Design tip: Fission PP's vs. Fusion for interplanetary ships

[BP]

...Fusion reactors are only a major source or radiation when they are turned on, with the reactor chamber remaining slightly radioactive after it's turned off (unless you use boron 11 and hydrogen then there is no leftover radiation). They can also be turned off very easily and quickly. Keeping them on is the difficult part. ...

It would be rare to turn off a PP in a ship, especially during combat. Release of radiation when confined plasma is suddenly, unexpected released is still a cause for radiation concern (of less importance than other issues in RL to be sure) - hence the Crew Hit Radiation Damage column use on a second hit to PP, one would presume.

...Fuel hits to liquid hydrogen tanks tend to vent into outer space because the tanks are usually placed adjacent to the outer surface of the ship and because vacuum is the path of least resistance.

All true - but the L-Hyd has to get to the PP... this implies internal plumbing which could very well pose risk to life and limb of an immediate nature especially when automated systems/self sealing hull prevents decompression.

Not that any of this is represented in the RAW.

...It still takes hours to shut down a fission reaction.

Not necessarily - even in the RW (just quench the reaction with absorbers - a question of geometry and material selection is all) - certain materials (ala Thorium) as self quenching relatively fast. Ignoring Traveller's Damper tech, of course.

In a pinch - just eject the core or the whole dang reactor (emergency batteries anyone?)...

After all, navies still use reactors despite these hazards due to their benefits in range and power (the later of which can be useful in avoiding damage to the reactor).

...Ships sink, so there is no mess to clean up afterwards.

Not if they are in a dock or near a shore... same as Trav ships dirt side, of course.

Space is even better than an ocean - after all, the right nudge and things plummet into the sun...

...Unlike Traveller, any attack that hits the reactor on a surface navy ship has probably already destroyed the ship.

Good possibility - but by no means a guarantee. Almost all US equipped surface ships (Carriers/Supercarriers last I checked - cruisers have been decommissioned...) even have multiple reactors (as did many Russian subs).

Note, in-game, for 100 ton+ ships, PP damage is on the Internal damage table - and on a 4 or 11 (i.e. lower end of the odds scale).

...

and radiation exposure can be dealt with and is rarely immediately life threatening.

Errr... No! Any major reactor breach in a confined space such as an SDB will probably be lethal dose within hours and the ship will still remain contaminated.

Ahem - emphasis on 'immediately life threatening'

If you are close enough to get an immediately lethal dose - you are probably already dead from the related damage. Just like in RL where immediate deaths are from explosions and collateral damage - not radiation.

Otherwise - several hours should be long enough for a battle to play out :twisted:

(Oh yeah - and to get radiation treatment... decon the ship, etc. )

...Fission powered ships should be built with a way to jettison the reactor, assuming that the mechanism was not damaged in the battle also.

Pray that last missile volley takes out the other ship while they are left dead in the water.

:lol:

100% agreed! (is this crossing the threads with the religion topic?)

Don't get me wrong - all I'm saying is its not totally outside the realm of things. For safety, fusion is, by and large, the way to go when its available. Especially for commercial when all safety issues are accounted for (not that financial 'concerns' wouldn't take precedence over mere life...).

But this doesn't rule out Fission PP. Heck, gas powered cars are a lot more deadly than horse and buggy (I presume - maybe I should just say walking). Humans are still insane enough to use them.

 

[Liam Devlin]

By 'Fission PP jump drives' presume that means dumping the whole 'hydrogen filled jump bubble' ...

Mssr BP,

I present it as a limited possibility to engage the lanthanum grid, this does not preclude a Jump-drive engine for FTL. By "limited" as an ATU idea, J-1 is the limit to this form of technology. Thus the interstellar society (ies) using this is hindered to the comfortable limit of whatever they can sustain as a stellar nation(al) state in time-lag communication. Possibly occupying only a subsector in size.

In the arguments of pro-con on expenses, in the long run, its cheaper than Fusion Power. Some of our Nuke-wet Navy ships can run 48 months before needing their fuel core replaced.

For game mechanic purposes:
an Antique Insystem freighter might go 48 months before "refuelling"

A Jump-capable ship (harnessing more energy effort to create the Jump-emergence hole on lanthanum grid) would need to replace its fuel core every 12 months.

Atomic energy comes along at TL6, and is quite "mature"/ clean & at its efficient maximum at TL9. Talk about refined and unrefined fuel differences between the tech levels!

Tweaking with HG rules, the armored bulkhead for the FPP here is rad shielding! Just thinkin' out loud again...[/b]

 

[BP]

By 'Fission PP jump drives' presume that means dumping the whole 'hydrogen filled jump bubble' ...

Mssr BP,

I present it as a limited possibility to engage the lanthanum grid, this does not preclude a Jump-drive engine for FTL.

