The potential use of a pulsed neutron source (PNS) to measure reactivity during nuclear fuel loading as a means to prevent core loading errors has been studied at the GUINEVERE facility. This ...facility couples the deuteron accelerator GENEPI-3C to the fast neutron subcritical reactor VENUS-F at the Belgian Nuclear Research Center SCK·CEN. The 14-MeV neutrons are produced in the reactor core center via
fusion reactions. PNS experiments were performed in five reactor configurations corresponding to the different loading steps of VENUS-F. The evolution of the neutron flux during these PNS experiments was measured by several
235
U fission chambers in various positions in the inner and outer reflector and analyzed using the area-ratio method. The results show that, despite strong spatial effects, a strong correlation between the reactivity values given by the area-ratio method and some reference reactivity values remains throughout the reactor unloading. Monte Carlo simulations were first validated by comparison with the data and then used to investigate the sensitivity of the method to a core loading error. First results show that some loading errors could be experimentally detected using a PNS.
The Source Jerk Integral (SJI) method has been extensively used to determine the subcriticality in VENUS-F zero-power experiments since 2012. The obtained results were in the range from −5 $ to about ...−20 $ and concerned the subcriticalities of accelerator-driven system MYRRHA mockup cores. Within the SALMON program, which is dedicated to the safe loading procedure of pressurized power reactors, five subcritical core configurations were assembled and studied in the VENUS-F reactor in 2019. These cores simulated the loading process in inverse mode: from more reactive to deep subcritical. The subcriticality of five variants of the SC11 VENUS-F core was changed in steps from −20 $ to about −100 $ by replacing the fuel assemblies with lead reflector assemblies. The subcriticality levels were determined with the pulsed neutron source (PNS) and SJI methods. The GENEPI-3C deuterium accelerator coupled with VENUS-F was used as an external neutron source. The results of the measurements obtained with the SJI method are presented in this paper. Time-dependent Monte Carlo calculations were performed to simulate the SJI experiments and to determine spatial-energy correction factors. Static Monte Carlo simulations were performed to calculate neutron spectra and reactivity. The results of the measurements (both SJI and PNS) are compared with the static MCNP calculations.
The GUINEVERE (Generation of Uninterrupted Intense NEutron pulses at the lead VEnus REactor) project was launched in 2006 within the framework of FP6 EUROTRANS in order to validate online reactivity ...monitoring and subcriticality level determination in accelerator driven systems (ADS). Therefore, the VENUS reactor at SCK-CEN in Mol, Belgium, was modified towards a fast core (VENUS-F) and coupled to the GENEPI-3C accelerator built by CNRS. The accelerator can operate in both continuous and pulsed mode. The VENUS-F core is loaded with enriched Uranium and reflected with solid lead. A well-chosen critical reference state is indispensable for the validation of the online subcriticality monitoring methodology. Moreover, a benchmarking tool is required for nuclear data research and code validation. In this paper, the design and the importance of the critical reference state for the GUINEVERE project are motivated. The results of the first experimental phase on the critical core are presented. The control rods worth is determined by the positive period method and the application of the Modified Source Multiplication (MSM) method allows the determination of the worth of the safety rods. The results are implemented in the VENUS-F core certificate for full exploitation of the critical core.
The Modified Source Multiplication method is used to determine an unknown reactivity level of a reactor from a known one if one has access to the detector counting for both levels when the reactor is ...fed by a constant neutron source like an Am-Be source. When available, an accelerator driven source, in continuous mode, can be useful as its intensity can be tunable and then adapted to the experimental conditions. However, in that case, the MSM technique must be extended to account for an external source whose intensity, energy and angular distributions can vary from one measurement to another. In this paper, this Modified Multi-Source Multiplication (MMSM) method is applied to measurements done during the FREYA project in the GUINEVERE facility, operated with the GENEPI-3C accelerator providing a mixture of (D,T) and (D,D) neutrons. The monitoring of these sources through the detection of the associated charged particles allows the calculation of the MMSM factors and the estimate of the reactivity values. The results are compared in different configurations with the reactivity obtained with an Am-Be source or in dynamic measurements performed with GENEPI-3C. Their excellent agreement shows the possibility of using such accelerator-based neutron sources for MSM measurements when they are correctly monitored. This is of great interest for deep sub-critical level characterization for which detector count rates per source neutrons might be low.
We report on direct experimental evidence of the population of the 3/2− intruder state in 27Ne in the knockout of a single neutron from the ground state of 28Ne. This low-lying negative parity state ...is consistent with a narrower shell gap for exotic nuclei with Z≪N and N≈20. Monte Carlo shell-model calculations with the modern SDPF-M interaction successfully describe neutron-rich nuclei in the vicinity of N=20 where normal and intruder configurations coexist at low excitation energy. This observation demonstrates the importance of direct reactions for the study of exotic nuclei and the predictive power of these large-scale shell-model calculations.
