NuclearDB
학습 트랙
04 · Nuclear Physics

From a single nucleus
to a shutdown reactor.

Four interactive modules tracing the four physical scales of reactor engineering — fission event, criticality, control, decay heat. Every numeric value cited to ENDF/B-VIII.0, ANS-5.1-2014, BNL NNDC, or Lamarsh / Stacey / Duderstadt.

Bridges between modules
ν · σ_f from A drives η in BDoppler in B moves the gauge in CCs-137 from A is the long-tail in DDelayed β in C lets us control · decay heat in D cannot be turned off
A · Fission

Single Fission Event

²³⁵U + n → FP₁ + FP₂ + ν̄ + ~200 MeV

A single uranium atom splits into two fragments, blasting out neutrons and gamma rays — and a huge amount of energy. One uranium pellet (~7 g, at real burn-up) packs roughly the energy of a ton of coal, with no CO₂.

AnalogyLike a domino: a fragment knocks the next uranium atom and the reaction keeps going.
Energy per fission~200 MeV
1 g U-235 fully fissioned ≈~3 t coal
Energy density vs coal~1 million×
Neutrons released (ν̄)~2.43

Switch to Detail to play the SMIL fission animation, see how 200 MeV splits across 7 channels, and toggle the ²³⁵U / Pu-239 / ²³⁵U-fast yield curves.

B · Six-factor

Six-Factor Formula

k_eff = η · ε · p · f · P_NL,f · P_NL,th

A reactor runs steady when neutrons produced in one generation exactly equal those starting the next — that ratio is k_eff. Above 1 it speeds up, below 1 it dies down.

AnalogyLike a sustainable campfire: too much wood and it rages, too little and it goes out — operators keep k_eff right at 1.
Operatingk = 1.000
Offk < 1
Risingk > 1
Run-away (prompt)k ≈ 1.0072

Switch to Detail to drive the five sliders (η · ε · p · f · P_NL), apply PWR / CANDU / BWR / Magnox / Fast presets, and watch the live k_∞ / k_eff regime gauge.

C · Reactivity

k_eff & Reactivity

ρ = (k − 1) / k · 1 dollar = β_eff · prompt-critical boundary

Reactivity ρ is the reactor's accelerator pedal. ρ = 0 holds power steady, ρ > 0 raises it, ρ < 0 lowers it. Operators dose tiny ρ values (in pcm or dollars) using control rods, boron, and temperature.

AnalogyLike a car pedal: nudge it gently and the speed eases up — but cross the prompt-critical line ($1) and brakes stop working.
Unitpcm = 10⁻⁵
1 dollar =β_eff (~0.0072 PWR)
Safe bandρ ≪ $1
Crossing $1Prompt critical

Switch to Detail for the 4-fuel gauge, ρ slider, the period-vs-reactivity log curve (inhour solver), and the collapsible 6-group delayed-neutron table.

D · Decay heat

Decay Heat & Half-Lives

ANS-5.1-2014 · why a SCRAM doesn't end the cooling problem

Even after shutdown a reactor keeps heating itself. Fission products' β/γ decay releases ~7 % of full power 1 second after shutdown, ~1.5 % at 1 hour, ~0.05 % at a year — and it cannot be turned off.

AnalogyLike an oven you just unplugged: the heating element is dark, but the cavity stays scalding for hours.
1 s after shutdown~7 %
1 h~1.5 %
1 day~0.4 %
1 year~0.05 %

Switch to Detail for the 3-plant overlay (PWR 1 GWe / Fukushima-1 / TMI-2) on a log-log curve, ±6 % ANS-5.1-2014 band, isotope filter, and Gen IV passive-cooling links.

Tip — drag any slider, click presets, or hover the curves. Cards are independent; bridges connect them.
Numeric data sourced to ENDF/B-VIII.0, ANS-5.1-2014, BNL NNDC NuDat 3.0, IAEA-TECDOC-1851, and standard reactor-physics textbooks. ANS-5.1-2014 cited by name; tabulated values recomputed from public ENDF data.