Banana equivalent dose

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Banana_equivalent_dose 

 

A banana contains naturally occurring radioactive material in the form of potassium-40.

Banana equivalent dose (BED) is an informal measurement of ionizing radiation exposure, intended as a general educational example to compare a dose of radioactivity to the dose one is exposed to by eating one average-sized banana. Bananas contain naturally occurring radioactive isotopes, particularly potassium-40 (⁴⁰K), one of several naturally occurring isotopes of potassium. One BED is often correlated to 10⁻⁷ sievert (0.1 μSv); however, in practice, this dose is not cumulative, as the potassium in foods is excreted in urine to maintain homeostasis. The BED is only meant as an educational exercise and is not a formally adopted dose measurement.

History

The origins of the concept are uncertain, but one early mention can be found on the RadSafe nuclear safety mailing list in 1995, where Gary Mansfield of the Lawrence Livermore National Laboratory mentions that he has found the "banana equivalent dose" to be "very useful in attempting to explain infinitesimal doses (and corresponding infinitesimal risks) to members of the public". A value of 9.82×10⁻⁸ sieverts or about 0.1 microsieverts (10 μrem) was suggested for a 150-gram (5.3 oz) banana.

Usage

The banana equivalent dose is an informal measurement, so any equivalences are necessarily approximate, but it has been found useful by some as a way to inform the public about relative radiation risks.

Approximate doses of radiation in sieverts, ranging from trivial to lethal. The BED is the third from the top in the blue section (from Randall Munroe, 2011)

The radiation exposure from consuming a banana is approximately 1% of the average daily exposure to radiation, which is 100 banana equivalent doses (BED). The maximum permitted radiation leakage for a nuclear power plant is equivalent to 2,500 BED (250 μSv) per year, while a chest CT scan delivers 70,000 BED (7 mSv). An acute lethal dose of radiation is approximately 35,000,000 BED (3.5 Sv, 350 rem). A person living 16 kilometres (10 mi) from the Three Mile Island nuclear reactor received an average of 800 BED of exposure to radiation during the 1979 Three Mile Island accident.

Dose calculation

Source of radioactivity

The major natural source of radioactivity in plant tissue is potassium: 0.0117% of the naturally occurring potassium is the unstable isotope potassium-40. This isotope decays with a half-life of about 1.25 billion years (4×10¹⁶ seconds), and therefore the radioactivity of natural potassium is about 31 becquerel/gram (Bq/g), meaning that, in one gram of the element, about 31 atoms will decay every second. Plants naturally contain radioactive carbon-14 (¹⁴C), but in a banana containing 15 grams of carbon this would give off only about 3 to 5 low-energy beta rays per second. Since a typical banana contains about half a gram of potassium, it will have an activity of roughly 15 Bq. Although the amount in a single banana is small in environmental and medical terms, the radioactivity from a truckload of bananas is capable of causing a false alarm when passed through a Radiation Portal Monitor used to detect possible smuggling of nuclear material at U.S. ports.

The dose uptake from ingested material is defined as committed dose, and in the case of the overall effect on the human body of the radioactive content of a banana, it will be the "committed effective dose". This is typically given as the net dose over a period of 50 years resulting from the intake of radioactive material.

According to the US Environmental Protection Agency (EPA), isotopically pure potassium-40 will give a committed dose equivalent of 5.02 nSv over 50 years per becquerel ingested by an average adult. Using this factor, one banana equivalent dose comes out as about 5.02 nSv/Bq × 31 Bq/g × 0.5 g ≈ 78 nSv = 0.078 μSv. In informal publications, one often sees this estimate rounded up to 0.1 μSv. The International Commission on Radiological Protection estimates a coefficient of 6.2 nSv/Bq for the ingestion of potassium-40, with this datum the calculated BED would be 0.096 μSv, closer to the standard value of 0.1 μSv.

Criticism

Several sources point out that the banana equivalent dose is a flawed concept because consuming a banana does not increase one's exposure to radioactive potassium.

The committed dose in the human body due to bananas is not cumulative because the amount of potassium (and therefore of ⁴⁰K) in the human body is fairly constant due to homeostasis, so that any excess absorbed from food is quickly compensated by the elimination of an equal amount.

It follows that the additional radiation exposure due to eating a banana lasts only for a few hours after ingestion, i.e. the time it takes for the normal potassium content of the body to be restored by the kidneys. The EPA conversion factor, on the other hand, is based on the mean time needed for the isotopic mix of potassium isotopes in the body to return to the natural ratio after being disturbed by the ingestion of pure ⁴⁰K, which was assumed by EPA to be 30 days. If the assumed time of residence in the body is reduced by a factor of ten, for example, the estimated equivalent absorbed dose due to the banana will be reduced in the same proportion.

These amounts may be compared to the exposure due to the normal potassium content of the human body of 2.5 grams per kilogram, or 175 grams in a 70 kg adult. This potassium will naturally generate 175 g × 31 Bq/g ≈ 5400 Bq of radioactive decays, constantly through the person's adult lifetime.

Radiation from other household consumables

Other foods rich in potassium (and therefore in ⁴⁰K) include potatoes, kidney beans, sunflower seeds, and nuts.

Brazil nuts in particular (in addition to being rich in ⁴⁰K) may also contain significant amounts of radium, which have been measured at up to 444 Bq/kg (12 nCi/kg).

Tobacco contains traces of thorium, polonium and uranium.

