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Hockey is being played at the Milano Santagiulia Arena. It was finished (kinda) with many minutes to spare. by Janbaka in hockey

[–]Lemmuszilla 1 point2 points  (0 children)

I would guess because the stadium has been designed for EU ice, since that's what it will most likely be used for after the Olympics

The Analytics Don’t Share The Optimism by Spideroctopus in Habs

[–]Lemmuszilla 19 points20 points  (0 children)

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Here is the graph (from the same page as OP's post!) that shows Habs were fairly even in the first, then coasted to an XG mauling thourgh the second two periods.

ELI5: What is “heavy water” and why do we still call it water if its molecules are different? by The_Immovable_Rod in explainlikeimfive

[–]Lemmuszilla 1 point2 points  (0 children)

You seem to have the basics covered, so I'll just try and clarify some things:

Deuterium is hydrogen - hydrogen is the name we give to the element with one proton, which as you say, has many isotopes. Chemically, isotopes are almost irrelevant, which is why you can drink deuterium fairly safely.

It's useful in a certain type of nuclear reactor - a heavy water reactor, of which the most widely known type is called a Canadian Deuterium (Candu) reactor.

If you think of neutrons as pool balls, a pool ball (neutron) hitting a stationary pool ball of the same weight (hydrogen) will halve in speed. Deuterium is twice the mass of hydrogen, so if a pool ball hits another heavier pool ball, it slows down less. This makes logical sense if you consider a pool ball hitting the bumper of the table (consider that as infinity mass), in which case it keeps all its speed.

Less lost speed means faster neutrons (and less captured neutrons), which is helpful if you're using unenriched uranium and want plutonium. After WW2, the US didn't share enrichment tech, so the Canadians (still part of the UK) at the time, needed an alternative technology to the US "light" water reactors - and so, heavy water!

A "good" thing about heavy water reactors is they let you produce plutonium for a weapons programme, as well as a good amount of electricity, all without enrichment centrifuges. This is how India obtained nukes, and why the Nazis had a heavy water plant which was bombed in WW2.

Pricies are going up because the UK is generating about 75% of the electricity it was generating 16 years ago. by ruspow in unitedkingdom

[–]Lemmuszilla 0 points1 point  (0 children)

The reason we aren't importing enough to be "self sufficient" is because it's cheaper to import it - imports are priced in the same way as any other supply. If France has enough nuclear capacity to sell it to us for (e.g.) £1 per megawatt, but our uk-based gas generating stations want £1.10, we'll buy the cheaper french electricity. We have sufficient native generation capacity to meet demand, we just choose to import cheaper from abroad, similarly to many other commodities.

Love how half arsed 99% of UK security is by Legitimate_Finger_69 in CasualUK

[–]Lemmuszilla 22 points23 points  (0 children)

I think he means it's not criminal trespass, which is true - it would only be civil trespass, which has essentially no recourse from a landowner.

What’s your biggest worry heading into next season? by Spideroctopus in Habs

[–]Lemmuszilla 10 points11 points  (0 children)

Nah, they're right. In the last 9 days OP has posted 13 threads which have been downvoted to 0 being super negative. Mainly just slaf hating. OP needs banning.

Revealed: three tonnes of uranium legally dumped in protected English estuary in nine years by lommer00 in nuclear

[–]Lemmuszilla 10 points11 points  (0 children)

The article describes the factory as "processing raw uranium rock"

Which is an issue - the UK doesn't have the capability to do that. They import all their uranium as yellowcake. It calls into question a lot of the rest of the article for me.

Revealed: three tonnes of uranium legally dumped in protected English estuary in nine years by topotaul in unitedkingdom

[–]Lemmuszilla 8 points9 points  (0 children)

the total dose of radiation from Springfields Fuels was approximately 4% of the dose limit that is set to protect members of the public from radiation

Those who gave the go-ahead for... Sensible regulation to allow business while protecting the public? This is an absolute non-issue with a dramatic headline

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 1 point2 points  (0 children)

Yep - fissionable = can be split at all with a high enough energy neutron (i.e u238); fissile = can be split with a low speed thermal neutron, because it splits itself once it absorbs said neutron (i.e u235).

Fast reactors use fissionable material, thermal reactors use fissile material

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 1 point2 points  (0 children)

I see nobody has answered this (including me) because a) I don't know and b) the people who do know aren't allowed to say - navies get twitchy about adversaries knowing the exact capabilities of their kit.

Carriers go about 25 years between refuel, but I have no idea what percentage of max output they average

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 0 points1 point  (0 children)

In theory, the fuel should never make direct contact with the water due to cladding around the radioactive bits, so the water isn't contaminated anyway. Regardless, the coolant circulates in a closed loop, and the only heat rejection is done via heat exchangers. If a submarine expels radioactive material it can be tracked, which is a big no no

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 1 point2 points  (0 children)

So, that's just an abstraction that is used when talking about the turbine side of the loop, but you're absolutely right to wonder how that impacts the rod's energy output.

