OOPS

tlb wrote:

Loren Pechtel wrote:Look at Chernobyl. While I have seen some debate as to whether the power excursion actually went prompt critical or merely came very close to it the result was an energy release far beyond what could be contained. (And note that stronger containment wouldn't have helped--if you somehow kept it from going boom it would have kept on generating ever more power until the reaction poisoned itself. The power excursion would have gone into large h-bomb levels.)

Likewise, if you're containing a lot of very hot plasma you simply can't build a reactor that can guarantee to contain it against all forms of battle damage.

cthia wrote:A hydrogen bomb type explosion never could have occurred. The structure would have destroyed itself.

Should that be atomic bomb, rather than hydrogen bomb; since we are talking about a fission reaction and not a fusion one?

Power of a h-bomb, even though the reaction is fission. Chernobyl contained far more fuel than the largest of atomic bombs. The essence of an atomic bomb is to make a supercritical mass and extract as much power as you can before the energy involved blows it apart. Since you have no way to contain the energy this means the reaction must go very, very fast--all the fancy engineering is to convert a subcritical mass into a mass with as high a multiplication factor as possible and to do it very, very quickly.

However, if you can put your fission reaction in an unobtaininum box that can hold it the supercritical mass won't disassemble itself in microseconds, the reaction continues until either the box breaks or the reaction is poisoned enough to stop.

(Note that you can also see very large fission blasts when you don't have to worry about assembly--note the fission-fusion-fission bomb design. Jacket an h-bomb in uranium (it need not be enriched, even depleted works fine), while the uranium can't sustain a reaction it's quite capable of fissioning from the neutrons thrown off by the fusion stage. It's a cheap way to boost an h-bomb or even make a dial-a-yield device. (Put the U-238 plates on if you want the bigger boom, or make the bomb jettison them before detonation if the smaller yield is desired.) For the ultimate example, consider Tsar Bomba. As dropped it was 53 megatons, but the U-238 was replaced with something inert. Put the U-238 on and it would be about 100 megatons--thus a 50 megaton fission yield.)

Loren Pechtel wrote:
Inverse square law. What can boil the hull at 1000km is barely a flash at 1,000,000km and the battles were probably much farther away than that.

The platforms around Manticore, Sphinx etc were a bit closer than a million KM to the atmosphere when all the ships blew up.

cthia wrote:

Loren Pechtel wrote:Look at Chernobyl. While I have seen some debate as to whether the power excursion actually went prompt critical or merely came very close to it the result was an energy release far beyond what could be contained. (And note that stronger containment wouldn't have helped--if you somehow kept it from going boom it would have kept on generating ever more power until the reaction poisoned itself. The power excursion would have gone into large h-bomb levels.)

Likewise, if you're containing a lot of very hot plasma you simply can't build a reactor that can guarantee to contain it against all forms of battle damage.

A hydrogen bomb type explosion never could have occurred. The structure would have destroyed itself.

Loren Pechtel wrote:Read my post again. Of course it couldn't contain it--what I'm saying is that if you beefed up the containment with unobtainium to withstand the Chernobyl blast you would simply have held the reactor together during it's power excursion, the power would have gone ever higher until something gave or it's fuel was too poisoned to sustain the reaction.

The point is you build fail-safes to avoid a prompt critical, there's nothing you can do to make it safe if it does happen.

I understood you. And I agree.

Effectively, managing to hold it all together would have had to overcome the design problems inherent in trying to develop a much more powerful bomb. Containment is one of the engineering problems of designing bombs with that sort of power. I was simply pointing out for prosperity that it never would have happened, for those who are worried. I should have led with "But of course," it never would have happened. The entire discussion reminds me of how the Russians solved the problem of increasing yield with it's three stage Tsar Bomba.

In fact, I caution this post upstream for the same reason you touch upon ...

ThinksMarkedly wrote:That's what I was thinking. Under normal circumstances, using gravity to create fusion is going to require vast amount more energy than you get out of the fusion ...