 

Naturally occurring radioactive material

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Naturally_occurring_radioactive_material 

Naturally occurring radioactive materials (NORM) and technologically enhanced naturally occurring radioactive materials (TENORM) consist of materials, usually industrial wastes or by-products enriched with radioactive elements found in the environment, such as uranium, thorium and plutonium and any of their decay products, such as radium and radon. Produced water discharges and spills are a good example of entering NORMs into the surrounding environment.

Natural radioactive elements are present in very low concentrations in Earth's crust, and are brought to the surface through human activities such as oil and gas exploration or mining, and through natural processes like leakage of radon gas to the atmosphere or through dissolution in ground water. Another example of TENORM is coal ash produced from coal burning in power plants. If radioactivity is much higher than background level, handling TENORM may cause problems in many industries and transportation.

NORM in oil and gas exploration

Oil and gas TENORM and/or NORM is created in the production process, when produced fluids from reservoirs carry sulfates up to the surface of the Earth's crust. Some states, such as North Dakota, uses the term "diffuse NORM". Barium, calcium and strontium sulfates are larger compounds, and the smaller atoms, such as radium-226 and radium-228, can fit into the empty spaces of the compound and be carried through the produced fluids. As the fluids approach the surface, changes in the temperature and pressure cause the barium, calcium, strontium and radium sulfates to precipitate out of solution and form scale on the inside, or on occasion, the outside of the tubulars and/or casing. The use of tubulars in the production process that are NORM contaminated does not cause a health hazard if the scale is inside the tubulars and the tubulars remain downhole. Enhanced concentrations of the radium 226 and 228 and the daughter products such as lead-210 may also occur in sludge that accumulates in oilfield pits, tanks and lagoons. Radon gas in the natural gas streams concentrate as NORM in gas processing activities. Radon decays to lead-210, then to bismuth-210, polonium-210 and stabilizes with lead-206. Radon decay elements occur as a shiny film on the inner surface of inlet lines, treating units, pumps and valves associated with propylene, ethane and propane processing systems.

NORM characteristics vary depending on the nature of the waste. NORM may be created in a crystalline form, which is brittle and thin, and can cause flaking to occur in tubulars. NORM formed in carbonate matrix can have a density of 3.5 grams/cubic centimeters and must be noted when packing for transportation. NORM scales may be white or a brown solid, or thick sludge to solid, dry flaky substances. NORM may also be found in oil and gas production produced waters.

Cutting and reaming oilfield pipe, removing solids from tanks and pits, and refurbishing gas processing equipment may expose employees to particles containing increased levels of alpha emitting radionuclides that could pose health risks if inhaled or ingested.

NORM is found in many industries including 

• The coal industry (mining and combustion)
• Metal mining and smelting
• Mineral sands (rare earth minerals, titanium and zirconium).
• Fertilizer (phosphate) industry
• Building industry

Hazards

The hazards associated with NORM are inhalation and ingestion routes of entry as well as external exposure where there has been a significant accumulation of scales. Respirators may be necessary in dry processes, where NORM scales and dust become air borne and have a significant chance to enter the body.

The hazardous elements found in NORM are radium 226, 228 and radon 222 and also daughter products from these radionuclides. The elements are referred to as "bone seekers" which when inside the body migrate to the bone tissue and concentrate. This exposure can cause bone cancers and other bone abnormalities. The concentration of radium and other daughter products build over time, with several years of excessive exposures. Therefore, from a liability standpoint an employee that has not had respiratory protection over several years could develop bone or other cancers from NORM exposure and decide to seek compensation such as medical expenses and lost wages from the oil company which generated the TENORM and the employer.

Radium radionuclides emit alpha and beta particles as well as gamma rays. The radiation emitted from a radium 226 atom is 96% alpha particles and 4% gamma rays. The alpha particle is not the most dangerous particle associated with NORM. Alpha particles are identical with helium-4 nuclei. Alpha particles travel short distances in air, of only 2–3 cm, and cannot penetrate through a dead layer of skin on the human body. However, some radium alpha particle emitters are "bone seekers" due to radium possessing a high affinity for chloride ions. In the case that radium atoms are not expelled from the body, they concentrate in areas where chloride ions are prevalent, such as bone tissue. The half-life for radium 226 is approximately 1,620 years, and will remain in the body for the lifetime of the human — a significant length of time to cause damage.

Beta particles are high energy electrons or positrons. They are in the middle of the scale in terms of ionizing potential and penetrating power, being stopped by a few millimeters of plastic. This radiation is a small portion of the total emitted during radium 226 decay. Radium 228 emits beta particles, and is also a concern for human health through inhalation and ingestion. Beta particles are electrons or positrons and can travel farther than alpha particles in air.

The gamma rays emitted from radium 226, accounting for 4% of the radiation, are harmful to humans with sufficient exposure. Gamma rays are highly penetrating and some can pass through metals, so Geiger counters or a scintillation probe are used to measure gamma ray exposures when monitoring for NORM.

Alpha and beta particles are harmful once inside the body. Breathing NORM contaminates from dusts should be prevented by wearing respirators with particulate filters. In the case of properly trained occupational NORM workers, air monitoring and analysis may be necessary. These measurements, ALI and DAC, are calculated values based on the dose an average employee working 2,000 hours a year may be exposed to. The current legal limit exposure in the United States is 1 ALI, or 5 rems. A rem, or roentgen equivalent man, is a measurement of absorption of radiation on parts of the body over an extended period of time. A DAC is a concentration of alpha and beta particles that an average working employee is exposed to for 2,000 hours of light work. If an employee is exposed to over 10% of an ALI, 500 mREM, then the employee's dose must be documented under instructions with federal and state regulations.