•Inverse Point Kinetics can be used for low-statistics rod drop analysis.•MSM factors can be calculated with a stochastic neutron transport code.•Sensitivity analysis shows that the MSM method is a ...robust technique.
The GUINEVERE project was launched in 2006 in order to study the feasibility of transmutation in Accelerator Driven subcritical Systems (ADS). This facility, hosted at the Belgian Nuclear Research Center SCK·CEN, couples the fast subcritical lead reactor VENUS-F with an external neutron source provided by the GENEPI-3C accelerator.
In order to test on-line subcriticality monitoring techniques, an independent measurement of the reactivity of VENUS-F was achieved using the Modified Source Multiplication Method (MSM). The unknown reactivity of the subcritical configuration of interest was determined by comparing detector count rates driven by an external neutron source in this configuration with those obtained in a slightly subcritical configuration whose reactivity was determined by rod drop experiments. To account for spatial effects, MSM correction factors were calculated for all the detectors using the Monte Carlo neutron transport code MCNP. The corrected reactivity values of all the detectors were found to be consistent. This led to a final estimate of −5.28±0.13$ for the reactivity of VENUS-F.
The MSM factors calculated with MCNP were found to be insensitive to the assumptions made for modeling the reactor and the detectors. Thus the MSM method appears to be a robust technique for measuring large subcriticality values with good accuracy.
'Magic' nucleus Si Fridmann, J; Wiedenhoever, I; Gade, A ...
Nature (London),
06/2005, Letnik:
435, Številka:
7044
Journal Article
Recenzirano
Nuclear shell structures: the distribution of the quantum states of individual protons and neutrons: provide one of our most important guides for understanding the stability of atomic nuclei. Nuclei ...with 'magic numbers' of protons and/or neutrons (corresponding to closed shells of strongly bound nucleons) are particularly stable. Whether the major shell closures and magic numbers change in very neutron-rich nuclei (potentially causing shape deformations) is a fundamental, and at present open, question. A unique opportunity to study these shell effects is offered by the Si nucleus, which has 28 neutrons: a magic number in stable nuclei: and 14 protons. This nucleus has a 12-neutron excess over the heaviest stable silicon nuclide, and has only one neutron fewer than the heaviest silicon nuclide observed so far. Here we report measurements of Si and two neighbouring nuclei using a technique involving one- and two-nucleon knockout from beams of exotic nuclei. We present strong evidence for a well-developed proton subshell closure at Z = 14
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Three sub-critical (SC) core configurations were investigated in the VENUS-F zero power reactor coupled with the GENEPI-3C accelerator. The SC10 and SC12 were a mock-up of a MYRRHA start-up core and ...SC11 represented a more complex MYRRHA core loaded with various types of in-pile-sections. The sub-criticality of 11 variants of these VENUS-F cores was changed in several steps from -6$ down to -30$ using the safety and control rods. Their sub-criticalities were determined with the Source Jerk Integral (SJI) method using 11 fission chambers located all over the reactor. For the data analysis, the 8-group delayed neutron parameters from the JEFF-3.1.2 evaluated nuclear data library were used. Reliability and reproducibility of the experimental results were tested by repeating the measurements, swapping the detectors and varying the accelerator beam intensity, thus changing the detector count rates and verifying the validity of the dead time corrections. The obtained results are compared with MCNP calculations.
•The “current-to flux” method for monitoring ADS subcriticality was successfully tested experimentally.•Spatial effects affecting the reactivity estimation can be corrected with Monte Carlo ...simulations.•The robustness and precision of the correction technique is demonstrated.
In this article, we evaluate the quality and robustness of a method envisaged for the on-line monitoring of the subcriticality of an ADS, called the “current-to flux” (CTF) method. For this evaluation, we performed a dedicated experiment at the GUINEVERE facility. It is hosted at the SCK-CEN and consists of the subcritical VENUS-F reactor coupled to a continuous external neutron source provided by the GENEPI-3C accelerator. During this experiment, the reactor control rods were moved in various patterns, and the subsequent dynamical evolutions of the reactor reactivity were monitored using nine fission chambers (FCs). The space-energy effects that bias the reactivity values are corrected using a procedure based on simulations computed with the Monte Carlo neutron transport code MCNP. We investigate the precision of this correction procedure by comparison with a reactivity value extracted with the beam interruption technique and we demonstrate its insensitivity to the simplifications made on the VENUS-F reactor modeling and to a simulation key parameter such as the boron carbide density filling the control rods.
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