You can't prevent the tachyon bursts, but you can protect the lab by:
- keeping it on the edge of the planet
- keeping it under forcefields
- keeping a cloaker or scout starship near it to provide counter-sniper coverage
- laying down tractor and/or grav coverage on the probable approaches
- having enough military between it and probable approaches that the enemy ships don't get close enough to kill it
- ordering your stuff to focus-fire anything that you've found to be particularly prone to just charging the lab and killing it
If none of that helps, please post the save and I'm sure someone here will be happy to give some more scenario-specific pointers