Circuit pressure

Windscale reactors, and some US reactors of the 1950 period, the fuel was cooled by air blown straight to atmosphere, and no use was made of the heat to produce power. In all power reactors now operating, the coolant is contained in a closed-circuit pressure vessel. Outer containment buildings, which can also withstand some pressure in the event of failure or leakage from the pressure circuit, enclose the US pattern pressurised water and boiling water reactors, but no such provision was made for the Russian boiling water reactor at Chernobyl. All defences (cans, pressure vessel, containment building if provided) must be breached before fission products can be released to atmosphere. 

Leak testing pneumatic control circuits in accordance with ISA Recommended Practice RP 7.1 Pneumatic Control Circuit Pressure Test, latest revision. 

Qualitative comparison of some thermohydraulic characteristics of sodium and lead coolants is presented in [6.1] with BREST reactor design taken as a reference [6.2]. Results of optional assessments performed by the author [6.2] are in a good agreement with the data presented in [6.1]. In the analysis, the following parameters are assumed identical reactor power, average temperature in the circuit, cross section for coolant flow, coolant temperature rise in the reactor, primary circuit pressure drop and coolant volume. 

Low primary circuit pressure drop (under accident conditions, 15% flow rate should be provided) ... 

It should be noted that the problem of sodium circuit hydraulic resistance is of vital importance due to some features of accident processes. Accidental pressure in the sodium volume in the vicinity of large water leak into sodium depends not only on the leak rate but also on the hydraulic "compliance" of the sodium circuit. The experience shows that, in view of the above circumstances, sodium circuit pressure drop within the boundaries of "SG-expansion gas volume inlet" section should not exceed 0.3 MPa value. 

It is provided for lowering under gravity using safety devices for CG-drives deenergization executing by increase of primary circuit pressure. ... 

Unlike the known designs of integral reactors being under development in many countries where either steam or steam-gas pressurizer is applied, the integral reactors developed by RDIPE use a gas pressurizer. Selection of such solution was motivated by several reasons, firstly, the intention to simplify and, consequently, enhance safety of the primary circuit pressure compensation system by elimination of heaters and sprinkler system. Secondly, this approach is based on our 40-year experience in designing and operation of ship-mounted NSSS with gas pressurizers in the primary circuit. It should be pointed out, however, that in the previous cases the pressurizes wee placed outside the reactor vessel. 

In the Three Mile Island core meltdown, it is known that there was also a Zircaloy-water chemical reaction leading to a considerable release of hydrogen. However, the reactor circuit pressure relief and containment system there prevented damage with no significant fission product release to the atmosphere. There was no free oxygen in the vessel so that hydrogen did not react chemically. 

LOCA during the primary circuit pressure test ... 

The design of hydraulic engineered safety features for LWRs has traditionally been performed according to high reliability and leak proof standards. These systems are usually called into operation to protect the fuel barrier in the case of a loss of the primary system barrier. In addition, being strictly connected to the primary circuit pressure boundary, they have to be equipped with leak proof isolation devices, normally closed during plant operation. 

Accordingly, in the most recent documents, the DID is based on four principal barriers against the external release of radioactive products (fuel matrix, fuel cladding, reactor cooling circuit pressure boundary, and containment system), and on five defence levels in order to best use these barriers (illustrated in Table 9-1). 

The logical procedure of accident analyses for RBMKs is shown in a general form in Fig. 2. The whole set of acceptance criteria or some part of it may be used, depending on the problem being considered. For instance, the criteria related to the ALS may be disregarded if the pipelines and components of the circulation circuit (pressure boundaries) have not lost their integrity. 

Primary circuit pressure control Safety relief valves (auto ) Manually controlled valves active active Spring-force, self-activated on pressure, but active. Manual order/Zmanual actuation... 

Primary circuit pressure control Pressurizer Safety Relief Valves Passive Provides overpressure protection... 

The primary circuit includes the equipment of the main circulation circuit, pressurization system and also auxiliary systems connected to the reactor. The fi ee volume above the reactor water level is used as steam-gas pressurizer for which gas is supplied to the pressurizer before reactor startup. The primary circuit operates in a non-boiling mode. 

Primary circuit pressure control PRHRS, RCPC,DRPS Passive Without discharge of primary coolant... 

The system is intended to prevent inadmissible increase of pressure in the primary circuit if all subsystems for residual heat removal fail following the reactor shutdown. Primary circuit emergency pressure decrease is provided by two systems. The first system consists of two sets of safety devices (SD) and of a 1.6 m cooled dump tank. When the primary circuit pressure reaches 19.6 MPa the SD actuates automatically and discharges a portion of coolant into the dump tank. The system can be used repeatedly following dump tank drainage. Automatic membrane safety devices (ASD) are provided to protect the primary circuit against damage in case... 

Primary circuit pressure control system (PCS) X Overpressure protection, PORV... 

Primary circuit pressure control 1 HT pressunzer with steam-bleed valves 2 Feed and bleed system 3 Automatic liquid rehef valves 4 Mam steam safety valves A Systems 1 and 2 provide primary circuit pressure control Systems 3 and 4 prevent overpressure and provide rapid depressurization... 

Primary circuit pressure control Pressunser m combmation with feed and bleed Active Instrumented relief valves ui PHT, prevent over pressurization I... 

Pnmary circuit pressure control Self pressurized performance passive Integrated primary cu cuit... 

Primary circuit pressure control not necessary Emergency miection is not necessary... 

Natural coolant circulation is used in the primary circuit. The primary circuit is a completely leak-tight system. The main circulation circuit is enclosed in the reactor vessel and includes core-upstream flow/section, steam generator, downstream flow section. There is an external pressurizing system and the reactor coolant purification/residual heat removal system. Nitrogen is used for primary circuit pressurization. 

In case of a leak each of the four SG sections can be isolated on both the steam and feed water sides by double shut-off valves. The pipelines before the shut-off valves are designed for primary circuit pressure. 

In the event of accidents with unauthorized addition of reactivity or loss of heat removal, complete failure of protective systems and operator inaction on primary circuit pressure increase, the plant will be tripped by a direct-acting pressure-actuated power breaker cutting supplies to the control rod drives. 

A part of secondary pipelmes is designed for pnmary circuit pressure R... 

Primary Circuit Pressure Control Active residual heat removal syston ARHRS Active ... 

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