OT: Green Power

CTMike · April 2023

In the middle of another refueling outage. This photo shows fuel assembly number 216 out of 217 being reloaded in to the core (the vertical mast coming down from the top is part of the refueling machine - it is used to pick up and lower the fuel assemblies - always under water to provide shielding).

The bright shiny assemblies are new, the others are reused. Each fuel assembly is used for 3 cycles and one third are changed out each outage. Each fuel assembly is 14’ tall, and about 12” square.

lousubcap · April 2023

Nice pic. How frequently are you in a refueling outage and about how long is the plant off-line for one?

kl8ton · April 2023

So this picture is taken inside a core? Core is about 16 feet in diameter? Thanks for the pic.

CTMike · April 2023

lousubcap said:

Nice pic. How frequently are you in a refueling outage and about how long is the plant off-line for one?

Refueling outages happen every 18 months. We are a two unit site so the second unit has an outage this fall. Outages typically last 28 - 35 days or so depending on the scheduled work.

CTMike · April 2023

kl8ton said:

So this picture is taken inside a core? Core is about 16 feet in diameter? Thanks for the pic.

The ID of the vessel is a little over 14’, but then the core basket (that forging inside the vessel that makes a round shape accept square assemblies) takes up a little more room.

The photo was actually taken from a video camera looking down in to the vessel through a required
minimum of at least 23’ of water above the fuel.

The large round opening on the right above the fuel is one of two hot legs (the other is 180 degrees out) where the heated coolant ( ~ 617 F) exits towards the steam generators.

This particular design has 4 cold legs where the cold water ( ~ 557 F) comes back in to the vessel from the steam generators and the pumps. It then flows down between the vessel wall and core basket, under the fuel, up through the coolant channels (removing the heat) and back out the hot legs.

CTMike · April 2023

Here is an older photo that I’ve posted before showing the characteristic blue glow of Cherenkov radiation. Cherenkov radiation occurs when a charged particle (such an electron emitted by a radioactive isotope undergoing Beta minus decay) passing through a medium (water in this case) exceeds the speed of light for that medium.

While it is currently known that nothing can exceed the speed of light in space (vacuum), the speed of light is significantly slower.

Gulfcoastguy · April 2023

Have you looked at Canadian CANDU reactors? Their rods are horizontal and they can be replaced one at a time without shutting down.

Langner91 · April 2023

Gulfcoastguy said:

Have you looked at Canadian CANDU reactors? Their rods are horizontal and they can be replaced one at a time without shutting down.

With really long tongs!

Image: https://us.v-cdn.net/5017260/uploads/editor/3t/nw6s06fe3h8a.gif

Ozzie_Isaac · April 2023

As amazing as nuclear power is, I am astonished we have cameras that work in such a hostile environment for an extended period of time.

CTMike · April 2023

Gulfcoastguy said:

Have you looked at Canadian CANDU reactors? Their rods are horizontal and they can be replaced one at a time without shutting down.

I actually went to a class with a Scottish dude who works at Bruce, and he showed us a video of the CANDU refueling process - pretty cool idea.

CTMike · April 2023

Ozzie_Isaac said:

As amazing as nuclear power is, I am astonished we have cameras that work in such a hostile environment for an extended period of time.

So this camera is sitting above 12’ above the surface of the water, which is at least 23’ over the top of the fuel. Water is a great shielding medium:
- Tenth Thickness (amount of shielding required to reduce a radiation field to 1/10th original value) for neutrons in water is about 10”, and for gammas is about 24”.

All this to say that the environment this camera is in isn’t very harsh at all.

There are other cameras we put down in the water to inspect the fuel during the core offload and they are much closer to the fuel. Needless to say they have a pretty short life span.

To put the radiation field in perspective, if you were to hug a fuel assembly that has spent a cycle in operation, you would receive a lethal dose within seconds. Whereas a new fuel assembly puts off next to nothing.

