The Canadian Supercritical-Water-Cooled Reactor (SCWR) is a vertical pressure tube reactor cooled with supercritical light water and moderated with heavy water. For normal operation, the local conditions of the coolant (density and temperature) and fuel (temperature) vary substantially along the channel. This means that to simulate adequately the behavior of the core under operating conditions or for anticipated accident scenario, expensive 3D transport calculations for a complete fuel channel are required. Here, we propose a simulation strategy that takes into account axial variations of the local conditions and avoids 3D transport calculations. This strategy consists in replacing the 3D simulation by a series of isolated 2D calculations followed by a single 1D simulation. It is shown that this strategy is efficient because the axial coupling along the fuel channel is relatively weak. In addition, the neutronic properties of a channel with axial reflector can be modeled using a simplified 3D transport calculation. 1. Introduction The Canadian Supercritical-Water-Cooled Reactor (SCWR) is a pressure-tube type generation-IV reactor [1] based on CANada Deuterium Uranium (CANDU) reactors [2]. The preliminary concept uses a calandria vessel containing the low-pressure moderator and the five meters long fuel channels [3]. This concept uses off-power batch refueling, and to simplify the fuelling process, the reactor core is oriented vertically. Another feature of this concept is that the coolant is forced vertically downwards; that is, the coolant enters the fuel channels at the top and exits at the bottom of the core. According to the pressure-temperature phase diagram for water, most of the current reactors operate in the liquid phase or on the saturation line. However, the main characteristic of the Canadian SCWR is that the coolant (light water) operates at pseudocritical and supercritical conditions, that is, at pressures and temperatures above the critical point of water (22.064？MPa and 373.95°C). The preliminary concept has a pressure of 25？MPa, a reactor inlet temperature of 350°C and a reactor outlet temperature of 625°C. Figure 1 shows the expected coolant conditions along a fuel channel. Figure 1: Expected coolant conditions along a Canadian SCWR fuel channel. Light water has an impact on neutron slowing down and on neutron absorption. The importance of this impact depends on the temperature and on the density of this water [4]. The effect of the large variation of the coolant conditions along a fuel channel on the global neutronic properties should
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