Regulation

United States

NORM is not federally regulated in the United States. The Nuclear Regulatory Commission (NRC) has jurisdiction over a relatively narrow spectrum of radiation, and the Environmental Protection Agency (EPA) has jurisdiction over NORM. Since no federal entity has implemented NORM regulations, NORM is variably regulated by the states.

United Kingdom

In the UK regulation is via the Environmental Permitting (England and Wales) Regulations 2010.

This defines two types of NORM activity:

• Type 1 NORM industrial activity means:

(a) the production and use of thorium, or thorium compounds, and the production of products where thorium is deliberately added; or

(b) the production and use of uranium or uranium compounds, and the production of products where uranium is deliberately added

• Type 2 NORM industrial activity means:

(a) the extraction, production and use of rare earth elements and rare earth element alloys;

(b) the mining and processing of ores other than uranium ore;

(c) the production of oil and gas;

(d) the removal and management of radioactive scales and precipitates from equipment associated with industrial activities;

(e) any industrial activity utilising phosphate ore;

(f) the manufacture of titanium dioxide pigments;

(g) the extraction and refining of zircon and manufacture of zirconium compounds;

(h) the production of tin, copper, aluminium, zinc, lead and iron and steel;

(i) any activity related to coal mine de-watering plants;

(j) china clay extraction;

(k) water treatment associated with provision of drinking water;

or (l) The remediation of contamination from any type 1 NORM industrial activity or any of the activities listed above.

An activity which involves the processing of radionuclides of natural terrestrial or cosmic origin for their radioactive, fissile or fertile properties is not a type 1 NORM industrial activity or a type 2 NORM industrial activity.

 

Environmental impact of hydraulic fracturing

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Environmental_impact_of_hydraulic_fracturing 

 

Hydraulic fracturing
Shale gas drilling rig near Alvarado, Texas

The environmental impact of hydraulic fracturing is related to land use and water consumption, air emissions, including methane emissions, brine and fracturing fluid leakage, water contamination, noise pollution, and health. Water and air pollution are the biggest risks to human health from hydraulic fracturing. Research has determined that hydraulic fracturing negatively affects human health and drives climate change.

Hydraulic fracturing fluids include proppants and other substances, which include chemicals known to be toxic, as well as unknown chemicals that may be toxic. In the United States, such additives may be treated as trade secrets by companies who use them. Lack of knowledge about specific chemicals has complicated efforts to develop risk management policies and to study health effects. In other jurisdictions, such as the United Kingdom, these chemicals must be made public and their applications are required to be nonhazardous.

Water usage by hydraulic fracturing can be a problem in areas that experience water shortage. Surface water may be contaminated through spillage and improperly built and maintained waste pits, in jurisdictions where these are permitted. Further, ground water can be contaminated if fracturing fluids and formation fluids are able to escape during hydraulic fracturing. However, the possibility of groundwater contamination from the fracturing fluid upward migration is negligible, even in a long-term period. Produced water, the water that returns to the surface after hydraulic fracturing, is managed by underground injection, municipal and commercial wastewater treatment, and reuse in future wells. There is potential for methane to leak into ground water and the air, though escape of methane is a bigger problem in older wells than in those built under more recent legislation.

Hydraulic fracturing causes induced seismicity called microseismic events or microearthquakes. The magnitude of these events is too small to be detected at the surface, being of magnitude M-3 to M-1 usually. However, fluid disposal wells (which are often used in the USA to dispose of polluted waste from several industries) have been responsible for earthquakes up to 5.6M in Oklahoma and other states.

Governments worldwide are developing regulatory frameworks to assess and manage environmental and associated health risks, working under pressure from industry on the one hand, and from anti-fracking groups on the other. In some countries like France a precautionary approach has been favored and hydraulic fracturing has been banned. The United Kingdom's regulatory framework is based on the conclusion that the risks associated with hydraulic fracturing are manageable if carried out under effective regulation and if operational best practices are implemented. It has been suggested by the authors of meta-studies that in order to avoid further negative impacts, greater adherence to regulation and safety procedures are necessary.

Air emissions

A report for the European Union on the potential risks was produced in 2012. Potential risks are "methane emissions from the wells, diesel fumes and other hazardous pollutants, ozone precursors or odours from hydraulic fracturing equipment, such as compressors, pumps, and valves". Also gases and hydraulic fracturing fluids dissolved in flowback water pose air emissions risks. One study measured various air pollutants weekly for a year surrounding the development of a newly fractured gas well and detected nonmethane hydrocarbons, methylene chloride (a toxic solvent), and polycyclic aromatic hydrocarbons. These pollutants have been shown to affect fetal outcomes.

The relationship between hydraulic fracturing and air quality can influence acute and chronic respiratory illnesses, including exacerbation of asthma (induced by airborne particulates, ozone and exhaust from equipment used for drilling and transport) and COPD. For example, communities overlying the Marcellus shale have higher frequencies of asthma. Children, active young adults who spend time outdoors, and the elderly are particularly vulnerable. OSHA has also raised concerns about the long-term respiratory effects of occupational exposure to airborne silica at hydraulic fracturing sites. Silicosis can be associated with systemic autoimmune processes.

"In the UK, all oil and gas operators must minimise the release of gases as a condition of their licence from the Department of Energy and Climate Change (DECC). Natural gas may only be vented for safety reasons."