Ozzie_Isaac · April 2023

CTMike said:

Ozzie_Isaac said:

As amazing as nuclear power is, I am astonished we have cameras that work in such a hostile environment for an extended period of time.

So this camera is sitting above 12’ above the surface of the water, which is at least 23’ over the top of the fuel. Water is a great shielding medium:
- Tenth Thickness (amount of shielding required to reduce a radiation field to 1/10th original value) for neutrons in water is about 10”, and for gammas is about 24”.
All this to say that the environment this camera is in isn’t very harsh at all.
There are other cameras we put down in the water to inspect the fuel during the core offload and they are much closer to the fuel. Needless to say they have a pretty short life span.
To put the radiation field in perspective, if you were to hug a fuel assembly that has spent a cycle in operation, you would receive a lethal dose within seconds. Whereas a new fuel assembly puts off next to nothing.

Thank you for the explanation, I did not realize water was so effective. I think of radiation in terms of the visible spectrum and if I can see through it, it must not be safe. Academically, I know that is wrong. Simply put plexiglass between an IR detector and the heat source and you will see that, but still seeing something so vilified is awe inducing.

Funny about new vs. spent fuel rods. I would have bet $1M new was more dangerous.

fishlessman · April 2023

the reactor we had on campus at u lowell had horizontal rods, and really long tongs. maybe not so safe, they had a wooden plank on top of the swimming pool for access with the tongs. i still cant believe they let students out on that thing

Botch · April 2023

Langner91 said:

All these years, and this is the first I've noticed the guy in the background falling off the ladder, while changing the accident sign. That's hilarious!

CTMike · April 2023

Couple more photos:

Image: https://us.v-cdn.net/5017260/uploads/editor/vw/jtjjfnodfg7a.jpeg

This photo shows the vessel after the upper internals were installed. The vertical shafts are attached to the control rods. The rods are made of a material that has a high cross section for absorbing neutrons, thus allowing control of the fission chain reaction.

This 140 ton behemoth is the reactor vessel head, it forms the upper portion of the reactor vessel pressure boundary as the system operates at 2,250 psia. The flange is about 3’ thick and has 54 studs ( shown in those racks in the foreground. Each stud is about 4’ tall and weighs 750 lbs (including the nut and washer).

The studs thread in to the flange in the vessel and protrude through the head flange shown above. A washer and nut are installed and the stud is hydraulically stretched about 50- thousandths of an inch with an tensioner and the nut is torqued to 100 ft-lbs. The resulting torque is over 1M ft-lbs when the tensioner is released.

nolaegghead · April 2023

fishlessman said:

the reactor we had on campus at u lowell had horizontal rods, and really long tongs. maybe not so safe, they had a wooden plank on top of the swimming pool for access with the tongs. i still cant believe they let students out on that thing

They probably couldn’t afford a Geiger counter….🤪

nolaegghead · April 2023

That’s cool Mike. I’m a proponent of nuclear power, it’s another of those technologies that have been held back by populism.

JohnInCarolina · April 2023

I love this kind of stuff, @CTMike

kl8ton · April 2023

Agree with above sentiments. Love seeing the insider pics.

Botch · April 2023

CTMike said:
The studs thread in to the flange in the vessel and protrude through the head flange shown above. A washer and nut are installed and the stud is hydraulically stretched about 50- thousandths of an inch with an tensioner and the nut is torqued to 100 ft-lbs. The resulting torque is over 1M ft-lbs when the tensioner is released.

I had to read that a couple times before I got it. I'm assuming doing it this way cuts down on friction/wear between the threads, by not torquing the nuts down directly?

alaskanassasin · April 2023

Botch said:

CTMike said:
The studs thread in to the flange in the vessel and protrude through the head flange shown above. A washer and nut are installed and the stud is hydraulically stretched about 50- thousandths of an inch with an tensioner and the nut is torqued to 100 ft-lbs. The resulting torque is over 1M ft-lbs when the tensioner is released.

