The main concern of US and EU authorities with respect to RBMKs and VVER-440s was the lack of a containment structure and the inability to contain the consequences of a loss of coolant accident (LOCA) or reactivity insertion accident (RIA), i.e., a core disruptive accident. Vessel embrittlement (somewhat related to LOCA) is another concern.

Another concern with respect to the RBMK is the positive void coefficient, which was a critical factor in the Chernobyl accident. "Reactors cooled by boiling water will contain a certain amount of steam in the core. Because water is both a more efficient coolant and a more effective neutron absorber than steam, a change in the proportion of steam bubbles, or 'voids', in the coolant will result in a change in core reactivity. The ratio of these changes is termed the void coefficient of reactivity. When the void coefficient is negative, an increase in steam will lead to a decrease in reactivity."
Yes this is a known fact about the lack of containment for RBMK's and the positive void coefficient, although after 1986 all existing RBMK's were retrofitted to decrease void coefficient and increase safety systems and make sure workers cannot make such blatant mistakes as before.
That being said then in 2011 Fukushima happened , quite frankly can we even calculate the risk of a well maintained and retrofitted RBMK having a destructive event VS any other Gen 2 reactor in operation even with a containment?

I do realize the RBMK flaws and any way we slice it it's history and no new block will ever be built.

Astronuc
Staff Emeritus
British engineering group Rolls-Royce has announced the establishment of a new business - Rolls-Royce SMR Limited - for the deployment and commercialisation of its small modular reactor (SMR) technology. The announcement follows the securing of GBP210 million (USD285 million) in funding from the UK government, matched by more than GBP250 million of private investment.
https://www.world-nuclear-news.org/Articles/Rolls-Royce-secures-funding-for-SMR-deployment

There are 3 main thrusts in the nuclear power (reactor) industry at the moment: 1) large power reactors (ostensibly for base load), 2) small modular reactors (SMRs), and 3) microreactors for remote areas or mobile deployment. The splits are based on MWt/MWe and/or mass of fissile content in the core. Almost all proposed commercial designs use straight UX as opposed to U,PuX or U,ThX, where X is some other element(s), e.g., O2, N, C, Si, CO, Zr, Mo, . . . .

