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>The graphite tips were key to getting an RBMK to operate without either enriched uranium (expensive) or a fancy moderator (heavy water, likewise expensive.)

Wait a moment. Where's the source on this?

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Yeah, something the show didn't really mention was that Chernobyl Unit 1 had actually suffered a similar (but much less severe) incident a few years earlier. It was not just a known issue, it was a known issue on site! And still, hushed up and hidden.

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You know the surprising thing I learned today is that reactors can work without enriched fuel. I thought all reactors needed enriched fuel before they can work.

Most of the reactor control rods are inserted from above; 24 shortened rods are inserted from below and are used to augment the axial power distribution control of the core. With the exception of 12 automatic rods, the control rods have a 4.5 m (14 ft 9 in) long graphite section at the end, separated by a 1.25 m (4 ft 1 in) long telescope (which creates a water-filled space between the graphite and the absorber), and a boron carbide neutron absorber section. The role of the graphite section, known as "displacer", is to enhance the difference between the neutron flux attenuation levels of inserted and retracted rods, as the graphite displaces water that would otherwise act as a neutron absorber, although much weaker than boron carbide; a control rod channel filled with graphite absorbs fewer neutrons than when filled with water, so the difference between inserted and retracted control rod is increased. When the control rod is fully retracted, the graphite displacer is located in the middle of the core height, with 1.25 m of water at each of its ends. The displacement of water in the lower 1.25 m of the core as the rod moves down could cause a local increase of reactivity in the bottom of the core as the graphite part of the control rod passes that section. This "positive scram" effect was discovered in 1983 at the Ignalina Nuclear Power Plant. The control rod channels are cooled by an independent water circuit and kept at 40–70 °C (104–158 °F). The narrow space between the rod and its channel hinders water flow around the rods during their movement and acts as a fluid damper, which is the primary cause of their slow insertion time (nominally 18–21 seconds for the reactor control and protection system rods, or about 0.4 m/s). After the Chernobyl disaster, the control rod servos on other RBMK reactors were exchanged to allow faster rod movements, and even faster movement was achieved by cooling of the control rod channels by a thin layer of water between an inner jacket and the Zircaloy tube of the channel while letting the rods themselves move in gas.

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To answer the question of why they didn't have more safety features, likely money.

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More intensely at the poles, since the equator's typically too hot for bodies of "methanum" (that's what Atlas Pro coined to refer to liquid methane). In fact, despite Titan being a very cold world, most of the surface isn't cold enough for methane to condense into a liquid state, so the poles are typically where you'll find lakes of methanum.

That was my first thought as well, but I wonder—in the spirit of the question—wouldn't that just be rain?

(This is obviously for OP to answer, the rest of us can only guess as to their meaning.)

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“Back away from the reactor. It’ll save itself.” Navy nuclear power program.

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After the Chernobyl disaster all the current active RMBK were fitted with safety features and actual shielding in the walls. Better late than ever...

>Following the accident at Chernobyl, all remaining RBMK reactors were retrofitted with a number of updates for safety. The largest of these updates fixed the RBMK control rod design. The control rods have 4.5-metre (14 ft 9 in) graphite displacers, which prevent coolant water from entering the space vacated as the rods are withdrawn. In the original design, those displacers, being shorter than the height of the core, left 1.25-metre (4.1 ft) columns of water at the bottom (and 1.25 metres [4.1 ft] at the top) when the rods were fully extracted.[3] During insertion, the graphite would first displace that lower water, locally increasing reactivity. Also, when the rods were in their uppermost position, the absorber ends were outside the core, requiring a relatively large displacement before achieving a significant reduction in reactivity.[40] These design flaws were likely the final trigger of the first explosion of the Chernobyl accident, causing the lower part of the core to become prompt critical when the operators tried to shut down the highly destabilized reactor by reinserting the rods. The updates are:

>* An increase in fuel enrichment from 2% to 2.4% to compensate for control rod modifications and the introduction of additional absorbers.

• Manual control rod count increased from 30 to 45.
• 80 additional absorbers inhibit operation at low power, where the RBMK design is most dangerous.
• AZ-5 (emergency reactor shutdown or SCRAM) sequence reduced from 18 to 12 seconds.
• Addition of the БАЗ or BAZ* system,[41] (rapid reactor emergency protection) which would insert 24 uniformly distributed rods into the reactor core via a modified drive mechanism within 1.8 to 2.5 seconds.
• Precautions against unauthorized access to emergency safety systems.

>In addition, RELAP5-3D models of RBMK-1500 reactors were developed for use in integrated thermal-hydraulics-neutronics calculations for the analysis of specific transients in which the neutronic response of the core is important.[42]

>*BAZ button is intended as a preemptive measure to bring down reactivity before AZ-5 is activated, to enable the safe and stable emergency shutdown of a RBMK.

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Man. All you need are those blue and red cards and it’s like the series. ;)

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There is actually a surprisingly large overlap between two systems. Both CRISPR and AAV can be used for targeted integrations (by using site specific homologous regions to direct the HDR machinery). AAV can also be used for a random integrations and expression from long-term episomes.

The major differences between the methods are some of the more practical aspects rather than the actual repair mechanism; things like delivery methods, necessary components, penetrance in in vivo systems, etc.

Delivery/components: CRISPR requires the transfection or injection of multiple components (Cas Proteins, sgRNAs, tracrRNA depending on the organism, homologous repair templates, etc). AAV requires transfection of a multi-component virus which encodes all necessary machinery. Additionally CRISPR generally requires introduction into either a germ or progenitor cells so that the edit can be spread throughout the entire organism, or into a subset of cells (which is easy to do when they are in culture but nearly impossible to do in a living organism (yet!)). AAV is much easier to target a particular subset of cells to make edits (such as specifically transfecting lung tissue or organ; see gene therapy methods for treating cystic fibrosis in lung tissue).

Penetrance: See above. If either methods are used to edit germ cells, then the edits will be organism wide in the mature adult (ideally). On the flip side, mosaicism is nearly always unavoidable using CRISPR when targeting somatic cells in a living organism. There are some exceptions (see CarT therapy) where certain cell populations can be removed from the body, edited and returned. However for most cell populations there is no feasible way to edit them specifically and efficiently. There is also a chance of mosaic integrations with AAV but without examining particular cases it is difficult to say what the percentages would be.

Overall: CRISPR and AAV are comparable when editing germ cells. AAV methods are much better when targeting somatic cells in a living system such a patient require gene therapy. Hope this helps. Source: Post-doctoral researchers who utilizes CRIPSR frequently in my own research (specifically in the nematode C. elegans), and has dabbled in AAV methods in cell culture.

Linking AAV article for more specifics:

"The Role of Recombinant AAV in Precise Genome Editing" doi: 10.3389/fgeed.2021.799722 PMID: 35098210

To me this looks like the equivalent of having a car with just one pedal that handles both the acceleration and the braking depending on how hard you push down on it.

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