and it was back when the US did project Pluto and put a reactor on a B36 with plans for open cycle nuclear turbojet pack
The NB-36 only carried a reactor in the bomb bay for trials, the engines were conventional. They had two companies competing designs for nuclear engines, one open and one closed cycle - the closed cycle won out before the programme was cancelled.
And the USSR has its own equivalent programme and flying testbeds, see my post at #24.