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Nuclear safety

Nuclear safety, or better: safety of nuclear power, is a complex issue, involving all aspects of nuclear power which could inflict directly or indirectly harm to the health and wellness of people and/or damage to material belongings.

Military and civil nuclear technology are inseparable

Military and civil nuclear technology are inseparable. Military applications (weapons, nuclear propulsion) are not discussed here. However, civil nuclear technology can be used for military purposes: if this happens in unfriendly countries the notion proliferation is often used. Another (semi) military threat which may originate from civil nuclear technology are terroristic actions with primitive nuclear weapons made from civil MOX fuel.

Proliferation

It is possible to apply civil nuclear technology to create nuclear weapons. By means of commercial enrichment bomb-grade uranium-235 can be produced (the fissile isotope of uranium). In research reactors bomb-grade plutonium can be generated from non-fissionable uranium-238. In a reprocessing plant the plutonium can be separated from the uranium and fission products. If the process is aimed at the production of weapon-grade plutonium the irradiation time of the nuclear fuel is kept short and the reprocessing of the spent fuel is not extremely demanding. The technology needed to make nuclear bombs from the fissile material seems to be available outside of the established nuclear-armed countries.

Nuclear terrorism and MOX fuel

Plutonium recycling in light-water reactors (LWRs) using MOX fuel (Mixed OXide) unavoidably generates uncontrollable risks of nuclear terrorism and proliferation. Using elementary chemistry MOX fuel can be separated into uranium and plutonium. The plutonium could be used to produce a crude nuclear weapon. Evidently such a weapon wouldn't have the reliability and yield of a military weapon, but even a nuclear explosion of a few kilotons in a town may be devastating. Even without a nuclear explosion the dispersion of several kilograms of plutonium over a town by a small plane may render the town inhabitable.

Reactor safety studies

Three major Probabilistic Risk Analyses (PRAs) on reactor safety have been done by the US Nuclear Regulatory Commission (NRC), the first being the famous 'Rasmussen report' in 1975. In a PRA the chances are calculated of the random failure of one component of a technical installation, in this case a nuclear reactor with its appendages, and the conceivable consequences of that failure for the performance of the installation as a whole. The results seem to be adopted as standards for other safety studies in Europe. The scope of these official studies is limited:

• Only Light-Water Reactors (LWRS) of US origin have been analyzed. So the results cannot be applied to other reactor types, for example heavy-water reactors, high temperature gas-cooled reactors or liquid-metal cooled fast reactors, nor to reactors from other vendors (Russia, China, Korea, India).

• The methodology of Probabilistic Risk Analyses does not cover all kinds of events that could cause a severe reactor accident.

• Other processes of the nuclear process chain, particularly those involving spent fuel, are not included in the published official studies. The emphasis on the reactor safety may partly prompted by the high public visibility of nuclear reactors. The back end processes are nearly invisible to the public but not necessarily less dangerous. On the contrary.

In the USA the Nuclear Regulatory Commission is found to be highly reliant on information from licensee risk assessments. There are no PRA standards, no requirements for licensee's PRAs to be updated or accurate, and the quality of the assessments varies considerably among licensees. How is the situation in other countries? Safety of nuclear power is an exceedingly complex issue, involving a lot more constributing factors than the chance of severe accidents caused by random technical failures. Non-technical factors could initiate severe accidents as well, as proved by the Chernobyl and Fukushima disasters. Nuclear safety comprises more than a few theoretical studies on reactor failure modes.

Spent nuclear fuel pools

Spent fuel cooling pools are high-risk facilities in the nuclear process chain, because they usually contain the spent fuel of many years of reactor operation, involving many thousands of nuclear bomb equivalents, and are vulnarable to accidents. If the cooling fails during a critical period (may be a number days, may be shorter) the pool may boil dry resulting in a meltdown of the spent fuel. This in turn may initiate a criticality event, with uncontrolled fission in the (partially) molten fuel. This happened at Fukushima reactor 3 in 2011. Because spent fuel pools are located outside of the safety containment if the reator, radioactive materals are released unhinderedly. Spent fuel pools at reprocessing plants contain many 10 000's ofnuclear bomb equivalents and may be the most dangerous places in the nuclear world. Safety studies did not include spent fuel storage facilities.

Nuclear safety is not set by safety studies, but by practice

To many people the terms 'safety' and 'safe' may have a connotation of 'little chance of accidents' and/or 'safeguarding against adverse consequences'. Think for example of the perception of safe airliners, of safety in the street (meaning 'little or no criminality') and of safe cars, meaning that the occupants are protected against the effects of an accident. The nuclear industry claims that nuclear power is safe with safe nuclear reactors. In their view the chance of a major reactor accident, involving a core meltdown (the worst case scenario), is one in the several millions of years. Negligible compared to other risks, posed by other events in the society, is said. The claim of safe reactors by the nuclear industry is based on a small number of theoretical studies [more i15]. Empirical evidence proves the results of the reactor safety studies to be of little meaning. During the past decades three major reactor core meltdowns occurred: Three Miles Island (1979), Chernobyl (1986) and Fukushima (2011), a chance of once every 10-20 years.

Main safety concern: dispersion of radioactivity

A unique feature of nuclear power is the generation of huge amounts of man-made radioactivity. All radioactivity is harmful and dangerous to humans. Apart from military and terroristic nuclear explosions, the safety issue of nuclear power concerns the possibilities of dispersion of the radioactivity into the human environment and the exposure of millions of people to radioactivity, leading to insidious and not seldom fatal diseases, usually after a long time delay. This threat exists every day and involves vast and densely inhabited regions of the world: all regions with nuclear power stations and/or activities related to nuclear power. In addition the chance of releases of massive amounts of radioactivity increases year by year, due to:

• rapidly increasing amounts of human-made radioactivity: 370000 nuclear bomb equivalents per year are added to the world inventory

• increasing number of temporary and vulnerable storage facilities,

• unavoidably progressive deterioration of the confinement of the stored radioactive materials [more i39, i43].

•increasing economic pressure, the more so in times of crisis, leading to less than optimal handling of the radioactive wastes.

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