The cost of the lawsuit to the activists doing the suing is the cost of lawyers fees, which is often pro-bono, and if the judge takes particular offense at the waste of time, they get stuck with court costs as well. The cost to the utility are lawyers fees, distruption to construction schedules, interest accumulated on building loans for 3 billion dollar projects, and the purchase of electricity from merchant operators to cover the commitments the not-yet-operating plant isnt meeting. This is not a symmetrical cost, and it was successful in deterring any build whatsoever in the us for decades. If the laws congress has recently passed in the nuclear area seem strange, its because they are designed to counter this tactic.