<story><title>Nuclear startup Oklo gets thumbs-down from regulators</title><url>https://www.canarymedia.com/articles/nuclear/nuclear-startup-oklo-gets-thumbs-down-from-regulators-what-does-this-mean-for-next-gen-nuclear</url></story><parent_chain><item><author>Animats</author><text>Sodium-cooled reactors have a long and troubled history.&lt;p&gt;* Sodium Reactor Experiment (Leak, minor sodium explosion, decommissioned)[1]&lt;p&gt;* Monju Nuclear Power Plant (Sodium fire, never worked properly, decommissioned)[2]&lt;p&gt;There&amp;#x27;s even been a sodium fire at a solar plant, one of those big focused mirror systems.&lt;p&gt;Many of these new reactor designs are based on complex arguments that the worst-case accident doesn&amp;#x27;t require a huge, expensive secondary containment vessel capable of containing a major accident. That&amp;#x27;s a tough sell, since Chernobyl didn&amp;#x27;t have a containment vessel and Fukushima&amp;#x27;s reactors had ones that were too small. On the other hand, Three Mile Island had a big, strong containment vessel, and in that meltdown, it held, containing the problem. In all three accidents, the actual accident was worse than the design maximum credible accident.&lt;p&gt;The NRC is right to be skeptical of weak containment designs.&lt;p&gt;It&amp;#x27;s frustrating. The reactor designs that have worked reliably for long periods are very simple inside the radioactive portion of the system. 
Sodium reactors had leaks and fires. Pebble bed reactors had pebble jams. Helium gas-cooled reactors had leak problems. Molten salt reactors include a radioactive chemical plant. So nuclear power is stuck with water as a working fluid.&lt;p&gt;[1] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Sodium_Reactor_Experiment&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Sodium_Reactor_Experiment&lt;/a&gt;&lt;p&gt;[2] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Monju_Nuclear_Power_Plant&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Monju_Nuclear_Power_Plant&lt;/a&gt;</text></item><item><author>PaulHoule</author><text>I don&amp;#x27;t think it&amp;#x27;s a bad reactor but I looked at the application and it wasn&amp;#x27;t a good application.  (The NRC says the same)&lt;p&gt;There was a large amount of hand-wringing about the risk of avalanches and other natural disasters that were extremely low probability.&lt;p&gt;They were skimpy on interesting details about the reactor such as &amp;quot;What do you do if the sodium coolant catches on fire?&amp;quot;  (e.g. sodium burns in water,  sodium burns in air, sodium burns in &lt;i&gt;carbon dioxide&lt;/i&gt;)  There are good answers to that in the U.S. and Russian experience.  They don&amp;#x27;t draw on that experience to show they can solve it.&lt;p&gt;If they fix the application and submit it again it could get approved.</text></item></parent_chain><comment><author>PaulHoule</author><text>EBR-II and FFTF were 100% successful in the USA.  Russia has also had very good experience with fast reactors.  Sodium fires are a problem,  but fires happen in industrial facilities all the time,  you just detect them and then you put them out.&lt;p&gt;Monju had many things wrong with the design,  it was a loop-type reactor that nobody is talking about building anymore.  Also it was nowhere near adequate from a seismic perspective it is kinda shocking they were allowed to build it at all.&lt;p&gt;Water reactors have no future for the same reason nobody has built a coal plant since 1980.  The steam turbine and associated heat exchangers are unacceptably large and capital intensive compared to modern fossil fuel power plants based on gas turbines.  (Look at how huge the steam generators are for the PWR)&lt;p&gt;Even if the construction problems were solved for the LWR,  the economics will not work, you are better off capturing the carbon from a fossil fuel gas turbine plant and pumping it underground.&lt;p&gt;For nuclear power to be competitive we have to develop closed cycle gas turbine powersets.  The 1970s model was that a fast reactor would be more capital intensive than an LWR but with the CCGT advanced reactors could be possibly be competitive -- if we can develop the powerset and reactors that run at high enough temperatures (not water) to support the powerset.</text></comment>
<story><title>Nuclear startup Oklo gets thumbs-down from regulators</title><url>https://www.canarymedia.com/articles/nuclear/nuclear-startup-oklo-gets-thumbs-down-from-regulators-what-does-this-mean-for-next-gen-nuclear</url></story><parent_chain><item><author>Animats</author><text>Sodium-cooled reactors have a long and troubled history.&lt;p&gt;* Sodium Reactor Experiment (Leak, minor sodium explosion, decommissioned)[1]&lt;p&gt;* Monju Nuclear Power Plant (Sodium fire, never worked properly, decommissioned)[2]&lt;p&gt;There&amp;#x27;s even been a sodium fire at a solar plant, one of those big focused mirror systems.&lt;p&gt;Many of these new reactor designs are based on complex arguments that the worst-case accident doesn&amp;#x27;t require a huge, expensive secondary containment vessel capable of containing a major accident. That&amp;#x27;s a tough sell, since Chernobyl didn&amp;#x27;t have a containment vessel and Fukushima&amp;#x27;s reactors had ones that were too small. On the other hand, Three Mile Island had a big, strong containment vessel, and in that meltdown, it held, containing the problem. In all three accidents, the actual accident was worse than the design maximum credible accident.&lt;p&gt;The NRC is right to be skeptical of weak containment designs.&lt;p&gt;It&amp;#x27;s frustrating. The reactor designs that have worked reliably for long periods are very simple inside the radioactive portion of the system. 
Sodium reactors had leaks and fires. Pebble bed reactors had pebble jams. Helium gas-cooled reactors had leak problems. Molten salt reactors include a radioactive chemical plant. So nuclear power is stuck with water as a working fluid.&lt;p&gt;[1] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Sodium_Reactor_Experiment&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Sodium_Reactor_Experiment&lt;/a&gt;&lt;p&gt;[2] &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Monju_Nuclear_Power_Plant&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Monju_Nuclear_Power_Plant&lt;/a&gt;</text></item><item><author>PaulHoule</author><text>I don&amp;#x27;t think it&amp;#x27;s a bad reactor but I looked at the application and it wasn&amp;#x27;t a good application.  (The NRC says the same)&lt;p&gt;There was a large amount of hand-wringing about the risk of avalanches and other natural disasters that were extremely low probability.&lt;p&gt;They were skimpy on interesting details about the reactor such as &amp;quot;What do you do if the sodium coolant catches on fire?&amp;quot;  (e.g. sodium burns in water,  sodium burns in air, sodium burns in &lt;i&gt;carbon dioxide&lt;/i&gt;)  There are good answers to that in the U.S. and Russian experience.  They don&amp;#x27;t draw on that experience to show they can solve it.&lt;p&gt;If they fix the application and submit it again it could get approved.</text></item></parent_chain><comment><author>DennisP</author><text>Not all MSRs have the radioactive chemical plant, just the thorium-fueled ones. Several MSR companies are working on uranium-fueled versions; e.g. Terrestrial Energy, where the reactor core is a sealed can that gets swapped out every few years.</text></comment>