HPFP failure in the Passat is very rare. It, however, is possible just as it's possible for any mechanical device to fail.
Two failures? I'd place money that the second failure was the result of the first. Somewhere somebody took a shortcut and didn't eliminate all contamination. It happens even though it shouldn't.
Shrapnel? More like metal shavings. Fuel is pumped out of the tank by a low pressure pump (or pumps depending upon design) and routed to the HPFP. The HPFP delivers fuel to the common rail which supplies the injectors. Excess fuel warmed by pressurization and circulation through various engine components is returned to the fuel cell. The effect of this circuit serves to cool engine components, lubricate the HPFP, and warm cold fuel in the cell.
When the HPFP fails the immediate result is usually a load of metal shavings being introduced into the fuel system. This is why we so highly suggest that the fuel filter should be carefully examined periodically as any sign of metal should serve as a warning of impending failure. (No glitter allowed.)
In any case a HPFP failure will shed metal throughout the fuel system. For this reason the entire system must be either replaced or flushed so that no trace of metal remains. Again, I suspect that your second failure was caused by incomplete cleaning after the first failure.
Slightly off subject but turbos are worth mentioning here. Depending upon the nature of a turbo failure there are certain indications and specific damage caused to the engine and exhaust system.
A failure on the compressor side has the potential of introducing metal and engine oil into the intake side. The first component affected is the intercooler, though any sensors along the path will also be contaminated. Oil in any significant quantity will begin to fuel the engine. This can cause a runaway condition as the engine will actually begin to feed upon itself. In the unlikely event that metal shards pass through the system into the engine, this just adds to the situation.
A failure on the hot or turbine side of the turbo will contaminate everything downstream. The primary victim will be the DPF as it will be overwhelmed by oil smoke. Obviously, if the turbo is "shedding its feathers" on this side of things, then there will be metal contamination as well. Worse yet it's possible to introduce foreign materials into the induction system through the EGR circuit. And in both cases there's the worry about blockage of oil lines servicing the turbo and oil contamination. This is why a $2000 turbo failure can easily cause a repair bill to top $7000.
Just to be clear both types of failure are catastrophic. To be just as clear I have to somewhat suspect that those of us who have experienced repeated failures are victims of an incomplete repair the first time around.
I cringe when an owner shares that his or her dealer replaced a turbo. Was it just the turbo? Was there no oil leakage or metallic contamination? If there isn't a 100% certainty that neither be the case, then a new turbo will merely mask for a time what will become another major problem. Neither HPFP or turbo failure is something that can be addressed by replacement of just one component. It's just not that simple.