Also transportation of necessary water volume for hydraulic fracturing, if done by trucks, can cause emissions. Piped water supplies can reduce the number of truck movements necessary.

A report from the Pennsylvania Dept of Environmental Protection indicated that there is little potential for radiation exposure from oil and gas operations.

Air pollution is of particular concern to workers at hydraulic fracturing well sites as the chemical emissions from storage tanks and open flowback pits combine with the geographically compounded air concentrations from surrounding wells. Thirty seven percent of the chemicals used in hydraulic fracturing operations are volatile and can become airborne.

Researchers Chen and Carter from the Department of Civil and Environmental Engineering, University of Tennessee, Knoxville used atmospheric dispersion models (AERMOD) to estimate the potential exposure concentration of emissions for calculated radial distances of 5 m to 180m from emission sources. The team examined emissions from 60,644 hydraulic fracturing wells and found “results showed the percentage of wells and their potential acute non-cancer, chronic non-cancer, acute cancer, and chronic cancer risks for exposure to workers were 12.41%, 0.11%, 7.53%, and 5.80%, respectively. Acute and chronic cancer risks were dominated by emissions from the chemical storage tanks within a 20 m radius.

Climate change

Hydraulic fracturing is a driver of climate change. However, whether natural gas produced by hydraulic fracturing causes higher well-to-burner emissions than gas produced from conventional wells is a matter of contention. Some studies have found that hydraulic fracturing has higher emissions due to methane released during completing wells as some gas returns to the surface, together with the fracturing fluids. Depending on their treatment, the well-to-burner emissions are 3.5%–12% higher than for conventional gas.

A debate has arisen particularly around a study by professor Robert W. Howarth finding shale gas significantly worse for global warming than oil or coal. Other researchers have criticized Howarth's analysis, including Cathles et al., whose estimates were substantially lower." A 2012 industry funded report co-authored by researchers at the United States Department of Energy's National Renewable Energy Laboratory found emissions from shale gas, when burned for electricity, were "very similar" to those from so-called "conventional well" natural gas, and less than half the emissions of coal.

Several studies which have estimated lifecycle methane leakage from natural gas development and production have found a wide range of leakage rates. According to the Environmental Protection Agency's Greenhouse Gas Inventory, the methane leakage rate is about 1.4%. A 16-part assessment of methane leakage from natural gas production initiated by the Environmental Defense Fund found that fugitive emissions in key stages of the natural gas production process are significantly higher than estimates in the EPA's national emission inventory, with a leakage rate of 2.3 percent of overall natural gas output.

Water consumption

Massive hydraulic fracturing typical of shale wells uses between 1.2 and 3.5 million US gallons (4,500 and 13,200 m³) of water per well, with large projects using up to 5 million US gallons (19,000 m³). Additional water is used when wells are refractured. An average well requires 3 to 8 million US gallons (11,000 to 30,000 m³) of water over its lifetime. According to the Oxford Institute for Energy Studies, greater volumes of fracturing fluids are required in Europe, where the shale depths average 1.5 times greater than in the U.S. Whilst the published amounts may seem large, they are small in comparison with the overall water usage in most areas. A study in Texas, which is a water shortage area, indicates "Water use for shale gas is <1% of statewide water withdrawals; however, local impacts vary with water availability and competing demands."

A report by the Royal Society and the Royal Academy of Engineering shows the usage expected for hydraulic fracturing a well is approximately the amount needed to run a 1,000 MW coal-fired power plant for 12 hours. A 2011 report from the Tyndall Centre estimates that to support a 9 billion cubic metres per annum (320×10⁹ cu ft/a) gas production industry, between 1.25 to 1.65 million cubic metres (44×10⁶ to 58×10⁶ cu ft) would be needed annually, which amounts to 0.01% of the total water abstraction nationally.

Concern has been raised over the increasing quantities of water for hydraulic fracturing in areas that experience water stress. Use of water for hydraulic fracturing can divert water from stream flow, water supplies for municipalities and industries such as power generation, as well as recreation and aquatic life. The large volumes of water required for most common hydraulic fracturing methods have raised concerns for arid regions, such as the Karoo in South Africa, and in drought-prone Texas, in North America. It may also require water overland piping from distant sources.

A 2014 life cycle analysis of natural gas electricity by the National Renewable Energy Laboratory concluded that electricity generated by natural gas from massive hydraulically fractured wells consumed between 249 gallons per megawatt-hour (gal/MWhr) (Marcellus trend) and 272 gal/MWhr (Barnett Shale). The water consumption for the gas from massive hydraulic fractured wells was from 52 to 75 gal/MWhr greater (26 percent to 38 percent greater) than the 197 gal/MWhr consumed for electricity from conventional onshore natural gas.

Some producers have developed hydraulic fracturing techniques that could reduce the need for water. Using carbon dioxide, liquid propane or other gases instead of water have been proposed to reduce water consumption. After it is used, the propane returns to its gaseous state and can be collected and reused. In addition to water savings, gas fracturing reportedly produces less damage to rock formations that can impede production. Recycled flowback water can be reused in hydraulic fracturing. It lowers the total amount of water used and reduces the need to dispose of wastewater after use. The technique is relatively expensive, however, since the water must be treated before each reuse and it can shorten the life of some types of equipment.

