The description of this reactor, which involves robotic fuel handling equipment operating within the containment constantly moving around fuel elements immersed in molten sodium metal seems doomed to create difficult repair problems as these mechanisms will fail and now need to be replaced/repaired within the hot zone of the reactor. It's quite easy to build a system which technically works, but ends up being uneconomic. To my knowledge there has yet to be a successful long-term operating power generation design of any kind using sodium coolant; the Monju plant in Japan was a failure largely because of problems with the coolant loop (including a leak and serious fire). Until these basic engineering issues are proven to be solved, the fuel physics seem kind of beside the point.
PITA factor is "Pain in the Ass" factor and refers to technologies that look great on paper but explode into a fractal of non-obvious design and operational difficulties when put into practice. He used the term to refer to hydrogen as rocket fuel for example.
Also surprising how even Bill Gates gets ignored on this issue. He's talked repeatedly about why nuclear, yet doesn't get a lot of traction.
The misconception is that wind and solar are able to replace fossil fuels. They can't as of now, that's just the unfortunate reality. They're a good supplement, but they don't produce 24/7, don't recycle well, take up tons of space, and batteries are orders of magnitude too expensive to be a complete solution. See the video I linked to where Gates explains this.
Instead, batteries would be used for short term leveling (diurnal, perhaps a few days). Beyond that, leveling would be by demand dispatch, transmission, dispatchable demand, and long term chemical storage (for example, hydrogen or ammonia). In the shorter term, covering the last 10% with natural gas would be workable, even if the CO2 had to be captured and sequestered.
Seriously, watch Bill's response to this and I'd be interested if you or anyone has a better answer: https://youtu.be/d1EB1zsxW0k?t=520
You might say "nuclear is only $110-180/MWh!". But that's for every MWh that nuclear pumps out; batteries are only on the hook for (some of) the times wind and solar aren't covering demand. So the levelized cost of stored and direct power from renewables will be cheaper.
Batteries are also declining rapidly in cost. Any nuclear plant started today will come online when storage costs could be half of what they are today, if this trend continues.
I will add that DC-coupled storage in PV fields should be cheaper than this, because the batteries don't need their own inverters or grid connection.
Tokyo has less cars per household than many Japanese cities but there's still about 3 million of them.
If those cars each had a 50KWh battery then that would be enough power to run the city for about 1/3rd of a day.
But since replacing all the ICE cars with electrics is forecast to save money and lives and help make cheap renewables even cheaper, it seems like they could work something out to tap into that when necessary and have solved a fair chunk of the problem without spending any money (in fact saving quite a lot which they can put towards this problem).
For some values of "best". There is no such thing as a one-size-fits-all power source.
We will eventually need to increase the fission base, if fusion continues to be 10 years away for much longer, but that's something that can wait until we have better designs than the current generations.
What nuclear really excels at is at replacing coal. It's pretty much a plug-in replacement: nuclear generation can be built pretty much wherever coal can and, from the grid's perspective, it looks a lot like coal. This, along with industry subsidies (both direct and as military expenditure) has always shifted economics towards it.
> What nuclear really excels at is at replacing coal
Coal is being displaced, but not by nuclear. Nuclear is actually rather bad at displacing coal. People were building coal fired power plants for decades when they could have been building nuclear plants, because nuclear failed at being attractive enough to replace coal.
BTW, burning coal for energy should be considered a crime against humanity. It should be replaced by anything, regardless of energy output ;-)
As for constancy... this is actually a negative for nuclear, since the business case for nuclear assumes it can sell its output at a high average price, 24/7. And increasingly that market isn't there.
Agreed about the current market factors, but constant is easier to manage.
Of course, this will be at an energy usage that is so incredibly high that it has no relevance to anything we do today. So it's a silly point of no relevance to current decisions.
 That’s not to suggest the right has embraced science by denying climate change is happening. As far as I can tell, the right’s solution to climate change is “god won’t let anything bad happen.” The left’s isn’t any better or more realistic. I’m at a Costco in the Maryland exurbs. A hugely diverse crowd (black, Hispanic, Asian, white) is doing their weekend shopping. Families with 2+ children in tow. No joke, some just shouted out “living the suburban dream” while we were eating froyo. Then they’re going to get into their SUVs and go home to their, on average, 2,000+ square foot house.
The idea that we’re going to solve climate change by having all these people move to 500 square foot apartments in the city, going only where the government decides to build public transit, and limiting themselves to one kid, is utter fantasy. In fact the opposite will happen. Chinese, Indians, Bangladeshis, Africans... they’ll get Costco and SUVs. Hoping otherwise is just as unrealistic as thinking God will fix things.
And given the dearth of new nuclear in the us, safely bringing up a reactor, if we started building tomorrow (ignoring the political challenges of where), would take the better part of a decade to be operational. Solar and wind brings faster returns.
Really we just need to stop subsidizing coal and similar.
I tell you what: if someone wants nuclear spacecraft, let THEM pay for it.
(BTW, the reactors in power plants would be useless for spacecraft.)
(As it is, China will ship us subsidized solar while developing thorium technology itself, enabling it to become the dominant technological superpower.)
The most powerful space nuclear reactor ever launched, the Soviet Topaz-I, had a specific power of 16 KW(e)/kg.
