Shipbucket

Bullfrog wrote:

heuhen wrote:you wouldn do that since you need the ability to take the rod out fast if the reactor is .... well pushing a bit hard.

And if it was possible to split an rod they would have don that ages ago... but they don't.

You don't take fuel rods out normally, certainly not when the reactor is "pushing a bit hard", it's not an everyday procedure, US carriers are only re-fueled once in their lifetime.
They do split fuel assemblies, there's nothing particularly novel about the idea, it's not common since in most reactors there is enough height above the reactor to remove a full size rod without difficulty, thus it's quicker and more convenient to use a single rod.

To scram ( shut don an out of controller reactor) you don't remove fuel rods you insert all control rods or inject neutron absorbers (reactor poisons ie Boron etc) and increase coolant volumes to quickly remove the decay heat, and cross your fingers......

I'm interested in bullfrogs idea but in the event of refuelling how is the first half of the fuel rod removed, it wouldn't be possible to grab the top of the fuel element as the fuel channels wouldn't be much bigger than the fuel rod. I would also be concerned about a Neutron imbalance if half a rod is still in the reactor......

Fuel elements in sections have been used in the past but mainly in early pile stile reactors, horizontally loaded and discharged through a rear charge face, these reactors were primarily designed for weapons grade material production and were not very fuel and energy inefficient and fuel was more cartridges than rods.... Examples are Windscale UK, Chicago Pile 1 and the Handford Early piles.

Ah, SCRAM (Safety Control Rod Axe Man),
They already have to grab a normal fuel rod when it is quite a way down the channel, the extra distance would pose a challenge but I doubt it'd be a deal breaker. Hypothetically some sort of clamp could slide down the channel and connect to the assembly when it reaches the correct depth.
As for a neutron imbalance, I know that rods have jammed in the past half inside reactors with no major problems, in one case the reactor was on full power at the time (AGRs have the capacity to refuel on full power) so I cannot foresee a significant issue as long as the half fuel rod is not left for extended periods of time. (There's something to do with time independent phenomena that would explain this I think but I'm too tired to find it.

Fuel rods jamming was a common thing on MAGNOX reactors and happened many times at Calder Hall and Chapel Cross some times resulting in fuel rods rupturing and uranium oxide fuel melting, I know of at least one instance when fuel in 2 or 3 channels melted at chapel cross resulting in long reactor down times whilst repairs were conducted, but the inherent safety of these reactors meant this was designed for, this was also true to AGR's too to an extent but I'm not sure how this would work on a PWR though..........
Many reactors were designed with so called Hot Refueling, mainly on designs steaming from the weapons program's, MAGNOX, AGR and Russian RBMK's.

I never heard of that, a Neutron Imbalance wouldn't of caused those leaks however. Hot refueling isn't done anymore on full power on AGRs after a few jams and it almost certainly wouldn't work on a PWR (it's pressurized)

Neutron balances frankly confuse me, I found this here which to me seems to indicate that there wouldn't be a problem with the overall balance but I've never given any of this more than a passing glance before.

Therefore, all phenomena which involve neutrons must result altogether in equality between neutron production and neutron loss (i.e., between neutron sources and sinks) at every position r in the reactor and for every neutron energy E.

I found it here, I'd be interested to see what you make of it,
https://www.google.co.uk/url?sa=t&rct=j ... 5853,d.ZWU

What I meant was there might be an imbalance in the reactor if there is still half a fuel rod present in the lower half of the active zone but not the upper half, it may cause an instability within the reactor. Reactors designed to Hot Refuel you are removing the whole rod so only for a brief period whilst the rod is being removed and a new rod inserted would there be a small instability.

But anyways like Ace said even if the Fuel rods for my chosen reactors are to long to use the CDG method as long as no immovable parts are in the structure above then a hole cut be cut in the deck every 10-15 years or so. But I think if I use sub reactors as in the CDG albeit more powerful I think the CDG Refueling method should be acceptable..

I've consulted an ex nuclear chemist and he doesn't think there would be any balance or stability issue with a half rod in the reactor, no problems with neutron balances, hot refueling PWRs is impossible but hot refuelling with a half rod has the potential to cause problems. In summary it'd work fine if the reactor had cooled before it was attempted.

It's been an interesting technical discussion, apologies if I went into too much detail but I don't exactly like being ridiculed without proof so I hope you understand why I did so.

did not mean to ridicule you, think there's been bit of a misunderstanding, I was merely interested in how your two part fuel element idea might work. I know it is impossible to refuel a PWR reactor whilst under power how we got onto Hot Refueling not sure......

shippy2013 wrote: did not mean to ridicule you, think there's been bit of a misunderstanding, I was merely interested in how your two part fuel element idea might work. I know it is impossible to refuel a PWR reactor whilst under power how we got onto Hot Refueling not sure......

I'm sorry, I didn't mean you,
I was more referring to ace and heuhen. Quite to the contrary I like the fact that my idea was discussed in an intelligent way, what I object to is being told it wouldn't work without even an attempt to explain why.

Bullfrog wrote:

shippy2013 wrote: did not mean to ridicule you, think there's been bit of a misunderstanding, I was merely interested in how your two part fuel element idea might work. I know it is impossible to refuel a PWR reactor whilst under power how we got onto Hot Refueling not sure......

I'm sorry, I didn't mean you, I was more referring to ace and heuhen.

That's due to Lost in translation, you see I am from Norway, and when we try to write English...

and ace is from Netherlands.

There will be some lost in translation on this forum since we have people from Japan to ... around the world... and not everybody are good in English.


But the difference between me just post an comment, just to say something or to comment in an really bad way. Is like me gettint a liftime ban from the entire Inter-web. Yeah I can do such things.

But this time it wasn't, this time it was just an comment from what little I know. But one thing I do know with that beami and long Hull on that CVN there would'n be a problem to have two reactors with standard roods, if Highte is a problem then he could always use four smaller reactors... or just do like the old CVN Enterprise, a "billion" of reactors.

Or take an oxi torch to the deck. Lol........