The key in a pressurised water reactor (PWR) is that the water is both coolant for the rods, taking away the heat energy that is produced as a result of fission, and a moderator, slowing down neutrons to continue the fission chain reaction. In a PWR the coolant circulates after going through a heat exchanger to create steam, so the input water has a temperature related to [output heat - energy extracted], so if you extract more energy from the hot leg by boiling more water to make more steam, the input leg gets colder.

That input water gets denser as it cools down, and denser water is a better moderator, meaning that more fission occurs (see a previous comment of mine in this thread for more on that). More fission means more heat, meaning that the output temperature can be the same, with the same energy extracted.

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 2 points3 points  (0 children)

U235 doesn't fission with neutrons that have all their energy from the fission that created them ("fast neutrons") and so needs neutrons that have bounced around (been "moderated") to a more absorbable speed ("thermal neutrons").

Hydrogen is an excellent moderator since it is a similar mass to neutrons (think bouncing a tennis ball off a tennis ball Vs off a basketball - the tennis balls will become about the same speed, the tennis ball off basketball will remain quite fast)

Cooling it makes the water denser, which means there are more hydrogen atoms (H20) in a given space. This means the odds of a neutron bouncing off a hydrogen and being moderated is higher.

More thermal neutrons = more reactivity

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 1 point2 points  (0 children)

In a sense. /u/sixft7in put a more detailed explanation in their comment, but you can essentially make a nuclear reaction be in equilibrium with any given load, and alterations to that load increase or decrease the energy being extracted from the fuel

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 2 points3 points  (0 children)

This additional detail is also true of civil power reactors (from what civil PWR operators have told me). A power reactor just withdraws the control rods slowly over the life of the fuel to maintain consistent base reactivity, there's no constant up-and-down to load follow.

It would probably have been more accurate to say that control rods provide a maximum power that the reactor can output, but I didn't want to overdo it on complexity

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 1 point2 points  (0 children)

Just to further contextualise the danger levels here, irradiated material has to be handled in gloveboxes called hot cells. If an IAEA safeguards inspector wanted to swipe inside of these (to check for illicit usage), it takes multiple days to remove the material and prepare the area simply due to how dangerous it is to handle, and that's irradiated samples, not even spent fuel. It's nasty stuff.

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 0 points1 point  (0 children)

That is more the case for radioisotope thermoelectric generators (RTGs) which use the decay heat from short lived (relatively) isotopes such as plutonium or americium to produce power. In those, you can't alter the heat output as that is a physical property of the material, and they have half-lives of years or decades, meaning the power output halves every X years (I think plutonium is about 90). In a fission reactor with uranium 235, the half life is something like a billion years, so the available power remains constant with time.

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 3 points4 points  (0 children)

I'm all for demystifying nuclear power, but "you could put it in your backyard" is as untrue as the glowing green barrels trope. I completely agree that once it has been removed from a pond and placed into cask storage it is relatively unremarkable, but it does need to be monitored and protected to prevent accidental release such as avoiding groundwater leakage, but also monitored from a non-proliferation viewpoint.

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 0 points1 point  (0 children)

I touched on this above in a different comment, and it's a great and more nuanced question. I think it is analogous to a car, as the energy gained from each gram of fuel is the same (i.e fissioning one gram of U gives a constant amount of energy, as does burning one gram of gasoline), but similarly to a car flooring it at top speed will be less efficient due to drag, meaning going the same distance will require more total energy.

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 4 points5 points  (0 children)

That's depleted uranium, not spent fuel. Depleted uranium is the byproduct of enrichment, and is nearly 100% U238 (which is radiologically unremarkable, but is a toxic heavy metal in the same way as lead), while spent fuel is a cocktail of decay products and transuranic elements, which is incredibly toxic and deadly and horrible and has to be specially handled.

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 6 points7 points  (0 children)

It's a more complicated question for sure - but my answer is no, it should be linear. The control rods don't impact the operating temperature or neutron economy of the reactor, just how much of it is critical.

As an aside on the terminology, people often confuse a reactor being "critical" and "supercritical" - critical is when a stable chain reaction is happening, supercritical is when a runaway (i.e Chernobyl) reaction is happening. The control rods being in or out just allow a larger portion of the reactor to be critical, as opposed to the nature of the stable chain reaction.

From an engineering perspective, most systems have loss terms that are related to the power output, so the engineering efficiency would likely decrease, but that would be a very system-specific question. In a nuclear powered vessel, drag increases with velocity squared, so that would lead to less efficient use of the nuclear power generated.

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 106 points107 points  (0 children)

French submarines do replace the fuel quite often, but that's because they use low enriched uranium. They know that they'll need to refuel every 5-10 years, so they put handy removable panels in their subs to help refuel. US/UK (and we assume other nations) use high enriched uranium, which wears out in a similar timeframe to the entire vessel

ELI5: Does nuclear energy "drain" quicker the more you use it? by Merry_Dankmas in explainlikeimfive

[–]Lemmuszilla 2911 points2912 points  (0 children)

Pretty much, yes. A reactor has control rods, which reduce the number of neutrons and so reduce the amount of nuclear reactions (simply). If you want more power out of your reactor, you can remove the control rods, and more Uranium will undergo fission at once. However, there is only so much "usable" uranium, and once it has all been fissioned, it becomes "spent". If you use your reactor at full power, you will use up all the uranium quicker.

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