$1.60 pulse on a TRIGA

[Azarien]

0:32 evil scientist's laugh

[PrometheanRunGood]

The pertiest blue you'll ever see. Now I want to see a video of blue ionization radiation from a core going critical in air.

Please oblige.

[Ulquiorrapwns]

God damn who put bees in the reactor!

[TimeLapseSteve]

Can someone explain how it is safe to stand this close to the core of a nuclear reactor going critical and releasing a shitload of neutrons? I'm guessing the water plays some sort of role in shielding?

[bothenook]

@TimeLapseSteve there is about 24 feet of water between the top of the core and the surface. that is an amazing amount of shielding, enough to allow us to stand over the top of the tank during the pulse. the only thing we have to do is insure there is enough cross flow over the core to keep the heat from causing a thermal riser, allowing the N16 enough time to decay before reaching the people space.

[TimeLapseSteve]

@bothenook Thank you. I find that fascinating.

[StoleTheL]

@bothenook i think id still does up on the Ki pills and wear some sort of lead apparatus before taking that walk. Once you wake up glowing blue in the middle of the night you cant go back...

[soverato3]

why r they using the word "dollar"??? is that becouse the pulse uses 1.60dollars worth of fuel???or am i way of???

[bothenook]

@soverato3 : one dollar is the terminology selected to indicate the amount of reactivity to take the reactor prompt critical.  when less than prompt critical, the reactor controls on a small fraction of the neutrons that are generated by the decay of fission fragments. those are called delayed neutrons. as long as you stay below one dollar, the reactor is easily controlled, since some of the neutrons causing fission don't show up to the party until 7 seconds after fission.

[TyrantRave0]

I wanna drink some of that water it must be soo fresh!

[aforencich]

@predictingpast No, it increases exponentially and generates a pile of heat, expands, and shuts down on its own. This is why you get a pulse, not a chernobyl or what K-19 could have been. American reactors > Russian reactors.

[revtkatt]

"Exactly prompt critical" is how a fission bomb works. Good thing its self moderating :-)

[powerfulpup]

So they remove control rods, which results in the pulse? Then almost immediately re-insert a control rod to absorb some neutrons to slow the reaction down? Is that basically what this is, or am I way off?

[bothenook]

@powerfulpup the transient rod is banked to provide the desired reactivity insertion, and the other 5 rods are banked to yield a steady state power around 50 watts. when the period is infinity (stable), the transient rod is pulsed out using N2 gas, yielding a power rise to about 340 Megawatts. the transient rod is immediately dropped, and the other 5 follow suit shortly. the pulse full width, half max value is around 30 milliseconds.

[bothenook]

@powerfulpup : you are basically right. the whole purpose of a pulse it to generate a huge number of neutrons in a very short period of time. very handy when doing electronics reliability testing rather than days in a normal irradiation position.

[edunuke]

@bothenook

That's all most correct, removing the control rod causes and exponential increase in prompt neutrons orders of magnitude higher than delayed neutrons, and so you see the bright blue Cherenkov radiation. However, the power falls back very quickly as it starts to raise up and thats because this reactor is built with a negative temperature coefficient of reactivity caused by Doppler broadening of the fission crossection spectrum. Pulsing is done mostly to consume fuel before disposal.

[bothenook]

@edunuke pulsing to consume fuel may be appropriate for some reactors, but that seems like a hazardous way to burn fuel off, considering at end of life, there is a large gas accumulation inside the fuel elements which will cause a huge pressure spike during the pulse. we use it to get 340 times the number of neutrons per second for experiment irradiations.

[edunuke]

@bothenook ..."or to obtain a desired neutron flux for irradiation or research purposes"... ;)

I also worked at one research reactor. It was mainly performed for the reasons you stated.

But since we were converting to LEU fuel and we still had plenty of fuel we started to pulse it to consume fuel. It was DOE approved procedure. Cheers.

[rebelgunnut]

wow are you not realy suppous to go over a dollar?

[bothenook]

@rebelgunnut : inserting 1 dollar makes the reactor exactly prompt critical, which is unstable and difficult at best to control.  that's why the transient rod is ejected and immediately falls back into the core.

[rebelgunnut]

@bothenook arn't you also useing hydrate fuel ?

[JonnyTommyGuns]

@bothenook WTF are you talking about. Please elaborate to the nuclear reactor noobs.

[bothenook]

@JonnyTommyGuns keep reactivity less than one dollar, reactor controls on delayed neutrons. great than one dollar, prompt, or fission neutrons control the reaction rate.

[JonnyTommyGuns]

@bothenook Alright it's official I know nothing about nuclear engineering. But I do understand now that 1 dollar is prompt and that means the reactor is good to go lol?

[suprasteve7187]

what is the purpose of pulsing such a reactor?

[CamilloVidani]

To create a very brief and extremely intense burst of neutrons: these can be extracted from the reactor and used for materials science and other kinds of research; otherwise a sample can be placed directly into the core, and be irradiated there by an extremely intense flash of radiation (for example, this is useful for testing nuclear fuel rods intended for other kinds of reactors)

[revtkatt]

@suprasteve7187  Amusing your friends?

