Simulation Of Sodium-water Reaction In Secondary Circuit Of Fast Reactor

CEFR is a small pool-type sodium cooled fast reactor, in which steam generatoracts as the heat exchanger between water and sodium. Because of fatigue caused bytemperature fluctuation, quality of welds, corrosion of tubes, variations of heat stress,heat transfer tube in SG always break down, which induce sodium-water reactionaccident when water or steam in the third circuit flow into the sodium loop. In thesodium-water reaction, large amount of hydrogen and energy are generated, at thesame time temperature and pressure will increase around the break. Generatedhydrogen greatly impedes flow of sodium, which lead to sharply increase of pressure.High pressure can make the SG explode and will lead to the failure of heat exchanger,which permit radioactive sodium from the primary circuit mix with that fromsecondary circuit and eventually produce radioactive contamination.Sodium-water reaction accident must be considered in the sodium-cooled fastreactor design and safety analysis. Because the accident will affect the safe operationof the entire system, the primary coolant system, the secondary coolant system, SGequipment and the accident protection system are established by the system modelingtool JTopmeret, the code can be used to calculate the system parameters as the flow,pressure, temperature and others at any point of this system. Both of the steady statecode and dynamic code have been validated, the results show that the steady statecode can be used to calculate the main parameters of the cooling system under moststeady state conditions, the dynamic code can analyze some typical transients.In this paper, sodium leak code is written in FORTRAN, using the theoreticalmodel of transient sodium water reaction and choosing the different chemical reactionequation according to the temperature. The program of sodium leakage module iscoupled with system program in SimExec platform. During the reaction special safetyfacilities are controlled and the program can calculate dynamic response of thesecondary circuit under different leakage rate at distinct position when sodium-waterreaction happens. What’s more, it can describe pressure variation and flow changes ofstreamline at every point in the system. The results has be compared with the safety analysis report verification, it proved that: this program can be used for the analysis ofsodium-water reaction accident, and the results can be accepted.In the next calculation, the system responses when the sodium-water reactionaccident occurred under different conditions have been discussed. The analysis of theresults showed that the worst sodium-water reaction accident occurred in thesingle-phase region of SG, but even if the most severe sodium-water reaction accidentoccurred, because of the conservative design and the principle of consistent defense indepth security ideas, the equipment of the secondary loop won’t be destroyed andthere is no excessive release of radioactivity.In a word, the program discussed in the paper can be used for safety analysis insmall sodium fast reactor during sodium-water reaction accident, which is of greatsignificance for the development of simulation platform of CEFR, and it can also beused for fast reactor operator training, and providing a reference for future large-scalefast reactor design and operation.