Changelog
What has changed in the simulator, newest first.
Older releases are collapsed — click a version to open it.
Accidents run on a real clock
Alpha 1.3.0
- ChangedLoss-of-coolant events run at real rates. Break flow, safety injection, accumulators, relief and charging all move true fractions of reactor coolant inventory per second, so the gallons-per-minute readouts are literal. A stuck-open pressurizer relief valve with injection secured now reaches core damage in about 2 hours 20 minutes — the Three Mile Island timeline, where it used to take minutes.
- ChangedThe relief valves are sized for this plant. The pressurizer PORV passes about 112 gpm and the code safeties 3.2 times that. Feed-and-bleed cooling is viable, and full safety injection out-runs one wide-open valve — which is why securing injection in 1979 was the decision that mattered.
- ChangedA large break blows down toward the containment building instead of stalling at the remnant's boiling pressure: a full-size break bottoms at 116 psi (0.80 MPa) where it floored at 170 psi (1.17 MPa). Smaller breaks are unchanged.
- FixedThe pressurizer level gauge no longer argues against a large break. It read 100 % at the moment the core top uncovered; with a hole in the loop the pressurizer now drains, while the Three Mile Island stuck-valve deception keeps its full strength on the paths where it is historical fact.
- AddedCore-exit thermocouple. The subcooling margin reads the hotter of the loop bulk and a new core-exit channel, so it goes hard negative over an uncovering core instead of reporting comfort from injection-chilled water.
- AddedChecklists check their prerequisites. A live checklist grades its procedure's preconditions against the plant and shows what the procedure expects against what the plant reads. It warns and never blocks, and clears itself when the plant is brought to where the procedure assumes.
- ChangedA reflooded core can recover. Core damage is no longer latched as terminal while water is coming back — a partially melted core that is re-covered stabilises, as Three Mile Island's did. Unmitigated accidents still end the same way.
- ChangedAtmospheric dump valve setpoint 1247 → 1272 psi (8.60 → 8.77 MPa), onto the sourced placement rule. A bottled steam generator now holds at 1276 psi (8.80 MPa) / 576.5 °F (302.5 °C).
The board stops flickering during transients
Alpha 1.2.2
- FixedElements blinking during large transients. Gauges, the trend chart, the alarm list and the clock were being rebuilt many times a second whether or not their values had changed, and could be caught mid-rebuild on screen.
- FixedBubbles in the reactor, steam generator and pressurizer restarting. The bubble fields are reused instead of rebuilt, so they keep rising instead of snapping back to the start.
- FixedVital gauge trends drawing outside their card, across the gauge band and onto the board, when a reading sat outside that gauge's scale. An off-scale reading now pins to the edge of its trace box.
A steadier board, and the atmospheric dumps start in auto
Alpha 1.2.1
- ChangedThe atmospheric dump valves start in AUTO. They hold a bottled steam generator at 1247 psi (8.60 MPa) instead of leaving it on its code safety valves. They still do not cool the plant on their own — lower the setpoint or open them for that.
- FixedFlickering during large transients. Gauges, the trend chart, the alarm list and the clock no longer strobe when a lot is happening at once.
- FixedAlarm acknowledgements that did not register. During an alarm flood a click could land on nothing. The alarm list can also be scrolled while alarms are coming in.
- FixedThe six vital gauge trends were blank above 600× speed. Their window now follows the speed setting and they sample between updates.
- ChangedThe vital gauge trends match the strip chart. They show a min/max band, hold a steady scale instead of rescaling every frame, and no longer drop brief spikes.
- FixedThe turbine exhaust pipe ran underneath the turbine control card.
- FixedSteam generator bubbles stopped partway up the water. They now rise to the surface and fade there.
- ChangedManual corrections. The full-open cooldown rate is re-measured at about 630 °F/hr, and the steam dump section carries current numbers.
Containment, atmospheric dumps, and automatic steam line isolation
Alpha 1.2.0
- AddedA containment building. It has pressure, temperature and a sump, and a break or relief discharge pressurizes it. A steam generator tube rupture does not — that break bypasses containment.
- AddedAtmospheric dump valves. You can cool the plant down with the condenser lost. They ship shut, and at full open they cool about three times faster than the 100 °F/hr limit.
- AddedAutomatic main steam line isolation on high steam flow together with low steam pressure. It cannot be reopened until the generator re-pressurizes.
- ChangedDecay heat is refitted to the published standard. Post-trip timings are longer: a station blackout reaches core damage at 2.6 hours, against under 2 before.
- ChangedThe graph shows the full range a value reached, its time windows follow the speed setting, and its resolution no longer depends on speed.
- FixedA leaking plant that goes water-solid now reaches its relief valve instead of filling to the model ceiling.
- FixedA steam line break no longer empties the generator to the model floor. It is a mass flow now, so the generator recovers to its safety band.
- AddedThe release number is shown beside the ALPHA badge on every page.
Cooldown rate indication, turbine stop valves, and a run of physics fixes
Alpha 1.1.0
- AddedRCS cooldown and heatup rate meter, with high-rate annunciators at ±100 °F/hr.
- AddedTurbine stop valves. A trip now shuts steam off in a fraction of a second, separately from the governor.
- ChangedFeedwater carries heat. Overfeeding overcools the plant, and auxiliary feedwater is a real heat sink.
- FixedSteam generator code safety valves act on steam pressure itself. A failed pressure transmitter can no longer stop them lifting.
- FixedPressurizer level no longer freezes at a normal reading as the plant heats. It rises to the top and the relief valve lifts.
- FixedA break stops cooling the plant once the coolant stops boiling.
- FixedA stopped reactor coolant pump no longer heats the coolant.
- ChangedTwo limits are stated in the manual: steam line isolation is a manual action, and the steam dump goes to the condenser only.
Pressurizer, relief and the control board
Alpha 1.0.1
- FixedA water-solid reactor coolant system now repressurizes. Emergency injection into a full plant lifts the relief valve instead of vanishing.
- FixedLosing coolant now moves pressure and subcooling margin, not just pressurizer level.
- FixedA break weakens as the plant depressurizes. Closing the pressure difference reduces leak flow, and an empty vessel stops discharging.
- FixedThe Three Mile Island scenarios and campaign play through again, and the decision point is now the one the 1979 crew faced: restore the injection that was just secured.
- ChangedThe tube-rupture procedure secures injection before depressurizing — without it, walking the pressure setpoint down does nothing.
- ChangedThe diagram shows delivered flow, not commanded flow. Pumps, valves and pipes stop animating when nothing is moving.
- ChangedPipe colours read the plant. Letdown, charging, emergency injection, accumulator and auxiliary feed lines take live temperatures; coolant green and orange are darker.
- AddedPressurizer spray flow indication and a main feedwater RESTORE control on the steam generator feed card.
Initial Alpha release
Alpha 1.0.0
- AddedInitial Alpha release. Pressurised water reactor.