100 million K

"Since fusion temperatures reach 100 million K, the detonation front
of a thermonuclear explosive travels at speeds in excess of 1,000 kilometers
per second. Using a convergent conical thermonuclear burn-wave with a
suitable liner, one could theoretically create a jet traveling at 10,000
kilometers per second, or 3 percent of the speed of light. (II)
Up to 5 percent of the energy of a small nuclear device reportedly can
be converted into kinetic energy of a plate..."
...
"I Devices based on this principle were pursued in the 1960s.
Project Orion examined their potential for space propulsion. Casaba and "nuclear howitzer" were names for weapon applications."

"II The detonation front shock-wave velocity is (32 kT/3M)^.5, where M is the
average mass per ion of the thermonuclear fuel. Suitable geometries can propel
matter at many times the detonation front velocity. Using cone geometry. the jet speed is v/sin Theta, where v is the detonation-front velocity and Theta is the cone's half-angle. A practical minimum for Theta has reportedly been found to be Theta = 0.1. See Winterberg, Thermonuclear Physics, p.41, 122. "