AMA (Ask Me Anything) #1

Some replies to questions posed so far, in the previous comments thread (and one on Twitter). Disclaimer: These are my personal opinions and/or represent my synthesis of the evidence I’ve seen. Caveat emptor.

Hank Roberts: Thoughts about proposed small nuclear reactors, please.

Difficult to licence, especially in Western markets. This is why the designs for the first-of-a-kind deployments will resemble small versions of monolithic light water reactors, whilst still embracing some of the innovations that come with being, well, small. NuScale is the current front-runner. SMRs are currently uneconomic, being caught in a Catch-22 situation. In theory, they might be cheaper and faster to build than large LWRs, if one settled on a standard design and made them in a tooled-up factory. But until the bulk orders are flowing, such factories are hard to justify and finance. Unfortunately, everyone wants to build the second one.

Bernard: I’d be interested in updates on economics of various energy sources, given the changes over the past five years. I also keep seeing/hearing people talking about CCS at work, and they seem to have rather, um, optimistic outlooks on that technology…

The default outlook on all emerging-energy technologies is too optimistic. Everything is going to take much more time than the new-energy Pollyannas would like to think. Vaclav Smil’s point, in a nutshell, has always been that energy transitions take way longer, and are more expensive, than the optimists/promoters of the day would hope. I used to think he lacked vision. But the past five years have proven him right. The next five will too.

Juho Laatu: Why has no country and no party taken (or even promoted) serious concrete steps to solve the obvious and imminent problems?

It’s in the self-interest of individual nations to be a technological- and economic-policy late movers (on energy transitions), and the required global cooperation is really hard to lock in. So few move, and those that do go slowly, or do it for other reasons (e.g., energy security). The impact of climate change is becoming more obvious each year, but it still doesn’t seem imminent to enought people, because most change is not threshold like, but is incremental. And the potentially nasty threshold-like impacts (e.g., tipping points for climate feedbacks) haven’t happened yet.

Pat Cassen: I would like to see an assessment of the issue described in this recent article in Science on the NuScale SMR passive cooling system.

Passive cooling systems are one of the big technological benefits of SMRs in general. They’re innovative for water-cooloed reactors, and transformative for liquid-metal or -salt cooled reactors. The Science article is here. As you can see from this diagram, the whole reactor is submerged:

NuScale’s case for how the passive cooling works is described in detail in the linked article. The critique, Edwin Lyman, is a go-to academic devil’s advocate on advanced reactors. His assertion amounts to the argument that it is irresponsible to claim safety benefits until the design is actually confronted by a real emergency. This has some merit, and I suspect they’ll have to do this with their demo reactor. Note that this was already one for EBR-II, the prototype of the IFR, and it passed with flying colours.

Paul Dalby: what is your best guess on where global temperatures will end up before we reach some sort of new equilibrium. Not what you hope, what you think is most likely.

The fast-feedback climate sensitivity seems to be in the range of 2.8 to 3.5 celsius (the range over 26 models in CMIP6 was 1.8 to 5.6 C). Ultimately, slow-feedbacks might double this, but will be, well, slow (multi-millennia). Bending the global CO2 emissions trajectory to a negative slope will take many more decades, such that I expect atmospheric CO2e of 550-600 ppm by 2100. That suggests a planetary heating of 3 to 5+C above pre-industrial. I doubt we’ll see this though, the impacts would be too severe to countenance. Instead, I’m persusaded by David Keith that we already have the capability of turning down the global-climate thermostat with geoengineering, cheaply and efficiently — most especially solar radiation managenent— albeit with undesirable side-effects. In theory, a nation (or even a multinational corporation) could do this, unilaterally. A great hope is that we’ll find cost-effective and scalable ways of CO2 draw-down too.


By Barry Brook

Barry Brook is an ARC Laureate Fellow and Chair of Environmental Sustainability at the University of Tasmania. He researches global change, ecology and energy.

10 replies on “AMA (Ask Me Anything) #1”

Re solar geoengineering — I noticed recently when the San Francisco Bay Area had its two “orange sky” days that people with solar photovoltaic panels were reporting zero power. I assume that means the PV panels were not tuned for energy from orange to red light.

What’s projected to happen to photovoltaics if high altitude geoengineering is instituted? And, er, what happens to land-based astronomy, for that matter?


Barry – Thanks for your response re: NuScale passive cooling.

The Science article is somewhat confusing in that it states “When the boron-poor water re-enters the core, it could conceivably revive the chain reaction…”, but the boron never leaves the core. So the reaction remains moderated despite the loss of some water. I am left with the impression that the critique involves a mixing issue, but that is not clear.


