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Hiddencamper t1_jc3b51m wrote

Reply to comment by Accelerator231 in Why were the control rods in the reactor featured in the HBO series 'Chernobyl' (2019) tipped with graphite? by Figorama

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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Accelerator231 t1_jc3bgem wrote

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?

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insta t1_jc3gufu wrote

This was a major benefit to RBMK. You can get limitless, carbon-free power from clean water and rocks you dug out of the ground. There's still 8 of them kicking around today, the design works well if you don't intentionally disable every single safety system at once.

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Accelerator231 t1_jc3mrcy wrote

This changes my understanding. I always thought part of the reason why nuclear wasn't used was because of difficulty of refining fuel.

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echawkes t1_jc3vk15 wrote

Not at all. In fact, unlike power plants that use fossil fuels (like coal), fuel costs aren't a huge part of the cost of running a nuclear power plant anywhere, regardless of enrichment. (Caveat: nuclear power plants use relatively low fuel enrichments, like 5% or less. If you had an NPP with a very high enrichment, the cost could change, but NPPs don't need high enrichments.)

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jadebenn t1_jcao7ll wrote

Fuel enrichment was originally an extremely expensive service: Part of the advantage to the CANDU and RBMK designs was they didn't need it (CANDU still doesn't, modern RBMK does). Back then, uranium enrichment was primarily accomplished through an extremely energy-intensive process called 'gaseous diffusion' that required large facilities and infrastructure. Then the gas centrifuges arrived, and cut enrichment costs by an order of magnitude.

The last US gaseous diffusion plant was shut down in 2013, but it was uneconomic far prior (IIRC, it was kept around for DoE weapons purposes since that uranium can't be civilian-procured). Modern enrichment is relatively cheap now, which is part of the reason the nuclear industry is interested in boosting enrichment rates (which would have been prohibitively expensive originally).

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Hiddencamper t1_jc3d3bq wrote

Correct. Graphite is a stronger moderator than water.

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

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Accelerator231 t1_jc3mv3g wrote

Actually come to think of it you got a paper or anything similar?

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