Increase xenon reactivity impact

tests/test_neutronics.py

@@ -40,6 +40,6 @@ def test_xenon_penalty_caps():
     dynamics = NeutronDynamics()
     state = _core_state()
     state.xenon_inventory = 50.0
-    assert dynamics.xenon_penalty(state) == 0.03
-    state.xenon_inventory = 5.0
+    assert dynamics.xenon_penalty(state) == 0.05
+    state.xenon_inventory = 0.2
     assert dynamics.xenon_penalty(state) == pytest.approx(0.01)