Steven Starr over at Nuclear Darkness has collected and expanded upon many studies of the consequences of nuclear war. In particular, check out Consequences of a large nuclear war and City on fire by Lynn Eden. City on fire challenges the U.S. government’s own analysis of the consequences of a nuclear strike using the case study of a 300kt detonation at the Pentagon:
The detonation of a 300-kiloton nuclear bomb would release an extraordinary amount of energy in an instant-about 300 trillion calories within about a millionth of a second. More than 95 percent of the energy initially released would be in the form of intense light. This light would be absorbed by the air around the weapon, superheating the air to very high temperatures and creating a ball of intense heat-a fireball.
By the time the fireball approached its maximum size, it would be more than a mile in diameter. It would very briefly produce temperatures at its center of more than 200 million degrees Fahrenheit (about 100 million degrees Celsius)-about four to five times the temperature at the center of the sun.
Because this fireball would be so hot, it would expand rapidly. Almost all of the air that originally occupied the volume within and around the fireball would be compressed into a thin shell of superheated, glowing, high-pressure gas. This shell of gas would compress the surrounding air, forming a steeply fronted, luminous shockwave of enormous extent and power-the blast wave.
Read more here and be sure to explore the rest of Nuclear Darkness while you’re there!