Set in the not-so-distant future, interplanetary travels are the norm. Most spaceships are powered by fission reactors, and accidents do happen due to negligence or flaws in the system. It will probably take decades before we can see high-yield fusion reactors on the market; in the meantime, we just have to deal with meltdowns. I am wondering why it is not a good idea to have an ejectable nuclear reactor on board so that it can be immediately tossed into the vacuum of space at supersonic velocity in case of emergency? Isn't there vast emptiness between planets and the redundancy measures to ensure that every spaceship must have at least 2 reactors, so why don't spaceships adopt such a design?
- Reactors are much safer than you think. Only three major nuclear accidents have ever happened on Earth compared to tens of thousands of reactors. Since those incidents, containment protocols have gotten much better. If we have the technology to conduct frequent interplanetary travel, I'll wager we have the tech to generate power safely.
- Ejecting a reactor is unsafe. In an interplanetary future, space junk will be a huge problem, particularly when launched around planets. Debris tends to collide and shatter. Imagine what would happen if a melted reactor entered such a chain reaction in near-Earth orbit! Granted, space is so vast that people likely wouldn't be hurt by one occurance of this, but after many reactor ejections, Earth's space junk will be thoroughly irradiated. Dangerous? Maybe. Frightening? Yes.
- Reactors are too expensive to throw out anyway. Getting mass into space is expensive, and radioactive elements tend to be really heavy. Assuming a science-based setting, you won't want to waste fuel. If reactors somehow go into meltdown, they can be detached from the ship on a tether, but not ejected, to prevent dangerous heat conduction; then, they can be diagnosed and repaired autonomously by drones.