> There are hundred of weaponizable reactors in not really good places of the world. Usually, a reactor is considered a proliferation problem if it allows you

> There are hundred of weaponizable reactors in not really good places of the world. Usually, a reactor is considered a proliferation problem if it allows you to produce plutonium easily. Getting radioactive material isn't good enough to be a significant security risk, because dirty bombs are much more complicated than conventional explosives, for an impact that isn't significantly bigger. So a reactor can be a risk if it lets you get plutonium easily (and, specifically, the Pu239 isotope). The other plutonium isotopes are not good weapon material, and so you want to be able to use a reactor that lets you produce material with as much pu239 as possible. Depending on design, if you can get easy access to the nuclear fuel, you can filter it frequently to retrieve the pu239, before it has a chance to react with another neutron and become one of the bad Pu isotopes. BWR and PWR reactors are bad for enrichment, because in order to access the fuel, you need to stop the reactor and depressurize the primary cooling circuit, which takes time. On the other hand, if you let the fuel spend a long time in the reactor, you end up with spent fuel that has lots of Pu240 and Pu241, which sucks. Other types of reactor, like CANDU, RMBK or UNGG reactors let you access the fuel more easily, without shutting down the reactor. Therefore, it is easier and quieter to retrieve the fuel frequently and get the Pu239 before it has time to react again. That is why some types of reactors are nicer to have if you want to build a bomb: they take less time and would raise less suspicion from other countries to collect the same amount of Pu239. Currently, most commercial reactors in the world use BWR/PWR technology. I think that sums up the gist of what it means to make a reactor less proliferation-friendly, and why it's important in order to make that technology more friendly to export.