Astronuc
Staff Emeritus
Long derided as a prospect that is forever 30 years away, nuclear fusion seems finally to be approaching commercial viability. There are now more than 30 private fusion firms globally, according to an October survey by the Fusion Industry Association (FIA) in Washington DC, which represents companies in the sector; the 18 firms that have declared their funding say they have attracted more than US$2.4 billion in total, almost entirely from private investments (see ‘Fusion funding’). Key to these efforts are advances in materials research and computing that are enabling technologies other than the standard designs that national and international agencies have pursued for so long. I remember when commercial fusion was 10 years down the road. Then a decade later, it was still 10 years down the road. Forty years later, it may be 10 years about - maybe. The latest venture at Culham — the hub of UK fusion research for decades — is a demonstration plant for General Fusion (GF), a company based in Burnaby, Canada. It is scheduled to start operating in 2025, and the company aims to have reactors for sale in the early 2030s. It “will be the first power-plant-relevant large-scale demonstration”, says GF’s chief executive Chris Mowry — unless, that is, its competitors deliver sooner. We'll see as things heat up. russ_watters I remember when commercial fusion was 10 years down the road. Then a decade later, it was still 10 years down the road. Forty years later, it may be 10 years about - maybe. It's easier to just say it's 30 years away , because then you have to say it less often. And after almost 30 years people might even forget you have ever said so...It's more convenient that way. Mentor I remember when commercial fusion was 10 years down the road. Then a decade later, it was still 10 years down the road. Forty years later, it may be 10 years about - maybe. According to the article the standard wisdom is now 30 years. It seems like as time goes by it gets further away. Unless one of these startups succeeds. If these projects hold significant promise, why are we bothering with ITER? Because nobody knows if they hold promise, because they are being done under a veil of secrecy, away from the skeptical eye of the scientific community. Smells fishy to me. Bystander Dale Mentor 2020 Award Unfortunately for the fusion power crowd, even 10 years from today for a first viable prototype is probably effectively too late. We are at a point where there is a recognized global need for clean power at the same time that global energy demand is increasing as existing 3rd world countries modernize their economies and global populations are still rising. As the 3rd world modernizes, their population will stabilize as will their demand for energy. At that point the global energy infrastructure will probably already be largely “clean”, so the demand for new clean energy technologies will drop. I don’t see how a power technology that is still in early development today will play any major role in the future. The economic opportunity is now and technologies that are available now will be used now. That said, it is sad that fission will probably be reduced for largely political reasons at this time when it is a well proven technology that could really help with simultaneous power decarbonization and power expansion. Astronuc Staff Emeritus Science Advisor If these projects hold significant promise, why are we bothering with ITER? Because nobody knows if they hold promise, because they are being done under a veil of secrecy, away from the skeptical eye of the scientific community. Smells fishy to me. Inertia of large projects. Back in April 2018, 3.5 years ago. https://physicstoday.scitation.org/do/10.1063/PT.6.2.20180416a/full/ Mentor Inertia of large projects. What I'm asking is if there really is any significant confidence that any of these private reactors will succeed. Remembering Lockheed's effort: The project began in 2010,[6] and was publicly presented at the Google Solve for X forum on February 7, 2013. In October 2014, Lockheed Martin announced a plan to "build and test a compact fusion reactor in less than a year with a prototype to follow within five years".[7] In May 2016, Rob Weiss announced that Lockheed Martin continued to support the project and would increase its investment in it. https://en.wikipedia.org/wiki/Lockheed_Martin_Compact_Fusion_Reactor#History Still waiting for an announcement that the 2015 test succeeded. If these projects hold significant promise, why are we bothering with ITER? Because nobody knows if they hold promise, because they are being done under a veil of secrecy, away from the skeptical eye of the scientific community. Smells fishy to me. Exactly , what is more interesting is that some of them (the private concepts) use the same methods just with different arrangement. I remember Lockheed made a lot of "hot air" with their design and somehow we don't hear anything anymore nor we see this technology being implemented into "secret military vessels". Oh I see you've beat me to it... When fission physics went silent back in the 40's , it wasn't for long when everyone knew why it had been so... A bright flash appeared over the horizon. At that point the global energy infrastructure will probably already be largely “clean”, so the demand for new clean energy technologies will drop. I'm not sure I would agree. I think there simply aren't that many "clean" energy options from a physics perspective to begin. I don't see how that situation will change anytime soon. Given energy consumption will increase beyond population increase (E vehicles etc) just goes to make this point stronger. Dale Mentor 2020 Award I think there simply aren't that many "clean" energy options from a physics perspective to begin. Why would we need more options? Given energy consumption will increase beyond population increase (E vehicles etc) just goes to make this point stronger. Increased consumption doesn’t require more options, simply more implementation of existing options. @Dale I simply meant to say that given our clean energy options without nuclear are not enough to cover our whole demand , nuclear will be on the table irrespective of how long from now. This equally applies to fusion I think, the moment it will prove itself viable economically it will see a market I think. Anything that gives something of real value has a market I believe. Astronuc Staff Emeritus Science Advisor A citation [7] from that article - https://news.yahoo.com/lockheed-say...fusion-energy-project-123840986--finance.html What I'm asking is if there really is any significant confidence that any of these private reactors will succeed. It's hard to say. Have they thought of something that others haven't? Or, have they realized a better piece of technology? I suppose they look at SpaceX, and think, "we could be the next SpaceX" of fusion/nuclear. There are something like 30 small startup groups looking at microreactors and medium or modular reactors. There groups like Terrapower that has transformed itself, teamed up with other like GEH, and received tens of millions of$ from the federal government to establish a demonstration plant. I believe X-energy is another recipient of federal \$.