Unlike a PWR, there is no primary and secondary loop.

Two things are characteristic for the pressurized water reactor ( PWR ) when compared with other reactor types: coolant loop separation from the steam system and pressure inside the primary coolant loop.

In a PWR, there are two separate coolant loops ( primary and secondary ), which are both filled with demineralized / deionized water.

Light water is used as the primary coolant in a PWR.

* PWR turbine cycle loop is separate from the primary loop, so the water in the secondary loop is not contaminated by radioactive materials.

In both the PWR and the BWR there are secondary systems ( and often even tertiary systems ) that will insert control rods in the event that primary rapid insertion does not promptly and fully actuate.

In the PWR, these neutron absorbing solutions are stored in pressurized tanks ( called accumulators ) that are attached to the primary coolant system via valves ; a varying level of neutron absorbent is kept within the primary coolant at all times, and is increased using the accumulators in the event of a failure of all of the control rods to insert, which will promptly bring the reactor below the shutdown margin.

In category B ( 2 + 3 + 4 ) is the surge line, which connects the hot leg with the pressurizer and helps to control the pressure in the primary loop of a PWR and uses a moving working fluid when fulfilling its mission.

Usually there are also other means of controlling reactivity: In the PWR design a soluble neutron absorber ( boric acid ) is added to the reactor coolant allowing the complete extraction of the control rods during stationary power operation ensuring an even power and flux distribution over the entire core.

A boiling water reactor is cooled and moderated by water like a PWR, but at a lower pressure, which allows the water to boil inside the pressure vessel producing the steam that runs the turbines.

However, sodium explodes violently when exposed to water, so care must be taken, but such explosions would not be vastly more violent than ( for example ) a leak of superheated fluid from a SCWR or PWR.

This and the risks posed by liquid sodium in the event of an accident at sea led Admiral Rickover to select the PWR ( pressurized water reactor ) as the standard US naval reactor type.

PWR fuel bundle This fuel bundle is from a pressurized water reactor of the nuclear passenger and cargo ship NS Savannah | NS Savannah.

* Because water acts as a neutron moderator, it is not possible to build a fast neutron reactor with a PWR design.

It is the second most common type of electricity-generating nuclear reactor after the pressurized water reactor ( PWR ), also a type of light water nuclear reactor.

The main difference between a BWR and PWR is that in a BWR, the reactor core heats water, which turns to steam and then drives a steam turbine.

In a PWR, the reactor core heats water, which does not boil.

It was promoted as a development of the operationally ( if not economically ) successful Magnox design, and was chosen from a plethora of competing British alternatives-the helium cooled High Temperature Reactor ( HTR ), the Steam Generating Heavy Water Reactor ( SGHWR ) and the Fast Breeder Reactor ( FBR )-as well as the American light water pressurised and boiling water reactors ( PWR and BWR ) and Canadian CANDU designs.

In commercial reactor operations, this emergency shutdown is often referred to as a " SCRAM " at boiling water reactors ( BWR ), and as a " reactor trip " at pressurized water reactors ( PWR ).

Like all operational U. S. naval reactors it was a pressurized water reactor ( PWR ) design.

Light water reactors ( BWR, PWR ) and heavy water reactors ( HWR ) operate with " thermal " neutrons, whereas breeder reactors operate with " fast " neutrons.

In pressurised water reactors ( PWR ), they are inserted from above, the control rod drive mechanisms being mounted on the reactor pressure vessel head.

The Rolls-Royce pressurised water reactor ( PWR ) series has powered British nuclear submarines since the Valiant class, commissioned in 1966.

All reactors will be compared to the Pressurized Water Reactor ( PWR ), as that is the standard modern reactor design.

:: A BWR is like a PWR without the steam generator.

Instead of using a single large pressure vessel as in a PWR, the fuel is contained in hundreds of pressure tubes.

Most BWR and PWR commercial reactors use uranium enriched to about 4 % U-235, and some commercial reactors with a high neutron economy do not require the fuel to be enriched at all ( that is, they can use natural uranium ).

( This is in contrast to early Soviet civil PWR designs where embrittlement occurs due to neutron bombardment of a very narrow pressure vessel.

* PWR technology is favoured by nations seeking to develop a nuclear navy, the compact reactors fit well in nuclear submarines and other nuclear ships.

In this event there is a high danger of hydrogen explosions, threatening structural damage and / or the exposure of highly radioactive stored fuel rods in the vicinity outside the plant in pools ( approximately 15 tons of fuel is replenished each year to maintain normal PWR operation ).

Nuclear fission is also used as a heat source for generating steam, either directly ( BWR ) or, in most cases, in specialized heat exchangers called " steam generators " ( PWR ).

The village itself is overshadowed by two separate nuclear power stations, the Magnox Sizewell A and Pressurized Water Reactor ( PWR ) Sizewell B, which are readily visible from the nearby holiday beaches.

However PWR reactors also require years of powered pumped cooling water.

These reactors can function much like a PWR in terms of efficiency, and do not require much high pressure containment, as the liquid metal does not need to be kept at high pressure, even at very high temperatures.

PWR containments are typically large ( up to 10 times larger than a BWR ) because the containment strategy during the leakage design basis accident entails providing adequate volume for the steam / air mixture that results from a loss-of-coolant-accident to expand into, limiting the ultimate pressure ( driving force for leakage ) reached in the containment building.

PWR reactor vessel

A typical PWR has fuel assemblies of 200 to 300 rods each, and a large reactor would have about 150 – 250 such assemblies with 80 – 100 tonnes of uranium in all.

* PWR reactors are very stable due to their tendency to produce less power as temperatures increase ; this makes the reactor easier to operate from a stability standpoint.

But the German company Siemens also retains 34 % of the shares of Areva's subsidiary, Areva NP, in charge of building the EPR, an advanced Generation III + PWR nuclear reactor.

Due to the nature of the core design, the size of containment for the same power rating is often larger than for a typical PWR, but many innovations have reduced this requirement.

File: Three Mile Island ( color )- 2. jpg | Three Mile Island was an early PWR design by Babcock and Wilcox, and shows a ' can ' containment design that is common to all of its generations

File: Pickering_Nuclear_Plant. jpg | A single unit of the Pickering Nuclear Generating Station, showing a slightly different shape from a typical PWR containment, which is mostly due to the larger footprint required by the Candu design.

The railway line to, which was originally a branch off the line between and, was opened by the Preston and Wyre Railway ( PWR ) on 29 April 1846.

The PWR was taken over jointly by the Lancashire and Yorkshire Railway ( LYR ) and the London and North Western Railway ( LNWR ) in 1849, its title being amended to Preston and Wyre Joint Railway ( PWJR ).

* The pressurized-water reactor ( PWR ) design developed by the AEC was a heterogeneous, water-cooled and water-moderated, stainless steel system, using highly enriched ( 93 %) uranium dioxide mixture as fuel.