Question for the designers on 2300AD-Fission core lifetimes

feld

Banded Mongoose
Why do fission cores need to be replaced every five years?
Is their a game balance reason?
I ask because 2300AD ship power plants are on the same order of magnitude output power as modern naval plants and most of those have lifetimes upwards of 20 years now.

I suppose you could say that stutterwarp ships operate at max power a larger fraction of their lives than naval ships…
 

2300AD4ME

Mongoose
I actually came to this board to learn about changes in the editions beyond Traveller 2300 and 2300AD. Perhaps this is one of those changes. In the original, both Fusion and Fission power plants had fuel you never had to change out. Honestly it's not that much of a game changer no matter how you go about it. I'd say just do whatever works best in your game.
 

feld

Banded Mongoose
I realize now I was unclear. Please let me restate. I was asking the designers why they made the choice. My apologies for the confusion my poorly worded question has caused.

Welcome to the community though and I’m sorry I don’t know the differences between the two systems well enough to be able to confidently describe the changes for you. I read your post with interest and look forward to someone more knowledgeable than I answering it.
 

Colin

Mongoose
Given their very compact nature, it felt right to have a limited lifespan on the usable fuel loaded into a starship fission plant. It could easily be stretched to 10 years, or even 20. Keeping it at 5 years means that it is something Travellers would likely have to deal with in the course of the game that could provide a stress/conflict point.

It's partly a balance rule, but more a limitation on the small, compact (relatively-speaking) fission reactors carried on starships. Aside from their crew requirements, they are the most effective power plants in the game.
 

Sigtrygg

Emperor Mongoose
Which is a good explanation.

Another thing to consider is that as you are having your 5 year fuel change you can also have a thorough inspection of other ship systems.
 

Bryn the 2300AD guy

Banded Mongoose
feld said:
Why do fission cores need to be replaced every five years?
Is their a game balance reason?
I ask because 2300AD ship power plants are on the same order of magnitude output power as modern naval plants and most of those have lifetimes upwards of 20 years now.

I suppose you could say that stutterwarp ships operate at max power a larger fraction of their lives than naval ships…

It was two years in GDW, which is the life of a commercial reactor rod. That's pretty much the answer - it was two years because that's what it is in real life with a "normal" reactor.

Modern naval reactors do not use commercial Uranium. They use especially "poisoned" weapons-grade U (or Pu), which is far more difficult to produce and about 100 times the cost to make. The poison burns up at about an equal rate to the U, meaning the reactor maintains a constant burn rate for about 15-20 years of actual constant use with the most modern sorts (ship cores might have 30 year lives, but much of that is because the ships are not always underway). The small size of the reactor (compared to a commercial one) is a consequence of the weapons-grade fuel.

To all intents and purposes, "fusion reactors" in 2300AD had about the expected characteristics of a naval nuclear reactor running weapons-grade fuel, which could also have been made smaller.

There's no way of extending the life of commercial fuel.

If memory serves, Mongoose 2k3 reactors use Thorium, which, of course, isn't actually fissile. Thorium can absorb neutrons from Pu or U to generate U-233 (which is fissile) and other byproducts. A pure Thorium reactor is impossible, but molten core mixed P/U-Th reactors are possible. Such a reactor has the problem of all molten reactors - it can never be shut down or it will freeze to a solid mass like the Chernobyl Elephant's Foot. It is inherently far less efficient than a U reactor, and inherently the fuel element would need to be changed more often as a result.
 

Arkathan

Cosmic Mongoose
Bryn the 2300AD guy said:
Modern naval reactors do not use commercial Uranium. They use especially "poisoned" weapons-grade U (or Pu), which is far more difficult to produce and about 100 times the cost to make. The poison burns up at about an equal rate to the U, meaning the reactor maintains a constant burn rate for about 15-20 years of actual constant use with the most modern sorts (ship cores might have 30 year lives, but much of that is because the ships are not always underway). The small size of the reactor (compared to a commercial one) is a consequence of the weapons-grade fuel.

Naval Reactors for ships do not use Pu. They use refined U that prefers slow as opposed to the fast neutrons of the more common U isotope. Pu is for breeder reactors, mostly at places like Oak Ridge, far from water.
The USS Eisenhower was built in 1975 and lasted about 15 years before the first refueling, which included about 60% operations except for the year plus shutdown for a refit in drydock prior to the refuel.
 

feld

Banded Mongoose
Bryn the 2300AD guy said:
It was two years in GDW...

