Aggregate decay-heat load from every batch sitting in a spent fuel pool, via the full ANSI/ANS-5.1-2005 standard (reused from the Decay Heat Calculator) with a Wigner-Way cross-check shown side by side — plus the pool's thermal response if cooling is lost: time-to-boil, boiloff, makeup, and time to fuel uncovery.
Heat load — current decay-heat power from all fuel in the pool. Time-to-boil — how long until the pool reaches 100°C if cooling stops. Boiloff / makeup — how fast water turns to steam once boiling, and the flow needed to replace it. Uncovery — when falling water would expose the top of the fuel.
All results are educational estimates — see the disclaimer below.
A simplified lumped mass-energy balance built on ANSI/ANS-5.1 decay heat, with conservative assumptions: no evaporative or radiative loss credit, uniform bulk pool temperature, no rack-level effects. Intended for engineers, RO/SRO candidates, students and researchers. This is not a licensing or safety-basis calculation — those require plant-specific ORIGEN/SCALE fuel inventories and qualified thermal-hydraulic codes — and it is not for operational decisions. Detailed rack-level thermal-hydraulics (CFD), zirconium-steam oxidation/hydrogen generation, and radiological dose are out of scope; those require RELAP5/MELCOR/MAAP-class codes.
Sets the default mode for new batches. Each batch can be switched individually using its Mode A/B button on the batch card.
Every batch's decay-heat curve plotted against calendar time, from now to the selected horizon. Stacked areas show each batch's contribution; the bold line is the total pool load. A scheduled future offload appears as a spike that decays.
The scrubber, the date field, and every result below (batch table, hero total, TTB, boiloff, makeup, margin) all read from the same reference timestamp — move any one and the rest follow.
Adds a new batch card above, dated N months from today, using whichever input mode (A or B) is currently selected — edit it there for exact power/burnup. It will appear on the chart as a future spike until its discharge date arrives.
Mode B batches derive their own mix from burnup instead of this default (higher burnup shifts weight toward Pu-239/Pu-241).
| Batch | Discharge | τ (cooling time) | T_irr | P_op | ANS-5.1 | % of total | Wigner-Way | Δ% |
|---|---|---|---|---|---|---|---|---|
Conservative lumped mass-energy balance on total loss of active cooling: uniform bulk pool temperature, no evaporative or radiative loss credit before saturation. Uses the ANS-5.1 total heat load above.
| Heat-up rate | – |
| Time-to-boil (TTB) | – |
| Boiloff rate | – |
| Time to uncover TAF (from onset of boiling) | – |
| Total time — now to TAF uncovery | – |
| Makeup flow to hold level | – |
Pool temperature from the moment cooling is lost, through saturation, to TAF uncovery. Hover for the phase, its operational meaning, and any safety flag.
Methodology. Primary engine: ANSI/ANS-5.1-2005, four fissioning nuclides (U-235, Pu-239, U-238, Pu-241) with optional neutron-capture correction G(t) and ²³⁹U/²³⁹Np actinide term — the same engine as the Decay Heat Calculator. Cross-check: Wigner-Way, Q/P_op = 0.0622·[τ-0.2 − (τ+T_irr)-0.2]. Total pool load is the batch sum Q_total(t) = Σ Q_i(τ_i(t)), τ_i(t) = t − t_discharge,i. Mode B bridges to the native engine via T_irr = 1000·B/q (days, B in GWd/MTU, q in MW/MTU) and P_op = q·MTU; burnup sets the isotopic mix by linear interpolation between reference fuel-mix points.
Pool thermal response. Lumped mass-energy balance on total loss of active cooling, uniform bulk temperature, no evaporative or radiative loss credit before saturation: heat-up rate dT/dt = Q_total/(m·c_p) with m = ρ·V_water; time-to-boil TTB = m·c_p·(T_sat − T_0)/Q_total, T_sat = 100°C; boiloff mass rate ṁ = Q_total/h_fg (h_fg ≈ 2.257 MJ/kg); time to uncover the top of active fuel t_uncover = V_above-TAF/(ṁ/ρ); makeup flow to hold level = ṁ/ρ. Cooling margin (optional) = Q_cool − Q_total, flagged if negative.
Out of scope in v1: rack-level thermal-hydraulics (CFD), zirconium-steam oxidation/hydrogen generation, and radiological dose — these require RELAP5/MELCOR/MAAP-class codes.
By Elliot Marsh — NeutronRise.