Nuclear marine propulsion

Nuclear marine propulsion is propulsion of a ship or submarine with heat provided by a nuclear power plant. The power plant heats water to produce steam for a turbine used to turn the ship's propeller through a gearbox or through an electric generator and motor. Naval nuclear propulsion is used within naval warships such as supercarriers. A small number of experimental civil nuclear ships have been built. Compared to oil or coal fuelled ships, nuclear propulsion offers the advantages of long intervals of operation before refueling. All the fuel is contained within the nuclear reactor, so no cargo or supplies space is taken up by fuel, nor is space taken up by exhaust stacks or combustion air intakes. However, the low fuel cost is offset by the high operating costs and investment in infrastructure, so nearly all nuclear-powered vessels are military ones. Most naval nuclear reactors are of the pressurized water type. A primary water circuit transfers heat generated from nuclear fission in the fuel to a steam generator.

This circuit operates at a temperature of around 250 to 300 °C. Any radioactive contamination in the primary water is confined. Water is circulated by pumps; the hot water from the reactor heats a separate water circuit in the steam generator. The water passes through steam driers on its way to the steam turbine. Spent steam at low pressure is run through a condenser cooled by seawater and returns to liquid form; the water continues the cycle. Any water lost in the process can be made up by desalinated sea water added to the steam generator feed water. In the turbine, the steam expands and reduces its pressure as it imparts energy to the rotating blades of the turbine. There may be many stages of fixed guide vanes; the output shaft of the turbine may be connected to a gearbox to reduce rotation speed a shaft connects to the vessel's propellers. In another form of drive system, the turbine turns an electrical generator, the electric power produced is fed to one or more drive motors for the vessel's propellers.

The Russian, US and British navies rely on direct steam turbine propulsion, while French and Chinese ships use the turbine to generate electricity for propulsion. Some nuclear submarines have a single reactor, but Russian submarines have two, so had USS Triton. Most American aircraft carriers are powered by two reactors; the majority of marine reactors are of the pressurized water type, although the US and Soviet navies have designed warships powered with liquid metal cooled reactors. Marine-type reactors differ from land-based commercial electric power reactors in several respects. While land-based reactors in nuclear power plants produce up to around 1600 megawatts of electrical power, a typical marine propulsion reactor produces no more than a few hundred megawatts. Space considerations dictate that a marine reactor must be physically small, so it must generate higher power per unit of space; this means. Its mechanical systems must operate flawlessly under the adverse conditions encountered at sea, including vibration and the pitching and rolling of a ship operating in rough seas.

Reactor shutdown mechanisms cannot rely on gravity to drop control rods into place as in a land-based reactor that always remains upright. Salt water corrosion is an additional problem; as the core of a seagoing reactor is much smaller than a power reactor, the probability of a neutron intersecting with a fissionable nucleus before it escapes into the shielding is much lower. As such, the fuel is more enriched than that used in a land-based nuclear power plant, which increases the probability of fission to the level where a sustained reaction can occur; some marine reactors run on low-enriched uranium which requires more frequent refueling. Others run on enriched uranium, varying from 20% 235U, to the over 96% 235U found in U. S. submarines, in which the resulting smaller core is quieter in operation. Using more-highly enriched fuel increases the reactor's power density and extends the usable life of the nuclear fuel load, but is more expensive and a greater risk to nuclear proliferation than less-highly enriched fuel.

A marine nuclear propulsion plant must be designed to be reliable and self-sufficient, requiring minimal maintenance and repairs, which might have to be undertaken many thousands of miles from its home port. One of the technical difficulties in designing fuel elements for a seagoing nuclear reactor is the creation of fuel elements which will withstand a large amount of radiation damage. Fuel elements may crack over time and gas bubbles may form; the fuel used in marine reactors is a metal-zirconium alloy rather than the ceramic UO2 used in land-based reactors. Marine reactors are designed for long core life, enabled by the high enrichment of the uranium and by incorporating a "burnable poison" in the fuel elements, depleted as the fuel elements age and become less reactive; the gradual dissipation of the "nuclear poison" increases the reactivity of the core to compensate for the lessening reactivity of the aging fuel elements, thereby lengthening the usable life of the fuel. The life of the compact reactor pressure vessel is extended by providing an internal neutron shield, which reduces the damage to th

Markos Dounis

Markos Dounis is a Greek professional footballer who plays as a forward for Football League club Trikala. He started his career at the youth teams of Panionios and was promoted to the first team on 8 July 2007. Before the end of the 2013–14 season Dounis agreed to join AEK Athens on a three-year contact, made effective on 1 July 2014, he made his debut on 29 August in 4-0 home win Fokikos for the Greek Cup. On 17 December 2014 he scored his first goal in a comfortable 4-0 win against Fostiras. Despite the three-year duration of his contact, he was released on 11 September 2015, as he wasn't part of the team's plans. On 16 September 2015 he signed for Aris. At the end of the season he celebrated promotion to the Football League. On 30 August 2016, he extended his contract for two seasons. On 12 February 2017, he scored once and was sent-off in a dramatic 2-2 away draw against Apollon Smyrni. On 25 November 2017, he scored one goal and had one assist in a dramatic 3-2 away win against Ergotelis, after a catastrophic first half, which found his team being down by two goals.

On 7 January 2018, he sealed. One week he opened the score in a 2-0 away win against Apollon Larissa. On 18 March 2018, Dounis came in as a substitute and scored a crucial 88th-minute equalizer with his first free-kick goal in a 1-1 away draw against Panachaiki. At the end of the season he celebrated promotion to the Superleague, before leaving the club, following the expiration of his contract. On 17 August 2018, he moved to Iraklis on a two-year deal. On 2 December 2018, he scored, his favorite football player is Cristiano Ronaldo and one day he wants to play with him in the same team. AEK AthensFootball League: 2014–15 Insports profile Markos Dounis at Soccerway

Pedro Miguel Aráoz

Pedro Miguel Aráoz was an Argentine statesman and priest. He was a representative to the Congress of Tucumán which on 9 July 1816 declared the Independence of Argentina. Aráoz was born in Tucumán to Francisca Nuñez de Herrera, he studied in Tucumán was educated in theology in Buenos Aires at the Real Colegio de San Carlos. He received his doctorate in 1782 at the University of Córdoba, was ordained in Tucumán, he became rector of Tucumán Cathedral. Aráoz assisted Manuel Belgrano in the Army of the North, he was served in 1816 for the declaration. After the Congress moved to Buenos Aires, he returned to his hometown, he collaborated in local politics with his close relative, Bernabé Aráoz, assisting in the 1820 formation of the Republic of Tucumán and serving as a legislator in the provincial assembly. He was the editor of the first provincial newspaper. After the death of Bernabé and the collapse of the Tucumán Republic, Aráoz played no further part in politics