I love that you mentioned Dr David Keith. He raises alarms that we shouldn’t cancel all our heating or we could end up with almost as many negative side effects as we’re trying to prevent. (Cooling of the Indian Ocean = radically cutting the Indian Monsoon – and resulting water scarcity for a billion people!) But he says there is probably a sweet spot at cutting about half our warming to give us a few extra decades. Some have even suggested mainly dumping the SRM (Solar Radiation Management) dust over the Arctic and Antarctic to try and reduce local temperatures a bit more – even though the dust would eventually spread globally. It’s encouraging to think that we could refreeze the Arctic circle and fortify that Siberian permafrost. Dr David Keith in this piece:


Harking back four years, I recall a claim that South Korea was operating coal fired power stations and, presumably, light water reactors of similar capacity. It was reported that the whole of life costs including decommissioning indicated a cost benefit for the nuclear power stations.
Secondly, the higher operational temperature of liquid salt or liquid metal cooled reactors results in a very much higher thermodynamic efficiency than for light water reactors.
Thirdly, the nine year Argonne laboratories research programme which led to the IFR proposal, was surely powerful proof of the operational safety and operating efficiency of liquid metal and liquid salt called reactors. Obviously the USA decision in 1999, not to proceed with these reactors and indeed with the IFR project, was motivated by the desire to extend the life of the coal mining industry. More recently, Donald Trump bought electoral support by offering to turn back the clock in Kentucky and West Virginia.
Fourthly, I understand that generation four reactors may be designed to be intrinsically safe. In normal operation, sufficient neutrons are released to produce the required thermal output. The reactor is designed so that the fuel elements expand if there is an increase in temperature, which will result in physical separation of the fuel, so that reactor activity reduces. Thermal runaway is impossible.
Fifthly, three SMR’s, each of 350 MW capacity, would very neatly replace the 1000 MW capacity of the two coal-fired power stations, which are to be decommissioned at Liddell in the Hunter Valley. There is no such thing as a free lunch. Whatever we do we have to pay the piper, in licensing fees. We have a manufacturing capacity and technology to build SMRs for a world market, and to establish the necessary fuel reprocessing facility. Give all those public servants at ANSTO a purpose in life! Post-pandemic, we must rebuild Australian industry and the economy, with new ventures and new world markets;
Changing the topic: South Australia has bent over backwards to meet the long-term objective of 100% renewable energy sources. They have intermittent wInd energy and, during daylight, surplus solar energy. They have purchased a very expensive lithium ion battery bank, with capacity to supply the State’s energy needs for 30 minutes, in the event of another failure of the grid network. The battery bank is, of course, an admirable solution to the problem of short term fluctuations in demand. They also have gas-fired generating capacity. Why not use that surplus renewable energy, to produce hydrogen by the catalysed electrolysis of water, and use the hydrogen to augment or replace supplies of natural gas? Not so long ago, every town had its own gasworks, manufacturing producer gas and water gas from coal. The gas was stored in large low pressure gas holders. We could pre-empt a future hydrogen energy system by using the pure hydrogen, through fuel cells, to power our heavy transport.
On the subject of battery storage, why do we persist in making use of lithium ion batteries? They are lightweight and so are very suitable for mobile applications. But sealed lead acid batteries have a similar, 10 year life, and can be manufactured in Australia at 20% of the cost of lithium ion technology. Sealed lead acid batteries have been used for many years in every telephone exchange in Australia.


Be careful about prognostications re Liddell Power Station. Many different capacities have been cited for it.

Here’s my understanding:
Commissioned from 1971, as 4x500MWe coal fired units.
Sold by NSW Gov to AGL late teens, 2010’s. Still 4x500MW, but soon reduced to operating normally at max 440MW but registered with AEMO at 4×500.
Reason: Probability of tube leaks.
Announced 1000MW “replacement” proposal from AGL, echoed variously by politicians and other pundits.

That 1000MW has been an elusive beast, but appears to be part gas, part PV, part batteries (which are not generators), part hydro. Some (most?) will not be on the same site or even in the same state.

What a mess! The capacity remains 4x500MW.

For comparison, LD’s best year was 2009, 11,586 GWh, ie 1300+MW 24/7/365.

That equates to 2000MW, @ 66% EF for a full year.

Replacement? I still don’t know what that means in a world of slippery definitions. It isn’t an SI unit.


In “Plentiful Energy“, the meaning of the word “pyroprocessing” changed as the history of the reactor evolved. Nowadays, rather than using* the term “pyroprocessing”, might we be less ambiguous to refer to the two separate concepts “melt refining” and “electroprocessing”? Melt refining was used on production scale in the EBR II to reprocess about 30,000 fuel pins. (“Plentiful Energy” page 170). The much more efficient electroprocessing was planned for the IFR and only reached laboratory scale proof before termination of the project. Electroprocessing is integral to the IFR concept in that it allows complete on-site recycling of the actinides, unlike melt refining.

(* e.g., As in Silver buckshot or bullet: is a future `energy mix’ necessary?)


Hi Roger,
do both processes collect all the actinides together – without selecting for specific bomb-grade purities? That is, the stuff collected can burn in a reactor but not go boom? That was my impression from Prescription for the Planet.


I was reading your paper at and came across a point I’ve made many times, referenced to footnote 67. I followed that and found the source paper which was published November 2010.

My own blog post on the same subject? Published the month before.
It’s way too much to think that they were reading The Ergosphere for inspiraton, but they were probably writing their piece at about the same time. Talk about riding the same wave.


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