Yet another nuclear danger

Published : Aug 04, 2001 00:00 IST

India and Pakistan, as novices in the field of nuclear weapons development, should be alive to the risk of accidents in weapons storage.

THE nuclear age can rightly be called the "age of dangers". The world first learnt of these dangers on August 6, 1945, when the United States dropped an atomic bomb on the Japanese city of Hiroshima, killing an estimated 1,30,000 people. On April 26, 1986, the world was exposed to another kind of nuclear devastation when Unit 4 of the Chernobyl reactor exploded, releasing an immense amount of radioactivity into the atmosphere. Practically every country in the northern hemisphere received some degree of radioactive fallout, with the number of deaths worldwide that may eventually result from that estimated at as high as several tens of thousands. Less known are the grave dangers of radioactive contamination from accidents involving nuclear weapons. Having chosen to build nuclear weapons, India and Pakistan must learn the right lessons from the experience of other nuclear powers.

In essence, a nuclear weapon consists of a shell of powerful chemical high explosive (H.E.) surrounding a core of either plutonium or highly enriched uranium. (In fusion weapons, there is a second stage that is in turn ignited by the fission weapon described here.) When the H.E. detonates, it crushes the fissile material core into a critical mass and triggers a chain reaction, which produces the nuclear explosion. It is this H.E. that is especially vulnerable to accidents.

In the early nuclear weapons of the U.S., key components were kept separately as a way of preventing accidental detonation. This simple and robust precaution was set aside under pressure from the Cold War arms race and the decision was taken to deploy nuclear weapons on aircraft and missiles at high stages of alert. Deployment of fully assembled nuclear weapons was recognised as leading to the risk of possibly severe accidents. Concern about nuclear weapons safety was responsible in large part for the 130 safety-related tests carried out by the U.S. The Union of Soviet Socialist Republics (USSR) reportedly conducted about 25 safety tests involving 42 weapons, between 1949 and 1990.

The fear of accidental detonation of nuclear weapons was well founded. An official summary released by the U.S. Department of Defence in 1981 lists 32 accidents involving U.S. nuclear weapons between 1950 and 1980. These accidents typically involve delivery vehicles, either aircraft or missiles. Most notable among the missile accidents was the 1960 accident involving a U.S. BOMARC missile at the McGuire Air Force base in New Jersey. There was an explosion and a fire involving the missile's fuel tanks. There have also been accidents involving aircraft, the most famous being over Palomares, Spain, and near Thule, Greenland. In both cases, the aircraft carrying nuclear weapons crashed and the H.E. surrounding the nuclear core detonated. This led to the dispersal of plutonium over a large region. There have been accidents involving U.S. naval nuclear weapons as well. An assessment by Greenpeace and the Institute of Policy Studies lists 383 accidents between 1945 and 1988. These include a number of instances in which nuclear weapons were lost at sea as a result of the sinking of submarines and ships.

Information about accidents in the erstwhile Soviet Union is harder to obtain, but there are reports of at least 25 serious accidents involving nuclear weapons there. They include a 1977 accident in which, reportedly, fuel leaked from a nuclear missile in its silo and subsequently exploded. A more recent accident occurred on June 16, 2000 near Vladivostok when a ballistic missile that was being unloaded from a transport ship caught on the pier railing. This led to a leak of approximately three tonnes of the oxidising agent, which exploded. A number of people were injured, and the residents of nearby villages had to be evacuated.

WHILE neither India nor Pakistan is believed to have deployed nuclear weapons as yet, it is worth noting that India's Draft Nuclear Doctrine calls for a "triad of aircraft, mobile land-based missiles and sea-based assets", and for them to be configured "for rapid punitive response". Pakistan has issued no comparable doctrine but it is likely to follow India in deploying its weapons. If they do so, the two countries shall face the risk of accidents involving nuclear weapons and their delivery systems.

Experience suggests that there may be significant risks of aircraft and missile accidents in the subcontinent. India's Comptroller and Auditor General reported in 1997 that there had been 187 accidents and 2,729 "incidents" involving Indian Air Force (IAF) aircraft between April 1991 and March 1997, in which the IAF lost 147 aircraft and 63 pilots. Data on Pakistan Air Force (PAF) accidents are less easy to come by. According to the Pakistan Institute for Air Defence Studies, there were 11 major PAF accidents between January 1997 and August 1998. There are no reports yet of accidents involving ballistic missiles in either country. But given the long history of accidents in other nuclear weapon states, the risk of such accidents cannot be under-rated, particularly since India's Prithvi and Pakistan's Ghauri missiles are propelled by highly volatile hypergolic (that is, self-igniting) liquid propellants.

An accident involving a nuclear-armed aircraft or ballistic missile could result in one of three possibilities, listed below in the increasing order of seriousness of consequence:

1. Burning of the chemical H.E. and the melting of the plutonium or uranium core;

2. Detonation of the H.E. leading to vapourisation of the plutonium or uranium and its dispersal into the atmosphere;

3. Detonation of the H.E. leading to a nuclear explosion.

Before elaborating on the possible consequences of these three kinds of accidents, it should be first pointed out that plutonium-based weapons have significantly more severe health effects than those using uranium. This is because the isotope of plutonium used in nuclear weapons (Pu-239) is 30,000 times more radioactive than the corresponding isotope of uranium (U-235). We will therefore focus on accidents involving plutonium-based weapons. India has used plutonium in its nuclear weapons while Pakistan has so far relied on uranium; with the commencement of production of plutonium from its Khushab reactor, Pakistan may follow India in developing plutonium-based weapons.