Not necessarily. The current yield of our present nuclear bombs is limited only by our inability to solve the problems that have been solved in the Honorverse. I would imagine there are insane yields of nuclear devices in the Honorverse. After all, nuclear energy is nothing if not efficient.

Loren Pechtel wrote:Inverse square law. What can boil the hull at 1000km is barely a flash at 1,000,000km and the battles were probably much farther away than that.

But the space stations were likely much closer than a million km away. We haven't been told where they actually are, but based on size I doubt they're in low orbit. That leaves either high orbit, geosynchronous orbit or in one of the Lagrangian points with Thorson (for Manticore). Even if Hephaestus was in the L4 or L5 in the Manticore-Thorson system, neither Gryphon nor Sphinx have nearby Lagrangian points (Gryphon has no satellites and Sphinx has more than one of comparable masses), so Vulcan and Weyland must have been at most 50,000 km from the surface.

ThinksMarkedly wrote:

Loren Pechtel wrote:Inverse square law. What can boil the hull at 1000km is barely a flash at 1,000,000km and the battles were probably much farther away than that.

But the space stations were likely much closer than a million km away. We haven't been told where they actually are, but based on size I doubt they're in low orbit. That leaves either high orbit, geosynchronous orbit or in one of the Lagrangian points with Thorson (for Manticore). Even if Hephaestus was in the L4 or L5 in the Manticore-Thorson system, neither Gryphon nor Sphinx have nearby Lagrangian points (Gryphon has no satellites and Sphinx has more than one of comparable masses), so Vulcan and Weyland must have been at most 50,000 km from the surface.

And it takes a whole lot less energy to set fire to dry grass than vaporize iron.

Jonathan_S wrote:But back to reactors in general. The fuel assembly may, or may not, contain some fixed neutron absorbing cladding or wrapping - that's very reactor design specific. For example the first reactor was air cooled and it was the graphite blocks the fuel assembly was installed in, and that the control rods slid through, that provided the fixed 'baseline' neutron absorption - not the fuel rods themselves. But I've never heard of fuel rods called moderator rods.

I have. It isn't commonplace to do so, but it is technically accurate when applied to graphite moderated reactors because they are part of the fuel assembly. Graphite moderators are essentially composed of solid graphite. Their moderating factor lies between light water and heavy water.

They have a tendency to crack and often has to be replaced. They are the weakest element (npi) of graphite moderated reactors. As I understand it, because of this fact they are made part of the fuel assembly which also houses the fuel rods. The design makes it easier to pull both the "moderator rods" and fuel rods, as I understand it. See diagram in link.

This information is part of the exhaustive documentation included with many simulators.

cthia wrote:

Jonathan_S wrote:But back to reactors in general. The fuel assembly may, or may not, contain some fixed neutron absorbing cladding or wrapping - that's very reactor design specific. For example the first reactor was air cooled and it was the graphite blocks the fuel assembly was installed in, and that the control rods slid through, that provided the fixed 'baseline' neutron absorption - not the fuel rods themselves. But I've never heard of fuel rods called moderator rods.

I have. It isn't commonplace to do so, but it is technically accurate when applied to graphite moderated reactors because they are part of the fuel assembly. Graphite moderators are essentially composed of solid graphite. Their moderating factor lies between light water and heavy water.

They have a tendency to crack and often has to be replaced. They are the weakest element (npi) of graphite moderated reactors. As I understand it, because of this fact they are made part of the fuel assembly which also houses the fuel rods. The design makes it easier to pull both the "moderator rods" and fuel rods, as I understand it. See diagram in link.

This information is part of the exhaustive documentation included with many simulators.

Certainly RBMK reactors like Chernobyl, while graphite moderated, don't make their graphite part of the fuel assembly. And that diagram is basically a cutaway view of an RBMK style reactor.

