Nuclear power is 98%.
No. It isn't even close to that.
Nuclear power is a thermal engine. It generates heat to go through a turbine and has to go through a condenser to cool the working water in order to make the cycle complete. It is bound by the Carnot cycle.
The average efficiency of the US nuclear power plants is 32.6%. They take on average 10,464 BTUs of heat to produce 1 kilowatt-hour of electrical energy. A kilowatt-hour has 3,412 BTUs.
The average Natural Gas power plant is 41.8% efficient taking 8,152 BTUs to produce a kilowatt-hour of electrical energy.
Average Operating Heat Rate for Selected Energy Sources
http://www.eia.gov/electricity/annual/html/epa_08_01.html
Is it possible you are confusing the capacity factor efficiency of nuclear power plants with energy efficiency?
One thing that nuclear power plant excel at is once running, they can normally keep running at or near full power for a long time. That power output versus maximum output is measured as efficiency, but it is not the same as energy conversion efficiency. They are not even related.
Operating at 98% Efficiency, U.S. Nuclear Plants Play Vital Role in Beating Sweltering Heat Wave
http://www.nei.org/newsandevents/newsreleases/operatingat/
Helping Americans to cope during the summer’s most sweltering heat, the nation’s nuclear power plants posted an average daily capacity factor of more than 98 percent during the first two weeks of August.
Capacity factor is a measure of power plant efficiency, measuring the amount of electricity the plant generates compared to the amount it could have produced at continuous full power operation during the same period.