Part of the pressurizer, a primary circuit component of the reactor, is vibrating at levels that exceed safety limits, said Pekka Valikangas, the regulator's section head for nuclear reactor regulation.
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Pressure in the pressurizer is controlled by varying the temperature of the coolant in the pressurizer. Water pressure in a closed system tracks water temperature directly; as the temperature goes up, pressure goes up and vice versa. To increase the pressure in the reactor coolant system, large electric heaters in the pressurizer are turned on, raising the coolant temperature in the pressurizer and thereby raising the pressure. To decrease pressure in the reactor coolant system, sprays of relatively cool water are turned on inside the pressurizer, lowering the coolant temperature in the pressurizer and thereby lowering the pressure.
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Pressure in the primary circuit is maintained by a pressurizer, a separate vessel that is connected to the primary circuit and partially filled with water which is heated to the saturation temperature (boiling point) for the desired pressure by submerged electrical heaters. To achieve a pressure of , the pressurizer temperature is maintained at 345 °C (653 °F), which gives a subcooling margin (the difference between the pressurizer temperature and the highest temperature in the reactor core) of 30 °C (54 °F). As 345 °C is the boiling point of water at 155 bar, the liquid water is at the edge of a phase change. Thermal transients in the reactor coolant system result in large swings in pressurizer liquid/steam volume, and total pressurizer volume is designed around absorbing these transients without uncovering the heaters or emptying the pressurizer.
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Unlike ordinary PWRs, the pressurizer is not contained in a separate vessel and connected to the primary side, but rather is the top of the pressure vessel itself. Water line will be at some preset value, and then sprays and boilers within the pressurizer can be used to control pressure and water level. The unique aspect of this is that the pressurizer is of much greater volume than current plants, which helps to keep the pressure constant in accident situations.
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Part of the pressurizer system is an over-pressure relief system. In the event that pressurizer pressure exceeds a certain maximum, there is a relief valve called the pilot-operated relief valve (PORV) on top of the pressurizer which opens to allow steam from the steam bubble to leave the pressurizer in order to reduce the pressure in the pressurizer. This steam is routed to a large tank (or tanks) in the reactor containment building where it is cooled back into liquid (condensed) and stored for later disposition. There is a finite volume to these tanks and if events deteriorate to the point where the tanks fill up, a secondary pressure relief device on the tank(s), often a rupture disc, allows the condensed reactor coolant to spill out onto the floor of the reactor containment building where it pools in sumps for later disposition.
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In a pressurized water reactor plant, the pressurizer is basically a cylindrical pressure vessel with hemispherical ends, mounted with the long axis vertical and directly connected by a single run of piping to the reactor coolant system. It is located inside the reactor containment building. Although the water in the pressurizer is the same reactor coolant as in the rest of the reactor coolant system, it is basically stagnant, i.e. reactor coolant does not flow through the pressurizer continuously as it does in the other parts of the reactor coolant system.
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There is therefore, a coolant level monitoring system on the pressurizer and it is the one reactor coolant system vessel that is normally not full of coolant. The other secondary function is to provide a "cushion" for sudden pressure changes in the reactor coolant system. The upper portion of the pressurizer is specifically designed to NOT contain liquid coolant and a reading of full on the level instrumentation allows for that upper portion to not contain liquid coolant. Because the coolant in the pressurizer is quite hot during normal operations, the space above the liquid coolant is vaporized coolant (steam).
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To pressurize the coolant system to a higher pressure than the vapor pressure of the coolant at operating temperatures, a separate pressurizing system is required. This is in the form of the pressurizer.
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There have been two incidents of level 2 severity on the International Nuclear Event Scale. On November 22, 2002 a pressure relief valve on the pressurizer inadvertedly opened while Tihange 2 was shut down. The reactor was being prepared to be restarted after a planned revision and refuel. While the pressure in the primary circuit was being increased to 155 bar one of the safety valves on the pressurizer inadvertedly opened leading to a quick decrease in pressure in the primary circuit.
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Pressure is controlled in a pressurized water reactor to ensure that the core itself does not reach its boiling point in which the water will turn into steam and rapidly decrease the heat being transferred from the fuel to the moderator. By a combination of heaters and spray valves, pressure is controlled in the pressurizer vessel which is connected to the reactor plant. Because the pressurizer vessel and the reactor plant are connected, the pressure of the steam space pressurizes the entire reactor plant to ensure the pressure is above that which would allow boiling in the reactor core. The pressurizer vessel itself may be maintained much hotter than the rest of the reactor plant to ensure pressure control, because in the liquid throughout the reactor plant, pressure applied at any point has an effect on the entire system, whereas the heat transfer is limited by ambient and other losses.
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The overall water level inside the pressurizer was rising despite the loss of coolant through the open pilot-operated relief valve, as the volume of these steam voids increased much more quickly than coolant was lost. Because of the lack of a dedicated instrument to measure the level of water in the core, operators judged the level of water in the core solely by the level in the pressurizer. Since it was high, they assumed that the core was properly covered with coolant, unaware that because of steam forming in the reactor vessel, the indicator provided misleading readings.Kemeny, p. 94.
