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Highlights • Assessment of detectors' locations and number of detectors in PGSFR. • Generation of spatial weighting function using forward fixed-source calculation in MCNPX. • Calculation of transient power during withdrawal of a single control assembly by using FREK. Abstract This paper presents the assessment of the ex-core detectors in the Prototype Gen-IV Sodium-cooled Fast Reactor (PGSFR) in response to the movement of single primary control assembly, to evaluate the detectors' locations and to determine a proper number of detectors. The detectors are located below the containment vessel and distributed in different ranges from the center and different azimuthal angles. Another position considered is in the radial direction of the core, at the sodium coolant gap between the outermost assembly and core shroud. To calculate the detection rate, the contribution of each fuel region to the detector and the core power distribution are required. Initially, the aforementioned contribution is generated by performing a continuous-energy forward fixed-source Monte Carlo calculation using MCNPX. The reactor kinetics code FREK simulates the power change due to an inadvertent withdrawal of a primary control assembly up to 10% from its critical position followed by full insertion of secondary control assemblies. The response from each detector location was evaluated, and consequently, the detectors located below the containment vessel, which can "see" all the fuel assemblies, responded better to the core power increase with a minor error of less than ∼0.6%. In addition, the impact of locating the detector below the containment vessel at different locations from the center or at different azimuthal angles was insignificant but several detectors should be distributed at even azimuthal angles for effective core monitoring and redundancy purposes. [ABSTRACT FROM AUTHOR]

• Sensitivity/Uncertainty analysis using SERPENT 2 and ENDF/B-VIII.0. • Error of k eff of CERCER core was significant and larger than that of CERMET one. • ENDF/B-VIII.0 was found to be insensitive to kinetic parameter simulation results. The reliability of eigenvalue and kinetic parameter calculation results for CERCER and CERMET fueled ADS was investigated by conducting sensitivity and uncertainty analysis by SERPENT 2 and ENDF/B-VIII.0 library. The total error of k eff of CERCER core was found to be 1268.7 pcm and larger than that of CERMET one (609.4 pcm). It mostly comes from cross section uncertainty of 237Np (n,g) – the biggest contributor, 239Pu (n,f), 232Th (n,g) and 237Np (n,f). Therefore, the accuracy of nuclear data of those isotopes is recommended to be improved to achieve more reliable eigenvalue results. For kinetic parameters, the uncertainty of evaluated results mainly originated from the 237Np (n,g), 239Pu (n,inl) and 23Na (n,ela) cross sections. Nevertheless, its impact on simulation accuracy is not significant (less than 1%). Thus, ENDF/B-VIII.0 nuclear data is sufficient to evaluate β eff , l eff, and λ eff and discuss the safety features of ADS. [ABSTRACT FROM AUTHOR]