3D modeling of the primary circuit in the reactor pressure vessel of a PHWR

RAMAJO DAMIAN; CORZO SANTIAGO; NIGRO NORBERTO; NICOLAS SCHILLIUK

NUCLEAR ENGINEERING AND DESIGN

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2013 vol. 265 p. 356 - 365

0029-5493

A computational fluid dynamics (CFD) simulation of the reactor pressure vessel (RPV) of the pressurizedheavy water reactor (PHWR) of 745 electrical MW Atucha II nuclear power plant was carried out. A threedimensional (3D) detailed model was employed to simulate coolant circuit considering the upper andlower plenums, the downcomer and the hot and cold legs. Control rods and coolant channel tubes at theupper plenum were included to quantify the mixing flow with more realism. The whole set of 451 coolantchannels were modeled by means of a zero dimensional methodology. That is, the effect of each coolantchannel was modeled through the introduction of a source point at the upper plenum and a sink point atthe lower plenum. For each coupled sink/source points (SSP) the mass, momentum and energy balancewere solved considering the local pressure difference and the temperature between the correspondingpoints where sinks and sources were placed. Based on this strategy, three models with increasingly levelof approximation were implemented. For the first model the 451 coolant channels were reduced to only57 pairs of SSP to represent all the coolant channels, concentrating the effect of several coolant channelsin a unique pair of sink and source while taking into account geometric design details. For the secondmodel, 225 pairs of SSP were introduced. Finally, for the third model each one of the 451 coolant channelswere modeled by means of one pair of SSP. Depending on the coolant channel location, the radial powerdistribution and the pressure loss caused by the corresponding flow restrictor present by design wereconsidered. Simulations carried out give insight in the complexity of the flow. As expected, the greaterthe details of the model the better the accuracy reached in the representation of the RPV behavior. Inaddition, the flow distributor located at the lower plenum showed to be very efficient since, the mass flowat each channel was found to be fairly similar to design. Moreover, temperature gradients at the upperplenum and thermal stratification at the hot-legs were found. Up to where it is known to the authors,this work is one of the few proposals to simulate the full reactor pressure vessel.