Peak Inverse Voltage (PIV)
The utmost amount of reverse bias that a diode shall be exposed to in a rectifier is said the peak inverse voltage or PIV of the rectifier. For the half wave rectifier, PIV is determine like
PIV = V2(pk)
The basis for this equation might be seen by referring to diagram. While diode is reversed biased, there is not any voltage drop across the load.
So, in the rectifier all of V2 is dropped across the diode.