Retune reactivity for withdrawn and partially inserted rods

tests/test_simulation.py

@@ -155,8 +155,26 @@ def test_full_rod_withdrawal_reaches_gigawatt_power():
     reactor.primary_pump_active = True
     reactor.secondary_pump_active = True
 
-    for _ in range(60):
+    early_power = 0.0
+    for step in range(60):
+        reactor.step(state, dt=1.0)
+        if step == 10:
+            early_power = state.core.power_output_mw
+    assert state.core.power_output_mw > max(2_000.0, early_power * 2)
+    assert state.core.fuel_temperature > 600.0
+
+
+def test_partially_inserted_rods_hold_near_three_gw():
+    reactor = Reactor.default()
+    state = reactor.initial_state()
+    reactor.shutdown = False
+    reactor.control.manual_control = True
+    reactor.control.rod_fraction = 0.4
+    reactor.primary_pump_active = True
+    reactor.secondary_pump_active = True
+
+    for _ in range(120):
         reactor.step(state, dt=1.0)
 
-    assert state.core.power_output_mw > 2_000.0
-    assert state.core.fuel_temperature > 400.0
+    assert 2_000.0 < state.core.power_output_mw < 4_000.0
+    assert 500.0 < state.core.fuel_temperature < 800.0