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It's 2:13 in the morning in 
Waynesboro, GA. 

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The lights are still on. 
The trucks are still coming. 

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For 17 hours straight, no one 
has stopped pouring concrete 

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because the camp. 
This is the base map pour for 

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Vogel Unit 4 and it will last 41
continuous hours. 

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No breaks, resets or mistakes. 
This is the moment a nuclear 

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plant begins to exist. 
Welcome back to NAKED Nuclear. 

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I'm Danielle Allen. 
And on Season 3, we are talking 

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about how to build a nuclear 
power plant. 

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And today we're talking about 
one of the least glamorous, most

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unforgiving and most important 
moment in building a nuclear 

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power plant. 
Pouring the foundation. 

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But this is not just about 
construction. 

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It's about the physics, material
science, seismic, engineering 

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and logistical nightmare. 
I mean operation that cannot 

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fail once it starts. 
So let's walk through what's 

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actually happening inside that 
pore. 

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Well, it's happening first 
months before the trucks first 

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arrive. 
The site is already engineered, 

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the soil is tested, compacted, 
and even in some cases improved 

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or reinforce. 
The concrete doesn't just sit on

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the ground, it interacts with 
it. 

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Then comes the rebar, thousands 
of tons of steel arranged in the

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dense grid. 
That gives concrete tensile 

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strength. 
Concrete is great in 

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compression, terrible in 
tension, so steel carries the 

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forces that would otherwise 
crack it apart. 

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And embedded inside the 
structure are anchor points and 

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interfaces that will connect to 
the reactor and containment 

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building later. 
And once the pour starts, all of

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that is locked in. 
At a basic level, the base mat 

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distributes weight, but in a 
nuclear power plant it also has 

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to one resist seismic forces, 2 
maintain structural integrity 

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under extreme loads, and three, 
act as a part of the containment

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system. 
And that last part is where 

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things get tricky, because the 
concrete is both structural and 

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a part of the radiation 
shielding. 

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So let's talk about radiation 
shielding. 

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Radiation doesn't just stop, it 
interacts with materials, and 

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concrete is surprisingly good at
slowing it down. 

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There are two main types of 
radiation we care about here. 

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Gamma radiation, which is very 
energetic and best reduced by 

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dense materials. 
So concrete works because it's 

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thick and heavy. 
The thicker the barrier, the 

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more energy gets absorbed or 
scattered before it can pass 

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through. 
Then there are neutrons and 

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neutron radiation. 
Neutrons don't respond the same 

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way. 
They're slowed down by 

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collisions with light atoms, 
especially hydrogen. 

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That's why a pool of spent fuel 
is filled with water. 

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The water is doing the 
shielding, and concrete actually

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contains water. 
That hydrogen content helps 

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reduce neutron energy, making 
them easier to absorb. 

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So when you hear a few feet of 
concrete, the thickness is 

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calculated to reduce radiation 
to safe levels outside the 

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structure. 
Now back to the pour. 

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Concrete starts as a fluid, and 
the moment it pours, a chemical 

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reaction begins. 
Cement reacts with water. 

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This is called hydration, and it
releases heat. 

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In a small slab, that heat 
escapes easily. 

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In a nuclear base mat, which can
be several feet, the heat gets 

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trapped inside, so you end up 
with a hot interior and a cool 

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exterior. 
That temperature difference 

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creates stress. 
If the outside cools too 

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quickly, it contracts. 
If the inside stays hot, it 

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expands and that mismatch can 
cause cracking. 

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So engineers actively manage 
this. 

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They design, mix, control, 
placement rates. 

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Sometimes they even use cooling 
strategies or stage poor to 

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limit temperature differences, 
because if a giant crack forms, 

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you can't just fix it. 
You've compromised something 

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that's supposed to last for 
decades, which is kind of a 

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problem. 
Now let's talk about seismic 

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design, AKA earthquakes. 
Because a nuclear base mat has 

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to survive an earthquake, 
Nuclear plants are designed 

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under what's called Seismic 
Category 1 standards, which 

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means they must remain 
functional during and after a 

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design basis earthquake. 
That includes the base map. 

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But what does that actually 
mean? 

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It means engineers analyze 
ground motion at the site, soil 

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behaviour, and how the structure
and ground interact together. 

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This is called soil structure 
interaction. 

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I know it's kind of on the nose.
That base mat isn't just sitting

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on the earth, it's actually 
coupled to it. 

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So during an earthquake, forces 
move through the ground, into 

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the foundation, and then into 
the structure above. 

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But the concrete, the rebarb, 
and the geometry of the base mat

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are all aligned to distribute 
those forces, prevent 

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catastrophic failure, and 
maintain alignment of critical 

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systems. 
We can't have our pipes getting 

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all cattywompus after an 
earthquake. 

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In some designs, this can 
actually include base isolation 

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or dampening strategies, but at 
its core, it comes down to this.

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The foundation has to move 
without failing. 

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Next, the logistics. 
Let's zoom out again because 

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while all of this science is 
happening, the poor is still 

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taking place and it's a 
continuous operation. 

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No stopping. 
Concrete is produced, delivered,

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place, and tested in a constant 
flow. 

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If that flow is interrupted, you
risk creating weak joints. 

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So everything is redundant. 
Multiple supply paths, 

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continuous monitoring, strict 
quality assurance. 

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So everything is tracked, 
verified and done the right way.

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Now come back to that night hour
one. 

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Everything is controlled. 
Hour 12, maybe the fatigue 

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starts creeping. 
Hour 24, floodlights rotating 

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crews, same pace. 
Hour 36 focus tightens because 

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the end is close but the risk is
still there. 

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And then hour 41, the final 
placement. 

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And just like that the pour is 
complete. 

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If you would like to see the 
full 41 hours, Southern Nuclear 

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has a time lapse of this exact 
pour. 

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We'll link it in the show notes.
And once the pour is complete, 

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that concrete will never be seen
again. 

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Well, maybe until 
decommissioning, but it will 

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have to carry everything, the 
reactors, the systems, the 

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future of that plant. 
And that's just part of the 

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science that touches on why 
concrete is one of the most 

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valuable materials in a nuclear 
power plant. 

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All of the quality assurance, 
all of the testing, all of the 

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logistics that have to be just 
near perfect. 

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Thank you so much for listening 
to this episode of Naked 

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Nuclear. 
I hope you learned a little bit 

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something about concrete nuclear
base mats and how long it 

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actually takes to pour one. 
If you thought this episode was 

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interesting or learn something 
new, please subscribe to our 

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show, share it with a friend and
let us know what you think. 

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You can follow us on LinkedIn at
Naked Nuclear, Spotify, Apple or

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wherever you get your podcast. 
I'm Danielle Allen. 

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This is naked nuclear. 
Until next time, stay curious.