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Sectional view of a pressurizer A pressurizer is a component of a pressurized water reactor. The basic design of the pressurized water reactor includes a requirement that the coolant (water) in the reactor coolant system must not boil. Put another way, the coolant must remain in the liquid state at all times, especially in the reactor vessel. To achieve this, the coolant in the reactor coolant system is maintained at a pressure sufficiently high that boiling does not occur at the coolant temperatures experienced while the plant is operating or in any analyzed possible transient state.
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One is providing a place to monitor water level in the reactor coolant system. Since the reactor coolant system is completely flooded during normal operations, there is no point in monitoring coolant level in any of the other vessels. But early awareness of a reduction of coolant level (or a loss of coolant) is important to the safety of the reactor core. The pressurizer is deliberately located high in the reactor containment building such that, if the pressurizer has sufficient coolant in it, one can be reasonably certain that all the other vessels of the reactor coolant system (which are below it) are fully flooded with coolant.
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On 27 June 1985 during startup of the first reactor unit, a human error (later attributed to inexperience and haste) unexpectedly opened a pressurizer relief valve, and steam entered the staff work area. Fourteen people were killed. This event is cited as one of the predecessors of the Chernobyl disaster.Medvedev, Grigory.
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On September 24, 1977, the relief valve for the reactor pressurizer failed to close when the reactor, running at only 9% power, shut down because of a disruption in the feedwater system.Walker, Samuel J. (2004) Three Mile Island: A Nuclear Crisis in Historical Perspective. Berkeley: University of California Press. p 68.
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Main propulsion was provided by the 645 N, 317 sec.Isp bipropellant (hydrazine and nitrogen tetroxide) large velocity assist (LVA) thruster. The model used was the LEROS 1b, developed and manufactured at AMPAC‐ISP's Westcott works, in the United Kingdom. The spacecraft was designed to carry of propellant and helium pressurizer for the LVA.
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The IRIS pressure vessel and systems contained within it The coolant system consists of a pressurizer, Steam generators, and reactor coolant pumps (RCPs). These are all located within the reactor pressure vessel, making a very small, short loop that forms the primary coolant system, see the figure on the right for the relative locations of the components.
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Because the steam generators are elevated relative to the RPV, natural convection will circulate reactor coolant in the event of RCP malfunction. The pressurizer is equipped with a pilot-operated relief valve which not only protects against Reactor Coolant System over-pressure, it also allows manual depressurization in the case of a total loss of feedwater.
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Because of its innate incompressibility, water in a connected piping system adjusts equally to pressure changes anywhere in the connected system. The water in the system may not be at the same pressure at all points in the system due to differences in elevation but the pressure at all points responds equally to a pressure change in any one part of the system. From this phenomenon, it was recognized early on that the pressure in the entire reactor coolant system, including the reactor itself, could be controlled by controlling pressure in a small interconnected area of the system and this led to the design of the pressurizer. The pressurizer is a small vessel compared to the other two major vessels of the reactor coolant system, the reactor vessel itself and the steam generator(s).
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96; Rogovin, pp. 17–18. At 4:15 am, the relief diaphragm of the pressurizer relief tank ruptured, and radioactive coolant began to leak out into the general containment building. This radioactive coolant was pumped from the containment building sump to an auxiliary building, outside the main containment, until the sump pumps were stopped at 4:39 am.Kemeny, p. 96.
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The old woman dies in the process. Bank informs new of a possible short-circuit and starts repairing the oxygen pressurizer. New almost collapses in the process, before she is safely brought to the top by Bank. When strange occurrences started to occur from dead bodies disappearing to possessed passengers started killing each other until Gift, Jamras, Phen, Bank and New are the only ones left.
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Primary coolant system showing reactor pressure vessel (red), steam generators (purple), pressurizer (blue), and pumps (green) in the three coolant loop Hualong One design The Hualong One, also known as Hualong-1 or HPR1000 (), is a Chinese pressurized water nuclear reactor design. The Hualong One is the most common reactor design under construction in China, and the mainstream technology in the near future. China also plans to export the reactor.
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It entered commercial operation in December 2018. Taishan 2 reached these milestones in May 2019 and September 2019, respectively. The Taishan project is led by Taishan Nuclear Power Joint Venture Co. (TNPJVC), a joint venture founded by CGN (51% ownership stake), EDF (30%), and Chinese utility Guangdong Energy Group (19%), also known as Yuedian. Companies involved in supplying equipment to Taishan Unit 1 include Framatome, which manufactured the steam generators and pressurizer in France, and China’s Dongfang Electric Corp.
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In total, the Ft. Calhoun reactor has of high level nuclear waste. The storage was not designed to house spent fuel permanently, but when plans for Yucca Mountain nuclear waste repository were terminated, OPPD stated that they are "prepared to safely store material on- site as long as necessary". The plant underwent refurbishment in 2006 by having its steam generators, pressurizer, reactor vessel head, low pressure turbines and main transformer replaced. In 2003, the plant had its operating license renewed for an additional twenty years.
