Flow Instability in Material Testing Reactors

摘要: Research reactors with power between 1 MW and 50 especially materials testing (MTR), cooled moderated by water at low pressures, are limited, from the thermal point of view, onset flow instability phenomenon. The is characterized a excursion, when rate heat flux relatively high; small increase in some cases causes sudden large decrease rate. occurs non-recurrent manner leading to burnout. burnout occurring under unstable conditions well below for same channel stable conditions. Therefore, plate type fuel design purposes, critical leads (OFI) may be more limiting than that Besides, phenomenon two-phase interest operation many industrial systems equipments, such as steam generators, therefore, exchangers, thermo-siphons, boilers, refrigeration plants chemical processing systems. In particular, investigation an important consideration nuclear due possibility excursion during postulated accident. OFI slope demand pressure drop-flow curve becomes algebraically smaller or equal loop supply curve. typical curves subcooled boiling shown Fig. (IAEA-TECDOC-233, 1980). With input S2, d stable, while b since slight will cause spontaneous shift a. For given system, there Sc (Fig. 1) tangent c correspond threshold excursive instability. At this any operating spontaneously a, drops abruptly M Mc. MTR using plate-type fuel, each surrounded channels parallel. characteristic respect perturbations (say, peak channel) essentially horizontal, independent pump characteristics. Thus, criterion zero good approximation assessing OFI, i.e.