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PostPosted: Mon Sep 17, 2018 8:13 am 
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Another fission power plant question:

Imagine you find a starship derelict which was lost or "abandoned" 30 or so years ago. Early in the original "incident", the crew managed to shut down the fission power plant. The plant is intact and undamaged. Can it be restarted? If so, how long will it take to regain full ship power?

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PostPosted: Mon Sep 17, 2018 3:51 pm 
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Note that Cassini's RTG was designed to produce 600-700 watts at end-of-mission. A human-sized freezer uses less than a tenth of that; probably considerably less with Traveller levels of technology. The good news is that RTGs scale close to linearly with output.


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PostPosted: Mon Sep 17, 2018 9:01 pm 
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thrash wrote:
Note that Cassini's RTG was designed to produce 600-700 watts at end-of-mission. A human-sized freezer uses less than a tenth of that; probably considerably less with Traveller levels of technology. The good news is that RTGs scale close to linearly with output.

So one RTG per 10 cryoberths. Or two of them, for redundancy.

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PostPosted: Tue Sep 18, 2018 12:50 pm 
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If you insist. I still say one unit 1/10th the size of Cassini's per berth makes more sense, though it might be good design to allow them to be connected together.

RTGs essentially cannot fail, except as a result of age. They have no moving parts and the physical processes run on their own.


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PostPosted: Tue Sep 18, 2018 1:11 pm 
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thrash wrote:
If you insist. I still say one unit 1/10th the size of Cassini's per berth makes more sense, though it might be good design to allow them to be connected together.

Good idea. Enough volume for that in the 0.5 ton (7 cubic meters) of a low berth assembly.

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PostPosted: Tue Sep 18, 2018 4:10 pm 
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Seriously???? You just didn't ask your own personal internal former Nuclear Power Plant Operator???? ( :) )

Nuclear reactors can easily change power levels - that is why they are so effective on submarines etc. A TL7 reactor can go from 5% to 100% power in a couple of minutes. The limiting factor is the ability to speed up the pumps etc. than the reactors ability to produce more heat.

Modern nuclear reactors are rated two different ways - Power Output (in MW) and Effective Full Power Hours (EFPH) - the last term is just what it says - how much fuel do you have as measured in operating the reactor at full power for a certain amount of time.

Modern reactors have EFPH's in the 10s of thousands of hours - commercial reactors maybe close to 100,000 EPFH. That is your fuel and endurance. Most submarines run at about 10% - 15% power except when needed. Commercial reactors try to operate as close to 100% output as they can for as long as they can.

When a reactor is "shut down" it is still producing low levels of power, much less than 1% - so a reactor could be shut down for probably a century and still be able to be restarted. The issue isn't the reactor itself (or the fuel), but the state of the equipment. Equipment, especially rotating equipment like pumps and generators, wear out long before the reactor runs out of fuel. So if you had a ship that had been shut down for several decades, the reactor could be started up, but all the systems would be cold-soaked and likely need lubrication replacement etc. which could take weeks or months to go through everything and make sure it works properly before starting the reactor.

At TL9 or so, they probably develop Piezoelectric systems which might be much more efficient at converting radiation (heat) into electricity and not have all the start-up issues - that would be your call. In that case, I would say a team of operators would probably spend a week or more testing everything before starting up the reactor - in an emergency they could try it in a few hours, but with a very real possibility of something not working right.

:)

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PostPosted: Wed Sep 19, 2018 6:58 am 
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Cyborg IM1 wrote:
Seriously???? You just didn't ask your own personal internal former Nuclear Power Plant Operator???? ( :) )

As this is still in pre-production, I wanted to open a discussion here, which seems very fruitful. Of course, once we enter production proper, we have you as our expert :-)

Cyborg IM1 wrote:
Nuclear reactors can easily change power levels - that is why they are so effective on submarines etc. A TL7 reactor can go from 5% to 100% power in a couple of minutes. The limiting factor is the ability to speed up the pumps etc. than the reactors ability to produce more heat.

Modern nuclear reactors are rated two different ways - Power Output (in MW) and Effective Full Power Hours (EFPH) - the last term is just what it says - how much fuel do you have as measured in operating the reactor at full power for a certain amount of time.

Modern reactors have EFPH's in the 10s of thousands of hours - commercial reactors maybe close to 100,000 EPFH. That is your fuel and endurance. Most submarines run at about 10% - 15% power except when needed. Commercial reactors try to operate as close to 100% output as they can for as long as they can.

Hmmm... Does that scale in a linear fashion? That is, if you run at 10% output, do you use 10% of the fuel used in full output?

Also, at what power level do you think starship reactors will run when their fusion-torch (and thus MHD) is off? And when their drive is on?

MGT1/CE reactors seem to have EFPH of 10,000 hours or so, assuming full power output (thus fuel lasts for a year). Is that realistic?

When a reactor is "shut down" it is still producing low levels of power, much less than 1% - so a reactor could be shut down for probably a century and still be able to be restarted. The issue isn't the reactor itself (or the fuel), but the state of the equipment. Equipment, especially rotating equipment like pumps and generators, wear out long before the reactor runs out of fuel. So if you had a ship that had been shut down for several decades, the reactor could be started up, but all the systems would be cold-soaked and likely need lubrication replacement etc. which could take weeks or months to go through everything and make sure it works properly before starting the reactor.

Cyborg IM1 wrote:
At TL9 or so, they probably develop Piezoelectric systems which might be much more efficient at converting radiation (heat) into electricity and not have all the start-up issues - that would be your call. In that case, I would say a team of operators would probably spend a week or more testing everything before starting up the reactor - in an emergency they could try it in a few hours, but with a very real possibility of something not working right.

Hmmm... Piezoelectric it is for Hard Space technology (TL9-10). Throw Engineering 10+ to successfully restart a long-dormant reactor in 1d6 hours; failure by an Effect of 4 or more means that the power plant takes a (combat) hit. Methodical work of 1D+6 days is sufficient to restore the reactor to full operations without a throw, assuming it hasn't suffered damage.

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PostPosted: Wed Sep 19, 2018 12:43 pm 
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1. Yes, the power/fuel usage is linear, so if you run at 10% power, it lasts 10 times longer. :)

2. The power level without the Torch drive is kind of up to you. On a modern submarine, it is about 5%-10%. Improving TL probably drops that a bit, but 10% is a nice round number. The vast majority of the power is going to be for the Torch Drive. 90/10 has a good "feel".

3. An EFPH of 10,000 hours is about what a modern (TL6-7) submarine nuclear reactor can use. Since this is physics, not science, the only way to get more EFPH is to get a bigger reactor, so yes, that is a very reasonable number.

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PostPosted: Thu Sep 20, 2018 6:00 pm 
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Cyborg IM1 wrote:
1. Yes, the power/fuel usage is linear, so if you run at 10% power, it lasts 10 times longer. :)

So space stations with small reactors can easily go for 10 years between refuelings...

Cyborg IM1 wrote:
2. The power level without the Torch drive is kind of up to you. On a modern submarine, it is about 5%-10%. Improving TL probably drops that a bit, but 10% is a nice round number. The vast majority of the power is going to be for the Torch Drive. 90/10 has a good "feel".

Hmmm... So the "1 year" figure for fuel is for torch-ships using their torches frequently. Ships spending much time in unpowered orbits can use far less fuel...

Cyborg IM1 wrote:
3. An EFPH of 10,000 hours is about what a modern (TL6-7) submarine nuclear reactor can use. Since this is physics, not science, the only way to get more EFPH is to get a bigger reactor, so yes, that is a very reasonable number.

Wonderful!

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