I'm sorry but I don't think this is true. In the GDW Star Cruiser Naval Architects manual page 3, Section 3 "FUEL" it says:

"All ships with MHD turbines or fuel cells for power plants will require fuel and fuel tankage. Fission and fusion plants have their fuel built into the drive, and that fuel will last the life of the drive."

I'm not aware of anywhere in the GDW canon that limits the life of anything we could call the "drive" (either the powerplant or stutterwarp) to two years. If you've got such a reference please point me to it as I'd like to get smarter.

Bryn the 2300AD guy said:
It was two years in GDW, which is the life of a commercial reactor rod. That's pretty much the answer - it was two years because that's what it is in real life with a "normal" reactor.

So the reactors I worked on were (like another poster here) naval and not commercial ... but I think we probably would do better than 2 years between re-fueling in 2300AD. At a minimum it'd be a nice way also to differentiate between your thorium (civilian) and uranium (military) cores. Re-coring a military unit ever 2 years is REALLY restrictive. Just ask the crew of USS NAUTILUS :)

Up to the designers but just giving you real world options...

v/r
feld
 

Condottiere

Emperor Mongoose
I believe the Washington is currently docked for refuelling, and it appears it's taking longer than it should, I think the current estimate is five years.

The Ford's reactors should have a longer range.
 

Bryn the 2300AD guy

Banded Mongoose
DG, 65:

Fission%20vs%20Fusion.png


What is not stated is how many fuel packages are needed. You can calculate it from RW data, and it's one package per 5 MW. A 15 MW fission plant requires 3 packages.

Costs are not given, because 2300AD was explicit players are unlikely to own a ship. See my post at https://2300ad-uk.blogspot.com/2022/01/2300ad-changes-2-trade-and-starship.html.
 

Arkathan

Cosmic Mongoose
Condottiere said:
I believe the Washington is currently docked for refuelling, and it appears it's taking longer than it should, I think the current estimate is five years.

The Ford's reactors should have a longer range.

That's how long the refuel and mid-life refit are taking, mostly due to COVID. Not how long the core lasts.
They rip out C&C and a lot of other systems to refurbish or upgrade. Think Movie 1701, but not as cool.
 

feld

Banded Mongoose
Bryn the 2300AD guy said:

Thank you. I am smarter. Any idea why the DG contradicts the Naval Atchitect’s Manual I quoted above? Reason I’m poking on this so hard is that, if you look at real aerospace papers and the open source SDI stuff it’s pretty clear that the GDW authors did their homework. Even in the 80s two years was pretty low for state of the art fission systems.

Edit:
Bryn…I think you should ignore or retcon that reference. The system described, while called “fission”, is apparently driven by “radioactive decay.” That’s not a fission power plant. It’s a radioisotope thermal generator. I can’t think of a fission fuel you’d actually ever want to use that decays that fast. I’ll go look at Thorium but it’s half life is in the billions of years. I’m 25 years from my reactor design courses..but I *did* take them. I think GDW goofed.

Turns out my copy of my reactor design text is at the office. I’ll try to check this tomorrow.
 

Bryn the 2300AD guy

Banded Mongoose
feld said:
Edit:
Bryn…I think you should ignore or retcon that reference. The system described, while called “fission”, is apparently driven by “radioactive decay.” That’s not a fission power plant. It’s a radioisotope thermal generator. I can’t think of a fission fuel you’d actually ever want to use that decays that fast. I’ll go look at Thorium but it’s half life is in the billions of years. I’m 25 years from my reactor design courses..but I *did* take them. I think GDW goofed.

Turns out my copy of my reactor design text is at the office. I’ll try to check this tomorrow.

The numbers are about correct for a reactor using standard uranium fuel, like a commercial power plant. They are orders of magnitude off for an RTG. Forgive GDW's imprecision.

I can remember trying to explain why RTG's were a bad power source. Essentially, they need specific synthetic elements (typically 238Pu), which are extremely difficult expensive and time-consuming to make. The starting material (237Np) is a byproduct of 239Pu production. Oak Ridge is running multiple breeder reactors with the aim of making 1.5 kg of it per year - enough for 810 watts (thermal) of RTG's. RTG's are approximately 5% efficient, with a theoretical cap of around 15%. In round terms, to make a 1 MWe RTG would need require 37 tons of decaying 238Pu, or approximately 25,000 years of current US production.

RTG's are great for something that requires 100 watts for a few decades, but essentially useless as power plants.

