It would be hard to get and keep a thousand tons of atomically pure 6Li/7Li, even without neutrons spalling pipe surface atoms into it. And, with enough neutron

It would be hard to get and keep a thousand tons of atomically pure 6Li/7Li, even without neutrons spalling pipe surface atoms into it. And, with enough neutron flux, seems like you should expect to get a fair bit of "relatively unusual" products that your regular H/He extraction process leaves to accumulate. But these are all second-order effects. A thousand tons of molten lithium is a big enough hazard even without radioactivated impurities. And even getting the 0.0000001% fraction of dissolved 3H out seems... difficult.