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PostPosted: Sat Sep 15, 2018 8:38 pm 
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I'm considering the (exclusive?) use of fission power plants in my Hard Space setting for the Cepheus Engine/Classic Traveller. But I wondered about one point:

Can you change the power settings/output of a fission reactor to conserve fuel? That is, for example, run it at minimal power to let the uranium fuel last much longer while keeping the Low Berths powered? If so, how long will the fuel last (per CE/MGT1 it lasts 1 year on maximum power output)?

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PostPosted: Sat Sep 15, 2018 8:52 pm 
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Golan2072 wrote:
I'm considering the (exclusive?) use of fission power plants in my Hard Space setting for the Cepheus Engine/Classic Traveller. But I wondered about one point:

Can you change the power settings/output of a fission reactor to conserve fuel? That is, for example, run it at minimal power to let the uranium fuel last much longer while keeping the Low Berths powered? If so, how long will the fuel last (per CE/MGT1 it lasts 1 year on maximum power output)?


How much power would low berths consume, compared to the power usage of an entire starship, i.e. the maximum power output of the reactor?

If it is not very much, your answer may be a radioisotope thermoelectric generator, or RTG for short (you may remember it played a small role in The Martian).

https://en.wikipedia.org/wiki/Radioisot ... _generator

Maybe your fission power plants are designed in a way that allows for the fuel to be moved between the reactor itself and an RTG assembly, meaning that depending on where the fuel is, the power plant either works as a standard fission reactor, or as an RTG to produce a minimum level of standby power?

The best part here is that an RTG does not actually use fuel - it utilizes the radioactive decay that happens anyway.

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PostPosted: Sun Sep 16, 2018 3:14 pm 
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Golan2072 wrote:
Can you change the power settings/output of a fission reactor to conserve fuel?

Depends on the design but in general, yes. There is normally some form of moderator (control rods, etc.) that can be inserted or withdrawn to adjust the rate of the reactions. A slower reaction produces less power but also uses less fuel.

There are limits, however. There may be a minimum power level required to run the generators, below which the plant is essentially shut down. On the other hand, radioactive decay will continue to occur at some level regardless, producing heat and burning fuel if nothing else.


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PostPosted: Sun Sep 16, 2018 3:17 pm 
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Hmmm... So potentially the Power Plant tonnage subsumes both the main reactor and the backup RTG powering emergency systems and low berths?

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PostPosted: Sun Sep 16, 2018 3:24 pm 
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If I were the engineer, I would include the backup power for the low berths directly in their design,

Emergency power for the ship as a whole is probably included in the power plant tonnage, though, yes.


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PostPosted: Sun Sep 16, 2018 4:13 pm 
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thrash wrote:
If I were the engineer, I would include the backup power for the low berths directly in their design

Hmmm. Is the RTG small enough to be part of the low berth's 0.5 dton? And how long will that last?

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PostPosted: Sun Sep 16, 2018 4:27 pm 
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Golan2072 wrote:
thrash wrote:
If I were the engineer, I would include the backup power for the low berths directly in their design

Hmmm. Is the RTG small enough to be part of the low berth's 0.5 dton? And how long will that last?


Image

This is the RTG used on Cassini.

The Wikipedia article says that usually, isotopes with half-lives of several decades are used. So depending on how much surplus it initially produces, the RTG may be good for a few decades.

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Earth is the cradle of humanity, but one cannot live in a cradle forever. Konstantin Tsiolkovsky
Man has earned the right to hold this planet against all comers, by virtue of occasionally producing someone completely bat**** insane. xkcd #556
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PostPosted: Sun Sep 16, 2018 4:58 pm 
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Hmmm... I can definitely see this used in a low berth. After all, the low berth assembly is 0.5 dton, or approx. 7 cubic meters, where this seems to be less than 2 cubit meters, and the cryotube itself isn't that large, either.

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PostPosted: Sun Sep 16, 2018 5:06 pm 
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Golan2072 wrote:
Hmmm... I can definitely see this used in a low berth. After all, the low berth assembly is 0.5 dton, or approx. 7 cubic meters, where this seems to be less than 2 cubit meters, and the cryotube itself isn't that large, either.


Don´t forget it´ll need some shielding, too. Both against whatever radiation it emits (which cannot be too much, judging from the lack of protective equipment in that picture), and against tampering - intentional as well as unintentional.

You do NOT want some idiot to stack combustbiles against the RTG, for example, what with the heat it emits.

Or a situation in which anything or anyone might bump into the RTG and crack it open - to quote Mark Watney: "If I make a mistake with the RTG, I will not ever make another mistake again."


Hmm... this would mean RTGs are not too common on ships expected to go into combat - too many opportunities for battle damage to crack the RTG.

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Space isn't remote at all. It's only an hour's drive away if your car could go straight upwards. Sir Frederick Hoyle
Earth is the cradle of humanity, but one cannot live in a cradle forever. Konstantin Tsiolkovsky
Man has earned the right to hold this planet against all comers, by virtue of occasionally producing someone completely bat**** insane. xkcd #556
Just like people, stars can be very important without being terribly bright. Phil Plait, "Bad Astronomy"


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PostPosted: Sun Sep 16, 2018 5:32 pm 
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Probably a big RTG or two for all cryberths aboard, subsumed in their tonnage.

Sir Chaos wrote:
Hmm... this would mean RTGs are not too common on ships expected to go into combat - too many opportunities for battle damage to crack the RTG.

On the other hand, my ships already have fission reactors as their main power plants anyway...

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Last edited by Golan2072 on Mon Sep 17, 2018 8:13 am, edited 1 time in total.

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