Mongoose traveller makes no mention of lanthanum grids that I'm aware of - nor a requirement that the J-Drive have a fusion PP to operate (only an equivalent rating).

The rules as written have jump requiring a 'bubble' of hydrogen... was simply querying the meaning of 'Fission PP jump drives'.

...In the arguments of pro-con on expenses, in the long run, its cheaper than Fusion Power.

Yeah - ingame, that is what I posted.

Short-term, it can be a size-able initial investment, depending on drive rating, for the fuel.

...Some of our Nuke-wet Navy ships can run 48 months before needing their fuel core replaced.

Older U.S. naval reactors last a decade plus between core changes - newest carriers are spec'd at half a century, IIRC.

For a game, of course, it can be whatever you want...

 

[Liam Devlin]

Mssr BP, this would inherent to the ruleset to have Lhyd make the "jump bubble". IMTU, the lanthanum grid is what radiates throughout this mini-verse trip on the hull.

Ergo, Notably then, with larger Fission PP's and same J-1 fuel tankage for the travelling vessels, a TL8 or TL9 Far Trader-class vessel will be larger than say, a 200dton TL9/10 Fusion-PP driven one. I'm not saying the ruleset's requirement be done away with for the Lhyd bubble, I postulate that a lower tech society could still be using it (especially if its a strand of water poor worlds, but richer in far with radioactives).

"poor man's Traveller", or lower tech, meaner-n-leaner gizmo/ gadget wise.

IIRC, in David Weber's Honor-Harrington-Verse, there was a stellar power that built rugged and tough fission-powered ships, since they did not have the time nor the technology base to compete with the Kingdom of Manticore, nor the Republican Navy's.

Bigger, blockier, but got the job done. Thats all I'm saying here.

 

[billclo]

IIRC, in David Weber's Honor-Harrington-Verse, there was a stellar power that built rugged and tough fission-powered ships, since they did not have the time nor the technology base to compete with the Kingdom of Manticore, nor the Republican Navy's.

Bigger, blockier, but got the job done. Thats all I'm saying here.

That would be the planet Grayson, and that fission tech led to installing it on some Manticore small attack craft later in the war.

 

[phavoc]

Fission makes a lot of sense. And with the abilty to easily maneuver within a system, its pretty friggin easy to dump any nuclear waste into the sun. That's been the chief issue with reactors here, is that we don't have a "safe" way to dispose of nuclear waste.. NIMBY rearing its ugly, stupid head and all that.

And, for the most party, I don't think anyone is gonna be worrying about the risk from a reactor breach during combat, what with meson guns, particle accelators and nukes being tossed around.

Oh, and btw, I read the other day the Chinese have finally figured out breeder reactor technology. Whee!

 

[GypsyComet]

A good alternate for smaller settings, but just not in the same orders of magnitude as using hydrogen. The starports become even more important, as wilderness refueling is no longer an option. Because the infrastructure requirements for ports are vastly increased, the Imperial model of the economically and governmentally isolated starport is probably not viable in a fission setting, or at least not universal.

For all the reasons given by prior posters, ship layouts will change. Layers of engine room isolation will become standard. If the dominant culture remains Vilani-like, fission reactors will tend toward complete isolation, with that once-a-year maintenance and refueling done by specialists. The "Engine Room" is where power is routed, not where it is generated, and "Chief Engineer" potentially takes on a Heinlein-like implied death sentence.

"This is Mr. Taggart, our Chief Engineer."
"What does a Chief Engineer do?"
"Well, if something goes wrong with the reactors that can't be fixed from here, the Chief puts on a heavy duty space suit and goes outside to fix the problem. Then Mr. Corcoran here becomes Chief Engineer."

 

[rust]

For at least some ships even radiothermal generators could be an option -
no moving parts, no maintenance, no repairs.

 

[DFW]

For at least some ships even radiothermal generators could be an option -
no moving parts, no maintenance, no repairs.

Remember, our current fission PP's only convert 10% of energy to power. We only use the IR emissions. As we have with alpha & beta, we will eventually figure out how to convert the remainder directly to usable power. Thus, PP's 1/10 the current size for the same output...

 

[billclo]

I looked into putting fission power plants on my capital ships. In my "navy" ships are fuelled for 4 weeks power plant endurance, and as such, fission power plants (even though at double-size minus TL size reductions) make great sense.

In a ship that only has 2 weeks powerplant fuel, it didn't make sense.

Though to reduce the chance of damage and contain radiation, I would suggest strongly requiring armored bulkheads for fission powerplants.

Example:

A TL15 (25% weight reduced) fusion plant = 13125 tons. 4 weeks fuel = 17325 tons, total = 30,450 tons.

A TL 15 (25% weight reduced) fission plant = 13125 tons x 2 (fission penalty) = 26250 tons, savings of 4200 tons (13.79%)

The ship would still need to refuel normally for using the jump drive, but it allows a major reduction in weight for the powerplant + it's associated fuel).

