The ESBWR is considered to be the best evolution of the BWR technology. The new invention has been created using simplified designs to boost its safety for consumption. The new design has also enhanced the reactors economics, plant security, plant availability, plant security as well as a broad seismic design. This project will discuss the ESBWR and describe the main components of the ESBWRs emergency core cooling system. The project will discuss the safety design bases that should be incorporated in the ECCS, in order for it to perform at an optimum level in all its three subsystems.
ESBWR has been structured to produce electricity through the usage of a turbine generator unit, which is steam generated. The ESBWR has better performance than all its predecessors because it is able to remove the heat that has been generated for the full range of the optimal operating conditions, as well as off-normal transients. Its effectiveness has also been facilitated by backup heat removal systems, which have been issued to ensure full performance in the event where normal removal systems have become inoperative. Such backup systems have the potential to adequately prevent the damage of the core by fuel cladding.
The three ECCS subsystems that will be featured in this research will include the short-term subsystem, the long term subsystem as well as the deluge subsystem. The information pertaining subsystems will be attained from the Status Report 100 publication that discusses the ESBWR. In this section, the different functions of each subsystem will be discussed, and a guideline of what takes part in each subsystem will also be described. This section will be followed by a discussion of the various ECCS systems. In this section, the paper will offer a brief description of the three forms of systems, which include high-pressure systems, depressurization systems as well as the low-pressure systems.
The content of this section will be attained from the GE Hitachi Nuclear Energy website. The source contains a comprehensive summary of the three types of ESBWR systems. This section will be followed by a brief description of other important parts of the ECCS. These includes the HPCI, IC, as well as the RCIC. A brief description of the three systems in the ECCS will also be portrayed. Ultimately, the essay will be concluded by the conclusion paragraph. This section will offer a brief highlight of all the key parts discussed in the essay.
Part II: ESBWR Emergency Core Cooling System (ECCS)
The ESBWR is a one thousand, five hundred and twenty, Generation III boiling water nuclear reactor. It is currently considered to the safest reactor in the world. This is because it features the lowest levels of core damage frequency, according to the defined energy industrys optimal measure of safety. This is also when classified in terms of Generation III as well III+ reactors. The reactor can cool itself safely, without any form of alternating current electrical power or other human actions, for a period of one week. The reactor is structured using the ABWRs latest proven technology, which has helped it to achieve simplicity in its designing.
ESBWR employs natural circulation in its functioning and it runs on twenty-five percent fewer pumps as well as mechanical drives, compared to all other active safety reactor plants CITATION ESB16 \l 1033 (ESBWR Nuclear Power Plant, 2016). It is estimated to have the least operating costs in the market as well as the least staffing and maintenance costs per every megawatt hour of any reactor plant existing today. The reactor has become highly acclaimed because it has reduced the volume of residue heat transferred to the atmosphere. Eleven systems, which were incorporated in the other reactor designs, have been removed in the ESBWR. In addition, twenty-five percent of the valves, motors as well as pumps have been removed in this reactor.
Emergency Core-Cooling System (ECCS)
The ESBWR is the safest boiling water reactor in the world. It choice as the best reactor in the market has been supported by facts such as it can emit large volumes of residue heat to the atmosphere. It also eliminated multiple systems, which were initially used with the previous versions of reactors. In addition, it has lesser valves, motors as well as pumps. This essay is a discussion of the ESBWRs emergency core cooling system, detailing the components of the ECCS as well as its three primary subsystems.
The ECCS is designed to ensure that there is sufficient core cooling. It entails a set of interrelated safety systems, which are designed to offer protection to the fuel located in the pressure vessel of the reactor from overheating. The pressure vessel is also referred as the reactor core. To achieve its function well within the reactor, the ECCS must fulfill four conditions. First, it averts the peak fuel temperatures from surpassing two thousand two hundred degrees Fahrenheit. Second, it averts the fuel claddings oxidation by more than seventeen percent. Third, the ECCS should avert more than one percent of the maximum hydrogen generation. This phenomenon is caused by zircalloy metal and water chemical reaction.
The ECCS should also maintain a controllable able to be cooled geometry, which should support long-term cooling. This can be attained if the ECCS systems are able to maintain a reactor pressure vessel (RPV) level of water cooling. Nevertheless, if this is impossible, the ECCS should be in a position to openly flood the reactor core with an effective coolant. The ECCS is made of two distinctive parts namely the GDCS as well as the ADS. The fore part is used as an abbreviation for a gravity driven cooling system while the latter is an acronym for auto-depressurization subsystem.
