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already be waiting. Hello everyone, and welcome to
the Afterpop, where we strip down nuclear ideas until they
are as clear as mud. Well, hopefully clearer than
that. Today we're tackling a big
question. What is reactor physics?
Now you might be thinking physics sounds hard.
Equations, symbols, maybe some late night math homework.
But reactor physics isn't just a stack of equations.
It's about understanding how tiny particles smaller than an
atom can create enough energy to light up entire cities.
And don't worry, I'm not about to hand out a test.
We're going to explain it like you're in science class, but
maybe a fun one. So first, reactor physics.
Our previous episode, we talked to Iquan Caleb about his journey
at University of Michigan studying reactor physics.
So we wanted to create this afterpop to dive in.
So what is reactor physics? Imagine you've got a giant pot
of popcorn kernels. Each kernel can pop, but it
needs a spark of heat to get things started.
Now picture one popcorn exploding and bumping into its
neighbors, making them pop too. That's kind of what's happening
in reactor physics. Reactor physics is the study of
how neutrons, tiny neutral particles inside the atom, move
around, hit other atoms, and sometimes even cause them to
split apart. That splitting apart is called
fission, and when fission happens, it releases more
neutrons, kind of like popcorn bumping into its neighbors
energy in the form of heat. The same way popcorn popping
releases steam and smaller atomic pieces called fission
fragments. I don't really have an analogy
for fission fragments. Maybe those are like the burnt
crispy pieces of the popcorn that you leave at the bottom of
the bag. Now, reactor physics is about
predicting and controlling all of that.
It's the math and the science that answers.
How many neutrons will be released?
Where will they go? Will they keep the chain
reaction going or will it fizzle out?
If chemistry is about mixing ingredients to bake cookies,
reactor physics is about making sure the oven doesn't burn them.
Let's start with the neutron life story.
We like to call this the neutron life cycle.
Let's walk through it step by step, like a storybook.
Step one birth. A neutron is born when uranium
or plutonium splits. Step 2.
Fast childhood. At first, this neutron zips
around at super high speeds, too fast to actually be useful.
Step 3. Slowing down.
In most reactors, we want neutrons to calm down so they're
easier to control. This happens in a moderator,
often made of water. Step 4.
Adulthood, AKA useful work. Once slowed down, the neutron
might hit another uranium atom and split it.
That's the chain reaction and Step 5, old age AKA absorption.
Eventually neutrons either escape, get absorbed by
materials that don't split, or are captured by control rods.
Understanding this life cycle is the heart of reactor physics.
If too many neutrons escape or die off, the chain reaction
stops. If too many are born and keep
multiplying, the chain reaction could speed up dangerously.
Reactor physics finds this balance.
So let's talk about the balance. The balancing act is also known
as criticality. Reactor physics uses the ideas
of criticalities. Sub critical, meaning not enough
neutrons. The reaction doesn't chain and
the fire quote UN quote fizzles out.
Critical, just the right number of neutrons, steady controlled
power. This is kind of like the
Goldilocks Zone. Then there's supercritical.
This is too many neutrons. This is where things can get out
of control. Overheated.
Here's an easy way to picture it.
Imagine a campfire. If you have just one spark, it
might not light. If you add a few sticks, it
grows. But dump a whole crispy
Christmas tree on it and you'll have chaos.
Reactor physicists designed the campfire of neutrons so it stays
in that Goldilocks zone. Not too small, not too wild, but
just right. So let's look at some of the
tools of the trade. What do reactor physicists
actually do? Reactor physics courses at
places like the University of Michigan, MIT, and NC State show
that students learn neutron transport equations.
Fancy math that predicts how neutrons move?
Think of it like weather forecasting but for particles.
Two diffusion models. A simpler version saying on
average neutron spread heat like from a campfire. 3.
Criticality calculations using computer codes to see if a
reactor design will sustain a chain reaction. 4 Reactor
kinetics. Studying what happens when power
changes quickly, like how fast you can press the gas pedal
without stalling the car. 5. Fuel behavior, How uranium
pellets inside rods can shape, heat or even crack over years. 6
control systems. How rods, coolants and geometry
keep everything balanced. It's a mix of math, computer
modeling, and hands on experiments from working with
reactor simulators to watching how neutrons behave in research
reactors. So why does it all matter?
Reactor physics makes sure that reactors run safely, never too
fast or unstable, helps design new types of reactors like small
modular reactors or fusion prototypes, predicts how much
fuel is needed and how long it will last, and guides how spent
fuel is handled safely. Basically, without reactor
physics, nuclear engineers would be guessing.
And when you're dealing with atoms that can release millions
of times more energy than a candle flame, guessing is not an
option. In our episode with Umich alum
Ikwan Kaleb, he used tea kettles and Jango blocks in his Tik Toks
to show analogies of what happens in reactor physics.
Reactors are just the fancy tea kettles making steam to spin
turbines. And Jenga blocks are like chain
reactions, carefully pulling and stacking blocks.
One action sets off many others. Reactor physics teaches you the
rules of the Jenga tower so it doesn't topple over.
So what is reactor physics? It's the science of keeping the
chain reaction balanced, safe, and useful.
It's popcorn that doesn't burn, a fire that doesn't fizzle, and
a tea kettle that powers entire cities.
And it's a career path, one that people like Iqwan Kaleb are
using not just to power homes, but to inspire the next
generation in classrooms and across the world.
Thanks again for listening to this episode of Naked Nuclear.
We hope you learned a little something about reactor physics.
Thanks again to our episode sponsor, Nuclear Talent Scout.
Until next time, stay curious.