Low-pressure coolant injection

Elapsed Time in Thousands of Reactor Years Fig. 2.7-1 ERMA simulation of a low pressure coolant injection system. The absence of oscillations in the convergence is evidence of voter statistics Reprinted with permission of EPRI. USA... 

An example of a multipurpose system is a reactor s low pressure coolant injection system which uses one out of four (1/4) pumps for a small LOCA, and three-out-of-four pumps for a large LOCA (3/4). The top event for the small LOCA might be "none of four LPCI pump u1... 

These plants are designed with two independent high-pressure injection systems, namely reactor cooling sure coolant injection (HPCl). The associated pumps are each potiered fay turbine. also have a multi-loop core spray system and a multi-mode residual heat re sy.stem that can be aligned for low-pressure coolant injection, shutdown cooling, suppre.ssion pc containment spray functions. 

ERMA simulation of a low pressure coolant injection system. 59... 

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)... 

Core make-up keep core flooding High pressure coolant injection system (2) Low pressure coolant injection system (2) Accumulator tank (2) High pressure coolant injection system (2) Low pressure coolant injection system (2) Rehieling tank (1) Core makeup water tank (2) Automatic depressurization system (2) Accumulator tank (2j Containment vessel water (Water-filled containment vessel) (1)... 

Long term coolant Low pressure coolant injection system (2) Re-circulation coolant system (1) Static residual heat removal system (2) (Natural circulates) Emergency decay heat removal system (3) (Natural circulates)... 

The capacities of the emergency core cooling systems suffice to provide water under all postulated pipe break conditions. This statement is also valid assuming that only two of the four redundant subsystems are operable. The postulated loss-of-coolant conditions include a hypothetical 80 cm leak at the bottom of the reactor vessel In this context, it can be noted that the capacity of the low pressure coolant injection punq)S has been reduced for BWR 90, following comprehensive core cooling analyses. As a secondary effect, it has been possible to simplify the auxiliary power supply systems. 

Low-pressure coolant injection inlet Core spray sparger... 

In Siemens BWRs, both, high and low pressure coolant injection systems feed water from the pressure suppression pool into the reactor pressure vessel either via the feedwater line or via separate nozzles directly connected to the feedwater spargers. 

In GE BWR/5 and BWR/6 plants, the LPCI (low pressure coolant injection) subsystem constitutes a portion of the emergency core cooling system. The LPCI restores and, if required, maintains the coolant inventory in the RPV after a loss-of-coolant accident by injecting water directly inside the core shroud. The LPCI coupling is a sleeve connection which accommodates the thermal expansion mismatch between the RPV and the core shroud as shown in Figure 2-14. 

Low pressure coolant injection and residual heat removal... 

Coolant Inventory Control and Core Heat Removal High Pressure Coolant Injection System Reactor Core Isolation Cooling System Low Pressure Coolant Injection System Low Pressure Core Spray System Control Rod Drive Cooling System Condensate System High Pressure Service Water System... 

Results from MELCOR (Version 1.8.0) calculations of three accident sequences in a W-PWR 900 Mwe three loop plant are presented. The scenarios considered include an AB sequence and two V type events a rupture of the Low Pressure Coolant Injection System in the auxiliary building, and the rupture of ten steam generator tubes in all cases without the intervention of the active emergency core cooling systems. Emphasis is put on the release and transport of core materials. It has been found that deposition of vapors from the most volatile species is high within the core structures. Later in the accident, revaporization induced by decay heat takes place, at times in coincidence with the production of steam due to core slumping, what may change the nature and composition of source terms. 

The V-sequence refers to a Loss of Coolant Accident (LOCA) through the Low Pressure Coolant Injection System (LPIS), which in this type of nuclear power plants has a common part with the Residual Heat Removal System (RHRS). The suction pipe of the RHRS connects two of the three hot legs in the primary circuit with the RHRS pumps placed into the Auxiliary Building. It has been assumed that three isolation valves fail in one of these pipelines (two of them are motorized valves) a break near the RHR pump has been postulated as a result of the over-pressurization generated in the pipe. 

Several other systems are available to control room operators to keep the reactor cool during an emergency. These include the High Pressure Core Spray System, Low Pressure Core Spray System, Residual Heat Removal System, Low Pressure Coolant Injection, and Suppression Pool Cooling. All of these systems require both AC and DC power, plus a sufficient flow of coolant water connected to the ultimate heat sink. At Fukushima this ultimate heat sink was the Pacific Ocean (US Nuclear Regulatory Commission, n.d.a). 

LOCA (primary) automatic initiation of containment isolation coolant injection to the RPV if necessary, automatic depressurization to get low pressure coolant inj. system in operation, combined with elimination of below core large nozzles, facilitates reliable core flooding... 

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". 

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. 

Low-Pressure Systems High-Pressure coolant injection Core spray... 

In some BWR transient scenarios, the high pressure injection systems are postulated to fail. To make use of the low pressure injection system, it is necessary to depressurize the reactor coolant system, a function performed by the automatic depressurization system (ADS). In the scenario considered, ADS actuation is manual because the signals for automatic initiation of the system are not present. 

Loss of (SG) feedwater operational redundancy in normal feedwater pumps, four train aux. FW supply system (HP coolant inj. system), pressure relief system permitting depressurization and operation of low pressure emergency coolant injection system reduce initiating frequency... 

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