Glossary - Letter R

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Radioactive Decay

Process affecting all radioactive elements in which they gradually and steadily lose atoms. It is expressed as half-life, which is the time it takes for half of an element’s atoms to decay. Half-life may be very short (fractions of a second) or extremely long (several billion years). This property is used to date objects (carbon-14 dating of objects a few hundred to 50,000 year old) and calculate the age of the Earth (uranium-238) or the universe (thorium-232).

Radioactive Waste

Describes the many by-products resulting from the fission of uranium-235, the fuel used in nuclear power plants, as well as all items and materials contaminated through use in the power plant. Radioactive waste is classified according to its radiation level (very low level to high level) and life span (a few seconds to several hundred thousand years). The most hazardous form of radioactive waste is high level long-lived waste, which represents just 0.2% of all waste but 96% of total radioactivity.


Discovered by French physicist Henri Becquerel in 1896, a natural phenomenon whereby unstable atomic nuclei split into two (sometimes three) lighter nuclei, releasing high-energy electromagnetic waves or particles.


Discovered by Pierre and Marie Curie in 1898 (which led to Marie Curie's second Nobel Prize, in 1911), a rare, naturally occurring radioactive element formed by the decay of uranium and thorium. Its use for unproved, non-medical preventive therapeutic and wellness purposes was banned in 1937 following a number of suspicious deaths.


Rare, odorless gas formed by the decay of radium (itself formed by the natural decay of uranium and thorium). Radon’s high radioactivity and its highly diffusive, gaseous nature make it the number one contributor to natural radiation exposure in humans. It can pose a critical health risk in confined spaces. Some regions, especially those with uranium in rock and soil, have higher levels of radon than others.


In mathematics, the relationship between two numbers (the ratio of x to y is equal to x/y). Often expressed as a percentage.

Recovery Rate (Oil and Gas)

Percentage of oil or gas that can be recovered from the deposit during production, versus the total amount of contained. Depending on the deposit, the recovery rate of crude oil ranges from 5 to 50%. It is crucial to the development of deposits: for large reservoirs, just a few percentage points more translate into huge quantities of oil. An additional 1% of production from all fields worldwide would be enough to meet global demand for two to three years.


Any waste treatment process that uses materials from identical or similar end-of-life products or manufacturing waste to produce new products.


An industrial facility where crude oil is converted into different petroleum products used for various purposes, for instance in engines, transportation and heating and as feedstock for such products as plastics.


All industrial processes used to obtain various petroleum products, such as gas, gasoline, heating oil and asphalt, from crude oil.

Refining Margin

The gross refining margin is the difference between the value of petroleum products, such as gasoline and diesel, when they leave the refinery and the value of the crude oil entering the refinery. These values are determined by the market based on inventory, demand, geopolitical and other factors. The net refining margin is equal to the gross refining margin minus committed fixed costs and operating costs.

Reforming (refining)

The various technologies deployed to convert certain hydrocarbon molecules into more technically or economically advantageous components. An example is the catalytic reforming of naphthenic (cyclic, saturated) hydrocarbons into aromatic (cyclic, unsaturated) hydrocarbons that have a better octane rating.

Refueling (Nuclear)

Operation to replace the nuclear fuel assemblies in the reactor vessel. One-third of the fuel assembles are replaced every three or four years. The reactor has to be shut down during refueling.

Renewable Energy

Energy sources that are naturally replenished so quickly — sometimes immediately — that they can be considered inexhaustible on a human time scale. The most widely used are solar energy, wind energy, hydropower, biomass and geothermal energy.

Reserves (deposit)

An oil or gas deposit’s reserves comprise the total amount of its producible resources, from first oil or gas to the deposit’s abandonment. They depend among other things on the development plan (number and location of production wells), production methods and producing life.
The term “strategic petroleum reserve” refers to the oil stockpiles held permanently by many governments, to deal with an emergency situation created by oil supply cutbacks or interruptions by foreign countries.

Reservoir Rock

Located beneath the cap rock, porous and permeable rock in which large amounts of oil and gas accumulate, similar to a sponge. The quality of a reservoir depends on how porous and permeable it is. There are two categories of reservoir rock: clastic (sandstone) and carbonate (limestone and dolomite).


In offshore oil production, risers link the seabed to the surface and are primarily used to transfer oil or gas to the production platform or vessel. Risers also include lines for injecting water, if needed, and, in the deep offshore, for transmitting data from the surface to subsea production units. They may be rigid or relatively flexible and are generally equipped with buoyancy modules.

Rotor (Wind Energy)

Part of a wind turbine comprised of a hub and blades. It converts wind energy into mechanical energy.