The graphite is a huge, house sized, fixed block pierced with about 1660 holes. Into those holes pressure tubes for fuel or control rods are inserted. The fuel rods themselves are not graphite coated; they are uranium pellets packed into a zircaloy tube; then two of these fuel rod tubes are inserted into a pressure tube. Other pressure tubes contain no fuel, but instead the control rods run through then. Light water is fed into the bottom of the various pressure tubes, and is heated as it rises (then in the pictured steam separator the pressure drops to the point it can boil into steam). The huge block of graphite is not actively cooled, so it runs very hot. OTOH it is also not expose to the erosive effects of flowing coolant as that is restricted to the pressure tubes.

And RBMKs, and their derivatives, are the only water cooled commercial graphite moderated reactors I'm aware of; and were the most common commercial graphic moderated reactors. the UK and France had their gas cooled Magnox and UNGG reactors And then Wikipedia does list a number of additional experimental ones.

The old UK Windscale Magnox reactor also used graphite moderation, but again used a fixed block of moderating graphite into which fuel canisters were placed. (It differed from Chernobyl by being gas cooled, and having a horizontal fuel through design were new aluminum coated fuel canisters inserted at the front would push older fuel canisters out the back into a cooling pool (allowing them to be extracted for reproccessing and plutonium extraction without shutting down the reactor). The French UNGG appears similar.

It wouldn't make any sense to call fuel rods in any of those designs moderator rods because they contain no moderator. They're inserted into a fixed moderator matrix (the huge block or stacked bricks of graphite). Though certainly if you pulled a fuel rod out of that matrix it would cease its fission chain reaction because the loss of the surrounding moderator would render the emitted neutrons from the ongoing radioactive decay to high energy to continue splitting additional uranium atoms.

Now looking through Wikipedia it does seem the experimental Dragon reactor did press its ceramic coated fuel together with graphite into blocks that were assembled into the core. Those were combined fuel + moderator; OTOH they weren't rod shaped so again I doubt they'd be called moderator rods.
Similarly experimental pebble bed reactors use graphite as part of the make-up of each pellet to moderate the reaction - but these are rod shaped.

So I'd be quite interested to see a reference to a reactor design that used a fuel + graphite rod assembly and called that unified rod a moderator rod.

cthia wrote:

Jonathan_S wrote:But back to reactors in general. The fuel assembly may, or may not, contain some fixed neutron absorbing cladding or wrapping - that's very reactor design specific. For example the first reactor was air cooled and it was the graphite blocks the fuel assembly was installed in, and that the control rods slid through, that provided the fixed 'baseline' neutron absorption - not the fuel rods themselves. But I've never heard of fuel rods called moderator rods.

I have. It isn't commonplace to do so, but it is technically accurate when applied to graphite moderated reactors because they are part of the fuel assembly. Graphite moderators are essentially composed of solid graphite. Their moderating factor lies between light water and heavy water.

They have a tendency to crack and often has to be replaced. They are the weakest element (npi) of graphite moderated reactors. As I understand it, because of this fact they are made part of the fuel assembly which also houses the fuel rods. The design makes it easier to pull both the "moderator rods" and fuel rods, as I understand it. See diagram in link.

This information is part of the exhaustive documentation included with many simulators.

Jonathan_S wrote:Certainly RBMK reactors like Chernobyl, while graphite moderated, don't make their graphite part of the fuel assembly. And that diagram is basically a cutaway view of an RBMK style reactor.

The graphite is a huge, house sized, fixed block pierced with about 1660 holes. Into those holes pressure tubes for fuel or control rods are inserted. The fuel rods themselves are not graphite coated; they are uranium pellets packed into a zircaloy tube; then two of these fuel rod tubes are inserted into a pressure tube. Other pressure tubes contain no fuel, but instead the control rods run through then. Light water is fed into the bottom of the various pressure tubes, and is heated as it rises (then in the pictured steam separator the pressure drops to the point it can boil into steam). The huge block of graphite is not actively cooled, so it runs very hot. OTOH it is also not expose to the erosive effects of flowing coolant as that is restricted to the pressure tubes.

And RBMKs, and their derivatives, are the only water cooled commercial graphite moderated reactors I'm aware of; and were the most common commercial graphic moderated reactors. the UK and France had their gas cooled Magnox and UNGG reactors And then Wikipedia does list a number of additional experimental ones.