The primary function of the GDCS is to flood the reactor with large volumes of cooling water. This is achieved in the event there occurs a loss of coolant accident condition (LOCA). This phenomenon occurs once the ADS has sufficiently depressurized the reactor to a state of near-drywell-calm pressure conditions. The cooling water used in the reactor originates from the GDCS pools, which are normally set at the upper elevations of the reactor containment. The water is pumped via four safety optimized piping trains, which connect the GDCS water pools to the reactors RPV. The water flows to the RPV via simplified passive gravity based draining mechanism.
In order for cooling to take place, automatized pyrotechnic-type injection valves open. This allows the water to flow into the RPV up to the optimal coolant levels. The levels drop due to the simultaneous actions of the ADS and Break steam outflows as well as the yielded steam boil-off attained from the core decay heat. In the first few seconds of GDCS injection, the cold water enters the annulus region of the reactor. This occurs through the eight GDCS RPV nozzles. The water cools the steam component of the lower annulus region as well as the core lower plenum.
In this case, the ADS set-point, as well as the vessel volume, are set in such a way that a full void-collapse of steam, in all the lower section of the plenum is experienced. At the same time, a two-phase minimum level that covers the active fuel is maintained. The minimum level is designed in such a way that it covers the least design margin that is equal to one meter. A short period after the plenum void collapse, the water inflows in the GDCS exceeds the decay heat emitted by both the steam boil-off as well as the depressurization voiding. At this point, both the water levels, both inside as well as outside the core shroud starts to increase.
At this point, the inflows are at a rate that although the warm-up of GDCS attained coolant takes place, the bulk steam boil-off ceases to occur. This is followed by steam discharges from both the Break as well as the ADS depressurization valves until it eventually stops. At this same time, within a duration of around forty minutes, the drywell does not receive any steam from the RPV. This makes the PCCS heat exchangers to slowly shutdown. PCCS is an abbreviation used to refer to the passive containment cooling system. While this is taking place, the water inflows from the GDCS continues to optimize the RPV water levels.
This process continues until the water levels inside the RPV attains a manometer-form equilibrium. At this point, there is a drained-down water level, which can be observed in the GDCS pools. It should be noted that at this point, the RPV water level in the reactor occurs at a point that is slightly below the ideal elevations on the RPV outlets. At this point, the GDCS pools are approximately fifty-percent drained down and occurs approximately sixty-minutes after the LOCA break. After this period, the core decay heat, which warms up in the GDCS flow inlets, creates a steaming out of the RPV.
This is followed by the PCCS heat exchangers, which starts to act again create a condensate. The condensate returns to the RPV via a set of RPV PCCS. After this step, the coolant cycles back from the RPV, to the drywell, to the heat exchangers in PCCS and eventually back to the RPV. This process occurs in an endless circuit, with the exception of the steam condensation that occurs on the drywell peripheries as well as in the internal structures. The GDCS is structured into four primary divisions, each comprising of three subsystems. The subsystems include the GDCS short-term subsystem, long-term subsystem as well as deluge subsystem.
Safety Design Bases
In order to satisfy the three subsystems, the GDCS must first fulfil four primary conditions/bases. First, the GDCS must act as an emergency core coolant, intervening in every event that may threaten the reactor coolant inventory. This step should occur in the event there is an RPV depressurization through the reactors ADS. Secondly, the GDCS must flood the drywell on the lower section of the reactor with water from the GDCS pools. This is in the event there is an accident, which may result in high temperature levels in the lower drywell.
Third, the GDCS system must, at all times, inject an adequate volume of cooling water into the reactors depressurized RPV. This is in an effort to keep the fuel in the chamber covered after the occurrence of a LOCA. Finally, the GDCS injection lines must have sufficient piping loop-seals, which must be capable of averting the drywell steam from reaching the chambers wet-well space. This phenomenon may take place due to any backflow that may occur, through long-term injection lines in the GDCS. This could be accessed through a break in the downstream line, at any point along its high-energy piping run section.
This is the first subsystem in the GDCS, and it features the following. The total demanded RPV injection rates should be supplied by three detached GDCS pools, through a set of four divisions of short-run injection piping trains. One of these trains must be conducted to the RPV using two detached short-term piping trains. The other two GDCS pools should be linked to the RPV through the remaining single-dedicated short-run injection trains. All the injection lines are electrically as well as mechanically independent, and they are also separated according to their applicable design guidelines. This aids in their separation in terms of safety related divisions.
In addition, the injection lines should have sealed piping loops, which are capable of preventing the drywell gas or steam in reaching the airspaces in the wet-well. This phenomenon mainly occurs through the short-run injection lines and can be accessed through downstream line breaks. The breaks could be situated along any section of the high-energy piping runs. All the drainable water volume held in the GDCS pools should be...
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