Physics behind the simulator
The plant — SLS-100
The SLS-100 (Single Loop Simulated) is a compact pressurized water reactor (PWR) of about 100 MWe: one reactor coolant loop (core, reactor coolant pump, U-tube steam generator, pressurizer), the steam and feed plant, charging and letdown, emergency core cooling with an accumulator, residual heat removal, containment, and reactor protection and safeguards. Cold shutdown (Mode 5, 122 °F) through full power is one continuous plant.
Model in short: six-group point kinetics · nine-node coolant loop, mass and energy conserved · breaks at a chosen loop location · water properties fitted to IAPWS-95 steam tables, with their error measured · load coupled through the secondary · protection on instrument channels · degraded regimes open · no spatial core.
Core power and reactivity
- Point kinetics, six delayed-neutron groups — one average power, no flux shape. Period and startup rate drive the nuclear instruments.
- Reactivity terms: rods (S-curve bank worth), Doppler (fuel temperature), moderator from coolant density (not a fixed MTC), void, boron, xenon, and core excess.
- I–Xe chain with burnout — whole-core only, no spatial oscillation.
- Decay heat with power-history dependence — four decay groups, each relaxing toward its own equilibrium fraction of power.
Heat, pressure, and inventory
- Coolant loop: nine nodes from downcomer to cold leg, mass and energy conserved at every junction; loop flow from integrated momentum. Lumped fuel, cladding and steam-generator nodes — not a licensing thermal-hydraulics code.
- Pressurizer: two regions — a steam space compressed by an insurge over a stratified liquid — with heaters, spray, relief valve and safeties; water-solid and empty are reachable.
- Inventory from CVCS, ECCS, accumulators, leaks, and relief. Subcooling tracked; primary can void; RCP cavitation from suction margin.
- Degraded regimes stay open — uncovered SG tubes cut heat transfer; voided primary and solid pressurizer are allowed states, not clamped out.
Secondary and electrical
- Steam-generator mass and energy balance: level moves with feed, auxiliary feed and steam flow; steam dumps, relief valves and isolation couple to primary heat removal; a drying generator stops removing heat.
- Turbine / condenser / generator: load is a steam demand on the primary; condenser vacuum is computed, so losing it takes away the steam dump.
Instruments and protection
Board quantities are lagged, noisy instrument channels that can be failed. Trips, interlocks, safeguards, and automatic controllers take those channel values — not true state. A failed transmitter misleads both the operator and the automation.
What is left out on purpose
- No spatial neutronics or xenon tilt.
- One loop, lumped nodes — no multi-loop or subchannel TH.
- Containment is one lumped volume with spray and fan coolers — no structural heat sink, no hydrogen burn. Not a licensing accident analysis.
- Core damage (cladding oxidation, hydrogen generation) is modelled for training, not for licensing.
- Not a digital twin of a named unit.
Coefficients, step order, and declared departures: simulation-physics chapter in the in-sim manual, or the engine sources on GitHub (AGPL).