Thermonuclear device (hydrogen bomb, or H-bomb) uses a nuclear fission reaction , split atoms apart, to drive a nuclear fusion reaction. The fission reaction creates the temperature and pressure necessary to bring atoms together, and release of sizable amounts of energy
The first test of a Thermonuclear device occured on November 1, 1952, nearly a decade after the test of the Atomic Bomb (A- bomb makes use of nuclear fission).
The detonation of an H-bomb, releases an Electromagnetic pulse, which fries all electronic devices within its path.
The reason for the shape of the mushroom cloud: hot air rises rapidly, leaving a void or empty space for cold air to enter (Nature abhors a vacuum). When the hot air hits the upper reaches of the atmosphere, it cools down, gravity kicks into gear with the most heaviest particles suspended in air dropping first,a process known as convection, hence the wide shape of the head of the cloud, known as a cap.
A Nuclear Winter, is a natural consequence of a detonaton of a high-yielding nuclear weapon. As a result of this impact, soil gets aerosolized (broken into smaller particles) and thrown into the atmosphere, blocking the sun, preventing photosynthesis and the eventual loss of vegetation and animal life. The duration of such of an event can theoretically last from days to years. The closest equivalent would be volcanic phenomena like the 1815 Tambora event, in which a reduced amount of sunlight fell upon the area for a year. In fact the event was callled " “year without a summer.”
Obviously, a Nuclear Winter is highly advantageous to creatures like the strigoi, because do not have to worry about avoiding the sun.