Water contamination

Injected fluid

In the United States, hydraulic fracturing fluids include proppants, radionuclide tracers, and other chemicals, many of which are toxic. The type of chemicals used in hydraulic fracturing and their properties vary. While most of them are common and generally harmless, some chemicals are carcinogenic. Out of 2,500 products used as hydraulic fracturing additives in the United States, 652 contained one or more of 29 chemical compounds which are either known or possible human carcinogens, regulated under the Safe Drinking Water Act for their risks to human health, or listed as hazardous air pollutants under the Clean Air Act. Another 2011 study identified 632 chemicals used in United States natural gas operations, of which only 353 are well-described in the scientific literature. A study that assessed health effects of chemicals used in fracturing found that 73% of the products had between 6 and 14 different adverse health effects including skin, eye, and sensory organ damage; respiratory distress including asthma; gastrointestinal and liver disease; brain and nervous system harms; cancers; and negative reproductive effects.

An expansive study conducted by the Yale School of Public Health in 2016 found numerous chemicals involved in or released by hydraulic fracturing are carcinogenic. Of the 119 compounds identified in this study with sufficient data, “44% of the water pollutants...were either confirmed or possible carcinogens.” However, the majority of chemicals lacked sufficient data on carcinogenic potential, highlighting the knowledge gap in this area. Further research is needed to identify both carcinogenic potential of chemicals used in hydraulic fracturing and their cancer risk.

The European Union regulatory regime requires full disclosure of all additives. According to the EU groundwater directive of 2006, "in order to protect the environment as a whole, and human health in particular, detrimental concentrations of harmful pollutants in groundwater must be avoided, prevented or reduced." In the United Kingdom, only chemicals that are "non hazardous in their application" are licensed by the Environment Agency.

Flowback

Less than half of injected water is recovered as flowback or later production brine, and in many cases recovery is <30%. As the fracturing fluid flows back through the well, it consists of spent fluids and may contain dissolved constituents such as minerals and brine waters. In some cases, depending on the geology of the formation, it may contain uranium, radium, radon and thorium. Estimates of the amount of injected fluid returning to the surface range from 15-20% to 30–70%.

Approaches to managing these fluids, commonly known as produced water, include underground injection, municipal and commercial wastewater treatment and discharge, self-contained systems at well sites or fields, and recycling to fracture future wells. The vacuum multi-effect membrane distillation system as a more effective treatment system has been proposed for treatment of flowback. However, the quantity of waste water needing treatment and the improper configuration of sewage plants have become an issue in some regions of the United States. Part of the wastewater from hydraulic fracturing operations is processed there by public sewage treatment plants, which are not equipped to remove radioactive material and are not required to test for it.

Produced water spills and subsequent contamination of groundwater also presents a risk for exposure to carcinogens. Research that modeled the solute transport of BTEX (benzene, toluene, ethylbenzene, and xylene) and naphthalene for a range of spill sizes on contrasting soils overlying groundwater at different depths found that benzene and toluene were expected to reach human health relevant concentration in groundwater because of their high concentrations in produced water, relatively low solid/liquid partition coefficient and low EPA drinking water limits for these contaminants. Benzene is a known carcinogen which affects the central nervous system in the short term and can affect the bone marrow, blood production, immune system, and urogenital systems with long term exposure.

Surface spills

Surface spills related to the hydraulic fracturing occur mainly because of equipment failure or engineering misjudgments.

Volatile chemicals held in waste water evaporation ponds can evaporate into the atmosphere, or overflow. The runoff can also end up in groundwater systems. Groundwater may become contaminated by trucks carrying hydraulic fracturing chemicals and wastewater if they are involved in accidents on the way to hydraulic fracturing sites or disposal destinations.

In the evolving European Union legislation, it is required that "Member States should ensure that the installation is constructed in a way that prevents possible surface leaks and spills to soil, water or air." Evaporation and open ponds are not permitted. Regulations call for all pollution pathways to be identified and mitigated. The use of chemical proof drilling pads to contain chemical spills is required. In the UK, total gas security is required, and venting of methane is only permitted in an emergency.

Methane

In September 2014, a study from the US Proceedings of the National Academy of Sciences released a report that indicated that methane contamination can be correlated to distance from a well in wells that were known to leak. This however was not caused by the hydraulic fracturing process, but by poor cementation of casings.

Groundwater methane contamination has adverse effect on water quality and in extreme cases may lead to potential explosion. A scientific study conducted by researchers of Duke University found high correlations of gas well drilling activities, including hydraulic fracturing, and methane pollution of the drinking water. According to the 2011 study of the MIT Energy Initiative, "there is evidence of natural gas (methane) migration into freshwater zones in some areas, most likely as a result of substandard well completion practices i.e. poor quality cementing job or bad casing, by a few operators." A 2013 Duke study suggested that either faulty construction (defective cement seals in the upper part of wells, and faulty steel linings within deeper layers) combined with a peculiarity of local geology may be allowing methane to seep into waters; the latter cause may also release injected fluids to the aquifer. Abandoned gas and oil wells also provide conduits to the surface in areas like Pennsylvania, where these are common.

A study by Cabot Oil and Gas examined the Duke study using a larger sample size, found that methane concentrations were related to topography, with the highest readings found in low-lying areas, rather than related to distance from gas production areas. Using a more precise isotopic analysis, they showed that the methane found in the water wells came from both the formations where hydraulic fracturing occurred, and from the shallower formations. The Colorado Oil & Gas Conservation Commission investigates complaints from water well owners, and has found some wells to contain biogenic methane unrelated to oil and gas wells, but others that have thermogenic methane due to oil and gas wells with leaking well casing. A review published in February 2012 found no direct evidence that hydraulic fracturing actual injection phase resulted in contamination of ground water, and suggests that reported problems occur due to leaks in its fluid or waste storage apparatus; the review says that methane in water wells in some areas probably comes from natural resources.

