Emergency boration system

Some reactor designs provide an emergency boration system to inject soluble neutron absorber promptly into the RCS and the core after an accident. 

The emergency boration system may interface with the following systems  

The emergency boration system should be functionally isolated from the RCS during normal operation. 

Isolation devices should not impair the adequate co-ordination of the system with the RCS when its operation is needed. 

The emergency boration system should function in such a way that the design limits of the fuel and of the RCS pressure boundary are not exceeded in accidents in which its operation is needed. 

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ATWS High reliability trip system 65 control rods Ncgati c temperature coefficient Emergency boration system... 

The Emergency Injection System prevents core exposure in case of LOCA. The system consists of tanks with borated water connected to the RPV. In the event of such accident, the primary system is depressurized with the help of the emergency condensers and at low pressure the rupture disks break starting the RPV flooding with borated water. 

Diverse Reactivity Control System Yes No negative temperature coefficient Manual emergency boration... 

The boric acid and demineralized water control system is necessary to adjust the boron concentration in the reactor coolant system. To increase boron concentration in the coolant, boric acid solution is injected through the volume control system to reduce boron concentration, an adequate volume of coolant is replaced by demineralized water. This system (as well as the other systems discussed here) is a purely operational system and is not required for control of a design basis accident the extra borating system fulfils the necessary safety functions. However, to guarantee continued supply to the volume control system during emergency power operation, the pumps and motor-operated valves of the system are connected to the emergency power supply system. 

The capacity of the emergency power supply (DGs) is high enough to supply also such systems as the high pressure boration system (primaiy circuit makeup) and auxiliary feedwater system (for plant startup and shutdown), although these systems are not classified as safety grade. 

The makeup system of the primary circuit is needed for depressurization and for speeding up the boration of the primary circuit. The activation of the auxiliary feedwater system before the startup of the emergency feedwater system reduces thermal shocks to the steam generators. ... 

Two full-system pressure emergency boration tanks (EBTs) to provide a diverse means of reactor shutdown by delivering borated water to the RV through the direct vessel injection (DVI) lines. By their operation these tanks also provide a limited gravity feed makeup water to the primary system. 

ADS Automatic Depressurization System ATWS Anticipated Transient without Scram CRDM Control Rod Drive Mechanism CV Containment Vessel DID Defence in Depth DOE Department of Energy DVI Direct Vessel Injection EBT Emergency Boration Tank EHRS Emergency Heat Removal System ESP Early Site Permit... 

The emergency shutdown system is explained in detail in Paper 2 to this conference. Explained briefly, negative reactivity Is injected in the form of lithium borate solution which is blown by stored helium pressure Into shutdown tubes which pass through the core in addition, the moderator is drained from the calandrla. The moderator draining does not act as quickly as the liquid tube shutdown but provides additional shutdown. 

At 1 59 a,m the No. 1 AFW pump suction transferred spuriously from the condensate storage tank to the service water system (malfunction number 10). This action was not significant, but it had occurred before and had not been corrected. Similarly, a source range nuclear instrument became inoperable after the reactor trip (malfunction number 11) and the operators initiated emergency boration pursuant to procedures. (Note One channel had been inoperable prior to the event.) The source range instrumentation had malfunctioned previously and apparently had not been properly repaired. Also, the control room ventilation system tripped into its emergency recirculation mode (malfunction number 12), which had also occurred prior to this event. 

A high pressure injection system (HPI) with three pumps for the injection of borated water in the reactor. In emergency operation, which is automatically activated by low pressure of the primary system or by high pressure in the containment building, two pumps activate. Analyses show that only one pump is necessary to prevent core damage in cases of small breaks in the cooling system. 

In ofT-normal situations, a reactor trip is initiated by rapid insertion (velocity about 2 m/s) of all control rods into the reactor core. In addition, sodium borate solution can be injected into the reactor pressure vessel, thus ensuring subcriticality of the core even in case the control rods fail to operate. In order to deal with the consequences of a loss-of-coolant accident, BWR plants are equipped with an emergency core cooling system similar to that in PWR plants, consisting of high-pressure and low-pressure injection systems and recirculation systems. By the action of these systems, sufficient removal of the decay heat is guaranteed so that no serious overheating of the fuel rods can occur. 

Reactor coolant system emergency makeup and boration Provide reactor coolant system makeup and boration during transients or accidents when the normal reactor coolant system makeup supply from the ehemical and volume control system is unavailable oris insuffieient. 

In the 1990s, considerable effort was expended in corporate laboratories to improve on the performance of borate cross-linkers in this application, notably to overcome their deficiency at high temperatures. The dual objective was to develop systems that operated at a higher pH but which were not consequently over cross-linked at surface temperatures. The technical solutions that emerged were based on delayed chemical release mechanisms, either for the borate source, the separately added alkali, or both. 

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