The PV system on the NASA Juno spacecraft, at 1 AU, had a specific power of 50 kW(e)/kg.
Perhaps you are talking about aspirational PowerPoint engineering nuclear concepts (and ignoring similarly advanced PV concepts), or maybe systems operating in the outer solar system. But otherwise, no, solar has the weight advantage over nuclear, not the other way around.
Your claims there with respect to terrestrial energy production are not justifications for nuclear. Wind and solar are much cheaper than nuclear, and rapidly getting even cheaper.
Took direct presidential order to dismantle the project and essentially bury nuclear space propulsion.
That said, US Congress did fund it, on a rather non-pork-barrel project, even. It just happened to have enmity pf Nixon's administration, to the point that they arranged for NASA to scrap Space Nuclear Propulsion Office and laid off everyone involved, despite 100m budget and the project being well on track.
Practically speaking, better solar will be more helpful to spacefaring than better fission.
Things are different in Canada, and that's why reactor startups like Terrestrial Energy are making good progress there. But the U.S. DOE has a lot of infrastructure that could really help.
> However, in January 2019 it was announced that the project had been abandoned due to technology transfer limitations placed by the Trump administration.
Elon Musk decided big disposable rockets where just not worth building - well big thermo-electric plants are just not worth building. Solar and wind are the paradigm change in power generation, any Manhattan project would be crazy not to focus on them now and supporting technologies.
 https://news.ycombinator.com/item?id=21156408 - "Global groundwater extraction a ticking time bomb”
So I don't think "running out of water" is a valid concern here. (Though some plants have had issues from lack of water flow in rivers, that's more a temperature issue than a lack of water one)
Its big resource intensive thermoelectric generation, with or without unlimited fuel source.
The powerplant requires a cold reservoir to discharge heat, as does any heat engine. Cooling towers that evaporate fresh water are one of several methods for doing that.
Coastal powerplants use seawater to discharge heat.
Reactors in megawatt range usually use passive cooling and air cooling, you could operate them in the middle of sahara.
That is untrue. They have the same cooling requirements as all thermoelectric power plants do, and some like eg. Diablo Canyon do straight up boil water away. Others heat up lakes or coastlines - which costs (more plant, land and maintenance) and can only be done in some places . Plants cooling requirements are a big part of their overall cost, even with the legacy environmental protection which has led to our current crises.
 - https://www.ucsusa.org/clean-energy/energy-and-water-use/wat... Types of cooling
( https://iopscience.iop.org/article/10.1088/1748-9326/7/4/045... )
I think the overall thrust of your post is in general agreement with mine - reactors have to discharge heat into seawater, or use cooling towers which evaporate water.
This the issue is of correctly designing the cooling of, and sighting of, the powerplant.
Furthermore, this is not an inherent quality of nuclear power, it's a product of deploying it in the form of >3000 MWt power-plants.
If we adopted the approach of small module reactors, they can be passively cooled.
> Furthermore, this is not an inherent quality of nuclear power
I never suggested it was - although nuclear plants due to having more complicated safety requirements than other thermoelectrics, do tend to have lower thermal efficiencies and higher cooling costs per energy unit produced.
My point was those costs are significant at any practical scale of generation. The heat output itself of thermoelectric plants can be environmentally significant, so the idea of reactor breakthroughs promising "unlimited" generation is, well, its basically a marketing line, for research funding.
Not to mention, fast reactors like the TWR can destroy the nuclear waste that people claim to be so worried about.
Waste is a solvable problem.
Though, there will be no way to turn it off until Cf burns out.
Let's suppose we have a just barely subcritical reactor with k = .99. Then, you're going to need about 1% Cf in the core to sustain a chain reaction.
The core of a 1 GW reactor contains about 100 tonnes of fuel, and fissions maybe a tonne of fuel per GW(e)-year. So, at k = .99, it would consume 10 kg of Cf per year. At current market prices this would cost $270 B/year, assuming even that much Cf were available.
It would be BY FAR cheaper to provide the neutrons to drive a subcritical reactor by means of an accelerator, rather than with californium. 1 GeV protons on a uranium target will produce about 60 neutrons per proton, from spallation and fast fission. This sort of scheme has been repeatedly investigated, but has no sufficient advantage over conventional reactors to justify the extra cost and complexity.
If you have an intense neutron emitter dispersed in fuel + moderation + reflectors you should be able to go with much lower k to generate a meaningful amount of power.
You should me able to go down to single grams of Cf per megawatt. Yes, not that economical, but at least possible for things like reactors for space use and such. At that price, that will be cheaper than current RTG material.
Correct me if I am wrong.
The energy of the Cf neutrons doesn't matter much, since after that first generation the neutrons will be ordinary U fission neutrons.
The comment about moderators/reflector is silly, since the purpose of those is to make k higher. One you know what k is, they are irrelevant.
The ratio of Cf burned to (Cf + U) is 1 - k, so unless k is very close to 1 you are going to use a hell of a lot of Cf. But if Cf is very close to 1, you need to control it anyway as fuel burns up, so you might as well just go critical. Cf buys you nothing.
It will also require regulation over the years as Cf burns out, and u238 fast fission products themselves product less neutrons than fission products of thermal neutron reactors.