That 'looks' like stainless, so yes - it can be fixed by specialist welding. How on earth did you manage to tear that? To get you through till spring when you can have it removed and repaired properly - you may well get away with a high tech marine pu adhesive, such as 3M 5200 (https://www.makewoodgood.com/product/3m-5200-adhesive-sealant/. Eye wateringly expensive (but so are stainless rads), can be applied wet too. I would suggest putting a universal hose clip around that to assist in keeping the sealant in as well. Of course, if it's not stainless it is probably just time to buy a new radiator and 'fix' it that way.
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