| Due to its superior performances such as compact structure, lower fuel inner temperature,higher heat transfer efficiency, and deeper fuel burn-up, plate-type fuel assembly has beenmore and more widely utilized in new type integrated reactors and experimental researchreactors, of which coolant is forced passing through the typical narrow rectangular channelsformed by plate-type fuel in the core. Under some accident conditions, such as irradiationdamage, materials debris or foreign objects flowing into the core with the coolant circulation,and flow assembly blockage accidents could occur. The accident may cause the reduction ofcoolant flow, make the fuel plate temperature increase, result in the phenomenon of dry-out,threaten the integrity of the fuel cladding, and even cause the release of radioactive materialinto the reactor coolant system.Previously, the numerical research about the flow blockage accident mainly confined to thelevel of using1D system analysis codes or2D CFD codes, but this paper has provided a3Dliquid-solid coupling CFD simulation of nine cases for flow blockage accident in plate-typefuel assembly including different positions (inlet, middle, and outlet) and blockagepercentages of the blocked channel. The calculation has simulated the transient process of theflow field of the coolant water in the three channels and the temperature field of the entirecalculation domain including the fuel plates and their cladding after the accident happened.The results showed that there was some common transient characteristics in the nine blockageaccident cases, although each of them had different flow and temperature fields: Coolantredistribution happened quickly after blockage, and caused the redistribution of the fuel plateheat flux in the same time, thus the flow and temperature fields of the blocked flow channelhad changed dramatically. However, with the face-type blockage, there was not coolantboiling phenomenon in all channels. The temperature peak shifted from the geometrical centerof the fuel plate to the side of the blocked coolant flow channel, but there was not theso-called “anti-heat transfer” phenomenon mentioned in some previous research, whichmeans the heat will be transferred back to the fuel plate from the coolant in the downstream ofthe blockage channel. Meanwhile, the highest temperature region of the fuel plate cladding had been calculated which is close to the blocked flow channel, and the results showed thatthe regions of different cases had different shapes and locations.Present results are valuable to further research of flow blockage accident and are of greatsignificance to the safety design and analysis of plate-type fuel assembly. |
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