Improve reactor controls, reactions, and maintenance UI

tests/test_fuel.py

@@ -0,0 +1,40 @@
+from reactor_sim.atomic import AtomicPhysics
+from reactor_sim.fuel import FuelAssembly
+from reactor_sim.state import CoreState
+
+
+def _core_state(
+    temp: float = 600.0,
+    flux: float = 1e6,
+    burnup: float = 0.05,
+    power: float = 100.0,
+) -> CoreState:
+    return CoreState(
+        fuel_temperature=temp,
+        neutron_flux=flux,
+        reactivity_margin=0.0,
+        power_output_mw=power,
+        burnup=burnup,
+    )
+
+
+def test_decay_reaction_power_positive_and_capped():
+    physics = AtomicPhysics(seed=7)
+    fuel = FuelAssembly(enrichment=0.045, mass_kg=80_000.0, atomic_physics=physics)
+    state = _core_state()
+    power = fuel.decay_reaction_power(state)
+    assert power > 0
+    # Should stay under 10% of current power_output_mw.
+    assert power <= state.power_output_mw * 0.1 + 1e-6
+
+
+def test_decay_reaction_power_scales_with_burnup_and_flux():
+    physics = AtomicPhysics(seed=9)
+    fuel = FuelAssembly(enrichment=0.045, mass_kg=80_000.0, atomic_physics=physics)
+    low = _core_state(burnup=0.01, flux=1e5, power=50.0)
+    high = _core_state(burnup=0.5, flux=5e6, power=200.0)
+    low_power = fuel.decay_reaction_power(low)
+    high_power = fuel.decay_reaction_power(high)
+    assert high_power > low_power
+    # Still capped to a reasonable fraction of the prevailing power.
+    assert high_power <= high.power_output_mw * 0.1 + 1e-6