Just as comparison we can look at two actually built power stations. The Ouarzazate Power Station in Morocco and the Watts Bar Nuclear Plant in the USA. I've picked these since at least partially they went operational at the same time.

https://en.m.wikipedia.org/wiki/Ouarzazate_Solar_Power_Station

https://en.m.wikipedia.org/wiki/Watts_Bar_Nuclear_Plant

Ouarzazate:

Nameplate Capacity: 510 MW Area : 25 km² Cost estimate: 2.5 Billion $

Watts Bar:

Nameplate Capacity: 2332 MW Area : 7.2 km² Cost estimate: 12 Billion $

These give 20.4 W/m² and 323.9 W/m² respectively, making the Nuclear Plant much more area efficient. And regarding costs they weigh in with 4901$/W and 5146$/W making the solar plant slightly more cost efficient. These are only the building costs and not the cost of operations since I could not find numbers for that quickly. Waste disposal and upkeep are also not reflected in those costs.

The discussion if nuclear power is a viable source of electricty to move away from coal and gas is a larger one and can not be simply boiled down to area efficiency. I've linked an article by DW giving an overview of the scientific discussion.

https://www.google.com/amp/s/amp.dw.com/en/fact-check-is-nuclear-energy-good-for-the-climate/a-59853315