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Correct. Graphite is a stronger moderator than water.

So is deuterium, which is why CANDU reactors can use natural uranium.

A full power BWR has a void defect around 40% of your total reactivity. When you scram, those voids go away, and you recover all of that reactivity. Voids are dominant in a BWR. The rule of thumb is Doppler 10^-5, moderator temp 10^-4, void coefficient 10^-3. So you always have enough to start back up in a BWR. And actually, especially if it’s a fast restart, more xenon helps a lot with getting to target rod pattern as it’s one of the things that impacts thermal limits and PCIOMR.

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I've worked around BWRs but never been an operator at one (my fleet had a two unit station BWR, while the rest were PWRs.)

I stand corrected in that case. Does make perfect sense when you game it out, as you can basically put a shitload of positive reactivity into a BWR.

I have heard of situations similar to Chernobyl at naval plants (all rods out, waiting on xenon decay, below POAH), but again, that was all stories as I only operated new naval plants as well.

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So... You don't need to refine material to get nuclear reactors?

Wow. I did not know that. So by adding graphite, the hurdles with using normal uranium can be overcome?

The graphite blocks are the key.

The tips are there to help levelize axial flux tilt (get power more uniform across the core) in a safe manner… when done correctly (and by safe, I mean in a way that when executed as intended allows you to get enough power from the bottom 1/3rd of the reactor without risking other transient conditions causing core damage).

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Pretty much the design of the reactor. It doesnt use enriched uranium nor heavy water. So it has to have another source of moderation to get the reaction going from a less fissile fuel. Hence, graphite.

Yes, that’s why I wrote “in theory”. In reality, it isn’t that clean, even with modification.

Integration may not just be occurring at AAVS1, but all over the place. Studies have detected things like complex vector rearrangements and truncated vector genomes across multiple animals models inserted around transcriptional units. There seems to be no preference for gene coding regions and no clustering of integration sites.

In fact, The FDA had a CTGTAC meeting in 2021 to discuss these issues: https://www.fda.gov/advisory-committees/cellular-tissue-and-gene-therapies-advisory-committee/2021-meeting-materials-cellular-tissue-and-gene-therapies-advisory-committee

>If one bit of the RNA the virus injects, when read by the cell's machinery and assembled into a protein, builds one bit of the copy virus' RNA, then the copies can't have both a full copy of the RNA and a capsule and other proteins.

Why not? Are you assuming the RNA is consumed when it's read? It's not. Or are you thinking it can only be read in one way? There are two different kinds of systems for reading genetic information and making something based on the sequence. The ribosome reads three RNA bases at a time, dictating a protein sequence. Polymerases read one base at a time by matching up base pairs before insertion.

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> > > > > Contrast that to AAV. AAV doesn’t really integrate into a genome (well isn’t supposed to in theory) - they work by creating what’s known as an episome (i.e a circular piece of dna that persists in cells and gets translated into the desired protein). AAVs can only shutoff a mutant gene if they carry a payload like siRNA/microRNA or something. AAVs never really fix the mutant gene, the episome just expresses the protein that’s not working. I suppose over the long run AAVs might not really ‘cure’ a genetic disease, because the episome will likely dilute out over time with cell divisions. You can only really administer an AAV once too because of immunogenicity issues.

That's often how they are used in practice, but unmodified AAVs are capable of insertion, in humans mostly at the AAVS1 locus.

My wife was watching Chernobyl with me and she said the red and blue cards were the first time it made sense…… she doesn’t like hearing me talk I guess : )

They did a great job in the show with the cards. There’s a little more nuance to the what and why but it was a great explanation that incorporated a lot of technical details.

BWRs never are xenon precluded. They always, at all parts of the operating cycle, have sufficient hot excess reactivity to have xenon override capability. They also naturally stabilize spatial and axial xenon tilt based on their design and the boiling boundary effect.

Pwr plants have total xenon override until the last 5-8% of cycle, when they are essentially at max dilution. They do not have natural flux tilt stabilization so the operator has to manually make adjustments to control tilt within limits.

I have personally started up a commercial BWR in peak xenon. It was very weird to have the reactor go critical moving a corner rod from 00 to 04, not see the criticality (power actually appeared to be going down at the time we notched it out), then as xenon burnout started happening we saw only one SRM period on scale. The PPC displays, when you have period in trend mode, you can see an inflection when critical occurs, and we saw the signature only on one instrument which didn’t make much sense. So we stopped pulling rods to watch, as a minute or two later the second SRM started to come on scale, then the third and fourth, as xenon burnout reduced shielding around the SRMs and allowed the core to finally couple. Then reactor period advanced over the next 12-15 minutes to about 82 seconds, when we finally hit point of adding heat and everything stabilized. Not a common evolution and I can see where other operators pulled too far and tripped their units, because you don’t see the core go critical on peripherals for quite a while.

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In actual use, AAVs often cannot integrate into the cellular genome. It's just used to temporarily deliver something else. In fact it's a commonly used vector for CRISPR/Cas systems.

But it's true that unmodified AAVs are capable of integration. It's a lot more specific about that than lentiviral vectors, because AAVs mostly just integrate into the human genome at the AAVS1 site.

Lentiviral vectors can insert at many, many sites throughout the genome. The same applies for transposon systems such as Sleeping Beauty and PiggyBac.

As for CRISPR/Cas, that's a whole range of systems that is mainly distinguished by the ability to easily program targeting of a specific sequence (in almost any context). That can be used to insert something at a specific genomic site, but it can also be used for all sorts of other things. Some Cas enzymes don't even target DNA but instead target RNA.