Loss of heat sink

Ice Loss of heat sink considered in plant design Volcanic activity Excluded by siting analysis... 

Loss of Heat Sink Failure of heat transfer between the primary and secondary cooling systems requiring emergency cooling. 

The Loss of Heat Sink has three subclasses total loss of primary system circulation (5%), los,s of secondary cooling from effluent header failures (1 %), and total loss of secondary cooling from inlet... 

Loss of heat load (process facility) Damage of SSC Loss of heat sink to reactor... 

In terms of nuclear reactor response, each of these chemical plant events is a partial or total loss of heat sink accident. 

There are several important consequences of the failure of the Bunsen reactor. The initial consequence of the failure is a lack of reactant flow to both the Section 2 and Section 3 chemical reactors. However, heat input is still present and each reactor still has an initial concentration of reactants present. Thus, the reactions will initially continue unabated in both sections. However, as the reactions continue, the concentrations of reactants will deplete, altering the reaction rates as well as the reaction heat input. Additionally, since the input to the pre-heater and evaporator is no longer present this will lead to a substantial immediate loss of heat sink for the nuclear reactor. 

Partial loss of heat sink (pre-heater/evaporation of a single section) progresses to total loss of heat sink. 

Preliminary accident analysis of MHTGR-IGT has been carried out by using THERMDC code. The results of the analysis indicates, under rating operation condition, the maximum temperature of fuel elements is about 980. In case of the depressurization with core heat-up, the fuel maximum temperature is 1477 . In case of the accident of loss of heat sink, the fuel maximum temperature is only lOSOt. It should be emphasized that, due to the integrated structure of the primary loop, the probability of losing primary operation pressure will be greatly reduced. 

Batch n°6 Tests related to helium injection circuit in the space between the vessels (fig. 3.1) in order to improve heat transfer in case of loss of heat sink. This possibility will be used according the nominal power to be decided. 

However, because the IPWR operates with the coolant in the core close to the saturation temperamre, a small amount of transient local overheating quickly produces a significant amount of void generation (nucleate boiling) in the core which immediately induces a large negative reactivity response. This feature reduces the core power rapidly in a loss-of-heat-sink event. 

Emergent power supply system (battencs, diesel gmierators) Total loss of heat sink ... 

Total loss of heat sink Non-cntical Total loss of SG feedwater Non-cntical Station blackout Non-cntical ... 

Total loss of heat sink Not critical for short-term, due to MS... 

Total loss of heat sink Total loss of SG - passive long-term RHR to ambiant air largely suppresses initiator... 

Possibility and simplicity of SG leaky section isolation L AT WS Increased values of negative reactivity coefficients, passive ERHR systems L Pnmary transients Greater pnmary inertia L Secondaiy transient Multichannel shutdown and RHR systems L Loss of electnc sources - Implementation of passive systems (battery power sources) L Total loss of heat sink Passive heat removal to ambient air, non-cntical L Total loss of S G feedwater non-cntical - Passive residual heat removal L Station Blackout non-cntical - Passive shutdown and RHR systems L... 

I xiss of eiectnc sources non-cntical Total loss of heat sink non-cnticat I otal loss of S G feedwater non-critical... 

LOSS of electnc sources notcntical 1 otal loss of heat sink not cntical 1 otal loss of the SO feed water not cntical Station blackout not cntical... 

Strong negative reactivity coefficients L Pnmary Transients - Great primary mertia, CPS actuation, PRHR actuation L Secondary Transients - Great primaiy mertia, CPS and PRHR actuation L Loss of Electric Sources - Implementation of passive systems (battery power sources) Total Loss of heat sink not cntical ... 

Total loss of heat sink Station blackout... 

Natural convection - L Secondary transients Natural convention - L Loss of electric sources Battery power - R Total loss of heat sink Passive DHR to the air and ground - S Station blackout Not critical ... 

The thermal shutoff system (TSS), separate from the RPS, is designed to automatically shut off the EM pumps on high sodium temperature, in case the heat sink (IHTS) is lost and the RPS fails to scram. For this scenario it is assumed that the loss of heat sink event starts from full power and that neither the PCS nor the RPS can shut down the reactor so that the reactor is left with only RVACS to remove heat. 

C. E. Lahm, J. R Koenig, P. R. Betten, J. H. Bottcher, W. K. Lehto, and B. R. Seidel, EBR-II Driver Fuel Qualification for Loss-of-Flow and Loss-of-Heat-Sink Tests without Scram, Nud. Eng. Des., 101, 25,1987. 

Both EdF reference sets of EOPs cover incident procedures, DBA procedures and BDBA procedures which remain valid until fuel damage. Thereafter, the EOP set is no longer apphcable and SAGs are to be entered. Transition criteria are clearly defined and concentrated in only one procedure executed by the safety engineer. On the other side of the spectrum of events, all incidents that may lead to an accident situation are included in the EOP set. Such typical examples are LOCA and SG tube ruptures without safety injection, spurious safety injection, electrical power losses and operation from a shut down panel. For BDBA, typical examples are total loss of essential water/ component cooling, total loss of heat sink (SG feedwater), or total loss of electrical power (on-site/off-site). 

In the consideration performed, two more failures were assumed in addition to one transient as an initiator therefore, this event is more severe than a typical protected loss of heat sink (PLOHS). The analytical conditions were as follows ... 

ACS - auxiliary cooling system RVACS, or RVACS + IRACS LOHS - Loss of heat sink UHS - Ultimate heat sink... 

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