The NPR news item (audio + transcript) Could Nuclear Power Aid In Travel To Mars? contains the following:
VISHAL PATEL: If you want to go to Mars, nuclear is a smart choice.
BRUMFIEL: Vishal Patel is a nuclear rocket scientist with a company called Ultra Safe Nuclear Corporation. They're working on a version of a rocket that would use a nuclear reactor. The reactor would heat hydrogen gas and shoot it out a nozzle. It's way more efficient than a chemical engine. A nuclear rocket could make a round-trip mission possible in as little as half the time needed using conventional rockets. It would also allow astronauts to turn back towards home if they encountered an emergency at the start of their trip. Patel recognizes that launching a nuclear reactor from Earth might make people nervous. But, he says, Ultra Safe Nuclear Corporation is working hard to make it ultrasafe.
Question: With what is known or suggested about Ultra Safe Nuclear Corporation's engine's performance using hydrogen as reaction mass and a reasonable estimate of what a one-way transport1 of a small crew to Mars might look like, how far from Earth could one get and still be able to return to Earth?
To keep it simple it will be okay if you want to assume that Earth-intercept is sufficient and the spacecraft can safely reenter even at interplanetary velocity (like sample return capsules do).