Another 2013 review found that hydraulic fracturing technologies are not free from risk of contaminating groundwater, and described the controversy over whether the methane that has been detected in private groundwater wells near hydraulic fracturing sites has been caused by drilling or by natural processes.

Radionuclides

Main article: Naturally occurring radioactive material

There are naturally occurring radioactive materials (NORM), for example radium, radon, uranium, and thorium, in shale deposits. Brine co-produced and brought to the surface along with the oil and gas sometimes contains naturally occurring radioactive materials; brine from many shale gas wells, contains these radioactive materials. The U.S. Environmental Protection Agency and regulators in North Dakota consider radioactive material in flowback a potential hazard to workers at hydraulic fracturing drilling and waste disposal sites and those living or working nearby if the correct procedures are not followed. A report from the Pennsylvania Department of Environmental Protection indicated that there is little potential for radiation exposure from oil and gas operations.

Land usage

In the UK, the likely well spacing visualised by the December 2013 DECC Strategic Environmental Assessment report indicated that well pad spacings of 5 km were likely in crowded areas, with up to 3 hectares (7.4 acres) per well pad. Each pad could have 24 separate wells. This amounts to 0.16% of land area. A study published in 2015 on the Fayetteville Shale found that a mature gas field impacted about 2% of the land area and substantially increased edge habitat creation. Average land impact per well was 3 hectares (about 7 acres)  Research indicates that effects on ecosystem services costs (i.e. those processes that the natural world provides to humanity) has reached over $250 million per year in the U.S.

Seismicity

Hydraulic fracturing causes induced seismicity called microseismic events or microearthquakes. These microseismic events are often used to map the horizontal and vertical extent of the fracturing. The magnitude of these events is usually too small to be detected at the surface, although the biggest micro-earthquakes may have the magnitude of about -1.5 (M_w).

Induced seismicity from hydraulic fracturing

As of August 2016, there were at least nine known cases of fault reactivation by hydraulic fracturing that caused induced seismicity strong enough to be felt by humans at the surface: In Canada, there have been three in Alberta (M 4.8 and M 4.4 and M 4.4) and three in British Columbia (M 4.6, M 4.4 and M 3.8); In the United States there has been: one in Oklahoma (M 2.8) and one in Ohio (M 3.0), and; In the United Kingdom, there have been two in Lancashire (M 2.3 and M 1.5).

Induced seismicity from water disposal wells

According to the USGS only a small fraction of roughly 30,000 waste fluid disposal wells for oil and gas operations in the United States have induced earthquakes that are large enough to be of concern to the public. Although the magnitudes of these quakes has been small, the USGS says that there is no guarantee that larger quakes will not occur. In addition, the frequency of the quakes has been increasing. In 2009, there were 50 earthquakes greater than magnitude 3.0 in the area spanning Alabama and Montana, and there were 87 quakes in 2010. In 2011 there were 134 earthquakes in the same area, a sixfold increase over 20th century levels. There are also concerns that quakes may damage underground gas, oil, and water lines and wells that were not designed to withstand earthquakes.

A 2012 US Geological Survey study reported that a "remarkable" increase in the rate of M ≥ 3 earthquakes in the US midcontinent "is currently in progress", having started in 2001 and culminating in a 6-fold increase over 20th century levels in 2011. The overall increase was tied to earthquake increases in a few specific areas: the Raton Basin of southern Colorado (site of coalbed methane activity), and gas-producing areas in central and southern Oklahoma, and central Arkansas. While analysis suggested that the increase is "almost certainly man-made", the USGS noted: "USGS's studies suggest that the actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes." The increased earthquakes were said to be most likely caused by increased injection of gas-well wastewater into disposal wells. The injection of waste water from oil and gas operations, including from hydraulic fracturing, into saltwater disposal wells may cause bigger low-magnitude tremors, being registered up to 3.3 (M_w).

Noise

Each well pad (in average 10 wells per pad) needs during preparatory and hydraulic fracturing process about 800 to 2,500 days of activity, which may affect residents. In addition, noise is created by transport related to the hydraulic fracturing activities. Noise pollution from hydraulic fracturing operations (e.g., traffic, flares/burn-offs) is often cited as a source of psychological distress, as well as poor academic performance in children. For example, the low-frequency noise that comes from well pumps contributes to irritation, unease, and fatigue.

The UK Onshore Oil and Gas (UKOOG) is the industry representative body, and it has published a charter that shows how noise concerns will be mitigated, using sound insulation, and heavily silenced rigs where this is needed.

Safety issues

In July 2013, the United States Federal Railroad Administration listed oil contamination by hydraulic fracturing chemicals as "a possible cause" of corrosion in oil tank cars.

Community impacts

Impacted communities are often already vulnerable, including poor, rural, or indigenous persons, who may continue to experience the deleterious effects of hydraulic fracturing for generations. Competition for resources between farmers and oil companies contributes to stress for agricultural workers and their families, as well as to a community-level “us versus them” mentality that creates community distress (Morgan et al. 2016). Rural communities that host hydraulic fracturing operations often experience a “boom/bust cycle,” whereby their population surges, consequently exerting stress on community infrastructure and service provision capabilities (e.g., medical care, law enforcement).

