One of the alternatives that are open to AECL is to redesign the fuel itself, as opposed to the targets, although the targets in fact contribute quite a bit to the power. When you design fuel, you can design it with certain power characteristics right up front, depending on how you make the fuel and what you put in it.
So AECL does have an option to redesign the fuel with a different set of characteristics that would enable it to have a very definite negative power coefficient of reactivity. But when you make new fuel, you have to go through a detailed qualification process before you can convince the CNSC, the regulator, that you can put it into a reactor and fire it up. That takes quite a few years. You have to actually put it into a research reactor and check again that each fuel design you've made will in fact behave exactly as you expected, and you do that in a research reactor before you do it in the production reactor. That's quite a long job and quite an expensive job.