Coolant loss

Inspect hoses. Tighten all hose connections, including those to the expansion tank, to protect against coolant loss. 

To avoid the possible overpressure in the system due to coolant loss that could consequently cause the bursting of the reactor, it is highly recommended to attach a large buffer reservoir to the system e.g., instead of the 2-L vessel in Fig. 2 in Section I). The volume of this vessel should be sufficient about 40 L to contain all of the gas at room temperature and at a pressure of <2 bar. The vessel should be pressure-tested and resistant to fluorine [e.g., an empty fluorine gas cylinder would be the most appropriate) filled with fluorine to 400 mbar (vapor pressure of fluorine at — 196°C). The buffer reservoir should be opened to the reactor immediately after condensation of fluorine in the reactor. After the synthesis is finished and excess fluorine distilled off, the buffer reservoir should be closed again. 

The CVI SiC/SiC composites are also promising for nuclear applications because of the radiation resistance of the p phase of SiC, their excellent high-temperature fracture, creep, corrosion and thermal shock resistances. Studies on the P phase properties suggest that CVI SiC/SiC composites have the potential for excellent radiation stability [5]. Furthermore, because of excellent thermal fatigue resistance, start-up and shut-down cycles and coolant loss scenarii should not induce significant stmctural damage [5]. The CVI SiC/SiC are also considered for applications as stmctural materials in fusion power reactors, because of their low neutron-induced activation characteristics coupled with excellent mechanical properties at high temperature [6-8]. 

Moreover, a containment atmosphere spray system exists aimed at reducing the temperature, and consequently the pressure, which could be created in the building itself as a consequence of primary coolant loss. 

For most cases, coolant loss will occur from the upper end of the subassemblies first. In general, then, with this criterion satisfied, coolant voiding will not produce consequential positive reactivity effects. Local... 

Small metallic or ceramic balls shall be available for insertion into the Vertical Safety Rod channels under emergency conditions idiere it becomes apparent that Vertical Safety Rod insertion may be iiqpossible that coolant loss is imminent and that Total Control strength should be available. 

With regard to long-lived radionuclides that show a low decontamination factor on the purification system (e. g. Cs in PWR primary coolant containing LiOH), the purification constant e also has to include the coolant losses via water exchange or leakages. On the other hand, fission products which form insoluble compounds or can be adsorbed onto non-dissolved corrosion product particulate matter may be removed from the coolant by plate-out onto the primary circuit surfaces. These and other parameters which are liable to affect the activity concentrations of the radionuclides in the primary coolant are the reason why a trustworthy calculation of source strengths can only be made using specific radionuclides such as fission product noble gas isotopes and iodine isotopes. 

Initiating event Reactivity excursion + loss of coolant Loss of coolant... 

The N-Reactor lattice is fall-safe upon loss of coolant. That is, the dry lattice is less reactive than the wet lattice. The coolant-loss reactivity effects for the green and ripe pile are given in Table 5 3 The values for the cold green reactor are experimental values (See Appendix III, Volume II). 

To prevent coolant loss in case of pipeline or system equipment failure, the nozzles connecting the system with the reactor unit are equipped with narrowing inserts. 

The ABV is an integral type PWR. The ABV design incorporates the following inherent safety features intended for the self-limitation of power, heat-up rate and coolant loss ... 

In design basis accidents with coolant loss, the core remains covered and fuel elements are not heated above nominal temperatures. The protective shell localizes the coolant flowing out of the reactor. Personnel intervention is not required for 8 hours after the initiating events. The irradiation doses for population are lower than the allowable levels requiring protective... 

In beyond design basis accidents with primary coolant loss and the failure of all ECCS pumps, provision is made for the core to remain covered during a period of not less than 1 hour, Fig. VI-4. 

