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By
Dr. Nick Touran, Ph.D., P.E.,
2021-12-21
, Reading time: 1 minute
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In 2017, there were 3482 PWR assemblies discharged in the USA, initially containing 1526.5 tonnes of uranium, and that on average the assemblies were burned to 46.2 MWd/kgHM [EIA]. HM means heavy metal, and refers to the mass of initial uranium of the fresh assembly. This means that a single average 2017 PWR assembly gave out 21.5 GW-days of (thermal) energy.

```
units -1 "1526.5 tonnes * 46.2 MW*day/kg/3282" "GW*day"
21.488208
```

PWRs are about 32% thermally efficient, so those thermal GW-days are roughly equivalent to 6.9 GW-days of electricity, or 1.7e8 kWh.

```
units -1 "1526.5 tonnes * 46.2 MW*day/kg/3282 * 0.32" "kW*hour"
1.6502944e+08
```

A typical dry cask (e.g. HI-STORM 100) holds 24 discharged PWR fuel assemblies [HOLTEC]. Thus, an average dry cask full of PWR spent fuel represents about 4e9 kWh of electricity.

```
units -1 "1526.5 tonnes * 46.2 MW*day/kg/3282 * 0.32 * 24" "kW*hour"
3.9607066e+09
```

Each kWh of nuclear electricity saves (490-12) = 478 grams of CO₂ (equivalent) over gas, full lifecycle [Schlomer 2014]. Thus, a single dry cask represents a savings of 1.9 million tonnes of CO₂-eq!!

```
units -1 "1526.5 tonnes * 46.2 MW*day/kg/3282 * 0.32 * 24 * ((490-12) grams/(kW*hour))" "million tonnes"
1.8932177
```

(Older spent fuel had lower average burnup but displaced coal instead of gas, so that’s a similar result)

*This page is a part of our Factlet collection.*