a56fcbedc2
First working nonlinear reach artifact for the PWR model. TMJets
Taylor-model scheme on the full 10-state closed-loop (unsaturated
ctrl_heatup, ramp reference via augmented time state x[11]).
Status:
T=10s : SUCCESS. 10583 reach-sets. T_c envelope [274.45, 295] C,
n envelope [-5.2e-4, 5.01e-3]. Over-approximation visible
(n can't be negative physically) but tube is sound and
bounded.
T=60s+ : FAILED. Exhausts 50k step budget then hits NaN in
precursor-decay term.
Root cause: prompt-neutron stiffness. Lambda=1e-4s forces TMJets'
adaptive stepper to ~1ms steps to resolve fast dynamics. 10583 steps
for 10s of sim time means we get ~10s/50000 = 2s horizon max before
step budget exhausts — inadequate for heatup's 5-hour obligation.
Remedy (next session): singular-perturbation reduction of the
neutronics. Treat n as quasi-static algebraic function of (T, C, rho)
rather than a dynamic state. Replaces stiff dn/dt with algebraic
relation, removes fast timescale from reach problem. Standard in
reactor-kinetics reach literature.
What this does prove:
- Julia/TMJets framework works for this system (previous
scaling-issue failure is gone with @taylorize'd RHS).
- Bilinear n*rho term handled correctly by Taylor models.
- Ramp reference via augmented time state x[11] is a workable
pattern for time-varying controller references in reach.
What this does NOT prove:
- Anything about heatup safety — 10s horizon is nowhere near the
mode's 5-hour obligation.
Includes sim_heatup.jl, a Rodas5 baseline using the same @taylorize-
able RHS form, for cross-validation of the reach tube against a
nominal trajectory once longer horizons are reachable.
WALKTHROUGH.md updated with the finding.
Hacker-Split: got partway up the Julia reach ladder, identified the
physical bottleneck (stiffness), named the fix (reduced-order PKE).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Julia port
Parallel implementation of the plant model (../plant-model/) in Julia,
intended as an eventual landing spot for reachability if we outgrow the
MATLAB / hand-rolled tooling.
Status
src/pke_params.jl,src/pke_th_rhs.jl,src/pke_linearize.jl— functional, match MATLAB term-for-term.controllers/controllers.jl— all five modes ported (null, shutdown, heatup, operation, scram). LQR factory included via MatrixEquations.jl.scripts/sim_sanity.jl— closed-loop simulation matches MATLAB to 3 decimals on the 100% → 80%Q_sgstep. ✅ passing.scripts/reach_operation.jl— ❌ stub. ReachabilityAnalysis.jl algorithms blow up on this stiff, badly-conditioned system. See the file header for diagnosis and planned fix (state rescaling).
When to prefer Julia over MATLAB
Today: nowhere. The sanity path exists so we don't regret the eventual port.
Once the reach scaling is resolved:
- Nonlinear reach for the P controller in operation mode (CORA / JuliaReach territory where MATLAB's linearization doesn't suffice).
- Heatup reach with its time-varying reference.
- Parametric studies where MATLAB license fees / CI friction matter.
Running
cd julia-port
julia --project=. -e 'using Pkg; Pkg.instantiate()'
julia --project=. scripts/sim_sanity.jl
First run will precompile the dependency stack (OrdinaryDiffEq, ReachabilityAnalysis, LazySets — a few minutes).