c0f173b
--- /dev/null
+++ b/tests/unit_tests/test_config.py
@@ -0,0 +1,43 @@
+from collections.abc import Mapping
+import os
+
+import openmc
+import pytest
+
+
+@pytest.fixture(autouse=True, scope='module')
+def reset_config():
+    config = dict(openmc.config)
+    try:
+        yield
+    finally:
+        openmc.config.clear()
+        openmc.config.update(config)
+
+
+def test_config_basics():
+    assert isinstance(openmc.config, Mapping)
+    for key, value in openmc.config.items():
+        assert isinstance(key, str)
+        assert isinstance(value, os.PathLike)
+
+    # Set and delete
+    openmc.config['cross_sections'] = '/path/to/cross_sections.xml'
+    del openmc.config['cross_sections']
+    assert 'cross_sections' not in openmc.config
+    assert 'OPENMC_CROSS_SECTIONS' not in os.environ
+
+    # Can't use any key
+    with pytest.raises(KeyError):
+        openmc.config['🐖'] = '/like/to/eat/bacon'
+
+
+def test_config_set_envvar():
+    openmc.config['cross_sections'] = '/path/to/cross_sections.xml'
+    assert os.environ['OPENMC_CROSS_SECTIONS'] == '/path/to/cross_sections.xml'
+
+    openmc.config['mg_cross_sections'] = '/path/to/mg_cross_sections.h5'
+    assert os.environ['OPENMC_MG_CROSS_SECTIONS'] == '/path/to/mg_cross_sections.h5'
+
+    openmc.config['chain_file'] = '/path/to/chain_file.xml'
+    assert os.environ['OPENMC_CHAIN_FILE'] == '/path/to/chain_file.xml'