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Illustrious-Sky1928 t1_iutlz36 wrote

Cool I met the author at a conference, their work was amazing! So high neutron flux is related to the fact that fusion neutrons are extremely faster than fission ones, and thus since the flux is dependent on the velocity of the neutron the flux in iter is very high. However, the net number of neutrons in the reactor is very small

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beerorist t1_iuvr1nk wrote

In that case you probably met my colleague.

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Illustrious-Sky1928 t1_iuvwlsp wrote

Then I probably just made a fool out of myself with that simplified explaination lol

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233C OP t1_iutk1kb wrote

For comparison, the average flux at the vessel wall of a common nuclear reactor is of the order of 10^9 n s^-1 cm^2

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UnitedBB t1_iutx578 wrote

as the legend has it in the link... that would 10e+9 ?

still hard to compare, at what point would the wall materials become radioactive? or how do we compare?

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685327592 t1_iuu8jqd wrote

Bigger problem is neutron embritlement whereby the strength of the material degrades over time dye to the effects of neutron bombardment.

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UnitedBB t1_iuur12b wrote

Yes!... uh, thats, neutron emritle. yes thats the one! ...is there that now? in the ol' Tokamak

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ericula t1_iuuxw93 wrote

10^9 is equal to 1e+9.

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UnitedBB t1_iuwne0z wrote

ah, and what is 10e+9 equal to?

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ericula t1_iuwrmqk wrote

10e+9 is equal to 1e+10. The e+n part is shorthand for 10^n so 10e+9 is equal to 10e+9 = 10*10^9 = 10^10 = 1*10^10 = 1e+10

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UnitedBB t1_iuwwy08 wrote

makes sense! Turns out i should have just double checked the linked post, it was in the 1e+9 format (1.00e+9). Was also confused by OPs comment using different format for the number and units.

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233C OP t1_iuy3nis wrote

cross sections at high energy are much lower than at low ones (neutrons lose their energy as they interact with matter, until eventually getting captures, ie activating the material ie "become radioactive").
Front facing material will have "less probability", but much higher fluxes (low chance of winning, but more lottery tickets), the deeper you go, the less flux you get, but the "probability of turning radioactive" increase as the neutron energy decreases.

As you can guess, the vessel wall of a regular nuclear reactor is fairly radioactive, so a ballpark mark is everything "blue" and higher will be pretty radioactive come decommissioning. Plus from a pure mass point of view, ITER is much much bigger than an NPP reactor vessel. The cryostat might end up only slightly activated, but the vacuum vessel and all will end up at comparative radioactivity level as NPP reactor vessels (and a dozen time the volume/mass).

ping u/beerorist to correct me.

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beerorist t1_iuvr5c4 wrote

I am one of the coauthors of this work. AMA!

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