Right. Pu238 alpha decay is aneutronic so it doesn't contribute to a chain reaction. However heating from too much Pu238 (or more importantly, Pu240) would be a

Right. Pu238 alpha decay is aneutronic so it doesn't contribute to a chain reaction. However heating from too much Pu238 (or more importantly, Pu240) would be a heat removal/thermal challenge.