 

[billclo]

I ran some numbers, concerning fission vs fusion powerplants on warships.

Case 1: Fission vs Fusion, 1 power plant level 6.
Fission= 13125 tons x 2 = 26250
Fusion = 13125 tons + 4 weeks fuel (17325tons) = 30450 tons.
In this case fission is the better bet by 4200 tons (13.7%)

Case 2: Fission vs Fusion, 1 power plant 6, with a Powerplant-4 backup system.

Fission: 26250 tons + 15750 tons = 42000 tons
Fusion: 13125 tons + 7875 tons + 4 weeks fuel for primary 17325 = 38325 tons.

If you assume that the backup fusion plant can use the fuel intended for the damaged primary, then fusion wins in this case by 3675 tons (8.75%).

Case 3: fission vs fusion. Primary powerplant is fission, backup is fusion with 4 weeks fuel).
Fission: 26250 tons + 7875 tons + 10395 (fuel) = 44520 tons.
Fission: 26250 tons + 7875 tons + 5198 (2 weeks fuel) = 39323.

So it's looking like for a single powerplant ship, fission wins on tonnage, and in a multi-powerplant ship fusion does.

This ignores cost of the respective powerplants.

Anyone have a comment?

 

[BFalcon]

One thing that does interest me on this is also the running cost... how often do the fission plants need refuelling and with what radioactive isotopes (and hence what's the fuel costs, risks and downsides (eg radioactive leaks rendering parts of the ship prone to suited access only) of using them) compared with the free fuel (unless you're in a hurry or desperate and need to buy it in) of the fusion...

And if anyone comes up with exotic isotopes, please reference research so that we can learn about them ourselves... not all of us are scientists.

 

[DFW]

And if anyone comes up with exotic isotopes, please reference research so that we can learn about them ourselves... not all of us are scientists.

Here's one that lends itself to civilian use in Trav:

"Another safe alternative involves swapping out uranium with a similar radioactive material known as Thorium. The naturally-occurring metal element has been researched as an alternative to uranium as early as the 1960’s right here in the U.S. at the Oak Ridge National Laboratory. The material alone can’t be used to sustain the chain reaction process known as nuclear fission, but can absorb slow neutrons to transform into U-233, an artificial version of uranium that is fissile.

Proponents of the technology often cite a whole host of reasons that makes thorium a more attractive fuel source than uranium. Some of the major advantages include:

Thorium is a lighter than uranium and leaves behind less radioactive waste. Also, the waste would only remain radioactive for 500 years whereas Uranium byproducts have toxic properties that last upwards of 10,000 years.
Unlike Uranium-fueled power plants, the thorium fission processes don’t produce plutonium, a byproduct that has raised nuclear weapon proliferation concerns in the past.
Most scientific estimates suggest that Thorium is three to four times more abundant than uranium.
But more importantly, the fact that thorium undergoes an entirely different fuel cycle lends itself to nuclear reactor designs that are also safer.

One such system, known as Accelerator Driven System, does away with uranium and plutonium altogether. Originally proposed by Nobel laureate Carlos Rubbia, ADS initiates the fission process by using a particle accelerator that shoots protons at a lead target to cause it to release neutrons as a way of kick-starting the thorium fuel cycle.

This kind of “sub-critical” reactor design, which differs from other reactors in that it requires neutrons from an outside source, essentially allows for an off-switch. Turn off the particle accelerator and the fission process is brought to a whimpering halt."

http://www.smartplanet.com/blog/thinking-tech/a-meltdown-proof-nuclear-reactor-may-alleviate-fears/6494

 

[BFalcon]

DFW: thanks... hmm... if it needs a particle accelerator, though, that would take up some room wouldn't it?

Mind you, I'm sure that with gravitic technology, they'd know how to accelerate neutrons quicker than we do...

 

[DFW]

DFW: thanks... hmm... if it needs a particle accelerator, though, that would take up some room wouldn't it?

It would be part of the total tonnage. Remember, it's not the weapon but, simply a "trigger" device.

 

[BFalcon]

I know - just thinking about how large particle accelerators are nowadays... like I said, TL bonuses...

 

[rust]

I know - just thinking about how large particle accelerators are nowadays... like I said, TL bonuses...

Looking at the particle accelerators used, for example, by hospitals for
the proton therapy of cancer patients, I think even today 1 dton would
be fully sufficient for a particle accelerator used as a trigger for the kind
of power plant described by DFW.

 

[BFalcon]

Cool

I know that neutrons have a fair bit of mass, that's why I had my doubts... that's all.

 

[TC]

In my TU, fission is favored by some. At any tech level that has Damper technology, the fuel doesn't need to be particularly reactive, the damper tech allows it to be while its on. More particularly, using damper tech, any fuel remains would possibly have been rendered totally inert. High efficiency indeed.