"Hi gb

The super-performance you're expecting from an NTR only happens at temperatures of over 2300 K - at that temperature the Vex is 7.5 km/s. To get 8 km/s requires about 2500 K. But the whole system is cooled by a high mass flow of propellant - likewise Zuppero's water rocket.

So don't worry, be happy ;-) "

Do you think that there is little difference between H20 and H2 in terms technical challenges.
In order words, if you had same temperature of say 2173 K would there be comparable challenge if either propellent were used. Or do you think water or Hydrogen would be significantly easier?
Next, would be expect there would be difference in the life of the engines. And how long could expect a engine operating at 1900 C and using water propellent to remain operational.

Finally, with a water propellent with Engine temperature of 1900 C [2173 K], what is the temperature of water when it is leaving engine. And what is it's ISP