Hmmmmmm. one micron = 39 millionths of an inch???
Small measure of length.
The problem is alpha radiation.
Alpha radiation occurs when an atom undergoes radioactive decay, giving off a particle (called an alpha particle) consisting of two protons and two neutrons (essentially the nucleus of a helium-4 atom), changing the originating atom to one of an element with an atomic number 2 less and atomic weight 4 less than it started with. Due to their charge and mass, alpha particles interact strongly with matter, and only travel a few centimeters in air. Alpha particles are unable to penetrate the outer layer of dead skin cells, but are capable, if an alpha emitting substance is ingested in food or air, of causing serious cell damage. Alexander Litvinenko is a famous example. He was poisoned by polonium-210, an alpha emitter, in his tea.
Alpha has a lot of mass and thus energy. You could bombard me with alpha and I would not be harmed. If ingested it causes massive damage to cells. Your skin will stop alpha. If ingested your DNA stops the alpha particle and this is bad, very very bad.
Relative to the fuel in transit in the tunnel it would be in sealed containers of great strength. I would be very amazed if their is any contamination. If their is contamination which is doubtful, seal the tunnel and call the concrete man. A lot of concrete and forget about it.