Fortran 90 utilities developed for my specialization thesis in Nuclear Reactors and Fuel Cycle (Instituto Dan Beninson / UNSAM, Argentina, 2010).
The work computes decay heat in the core of the Embalse CANDU reactor (648 MWe, Córdoba, Argentina) after shutdown, accounting for the full spatial distribution of power and burnup across all 4,560 fuel bundles — rather than using a single core-averaged value as previous analyses had done.
📄 Read the full thesis (PDF, Spanish)
When a nuclear reactor shuts down, fission products and actinides continue releasing heat for days to years. Knowing how much — and how fast it decays — is critical for safe cooling system design.
Previous calculations for Embalse used a single average power and burnup value. This work builds a pipeline to do it properly: each of the 4,560 fuel bundles gets its own decay heat contribution, interpolated from a pre-computed database, then summed.
Using the spatial distribution vs. core-averaged values:
- At t = 0: spatial method gives ~0.5% higher decay heat (6.23% of rated power)
- After ~20 seconds: the mean-value method becomes the larger estimate
- Peak difference: ~18% at ~90 days, settling to ~12% at 380 days
The mean-value approach is therefore conservative for long-term cooling analysis, but the spatial method is more accurate and remains useful for analyzing subsets of fuel bundles.
Three Fortran 90 programs form a sequential pipeline:
armar_entradas_O_S.f90 → CdD_OS.f90 → suma_calores.f90
(generate (extract (interpolate &
ORIGEN-S inputs) decay heat DB) sum for core)
Generates and runs ORIGEN-S input files for all combinations of irradiation power and burnup. For this work: 12 power levels × 17 burnup levels = 204 ORIGEN-S cases.
Inputs: armar_entradas_O_S.inp (power/burnup grid), a base ORIGEN-S input file
Outputs: 204 ORIGEN-S input/output file pairs
Parses ORIGEN-S output files and extracts total decay heat (fission products + actinides) for each power/burnup/time combination into a compact database.
Inputs: ORIGEN-S output files from previous step
Outputs: calor_decaimiento_O_S.dat — the decay heat database
Given a real core configuration (power + burnup for each of the 4,560 bundles from the PUMA fuel management code), interpolates the database for each bundle and sums contributions to get total core decay heat vs. time.
Interpolation: cubic splines (Akima method) in burnup (non-linear behavior at low burnup), linear in power.
Inputs: decay heat database, PUMA core configuration file (.prp)
Outputs: suma_calores.dat — total core decay heat vs. time
| File | Description |
|---|---|
armar_entradas_O_S.inp |
Power (kW) and burnup (MWd/tU) grid for database generation |
calor_decaimiento_O_S.inp |
Same grid, used by CdD_OS |
suma_calores.inp |
Configuration for the summation step |
suma_calores.dat |
Sample output: total core decay heat for a typical shutdown |
Power range: 30–950 kW/bundle | Burnup range: 10–10,500 MWd/tU
These programs wrap ORIGEN-S (Oak Ridge Isotope GENeration), part of the SCALE code system by Oak Ridge National Laboratory. ORIGEN-S is not included and requires a separate license.
Cross-section library used: CANDULIB-AECL — burnup-dependent ORIGEN-S libraries for CANDU reactor fuel characterization.
Compiled with Compaq Visual Fortran 90 v6.6c. Should compile with any standard Fortran 90 compiler.
The Embalse Nuclear Power Plant is a CANDU-type PHWR (Pressurized Heavy Water Reactor) in Córdoba, Argentina, in commercial operation since 1984.
- 380 horizontal fuel channels × 12 bundles/channel = 4,560 fuel bundles
- Natural uranium fuel (UO₂), heavy water moderator and coolant
- Thermal power: 2,115.9 MW → 648 MWe gross
- On-power refueling: ~2 channels replaced per day
Arizmendi, F. (2010). Cálculo del Calor de Decaimiento de la Central Nuclear Embalse Considerando una Distribución Espacial de Potencia y Quemado. Tesina de Especialización en Reactores Nucleares y su Ciclo de Combustible. Instituto Dan Beninson / UNSAM, Argentina.
Códigos Fortran 90 desarrollados para la tesina de la Especialización en Reactores Nucleares y su Ciclo de Combustible (Instituto Dan Beninson / UNSAM, 2010).
El trabajo calcula el calor de decaimiento del núcleo de la Central Nuclear Embalse luego de una parada, considerando la distribución espacial real de potencia y quemado de los 4.560 elementos combustibles. Se comparan los resultados con valores medios y con el informe de diseño de AECL (informe 5704, 1977).
La tesina completa está disponible en este repositorio: tesis_IDB.pdf