| 1. |
- Andersson, Mikael, 1986, et al.
(författare)
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Control Rod Calculation in Axially-Heterogeneous Fast Reactors. Part I: Influence of the Absorber Environment
- 2017
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Ingår i: Nuclear Science and Engineering. - : Informa UK Limited. - 0029-5639 .- 1943-748X. ; 185:2, s. 263-276
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Tidskriftsartikel (refereegranskat)abstract
- In axially heterogeneous fast reactor concepts, such as the ASTRID CFVcore, the accurate neutronic prediction of control rods is a challenge. In suchcores, the performance of the classical 2D equivalence procedure, used forcontrol rod homogenization in homogeneous fast reactors, is questionable.In this work (Part I of II), a number of axially heterogeneous environ-ments, representative of a CFV-type core are investigated using 2D (X-Z )models, with the objective to distinguish regions where the classical equiva-lence procedure is valid from those where it is not.It is found that the environments that affect the control rod absorber themost, and are likely to invalidate the procedure, are the internal control rodinterfaces, such as the absorber/follower interface and the interface betweenzones of different boron enrichments. The range of the main spectral impactcould be seen within 0-10 cm from the material interfaces studied.In a companion Paper (Part II), a full core investigation is performed,which builds upon the results of this paper.
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| 2. |
- Andersson, Mikael, 1986, et al.
(författare)
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Control rod calculation in axially-heterogeneous fast reactors. Part II: Impact of 3D homogenization on core parameters
- 2017
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Ingår i: Nuclear Science and Engineering. - : Informa UK Limited. - 0029-5639 .- 1943-748X. ; 185:2, s. 277-293
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Tidskriftsartikel (refereegranskat)abstract
- Advanced sodium-cooled fast reactors with improved safety features, such asthe French ASTRID CFV-core concept, is characterized by an axial heteroge-neous core, which will present a challenge on the homogenization proceduresused today, taking into account all the different axial material transitions.Reliable modeling of the control rod and accurate prediction of the controlrod worth are essential to determine the shutdown margins and to ensuresafe operation.In this work (Part II of II), two different homogenization schemes are com-pared. One is based on the traditional reactivity-equivalence procedure in 2D,and the other a newly implemented 3D version of the reactivity-equivalenceprocedure, with approximations based on the results in a companion pa-pers (Part I). The deterministic results are compared with a Monte Carloreference.Both of the cross section sets, from the two homogenization schemes, yielded results within the requested 5% error margin in reactivity. Thelargest discrepancy was found for the classical procedure for the case with aslightly inserted control rod (normal operating conditions).Both sets of cross sections yielded similar power profiles in the fuel sub-assembly neighboring the control rod within the 2 Monte Carlo standarddeviation. Neither of the cross section sets were able to predict the largegradients in capture rates close to the internal control rod interfaces.The study showed that the traditional 2D reactivity-equivalence proce-dure produces homogenized cross sections which yield reliable results in aCFV-type core. One exception from this was found for slightly inserted con-trol rods, where the effect of the follower/absorber interface could not be fullycaptured by the 2D scheme, and for such cases, 3D modeling is recommended.
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| 4. |
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| 5. |
- Andersson, Mikael, 1986, et al.
(författare)
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Impact of Control Rod Position and Homogenization on Sodium Void Effect in CFV-type SFR
- 2016
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Ingår i: PHYSOR 2016. - 9781510825734 ; 4, s. 2658-2667
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Konferensbidrag (refereegranskat)abstract
- In complex innovative fast reactor concepts, fairly detailed core modeling is essential for reliable safety analysis during severe accident scenarios. The CFV core with its axially heterogeneous design, has a negative sodium void reactivity effect, a favorable feature wich increases the inherent system safety in case of sodium boiling. In this work, we studied the impact that the control rod homogenization model used, and the control rod position, have on the sodium void-reactivityeffect and the control rod worth, in the case of a voided CFV core. Three different control rodhomogenization models were studied, the traditional 2D equivalence procedure, and two models based on a 3D equivalence procedure, taking into account the axial heterogeneity of the CFV core.It was found that the impact of control rod homogenization has a negligible effect on the sodium void reactivity effect. However, between different control rod positions, a difference of up to 1$ in the sodium void reactivity effect was found, hence the control rod position has to be carefully considered when calculating the sodium void reactivity effect. For the control rod worth in a voidedCFV core, the traditional 2D procedure, could lead to discrepancies of up to 11% for control rod positions at the top of the core. These discrepancies could be much reduced by control rod homogenization with the 3D equivalence procedure. For the total control rod worth, all models andprocedures produced results within the desired error margin of 5%.
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| 6. |
- Andersson, Mikael, 1986, et al.
(författare)
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Influence of Local Spectral Variations on Control-Rod Homogenization in Fast Reactor Environments
- 2015
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Ingår i: Nuclear Science and Engineering. - 0029-5639 .- 1943-748X. ; 181:2, s. 204-215
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Tidskriftsartikel (refereegranskat)abstract
- Advanced fast reactor concepts, such as the CFV core (French acronym of "Coeur a Foible effet de Vide Sodium," meaning "low sodium void effect core"), are characterized by a heterogeneous axial core arrangement, with an inner fertile zone and a sodium plenum above the fuel. Such concepts represent a strong challenge for accurate predictions of the control-rod antireactivity effects, and the surrounding local fuel pin power. Classical equivalence procedures, which were developed for axially homogeneous cores, are put to the test when applied to such axially heterogeneous cores. In this work, we investigate the influence of variations in the local neutron spectra, for different control-rod environments, with the objective of understanding the impact of spectral variations in control-rod homogenization. This was conducted by considering a simple one-dimensional model of the equivalence procedure in which a transition zone between the fuel and control rod was introduced to represent different control-rod environments. Two types of situations were studied, one corresponding to softened neutron spectrum environments, for which the impact in the homogenized control-rod cross section was found to be smaller than 5%. The second situation was with wide elastic scattering resonances in the control-rod environment, which could locally lead to differences of up to 15% in the resulting equivalent cross sections. The reactivity effect of these changes was calculated to be less than 2%. In some cases, the numerical stability of the equivalence procedure was adversely affected, mainly in high-energy groups, due to the softening of the neutron spectra.
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| 7. |
- Verma, Vasudha, et al.
(författare)
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Assessment of the neutron noise induced by stationary fuel assembly vibrations in a light water reactor
- 2019
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Ingår i: International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering, M and C 2019. ; 2019, s. 1124-1133
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Konferensbidrag (refereegranskat)abstract
- A systematic increase of the neutron noise levels over time has been observed in some of the pre-KONVOI PWRs operating in Europe. A possible reason for this anomaly was identified as increased mechanical vibrations of reactor internals, specifically of fuel assemblies. To verify this conjecture, the modeling of stationary vibrations of fuel assemblies and of the corresponding neutron noise is essential. In this paper, using the epsilon/d model basis, we illustrate the modeling of the neutron noise sources for fuel assembly vibrationsand study the effect of homogenization of cross sections on such stationary perturbations. A comparative analysis between the classical nodal approach (both localized at the boundaries of the vibrating fuel assembly or involving the entire neighboring fuel assemblies) and a pin-wise approach shows that the ‘boundary-localized’ nodal approach seems to capture local noise information, as a pin-wise approach would do, without the need of a complex pin-by-pin model when the detectors are placed close to the perturbation. However, when considering region of the active core away from the perturbation, all three approaches lead to comparable results.
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