Nuclear component heat capacity

[D0SBoots]

Plenty of people are talking about the ratios of nuclear reactors to heat exchangers to turbines to pumps, and how much energy water tanks can store now that we have 500C steam. (Answer: 2.425GJ!) But I haven't seen anyone run the numbers on how much energy is stored by the reactors and heat pipes themselves, in terms of heat. We can see the temperature that they are at, but without knowing how much energy it takes to raise their temperature by 1 degree, we don't know how much heat they store.

Nuclear Heat Test.jpg (46.57 KiB) Viewed 4703 times

Doing the test is pretty simple: Set up a small reactor, with water disconnected from the heat exchanger. Run the reactor until the fuel is burned up, and note the final temperatures using the console. (It seems that there is a 1 degree/connection gap on nuclear heat components, so in my test picture above when the reactor is at 1000C, the heat pipe tops out at 999C and the heat exchanger at 998C.) Then connect the input pipe, wait until the temperature drops to 500C, and use the console to find out how much steam was generated. Note the final temperatures at the end, too.

By using different numbers of reactors and heat pipes, I solved for the unknowns and found a very nice, round answer: Reactors have a heat capacity of 10 MJ/K, while heat pipes and heat exchanges are 1 MJ/K. Or, considering the full usable temperature swing from 500C to 1000C, reactors can store 5GJ, while heat pipes and heat exchanges store 500MJ. This is crazy high - the water in a full pipe (which should be sort of analogous to a heat pipe) only has a heat capacity of 20 kJ/K! Spacewise, this is even better than a storage tank. (Edit: Originally, I miscalculated, because I misremembered tanks as being 2x2.)

We can make use of this for cheaper pulsed-nuclear setups. A traditional pulsed-nuclear build saves on the number of steam turbines by storing the extra energy pulse in storage tanks, but you still need the full number of heat exchangers to keep up with the heat generation. However, if you build extra heat pipes to store the heat, you can cut back and only build as many heat exchangers as you need to keep up with demand.

[Nasabot]

This is something I wondered about. Yes, heat pipes are very good to store energy.

[cbhj1]

Good to see the numbers match up with what I found in my own tests - SCIENCE!

there is one thing to be concerned with with using this for storage, in lightly loaded reactors, the core might bump 1000 C if the capacity is close to the amount generated with the new heatpipe calculations, but that goes away once more load is used.

Might I ask what method you used to measure?, mine was to take a fresh reactor and add a single cell to get the heat per C for that, then similar fresh reactors with one each of heatpipe or exchanger, then compare the temperatures to find out how much heat was in the second part and from there get the heat per C.

[D0SBoots]

I gave my test procedure (admittedly in a very abbreviated form) in the original post. I used the temperature of the nuclear components (once the fuel was completely burned) to generate 500C steam, which has a well-known energy/unit, and then counted the steam with the console. By varying how many reactors or heat pipes I had, I set up different scenarios so I could solve for all three variables.

[BlakeMW]

I've known this for a while because I looked in the raws. Though it's always nice though to have experimental verification that the game uses the data as it should (but the game has proven itself to be extremely trustworthy in terms of energy). I've done some maths on the total heat storage of a Simple 160MW Nuclear setup. Basically most sensible reactor designs will be able to buffer a full fuel cycle even without steam tanks or added heat pipes. Though of course you need either a steam tank or an accumulator solution to detect when the heat exchangers stop producing steam.

[Mehve]

I've experimented with deliberately using heatpipes as buffers (although I hadn't realized how effective they are!), but I found that it tended to work against reactor control schemes, because it takes that much longer for all the exchangers to heat up again once you finally add fuel, thus requiring even more steam tanks to keep up the power levels.

[BlakeMW]

I've experimented with deliberately using heatpipes as buffers (although I hadn't realized how effective they are!), but I found that it tended to work against reactor control schemes, because it takes that much longer for all the exchangers to heat up again once you finally add fuel, thus requiring even more steam tanks to keep up the power levels.

Not if you put a low steam detection mechanism on the heat exchanger most distant from the reactors. The main important thing is to have instant response to a low steam condition and a 200s fuel timer to prevent over-insertion of fuel, the controls can't be "sloppy" when using a design without steam storage tanks. The other thing is power plants are usually over-sized at least a little (it's hard to use exactly the output of a reactor, and bad if it doesn't have a little headroom) so if the (maximum) output drops by a few percent when the fuel is cycled this won't tend to be a big deal.

[bartekltg]

But I haven't seen anyone run the numbers on how much energy is stored by the reactors and heat pipes themselves,

You just haven't read my posts;-) But it was inside other threads.

I like it phrased in that way: to store one fuel cell (8GJ, "burned" without bonus) we need 16 heatpipes (working between 500 and 1000).
A reactor is the same as 10 heatpipes.

The energy density (per tile) is greater than with tanks, but the main advantage is that one can build effective setup (2x2 or 2xn reactors) even when only small power is needed, without enormous steam installation! Just add one cell fuel to each reactor, it will heat heatpipes, and then heat exchangesr will slowly consume that heat. After it drops to 500deg, steam is not generated and next fuel cells will be added.

Here
viewtopic.php?f=3&t=47929&start=100#p278690
is 116MW setup using 2x2 reactor matrix. No fuel is wasted. The post is about feeding reactor, but the setup with heat buffer is also explained. I copied image and blueprint:

picture

blueprint

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[Mehve]

I've experimented with deliberately using heatpipes as buffers (although I hadn't realized how effective they are!), but I found that it tended to work against reactor control schemes, because it takes that much longer for all the exchangers to heat up again once you finally add fuel, thus requiring even more steam tanks to keep up the power levels.

Not if you put a low steam detection mechanism on the heat exchanger most distant from the reactors. The main important thing is to have instant response to a low steam condition and a 200s fuel timer to prevent over-insertion of fuel, the controls can't be "sloppy" when using a design without steam storage tanks. The other thing is power plants are usually over-sized at least a little (it's hard to use exactly the output of a reactor, and bad if it doesn't have a little headroom) so if the (maximum) output drops by a few percent when the fuel is cycled this won't tend to be a big deal.

Yeah, my current design that I've been working on uses 16 heat exchangers, arranged single file away from the reactor (the goal was to be tile-able within the width of a single reactor), so there's a fair distance for the heat to travel before I'm getting ~100% power again. I've tuned the fuel cycle trigger so it trips after less than 500 steam is consumed from the tanks, but at >90%+ output the 16 exchangers will still drain over two entire tanks of steam before the heat manages to reach the 16th exchanger and get it producing steam again. In the end, I eventually had to resort to using four steam tanks instead of just two, and that did the trick.

That said, I realize that I wouldn't be having anywhere near these problems with a more compact design, with a much shorter maximum heat pipe distance.

[Aeternus]

Heatpipes (and heat exchangers, those count as an extra heatpipe) can store some energy yes, but I would recommend only using the reactors for heat storage. Given that heat pipes need to stay relatively short these days... Yea, you could put a mess of heatpipes around reactors, but storing steam is about as efficient as 9 heat pipes. A filled tank with 500dgr steam stores 2.425 GJ and can be filled to the maximum. A single heat pipe can effectively store 500MJ -at most-, but anything over 1000 degrees is wasted, so you cannot use the full capacity of a heatpipe.