I had to read that a couple times before I got it. I'm assuming doing it this way cuts down on friction/wear between the threads, by not torquing the nuts down directly?

Or you would need a cheater pipe a mile long to hit a million foot pounds?

lousubcap · April 2023

The shielding effect of water has been addressed by @CTMike above and it is a great moderator. From my limited perspective, at a macro level the basic refueling process has been used and refined independent of the size of the project for several decades.

Now do downsize and put in a car...

But...we do that sort of power supply for things in space today.

Legume · April 2023

Stupid question here - is a steam circuit the only way to harness the energy?

nolaegghead · April 2023

Legume said:

Stupid question here - is a steam circuit the only way to harness the energy?

I have heard of designs that use sodium as a primary loop coolant.

lousubcap · April 2023

@nolaegghead - Yep, Rickover and his team were test running a sodium cooled submarine reactor power plant in the 1950's. Too many challenges back then although the Soviets also went down that road.

The reactor coolant medium is under high pressure so it is always in a liquid form. The exchange of the hot pressurized coolant energy to a power generating system is thru a steam generator, scaled by the power of the reactor. FWIW-

Legume · April 2023

Thanks - that's essentially what I was asking - it's alway going to be heat that you start with and have to convert.

CTMike · April 2023

lousubcap said:

The shielding effect of water has been addressed by @CTMike above and it is a great moderator. From my limited perspective, at a macro level the basic refueling process has been used and refined independent of the size of the project for several decades.
Now do downsize and put in a car...
But...we do that sort of power supply for things in space today.

For those wondering what Cap meant by moderator, neutrons born from fission are called “fast neutrons” as they have a high kinetic energy, but U-235 is a thermal fuel - meaning it has a high microscopic cross section for absorption for thermal neutrons (kinetic energy of less than 1 electron-volt), but a low cross section for absorbing fast neutrons. The purpose of the moderator is too slow down, or thermalize those fast neutrons so they become thermal. This happens via a process of collisions where a fast neutron will hit another atom in the water (moderator) - either the hydrogen or an oxygen atom, thus imparting some of its energy to said atom. Think one billiard ball striking another on a pool table. Eventually after enough collisions the neutron is thermalized and is able to go on and cause another fission - if it doesn’t leak out of the core, get absorbed by the control rods, or get absorbed by a poison (poison is an isotope that has a large cross section for absorbing a neutron but doesn’t fission) such as Xe-135, Sm-149, B-10, etc.

CTMike · April 2023

nolaegghead said:

Legume said:

Stupid question here - is a steam circuit the only way to harness the energy?

I have heard of designs that use sodium as a primary loop coolant.

There is currently a lot of interest and design work going in to Thorium salt reactors. Thorium is much more plentiful than Uranium, decay products have a much shorter half-life, and the entire cycle is much more efficient as it operates at a much higher temperature than light water reactors. A molten salt is used as the coolant, and one of the issues to overcome is the corrosion that comes along with using a salt.

Bill Gates is backing one of the projects via a company called TerraPower. There is also a number of small modular reactors (SMR) in the design process and li ending process. One use for SMRs is to power remote towns in Alaska and the like.

alaskanassasin · April 2023

https://world-nuclear-news.org/Articles/US-Air-Force-confirms-site-for-first-microreactor

I heard about this one but I wasn’t aware they were planning to use them in the sticks. The government builds power stations in rural Alaska and unfortunately they slowly go offline because the locals have no idea how to maintain them.

CTMike · April 2023

alaskanassasin said:

https://world-nuclear-news.org/Articles/US-Air-Force-confirms-site-for-first-microreactor

I heard about this one but I wasn’t aware they were planning to use them in the sticks. The government builds power stations in rural Alaska and unfortunately they slowly go offline because the locals have no idea how to maintain them.

That wouldn’t happen with a nuclear reactor as there are strict NRC requirements for staff manning, training, etc.

caliking · April 2023

Whoever said/thought this is just a bbq forum?

OT: Green Power

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