Indigenous and agricultural communities may be particularly impacted by hydraulic fracturing, given their historical attachment to, and dependency on, the land they live on, which is often damaged as a result of the hydraulic fracturing process. Native Americans, particularly those living on rural reservations, may be particularly vulnerable to the effects of fracturing; that is, on the one hand, tribes may be tempted to engage with the oil companies to secure a source of income but, on the other hand, must often engage in legal battles to protect their sovereign rights and the natural resources of their land.

Policy and science

Main article: Regulation of hydraulic fracturing

There are two main approaches to regulation that derive from policy debates about how to manage risk and a corresponding debate about how to assess risk.

The two main schools of regulation are science-based assessment of risk and the taking of measures to prevent harm from those risks through an approach like hazard analysis, and the precautionary principle, where action is taken before risks are well-identified. The relevance and reliability of risk assessments in communities where hydraulic fracturing occurs has also been debated amongst environmental groups, health scientists, and industry leaders. The risks, to some, are overplayed and the current research is insufficient in showing the link between hydraulic fracturing and adverse health effects, while to others the risks are obvious and risk assessment is underfunded.

Different regulatory approaches have thus emerged. In France and Vermont for instance, a precautionary approach has been favored and hydraulic fracturing has been banned based on two principles: the precautionary principle and the prevention principle. Nevertheless, some States such as the U.S. have adopted a risk assessment approach, which had led to many regulatory debates over the issue of hydraulic fracturing and its risks.

In the UK, the regulatory framework is largely being shaped by a report commissioned by the UK Government in 2012, whose purpose was to identify the problems around hydraulic fracturing and to advise the country's regulatory agencies. Jointly published by the Royal Society and the Royal Academy of Engineering, under the chairmanship of Professor Robert Mair, the report features ten recommendations covering issues such as groundwater contamination, well integrity, seismic risk, gas leakages, water management, environmental risks, best practice for risk management, and also includes advice for regulators and research councils. The report was notable for stating that the risks associated with hydraulic fracturing are manageable if carried out under effective regulation and if operational best practices are implemented.

A 2013 review concluded that, in the US, confidentiality requirements dictated by legal investigations have impeded peer-reviewed research into environmental impacts.

There are numerous scientific limitations to the study of the environmental impact of hydraulic fracturing. The main limitation is the difficulty in developing effective monitoring procedures and protocols, for which there are several main reasons:

• Variability among fracturing sites in terms of ecosystems, operation sizes, pad densities, and quality-control measures makes it difficult to develop a standard protocol for monitoring.
• As more fracturing sites develop, the chance for interaction between sites increases, greatly compounding the effects and making monitoring of one site difficult to control. These cumulative effects can be difficult to measure, as many of the impacts develop very slowly.
• Due to the vast number of chemicals involved in hydraulic fracturing, developing baseline data is challenging. In addition, there is a lack of research on the interaction of the chemicals used in hydraulic fracturing fluid and the fate of the individual components.

Relativistic rocket

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Relativistic_rocket 

Relativistic rocket refers to any spacecraft that travels at a velocity close enough to light speed for relativistic effects to become significant. The meaning of "significant" is a matter of context, but often a threshold velocity of 30% to 50% of the speed of light (0.3c to 0.5c) is used. At 30% of c, the difference between relativistic mass and rest mass is only about 5%, while at 50% it is 15%, (at 0.75c the difference is over 50%) so that above this range of speeds special relativity is required to accurately describe motion, whereas below this range sufficient accuracy is usually provided by Newtonian physics and the Tsiolkovsky rocket equation.

In this context, a rocket is defined as an object carrying all of its reaction mass, energy, and engines with it.

There is no known technology capable of accelerating a rocket to relativistic velocities. Relativistic rockets require enormous advances in spacecraft propulsion, energy storage, and engine efficiency which may or may not ever be possible. Nuclear pulse propulsion could theoretically achieve 0.1c using current known technologies, but would still require many engineering advances to achieve this. The relativistic gamma factor (${\displaystyle \gamma }$) at 10% of light velocity is 1.005. The time dilation factor of 1.005 which occurs at 10% of light velocity is too small to be of major significance. A 0.1c velocity interstellar rocket is thus considered to be a non-relativistic rocket because its motion is quite accurately described by Newtonian physics alone.

Relativistic rockets are usually seen discussed in the context of interstellar travel, since most would require a great deal of space to accelerate up to those velocities. They are also found in some thought experiments such as the twin paradox.

Relativistic rocket equation

As with the classical rocket equation, one wants to calculate the velocity change ${\displaystyle \Delta v}$ that a rocket can achieve depending on the exhaust velocity ${\displaystyle v_{e}}$ and the mass ratio, i. e. the ratio of starting rest mass ${\displaystyle m_{0}}$ and rest mass at the end of the acceleration phase (dry mass) ${\displaystyle m_{1}}$.

In order to make the calculations simpler, we assume that the acceleration is constant (in the rocket's reference frame) during the acceleration phase; however, the result is nonetheless valid if the acceleration varies, as long as exhaust velocity ${\displaystyle v_{e}}$ is constant.