[alidab34r]

What variety of TRIGA is this? Just curious...anywhoo, this was -really- awesome. What power does the reactor normally run at? I love how you can see the changes in power with the changes in intensity of Cerenkov radiation - it's pretty, and one of my favorite part of reactors.

[bothenook]

@alidab34r : modified MKII TRIGA, 2 MW steady state

[10mintwo]

but how do you get the control rod re-inserted to quench the reaction so fast? or don't you. maybe the reaction poisons itself b/c of xenon etc.? If this is not the case though, can the reactor conceivably be run steady state at 300MW? would it melt down if this is possible? anyway it's interesting to consider that the core of a nuclear power plant must be just blindingly white with cherenkov radiation like this - not something you normally think about.

[bothenook]

the pulse rod is dropped immediately. during the video, you can hear it drop right after the pulse. several seconds later, you can hear the rest of the control rods drop. it's all done automatically with gain changes to the nuclear instruments. and no, there would be no way to operate this type of reactor at 300 MW for anything longer than a few milliseconds.  if nothing else, heat removal from the fission process would limit your ability to run at elevated power.

[CamilloVidani]

True, you cannot quench the reaction that fast with a mechanical system. The beauty is, you don't need to: the pulse is self-limiting. The fuel used in TRIGA reactors has a strongly negative "thermal coefficient of reactivity", i.e. the hotter it is, the less efficient it becomes. During a pulse the rods heat extremely fast, so fast that after sume hundredths of a second the reactor becomes subcritical again because of that effect, and it goes back to a low power level by itself.

[10mintwo]

oh I see, I didn't think of that. so is the effect mostly due to the doppler broadening of the neutron absorption cross section of U238 or is it due to the actual physical density of the U in the reactor being sufficiently reduced so as to lower the overall likelihood of any one atom colliding with a neutron. I suspect the former, because if the reactor core's density were reduced enough for the latter effect to occur, I would guess that it would need to physically blow itself apart.....right?

[milesontario]

A good portion of the moderator of the system is built into the fuel alloy. As the temperature increases, the fuel ceases to slow down the neutrons, and at a point, begins adding energy to the neutrons, shifting them out of the fission spectrum of U235. Once the neutrons leave the core, they find moderation in the surrounding pool water, and ultimately are absorbed there. Leakage of the neutrons results in K < 1, quenching the reaction (negative coefficient of reactivity, see above).

[ajpmathwiz]

Both, and also reduced moderation as water surrounding the reactor begins to boil. The majority is Doppler broadening, though.

[soylentgreenb]

You don't need to get the control rod back, the reactor has a very large temperature coefficient of reactivity.

I don't know what particular mechanism is used in the TRIGA but the usual suspect is a doppler broadening.

[kubetail12]

@soylentgreenb I would imagine it have a negative void coefficient too... not sure how strong.

[sbu6]

How they make such pulses?

[bothenook]

reactor is taken critical, at a very low power level. one control rod is designed to be ejected from the core with nitrogen gas. the amount of rod withdrawal determines the size of the pulse.

[kaltmacherde]

@bothenook Is the Xenon dismantled so fast that it gives the core a kick to 340megawatts in just 30miliseconds? Where will that power go? Will it heat the water instantly? Is this "experiment" not dangerous,if the protectional circuits fail? (yes, radiation is fascinating and very dangerous at the same time :-)) The Cherenkow light. Does this prove that its possible to move faster than light? :-)

And .. why the fuck cant i have such a reactor at home? The cher. light is so unbelievable cute! :-)

[googlephi]

@kaltmacherde

The Cherenkov radiation is the result of charged particles exceeding the speed at which light travels through water (about three quarters of light's maximum speed). A cone of photons (including a bit of visible light) is kicked up ahead of each particle.

I'm no physicist, so can't comment on the safety of this demonstration. I can estimate that the 250KW TRIGA in Ljubljana would take somewhere in the neighborhood of three minutes of that 300MW to boil off all the coolant water.

[ArthrusGigawitAnteon]

@kaltmacherde Xenon doesn't come into effect in that short of a time span. The reaction is immediately shut down by thermal feedback (the water that allows the reaction to happen is not dense enough when it is that hot, stopping good moderation). Also it is fairly safe, because even if every at least doubly redundant circuit would fail, there is always several master power switches which if hit would cause the rods to drop.

[spitz888]

You relly have to watch this in action to get the full effect of it. The pulse only lasts a split second, but produces alot of energy during that time.

The one here at Oregon State is still in use and I will be watching this again here in the near future. It pays to be a Nuclear Engineer.

[subach]

I want one, too bad there's only 35 of them in the US.

[carterwj1964]

I witnessed the Triga at the University of Arizona pulse like that often enough. Now it is all but decommissioned. Where is this Triga of yours located?

[zackkline]

This one is located at an airport ouside of davis CA

[Mirage2000H]

Great vid ^^

How much does that Triga reactor cost?

[zackkline]

Love this video, too bad I couldn't see a pulse in RL. Kudos for Jessica convincing that guy to put it up on youtube!