Naval reactors often use different material than commercial power plants. American and British reactors use highly-enriched U (HEU, i.e. weapons-grade at 93%+), as French reactors used to as well. The Russians used a middling grade (30-40%), and the Chinese and French (now) use commercial low-enriched U (LEU, ca. 5% for the Chinese and 10% for the French). The advantages of a well-designed HEU reactor is that they can last upto ca. 30 years before a core change, whereas LEU reactor core will have much shorter lifes.

The French went from HEU to LEU. They found no difference in performance of their submarines. The only difference was core life. Commercial fuel in a power plant lasts about 2 years when constantly running at fairly high power. This is, of course, how our starships will be running. Submarines don't dash about at full power, and so the fuel lasts longer. A French SSN gets about 8-10 years out of one LEU core (so the plant is averaging about 20% output over this time). Whereas a British or US submarine will get 20+ years out of a HEU core. However, stick that same reactor on a merchant running the reactor at high power most of the time (like an electricity supplier) then core life would shorten to ca. 2 years.

A nuclear powered merchant will need refuelling about every two years. A warship that spends much less time underway may have a significantly longer core life on the same fuel, because they aren't burning it as fast.

Fusion plants are stated to be sealed. The life of a fusion plant would depend on how much use it has. The fusion plant has to constantly operate to maintain containment, and the PP rating is essentially the maximum excess after housekeeping. Housekeeping is around a third of the total output by some back of the envelope calculations a while back, and so a 150 MWe plant is actually producing 200 MWe and consuming 50 MWe itself (say). So, running the plant at a usable 150 MWe is consuming fuel at twice the rate of 50 MWe. The life of the ship is dependent upon the amount of use it has gone through. The earliest fusion ships, the French Ypres class, are nearly the end of their lives after ca. 40 years service. Over time, the output of the reactor is likely to start dropping as the fuel becomes less abundant, but the housekeeping overhead is the same or higher. Fusion plants will likely start having lower outputs over time, and the Ypres being sold off may well be into that period.

Fusion powered merchants are likely to have a shorter life than warships, because they will be using full power much of the time. If the Ypres is coming to an end to her useful life after 40 years, assuming hard war-service, merchants would have around 20 years or less useful life.
 

feld

Banded Mongoose
Bryn,

Thanks for that! Now I think I understand how this choice was made. I’ll bite my tongue

For the record the telling part was your commercial argument and thinking more about all the various national non proliferation concerns in 2300AD. And the almost obsessive fear of nukes in the setting.

One question: why do you think GDW didn’t use LEU/HEU or Th/U to make a distinction between commercial and military fission reactors? They could’ve given players a nice restriction like you and Colin have suggested but still kept a more completely realistic tech base in the setting. I really liked that the current edition does the Th/U split.

I wouldn’t use the French SSN thing if you had to argue that again: the comparison looks good on the face of it but is really not valid. French and US SSNs don’t have remotely similar operations profiles. Any comparison between them I’ve ever seen in the open source inevitably leaves this out and it’s crucial to your argument.

V/R
feld
 

Condottiere

Emperor Mongoose
As I recall, the Soviets did have nuclear powered ice breakers.

As regards nuclear powered warships. as I understand it, the designers tend to pick what at that moment is most expedient or cost effective; I don't recall the French reasoning, but for the British and Americans it's to extend the lifetime of the platform.
 

Bryn the 2300AD guy

Banded Mongoose
Condottiere said:
As I recall, the Soviets did have nuclear powered ice breakers.

As regards nuclear powered warships. as I understand it, the designers tend to pick what at that moment is most expedient or cost effective; I don't recall the French reasoning, but for the British and Americans it's to extend the lifetime of the platform.

The French Navy used HEU procured from nuclear weapons production. When France stopped manufacturing warheads, the Navy either had to take on the enrichment plants themselves, or switch to a commercial supplier. They did the latter. The US is currently considering doing the same, as the supply of HEU left over from weapons production is running out. HEU production in the US was halted in 1992. Submarines and carriers are using legacy HEU.

The conversion is that one submarine reactor uses the same amount of HEU as ca. 20 nuclear warheads (half a ton).

The US is currently seriously considering converting to LEU for reactors, because they otherwise they need to build a new enrichment facility and start producing weapons-grade U again, which is extremely expensive, and is a proliferation risk. By about 2040, if no new production is made, the US will have used all its' available HEU.
 
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