Effect of Nuclear Weapons

Jean Bele, MIT

This lecture presents a description of the effects of Nuclear Explosions, with the goal mostly on the structures and population in the urban areas.

Introduction

The effects vary according to many factors such:

• The weapon design (material and method used for the construction of the weapons) • The weather conditions in time of the explosion • The targeted areas (Urban, refineries, industrial) • The geographical layout (mountain, plain, savanna…)

Types of Nuclear Explosions

The altitude at which the weapon is detonated will largely determine the relative effects of blast, heat, and nuclear .

There five general classifications of bursts

Air Burst Explosion in altitude below 100,000 feet (30,480 meters) High-altitude Burst Explosion in altitude over 100,000 feet (30,480 meters) Underwater Burst Explosion beneath the surface of the water Underground Burst Explosion happens beneath the surface of the land Surface Burst Explosion slightly above the actual surface of the land or water

Sequence of events:

1. Fireball

• Occurs within less than one millionth of one second of the weapon's detonation. • Extremely hot and highly luminous spherical mass of air and gaseous weapon residues. • Grow in size, engulfing the surrounding air. • Triggers the destructive effects of the nuclear explosion

Plutonium implosion fission, July 16 1945 Site, New Mexico 20 kilotons of TNT (84 TJ),

2. Radioactive fallout • Radioactive particles that fall to earth because of a nuclear explosion. • It consists of weapon debris, fission products, and, in the case of a ground burst, radiated soil.

3. Air blast • Cause significant damage to the structure. • it travels at supersonic velocities • Slows down to the normal speed of sound in the atmosphere, after leaving the vicinity of the fireball 4. Nuclear radiation • Arrives during the first minute after an explosion • Mostly gamma radiation and radiation. • The level decreases rapidly with distance from the fireball to where less than one roentgen may be received five miles from ground zero. • Three percent of the total energy in a nuclear explosion.

5. Delayed nuclear radiation • Depends on height of burst, weather conditions, etc. • From the radioactive fallout (weapon debris, fission products, and, in the case of a ground burst, radiated soil.)

Distribution of energy released during a nuclear explosion

• The "yield" of a is a measure of the amount of explosive energy it can produce. • The yield is given in terms of the quantity of TNT that would generate the same amount of energy when it explodes. • 1-kiloton nuclear weapon is one, which produces the same amount of energy in an explosion, as does 1 kiloton (1,000 tons) of TNT. • 1-megaton weapon would have the energy equivalent of 1 million tons of TNT. One megaton is equivalent to 4.18 x 1015 joules. • The destructive power of a weapons system is evaluated using the concept of equivalent megatons (EMT). EMT = Y2/3 where Y is in megatons. • The destructive power of a does not vary linearly with the yield. • The volume the weapon's energy spreads into varies as the cube of the distance, but the destroyed area varies at the square of the distance.

The Blast Effect

• Blast effects are measured by the amount of overpressure, the pressure in excess of the normal atmospheric value, in pounds per square inch (psi). • After 10 seconds, when the fireball of a 1-megaton nuclear weapon has attained its maximum size (5,700 feet across), the shock front is some 3 miles farther ahead. • At 50 seconds after the explosion, when the fireball is no longer visible, the blast wave has traveled about 12 miles. • It is then traveling at about 784 miles per hour, which is slightly faster than the speed of sound at sea level. • Peak overpressure: The maximum value at the blast wave or (shock) front

• Early stage of explosion, the variation of the pressure with distance from the center of the fireball at a given instant for an ideal rising shock front. • Pressure at the shock front are two or three times as large as the already very high pressures in the interior of the fireball

Figure 3.03(Glasstone). Variation of overpressure with distance in the fireball

• Fig shows the overpressure at six successive times. • The blast wave travels in the air away from its source • The overpressure at the front decrease • The pressure behind the front drops regularly below that of the surrounding atmosphere • The negative phase of the blast wave forms • From t1 to t5, the pressure in the blast wave is above or equal the atmospheric. In the t6, the overpressure has a negative value, that is an “underpressure”

Source: Glasstone, Figures 3.04

Source: Glasstone, Figures 3.21, Table 3.07

Peak overpressure Maximum Wind Speed 50 psi 934 mph 20 psi 502 mph 10 psi 294 mph 5 psi 163 mph 2 psi 70 mph From http://www.atomicarchive.com

Overpressure Physical Effects 20 psi Heavily built concrete buildings are severely damaged or demolished. 10 psi Reinforced concrete buildings are severely damaged or demolished. Most people are killed. 5 psi Most buildings collapse. Injuries are universal, fatalities are widespread. 3 psi Residential structures collapse. Serious injuries are common, fatalities may occur. 1 psi Window glass shatters Light injuries from fragments occur. From http://www.atomicarchive.com

The effects of the blast wave on a typical wood framed house.