The calculation results are presented in Fig. X-7. After the reactor vessel bottom rupture, total NPP blackout and the prompt coolant loss and vessel decompression are observed. The pressure inside the primary containment increases up to 2 bar. After that, the ECCS operation starts, and cold water from the ECCS is released through the ruptured reactor vessel bottom. The core becomes voided in about 100 seconds, and during this period its temperature decreases from 300°C to about 120°C. After that, fast heating of the core starts due to the residual heat. Core cooling is performed by natural convection of steam between the core and the ECCS condenser at a pressure of 2 bar. The natural convection flow rate increases from zero to 10 kg/s in about 10 minutes. In about 40 minutes, the core temperature reaches its maximum of 720°C, Fig. X-7. Further on, a slow decrease of the core temperature is observed. Within the range of temperatures observed in Fig. X-7, the release of radioactivity from micro fuel elements will be nearly the same as in normal operation, i.e. 10. ... 

The principle of modular design of nuclear steam-supply systems (NSSSs) is most economically effective for the reactors in which inherent safety features against severe accidents have been realized to the maximum possible extent. Primarily, this should be attributed to accidents with coolant loss, such as LOCA. To cope with these accidents in light water reactors, many safety systems are needed that are not necessary for the SVBR-75/100. This considerably simplifies the technology of construction and assembly and reduces the scope of construction for the reactor compartment. 

Number of HPSI systems - the number of high-pressure safety injection systems designed to make up for reactor coolant losses in the case of a relatively small leakage, when the pressure drop is small. For reactors without a HPSI system, data providers should enter "N/A". 

Related to the fail-safeness of the lattice on coolant loss is the converse effect of increasing the amount of water in the reactor. Either a cold water Insertion at reactor equilibrium level (whldh would Increase the coolant density and hence the amount of water in the process tubes) or flooding of the graphite structure can add reactivity. 

Therefore, accidents which take place during low power and shutdown conditions (LPS) have been under extensive study all over the world for several years. Results have shown that the risk of an accident initiation during the shutdown and refueling phase is high. Important contributors to risk are boron dilution, loss of residual heat removal with the reactor cooling system in reduced inventory conditions, loss of primary coolant, loss of off-site power, fires and human errors. 

Titanium sheathing Is used for the control and safety rods of the NHl. Extensive literature review has Indicated that water-cooled titanium will perform satisfactorily In the reactor environment. The material was chosen primarily because of Its high melting temperature, which will permit the control rod to continue to perform its function even after tube coolant loss had permitted the Internal aluminum parts to melt. 

For safety reasons the core, consisting of about 600 power channels, is divided into four independent zones, so that coolant loss in one of them would not cause the sudden voiding of the rest. Each of these zones is divided into two partly independent circuits. In case of a sudden pressure loss in a steam drum (there are two of them for each zone), voiding would be fast in one half-zone only, while it would be delayed in the other half, so as to enable the safety and control systems to intervene. 

This method, avoiding the use of enriched uranium boosters, has the advantage of inserting more uniformly the reactivity all over the core and also diminishing substantially the Insertion of positive reactivity in case of a coolant loss when the reactor is operating at reduced load. 

Use of procedures is a highly important aspect for increasing the mitigation capabilities (this actually covers both the system availability and recovery capabilities). Many plants introduced specific emergency operating procedures to cope with specific losses of function (like loss of coolant. Loss of RHR). Those procedures would address both the recovery of normal systems and use of alternate systems and cooling modes. One plant have a procedure for flooding the reactor after the loss of the RHR. Another has a specific procedure which allows for use of all three redundancies when the core is in the vessel. 

The moderator recovery system (MRS) is intended to supply reactor coolant makeup for small breaks in the PWS pressure boundary. The system safety function is to ensure that specified acceptable fuel design limits are not exceeded as a result of primary coolant loss due to leakages from the PWS pressure boundary and rupture of small piping or other small components which are part of this boundary. If light water systems are leaking concurrent with a PWS small break/leak,- the MRS may pump degraded moderator into the PWS. 

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