The old UK Windscale Magnox reactor also used graphite moderation, but again used a fixed block of moderating graphite into which fuel canisters were placed. (It differed from Chernobyl by being gas cooled, and having a horizontal fuel through design were new aluminum coated fuel canisters inserted at the front would push older fuel canisters out the back into a cooling pool (allowing them to be extracted for reproccessing and plutonium extraction without shutting down the reactor). The French UNGG appears similar.

It wouldn't make any sense to call fuel rods in any of those designs moderator rods because they contain no moderator. They're inserted into a fixed moderator matrix (the huge block or stacked bricks of graphite). Though certainly if you pulled a fuel rod out of that matrix it would cease its fission chain reaction because the loss of the surrounding moderator would render the emitted neutrons from the ongoing radioactive decay to high energy to continue splitting additional uranium atoms.

Now looking through Wikipedia it does seem the experimental Dragon reactor did press its ceramic coated fuel together with graphite into blocks that were assembled into the core. Those were combined fuel + moderator; OTOH they weren't rod shaped so again I doubt they'd be called moderator rods.
Similarly experimental pebble bed reactors use graphite as part of the make-up of each pellet to moderate the reaction - but these are rod shaped.

So I'd be quite interested to see a reference to a reactor design that used a fuel + graphite rod assembly and called that unified rod a moderator rod.

If you are correct, and you certainly could be, then I completely misunderstood the setup, and the docs. It's entirely possible because I'm definitely not a nuclear engineer. I'm simply a hobbyist playing with simulators.

You misunderstood me. Moderator rods are NOT "formally" referred to as fuel rods. Or vice versa. How can they be? They are two different things. I simply accepted what another poster wrote because I have seen the term used interchangeably in graphite moderated reactors. But again, I could have been wrong.

The terms were sometimes used interchangeably because of the design. AS I UNDERSTOOD. And yes, the graphite assemblies are huge. The rods sometimes numbered in the several thousand.

When I get a chance, I'll fire up the simulator and do a bit more research. But, that's how I understood it.

I know that is a cutout.

P.S. I'll post that I'm wrong if I am. Likewise, I'll post any supporting docs.

ThinksMarkedly wrote:

Loren Pechtel wrote:Inverse square law. What can boil the hull at 1000km is barely a flash at 1,000,000km and the battles were probably much farther away than that.

But the space stations were likely much closer than a million km away. We haven't been told where they actually are, but based on size I doubt they're in low orbit. That leaves either high orbit, geosynchronous orbit or in one of the Lagrangian points with Thorson (for Manticore). Even if Hephaestus was in the L4 or L5 in the Manticore-Thorson system, neither Gryphon nor Sphinx have nearby Lagrangian points (Gryphon has no satellites and Sphinx has more than one of comparable masses), so Vulcan and Weyland must have been at most 50,000 km from the surface.

There's actually a decent argument for low orbit: the transit time of the debris entering the atmosphere. If they'd been in lagrange orbits the debris would have taken hours to hit the planet, or more likely would have simply fell into a much closer eccentric orbit. Even a 25000-ish km synchonous orbit would have allowed for reaction and mitigation time.

cthia wrote:You misunderstood me. Moderator rods are NOT "formally" referred to as fuel rods. Or vice versa. How can they be? They are two different things. I simply accepted what another poster wrote because I have seen the term used interchangeably in graphite moderated reactors. But again, I could have been wrong.

The terms were sometimes used interchangeably because of the design. AS I UNDERSTOOD. And yes, the graphite assemblies are huge. The rods sometimes numbered in the several thousand.

I looked back and it appears you were the first to say fuel reds were moderator rods here:

cthia wrote:The control rods are NOT the moderator rods. The fuel rods are both the coolant and moderator rods.

Control rods reduce the reaction rate. Reactors are sometimes shut down to replace spent or depleted fuel rods, but other reactors remain running to supply the necessary power to support the fail-safe systems.

The only earlier mention wrote the control rods were "moderator rods" and this was your response.