Low-pressure safety injection system

Number of LPSI systems - the number of low-pressure safety injection systems designed to remove residual heat from the reactor core in the case of a considerable loss of coolant, when the coolant pressure drops significantly. Such LPSI systems with a high flowrate may also be used for residual heat removal after normal reactor shutdown. For reactors without an LPSI system, data providers should enter "N/A". 

In WWERs, residual heat is removed in emergency conditions, and for some of them in shutdown conditions, through heat exchangers of the low pressure safety injection systems. These are cooled by the essential service water system which transfers the heat directly to a spray pond or to a lake, depending on the plant in question. There is no closed loop intermediate cooling system. 

The absence of AC powered safety systems (except for the low pressure safety injection system that operates at low flow rate) reduces the need for complex active systems with sensors, actuators, etc. that must be qualified for reliable operation over the full range of conditions (e.g. fire, seismic events) that might be encountered. Another important implication of the design simplification might be related to improved human reliability, as discussed in more detail below. 

The turbine plant building is similar to those of standard nuclear power plants. The containment houses the primary circuit, which is located in the lower part of the containment building. All the safety systems (low pressure safety injection system, decay heat removal system, etc.) are located inside the containment building. 

Oberjohn, W. J., and R. H. Wilson, 1966, The Effect of Non-uniform Axial Flux Shape on the Critical Heat Flux, ASME Paper 66-WA/HT-60, Winter Annual Meeting, ASME, New York. (5) Ogasawara, H. et al., 1973, Cooling Mechanism ofthe Low Pressure Coolant-Injection System of BWR and Other Studies on the Loss-of-Coolant-Accident Phenomena, ANS Topical Meeting Water Reactor Safety, p. 351, Salt Lake City, UT. (4)... 

The ABV reactor is equipped with the low pressure boron injection system and reactor cavity flooding system. Both are non-automatic and non-safety graded systems and designed for severe accident management... 

LPSI system pressure - means the water pressure delivered by the LPSI system to the reactor. Normally, LPSI head pressure at the rated LPSI pump flowrate should be entered. For other systems of low pressure safety injection, the maximum attainable pressure of water being injected by LPSI to the core should be entered. The appropriate value should be expressed in MPa. 

The WWER-1000 plants are equipped with ECCS and containment spray systems that have a similar design basis and similar basic configuration as in western PWRs. These systems have 3 100% redundancy with the exception of the ECCS water storage tank which is common to all subsystems. The same tank serves as a containment sump. The tank is located under the containment and has open connections to the containment through the bottom plate. Each of the three safety system trains has one suction line from the ECCS water storage tank to the residual heat exchangers and further to the low pressure safety injection, high pressure safety injection and spray pumps. The suction line is equipped with one containment isolation valve. 

H4 (loss of the containment spray or loss of the low pressure safety injection) the SCOR has no containment spray, because it has a pressure suppression type containment. The low pressure safety injection has a less significant role than in standard PWRs because of the large primary circuit inertia, the elimination of large LOCAs and the effectiveness of the decay heat removal systems. 

The core of a light water reactor must always be kept covered with water, to prevent a melt down and the consequent release of radioactive products. The safety injection system task is to ensure that the core will remain covered with water in the event of a Loss of Coolant Accident (LOCA). In this event, the pressure vessel water level will begin to decrease. Before the water level is low enough to endanger the core, the injection system is triggered and floods the pressure vessel vwth water, preventing core uncovering. 

Passive safety injection system reduces core damage probability Pressure suppression containment high retention factor and so limits consequences LOCA (Secondary) Low steam generator secondary side water inventory limits consequences LOCA (Interfacing)... 

Under the selected low-pressure option, safety injection system of only one type with an operating pressure of about 25 bar (instead of 110, 40 and 20 bar in a standard PWR) can be envisaged. 

Since large LOCAs are eliminated by design and since the primary system thermal inertia is larger than in loop-type PWRs, the safety injection system requires devices with a smaller flow rate. Given the intrinsic low-pressure option for the reactor, there is only one type of safety injection with a pressure of about 2.0 MPa. The pump power needed for the safety injection is very small, about 35 kW(e). 

A low-pressure core coolant system yields two significant safety advantages over a high pressure system (a) reduced risk because of coolant system depressurization events and (b) compatibility with passive safety injection systems. 

A low-pressure coolant system also is advantageous because replenishment of core coolant inventory can be accomplished with passive safety injection systems. With a high pressure system, safety injection must be accomplished with active components such as centrifugal pumps. Thus, failure of these active components must be accounted for when evaluating risk. With a low-pressure system, a tank of water that is elevated above the primary coolant system is capable of injecting coolant into the system. The probability of failure in such an injection system is significantly less than that of the typical active system. 

Manifold barriers confine the radioactivity to the 1) ceramic fuel pellet 2) clad 3) cooling water, as demonstrated by the TMI-2 accident 4) primary cooling loop 5) containment and 6) separation from the public by siting. Further protection is provided by engineered safety systems pressurizers, depressurization, low pressure injection, high pressure injection and residmil heat removal systems. 

Simple systems. Because of higher level inherent safety, there is no safety class electro-power source,. As well as high pressure and low pressiue injection systems. 

This evaluates the liquid flow rate entering the primary system using Equation A11.9. It is composed of the efflux of the two series of accumulators (intermediate and low pressure) whose characteristics are specified in the input data and by the efflux of an injection safety system (ECCS), operating between two given times (TUIGS and TU2GS) for a given flow rate GS. 

H4 Mobil link EAS-ISBP (Containment spray system - Safety injection at low pressure) installed some days after a LOCA is used to insure a mutual backup. After some days back-up of exchangers and pumps can be realized through mobile equipments (see U3 procedure). 

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