Browsing by Author "Waata, Christine Lylin"

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    Coupled neutronics thermal hydraulics analysis of a high-performance light-water reactor fuel assembly
    (2006) Waata, Christine Lylin; Laurien, Eckart (Prof. Dr.-Ing.)
    The use of water at supercritical pressure as coolant and moderator introduces a challenge in the design of a High-Performance Light-Water Reactor (HPLWR) fuel assembly. At supercritical pressure condition (P=25 MPa), the thermal-hydraulics behaviour of water differs strongly from that at sub-critical pressure due to a rapid variation of the thermal-physical properties across the pseudo-critical line. Due of the strong link between the water (moderation) and the neutron spectrum and subsequently the power distribution, a coupling of neutronics and thermal-hydraulics has become a necessity for reactor concepts operating at supercritical pressure condition. The effect of neutron moderation on the local parameters of thermal-hydraulics and vice-verse in a fuel assembly has to be considered for an accurate design analysis. In this study, the Monte Carlo N-Particle code (MCNP) and the sub-channel code STAFAS (Sub-channel Thermal-hydraulics Analysis of a Fuel Assembly under Supercritical conditions) have been coupled for the design analysis of a fuel assembly with supercritical water as coolant and moderator. Both codes are well known for complex geometry modelling. The MCNP code is used for neutronics analyses and for the prediction of power profiles of individual fuel rods. The sub-channel code STAFAS for the thermal-hydraulics analyses takes into account the coolant properties beyond the critical point as well as separate moderator channels. The coupling procedure is realized automatically. MCNP calculates the power distribution in each fuel rod, which is then transferred into STAFAS to obtain the corresponding thermal-hydraulic conditions in each sub-channel. The new thermal-hydraulic conditions are used to generate a new input deck for the next MCNP calculation. This procedure is repeated until a converged state is achieved. The coupled code system was tested on a proposed fuel assembly design of a HPLWR. An under-relaxation was introduced to achieve convergence. The test results showed a satisfactory convergence with a small under-relaxation factor of 0.2. Results from the test analysis of a HPLWR fuel assembly showed an axial power profile with two peaks. A stronger peak in the lower part is caused by the strong moderation from the coolant and a weaker one in the upper part caused by moderator water. A 5% enrichment in the most inner fuel rods and lower enrichment of 4% in the corner rod was used to eliminate the hot spot at the corner of the fuel assembly and to obtain a well uniform power distribution in the fuel bundle. A well uniform temperature distribution was achieved in any cross section. A maximum temperature difference of 50°C in the upper part was obtained between the hottest and the coldest sub-channel. The local maximum cladding temperature of the bundle is within the allowable limit of 620°C.