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Layout of the four primary cooling circuits and the pressurizer of a VVER-1000 Construction of a VVER-1000 reactor vessel at Atommash. As stated above, the water in the primary circuits is kept under a constant elevated pressure to avoid its boiling. Since the water transfers all the heat from the core and is irradiated, the integrity of this circuit is crucial. Four main components can be distinguished: # Reactor vessel: water flows through the fuel rod assemblies which are heated by the nuclear chain reaction.
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Indications of high water levels contributed to the confusion, as operators were concerned about the primary loop "going solid", (i.e., no steam pocket buffer existing in the pressurizer) which in training they had been instructed to never allow. This confusion was a key contributor to the initial failure to recognize the accident as a loss-of-coolant accident, and led operators to turn off the emergency core cooling pumps, which had automatically started after the pilot-operated relief valve stuck and core coolant loss began, due to fears the system was being overfilled.Rogovin, p.
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16, Walker, pp. 76–77. With the pilot-operated relief valve still open, the pressurizer relief tank that collected the discharge from the pilot-operated relief valve overfilled, causing the containment building sump to fill and sound an alarm at 4:11 am. This alarm, along with higher than normal temperatures on the pilot-operated relief valve discharge line and unusually high containment building temperatures and pressures, were clear indications that there was an ongoing loss-of-coolant accident, but these indications were initially ignored by operators.Kemeny, p.
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WNP-3/5 WNP-3/5 would have been pressurized water reactors, with the nuclear steam supply system provided by Combustion Engineering. The architect/engineer for the plant was EBASCO, who also were responsible for plant construction. Like contemporary C-E designs, the System-80 NSSS in each unit would have featured a two-loop design, with two steam generators, four reactor coolant pumps and one pressurizer to maintain reactor coolant system pressure. The System-80 NSSS was designed to be capable of burning mixed-oxide (MOX) fuel.
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Recent progress on unit 4 includes the installation of the final steam generator and pressurizer. Unit 4 is being constructed utilizing lessons learned from Unit 3 and from the failed Virgil C. Summer Nuclear Generating Station (V.C. Summer) project and as a result the order in which some components are being installed has been modified. On November 22, 2019 the third ring of the containment vessel was set for unit 4, and on December 8, 2019 the unit 3 shield building roof was set above the unit 3 containment vessel.
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Like the OPR-1000 and preceding C-E designs, the APR-1400 has two reactor coolant loops. In each loop, heated primary coolant leaves the reactor pressure vessel (RPV) through one hot leg, passing through one steam generator (SG), returning to the reactor vessel through two cold legs, each equipped with a reactor coolant pump (RCP). In loop 2, there is one pressurizer (PZR) on the hot leg, where a steam bubble is maintained during operation. The loops are arranged symmetrically, so the hot legs are diametrically opposed on the RPV's circumference.
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11, issue 10: page 378); "News Roundup: Package Reactor" prepared by Helen C. Allison; accessed 11 March 2012. Alco Products supplied the reactor, pressurizer and steam generator, while Westinghouse Electric Corporation supplied the canned-rotor pumps, General Electric supplied the turbine and generator, the Lummus Company supplied the condenser, and Minneapolis-Honeywell installed the controls. By late October 1955, the Army pushed ALCO to accelerate construction towards a completion date of 10 July 1957.Suid, Lawrence H. The Army's Nuclear Power Program: The Evolution of a Support Agency (Greenwood Publishing: 1990), page 32; accessed 11 March 2012.
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Pictorial explanation of power transfer in a pressurized water reactor. Primary coolant is in orange and the secondary coolant (steam and later feedwater) is in blue. Primary coolant system showing reactor pressure vessel (red), steam generators (purple), pressurizer (blue), and pumps (green) in the three coolant loop Hualong One design Nuclear fuel in the reactor pressure vessel is engaged in a fission chain reaction, which produces heat, heating the water in the primary coolant loop by thermal conduction through the fuel cladding. The hot primary coolant is pumped into a heat exchanger called the steam generator, where it flows through hundreds or thousands of small tubes.
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The operators had not been trained to understand the ambiguous nature of the pilot-operated relief valve indicator and to look for alternative confirmation that the main relief valve was closed. A downstream temperature indicator, the sensor for which was located in the tail pipe between the pilot-operated relief valve and the pressurizer relief tank, could have hinted at a stuck valve had operators noticed its higher-than-normal reading. It was not, however, part of the "safety grade" suite of indicators designed to be used after an incident, and personnel had not been trained to use it. Its location on the back of the seven-foot-high instrument panel also meant that it was effectively out of sight.
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While the Shippingport Reactor has been decommissioned, Beaver Valley Nuclear Generating Station Units 1 and 2 are still licensed and in operation at the site. The $98 million (1985 estimate) cleanup of Shippingport has been used as an example of a successful reactor decommissioning by proponents of nuclear power; however, critics point out that Shippingport was smaller than most commercial nuclear power plants, most reactors in the United States are about 1,000 MWe, while Shippingport was only 60 MWe. Others argue that it was an excellent test case to prove a reactor site could be safely decommissioned and a site released for unrestricted use. Shippingport, while somewhat smaller than a large commercial reactor today, was representative, with four steam generators, pressurizer and reactor.
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