In the nonrelativistic case, one knows from the (classical) Tsiolkovsky rocket equation that

${\displaystyle \Delta v=v_{e}\ln {\frac {m_{0}}{m_{1}}}.}$

Assuming constant acceleration ${\displaystyle a}$, the time span ${\displaystyle t}$ during which the acceleration takes place is

${\displaystyle t={\frac {v_{e}}{a}}\ln {\frac {m_{0}}{m_{1}}}.}$

In the relativistic case, the equation is still valid if ${\displaystyle a}$ is the acceleration in the rocket's reference frame and ${\displaystyle t}$ is the rocket's proper time because at velocity 0 the relationship between force and acceleration is the same as in the classical case. Solving this equation for the ratio of initial mass to final mass gives

${\displaystyle {\frac {m_{0}}{m_{1}}}=\exp \left[{\frac {at}{v_{e}}}\right].}$

where "exp" is the exponential function. Another related equation gives the mass ratio in terms of the end velocity ${\displaystyle \Delta v}$ relative to the rest frame (i. e. the frame of the rocket before the acceleration phase):

${\displaystyle {\frac {m_{0}}{m_{1}}}=\left[{\frac {1+{\frac {\Delta v}{c}}}{1-{\frac {\Delta v}{c}}}}\right]^{\frac {c}{2v_{e}}}.}$

For constant acceleration, ${\displaystyle {\frac {\Delta v}{c}}=\tanh \left[{\frac {at}{c}}\right]}$ (with a and t again measured on board the rocket), so substituting this equation into the previous one and using the hyperbolic function identity ${\displaystyle \tanh x={\frac {e^{2x}-1}{e^{2x}+1}}}$ returns the earlier equation ${\displaystyle {\frac {m_{0}}{m_{1}}}=\exp \left[{\frac {at}{v_{e}}}\right]}$.

By applying the Lorentz transformation, one can calculate the end velocity ${\displaystyle \Delta v}$ as a function of the rocket frame acceleration and the rest frame time ${\displaystyle t'}$; the result is

${\displaystyle \Delta v={\frac {at'}{\sqrt {1+{\frac {(at')^{2}}{c^{2}}}}}}.}$

The time in the rest frame relates to the proper time by the hyperbolic motion equation:

${\displaystyle t'={\frac {c}{a}}\sinh \left({\frac {at}{c}}\right).}$

Substituting the proper time from the Tsiolkovsky equation and substituting the resulting rest frame time in the expression for ${\displaystyle \Delta v}$, one gets the desired formula:

${\displaystyle \Delta v=c\tanh \left({\frac {v_{e}}{c}}\ln {\frac {m_{0}}{m_{1}}}\right).}$

The formula for the corresponding rapidity (the inverse hyperbolic tangent of the velocity divided by the speed of light) is simpler:

${\displaystyle \Delta r={\frac {v_{e}}{c}}\ln {\frac {m_{0}}{m_{1}}}.}$

Since rapidities, contrary to velocities, are additive, they are useful for computing the total ${\displaystyle \Delta v}$ of a multistage rocket.

Matter-antimatter annihilation rockets

It is clear on the basis of the above calculations that a relativistic rocket would likely need to be a rocket that is fueled by antimatter. Other antimatter rockets in addition to the photon rocket that can provide a 0.6c specific impulse (studied for basic hydrogen-antihydrogen annihilation, no ionization, no recycling of the radiation) needed for interstellar space flight include the "beam core" pion rocket. In a pion rocket, antimatter is stored inside electromagnetic bottles in the form of frozen antihydrogen. Antihydrogen, like regular hydrogen, is diamagnetic which allows it to be electromagnetically levitated when refrigerated. Temperature control of the storage volume is used to determine the rate of vaporization of the frozen antihydrogen, up to a few grams per second (amounting to several petawatts of power when annihilated with equal amounts of matter). It is then ionized into antiprotons which can be electromagnetically accelerated into the reaction chamber. The positrons are usually discarded since their annihilation only produces harmful gamma rays with negligible effect on thrust. However, non-relativistic rockets may exclusively rely on these gamma rays for propulsion. This process is necessary because un-neutralized antiprotons repel one another, limiting the number that may be stored with current technology to less than a trillion.

Design notes on a pion rocket

The pion rocket has been studied independently by Robert Frisbee and Ulrich Walter, with similar results. Pions, short for pi-mesons, are produced by proton-antiproton annihilation. The antihydrogen or the antiprotons extracted from it will be mixed with a mass of regular protons pumped inside the magnetic confinement nozzle of a pion rocket engine, usually as part of hydrogen atoms. The resulting charged pions will have a velocity of 0.94c (i.e. ${\displaystyle \beta }$ = 0.94), and a Lorentz factor ${\displaystyle \gamma }$ of 2.93 which extends their lifespan enough to travel 2.6 meters through the nozzle before decaying into muons. Sixty percent of the pions will have either a negative, or a positive electric charge. Forty percent of the pions will be neutral. The neutral pions will decay immediately into gamma rays. These can't be reflected by any known material at the energies involved, although they can undergo Compton scattering. They can be absorbed efficiently by a shield of tungsten placed between the pion rocket engine reaction volume and the crew modules and various electromagnets to protect them from the gamma rays. The consequent heating of the shield will cause it to radiate visible light, which could then be collimated to increase the rocket's specific impulse. The remaining heat will also require the shield to be refrigerated. The charged pions would travel in helical spirals around the axial electromagnetic field lines inside the nozzle and in this way the charged pions could be collimated into an exhaust jet that is moving at 0.94c. In realistic matter/antimatter reactions, this jet only represents a fraction of the reaction's mass-energy : over 60% of it is lost as gamma-rays, collimation is not perfect, and some pions are not reflected backwards by the nozzle. Thus, the effective exhaust velocity for the entire reaction drops to just 0.58c. Alternative propulsion schemes include physical confinement of hydrogen atoms in an antiproton and pion-transparent beryllium reaction chamber with collimation of the reaction products achieved with a single external electromagnet; see Project Valkyrie.