The two primary routes of plutonium exposure are ingestion and inhalation. Ingestion is a less significant risk since almost all of the plutonium is excreted from the human body within a few days. The more serious risk comes from inhalation of very small plutonium particles, which can stay imbedded deep in the lungs, typically for periods as long as a year. The primary effects of limited exposure to plutonium are an increased risk of lung, liver and bone cancers; inhaling one hundredth of a milligram of plutonium increases the risk of cancer by 3-12 per cent.

The first kind of accident, in which the H.E. burns but does not detonate, releases a limited amount of plutonium into the environment. There is little chance that this plutonium will get spread over a very large area, so its impact is localised to the immediate vicinity of the accident. This limits the severity of its effect on the environment and on public health.

THE second of the three kinds of accidents listed above poses considerable danger to public health by way of inhalation of plutonium. If the H.E. detonates, effectively all of the plutonium will be transformed into a fine aerosol. This aerosol will rise with the hot gases created by the explosion, mix with the air and spread. Wind would transport it to considerable distances, up to tens of kilometres. People and animals in this region would inhale this plutonium-laden atmosphere. The consequences of such an accident should it happen in South Asia, is estimated here.

Imagine there is a nuclear weapon accident at an air force base or facility which happens to be at the edge of a major city like Delhi or Bombay, Karachi or Lahore. If the city happens to be downwind at the time of the explosion, our calculations show that the number of people who would be exposed to plutonium inhalation could be so great that there could be approximately 5,000-20,000 additional cancer deaths.

We believe that the prospect of such a catastrophe cannot be ruled out. There are bases and facilities at the edges of large cities and there is no publicly available information that assures us that a nuclear weapon will not be stored in or transit through one of these.

Even if such an accident took place not at the edge of a major city, but say 50 km upwind of a middle-sized city, the resulting cancer toll would be considerable. Our calculations show that it would lead to approximately 200-900 fatalities from the town and the surrounding countryside.

In both these cases, in addition to the fatalities there will be the medical costs of treating the fatal and non-fatal cancers. There is also a massive financial cost at stake in even a limited cleaning up of just the immediate neighbourhood of the accident, because the contamination levels would be very high. This could be at least hundreds of crores of rupees.

The likelihood of this kind of a nuclear weapon accident is hard to assess. We admit that the probability of such accidents may not be large, but it is certainly not zero. It is worth recalling that India and Pakistan have officially claimed only six nuclear tests each with no suggestion that any of them were intended purely to test safety. With respect to the kind of accidents we have considered in depth - namely those resulting from the dispersal of plutonium - possible safety measures to reduce the risk of such accidents would involve the use of features like Insensitive High Explosive (a kind of explosive that cannot be set off so easily) and Fire Resistant Pits. Both these would add to the weight of the nuclear device. It is likely that countries in the early stages of hoarding nuclear armament and seeking to develop small, light nuclear warheads that can be fitted more easily on ballistic missiles would not have installed these safety features.

Our analysis suggests that mere detonation of the H.E. in a nuclear weapon could by itself be a major catastrophe. Far worse, of course, would be an accident where a nuclear chain reaction is triggered and produces a nuclear explosion. The result of such an accidental explosion would be the same as that of a nuclear weapon used deliberately in war. An accidental nuclear explosion with a yield of 15 kilotons (the same as that of the weapon detonated over Hiroshima, and similar to the fission weapon tested by India in its 1998 tests) would destroy everything within 5 sq km through the combined effects of blast and fire. An area of over 24 sq km would be subject to radioactive fallout at levels that will cause half the healthy adult population living there to die from radiation sickness. If this were to happen in the vicinity of a large South Asian city, several hundreds of thousands of people will die.

Such a possibility cannot be ruled out. Nuclear weapons in the U.S. arsenal are "one-point safe", that is, their design includes safety measures that ensure a nuclear explosion is not triggered in the event of an accidental explosion of just one of the H.E. packages. With weapons of India and Pakistan still in the early stages of development, it is unlikely that they will have such design-level safety.

It is clear that a mere dispersal of plutonium due to a high explosive detonation could lead to possibly several thousand cancer deaths. An accidental nuclear explosion could lead to hundreds of thousands of deaths. Thus, prudence, if nothing else, dictates that India and Pakistan take basic safety measures to prevent the possibility of an accident. They should not deploy nuclear weapons; they should store nuclear weapons far away from missiles and aircraft carrying potentially explosive fuel; and they should keep the weapons disassembled, so that the H.E. is not close to the fissile material core. All these steps would reduce not only the danger of accidental explosions, but the risk of a nuclear weapon being launched because of error, panic or miscalculation.

R. Rajaraman is Professor of Theoretical Physics at Jawaharlal Nehru University, Delhi. Zia Mian and M.V. Ramana are research scholars at the Programme on Science and Global Security, Princeton University, U.S. The technical calculations and analyses this article is based on were published in the May 25, 2001 issue of Current Science.

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