We use a Radiation progenitor because it cannot combine, and this build requires pure cold or pure toxin if you feel like changing to Primary Blight. Our base damage comes from having 3 or more status procs on an enemy at 80%/status, 3 statuses gives us 240% base damage, PPB gives is an additional 165%, for a total of 405% base damage.

This leaves us with [Primed Chilling Grasp] as opposed to [Contagious Spread]. While it doesn't fair as good against shields, the corpus shields don't give me a problem until in the several thousands, and if I plan to take corpus specifically I use other weapons.

But we elect to utilize [Primed Chilling Grasp] because 165%>90%. Radiation isn't weak against many things, but luckily that can be solved by hitting that with cold damage. They support each other very well.