Name: 24.瞬態、反饋和時間依賴性中子學。 (24. Transients, Feedback, and Time-Dependent Neutronics)
Uploaded: 2021-01-14T10:26:53.000Z
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MICHAEL SHORT: So today is going to be the last day of neutron

As promised, we're going to talk about what

happens as a function of time when you perturb the reactor,

Did any of you guys notice the old-fashioned analog panel

meter that said, reactor period, when you were doing your power

And you're going to explore that on the homework.

So I'm arranging for all of your actual power manipulation

So each one, you'll have your own reactor data.

You'll be able to describe the reactor period

and see how well it fits our infinite medium single group

equations, which it turns out is not very well.

But that's OK, because you'll get to explain the differences.

I wanted to talk a bit about criticality and perturbing it.

So let's say we had our old single group kit criticality

And I'd like to analyze, just intuitively or mentally

with you guys, a few different situations.

Let's say we're talking about a light water

reactor or a thermal reactor, like the MIT reactor, or pretty

much all the reactors we have in this country.

What sort of things could you do to perturb it?

For example, let's say you shoved in a control rod.

And then, what would happen to k effective?

a nu bar, number of neutrons produced per fission.

As you start to consume U238 add neutrons.

And as you guys saw through a complicated chain of events

on the exam, eventually make plutonium 239,

The nu for 238 is actually different than the nu for 239.

So I don't want to say that nu never changes.

It's just that shoving the control rods into the reactor

But it does change slowly over time as you build up plutonium.

If this were a blended homogeneous reactor

or a reactor in a blender, what would happen to sigma fission

as you then shove in an absorbing material?

So in this case, remember if we define the average sigma

of each material's volume fraction, or let's say

atomic fraction, times each material's sigma fission,

if we throw nu materials into the reactor,

If you put in a control rod where let's say the control

rod's sigma fission would be equal to zero,

So let's say a little down arrow like that.

The volume is still small, but a control rod by definition sigma

MICHAEL SHORT: It's going to increase a little or a lot?

Now let's look at the diffusion constant.

And remember that the diffusion constant is 1 over 3 sigma

total, minus the average cosine scattering angle

What do you think is going to happen to the neutron diffusion

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24.瞬態、反饋和時間依賴性中子學。 (24. Transients, Feedback, and Time-Dependent Neutronics)

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