Experience in the United States suggests that the key subsidy is a loan guarantee, because that makes the finance available. Essentially it means that the bank is lending money to the federal government. That's a very safe loan; it means that the cost of borrowing can be very low. For example, the Finnish plant had loan guarantees from the French government and the Swedish government, and that meant it could borrow money at what I think was a rate of 2.6%.
Without those loan guarantees and with exposure to the risk of cost escalation, the banks would impose a very high interest rate, which would make the economics of nuclear power completely untenable.