Although the Monte Carlo method is considered to be the most accurate method available for solving radiation transport problems, its applicability is limited by its computational expense. Thus, bia...

Automated variance reduction of Monte Carlo shielding calculations using the discrete ordinates adjoint function

Monte carlo variance reduction with deterministic importance functions

In the nuclear industry, an increased demand exists to provide modeling results with credible confidence bounds not only for simple but also for refined modeling. With the objective to facilitate a...

Multidimensional deterministic nuclear data sensitivity and uncertainty code system : Method and application

FR) Le Règlement 258/2012 vise à réduire le risque de trafic illicite d’armes à feu à usage civil en établissant des règles communes pour l’exportation, l’importation et le transit extra-UE d’armes à feu, de leurs pièces, éléments et munitions. L’étude analyse dans quelle mesure le Règlement 258/2012 a été efficace, efficient, pertinent vis-à-vis des besoins de l’UE, cohérent et complémentaire avec les instruments de l’UE et internationaux dans le domaine du contrôle d’armes, et a apporté une valeur ajoutée de l’UE. L’étude confirme que le Règlement 258/2012 est globalement une initiative pertinente pour répondre aux risques de trafic illicite, et notamment de détournement, d’armes à feu civiles. Les pratiques nationales de mise en œuvre du Règlement ont abouti à la création d’un système préventif et à l’adoption de règles minimales communes sur l’exportation, l’importation et le transit qui limitent les risques liés à la sécurité des échanges internationaux. Cependant, l’étude met en évidence qu’il serait possible d’harmoniser davantage les pratiques nationales et d’améliorer l’échange d’information, d’augmenter la pertinence globale de l’initiative de l’UE en répondant aux risques que représentent les objets convertibles, et d’améliorer la cohérence en clarifiant les « zones grises » avec la Position commune 2008/944/PESC et les incohérences avec la Directive révisée sur les armes à feu. En s’appuyant sur l’évaluation, l’étude identifie des recommandations, avec différents niveaux de priorité, et des actions spécifiques de mise en œuvre.

Final Report on

of the NRCs regulations, techniques used by the staff in evaluating specific problems or postulated accidents, and data needed by the NRC staff in its review of applications for permits and licenses. Regulatory guides are not substitutes for regulations, and compliance with them is not required. Methods and solutions different from those set out in the guides will be acceptable if they provide a basis for the findings requisite to the issuance or continuance of a permit or license by the Commission.

USNRC Draft Regulatory Guide: DG-1053, Calculational and Dosimetry Methods for Determining Pressure Vessel Neutron Fluence

Recent pressure vessel fast fluence calculations have revealed numerical difficulties (spatial oscillations) in the S{sub N} solutions, which have persisted in spite of mesh refinement. It is demonstrated that other shielding/deep-penetration applications may be affected; in fact, any S{sub N} solution in which the uncollided flux component is significant is likely to exhibit such difficulties. Test problems have been designed to characterize and understand numerical difficulties. Main analyses are performed using the diamond-difference (DD) scheme, which is linear and forms the basis for other (more complex) low-order differencing schemes. Other low-order differencing schemes (e.g., the DD with negative flux fixup and the {theta}-weighted) may partly remedy the situation by reducing the oscillations or by eliminating the oscillations at a cost of oversmoothing the results everywhere (e.g., the zero-weighted scheme). These schemes provide more robust solutions, but the inherent difficulties (although reduced) still remain. Types of discontinuities that trigger the oscillations are also examined; it is difficult to envisage an actual practical application free of such discontinuities. The magnitude of numerical difficulties (oscillations) and their practical relevance will depend on all S{sub N} model features, the differencing scheme being used, and the application requirements, but this study has shown that theymore » are inherent to multidimensional finite-difference S{sub N} algorithms.« less

Analysis of Inherent Oscillations in Multidimensional SN Solutions of the Neutron Transport Equation

The application of Monte Carlo methods for reactor pressure vessel (RPV) neutron fluence calculations is examined. As many commercial nuclear light water reactors approach the end of their design lifetime, it is of great consequence that reactor operators and regulators be able to characterize the structural integrity of the RPV accurately for financial reasons, as well as safety reasons, due to the possibility of plant life extensions. The Monte Carlo method, which offers explicit three-dimensional geometric representation and continuous energy and angular simulation, is well suited for this task. A model of the Three Mile Island unit 1 reactor is presented for determination of RPV fluence; Monte Carlo (MCNP) and deterministic (DORT) results are compared for this application; and numerous issues related to performing these calculations are examined. Synthesized three-dimensional deterministic models are observed to produce results that are comparable to those of Monte Carlo methods, provided the two methods utilize the same cross-section libraries. Continuous energy Monte Carlo methods are shown to predict more (15 to 20%) high-energy neutrons in the RPV than deterministic methods.

Monte Carlo Transport Calculations and Analysis for Reactor Pressure Vessel Neutron Fluence

An accurate prediction of the reactor pressure vessel (PV) fast neutron fluence (E> 1.0 MeV or E> 0.1 MeV) is necessary to ensure PV integrity over the design lifetime. The discrete ordinates metho...

Effects of SN Method Numerics on Pressure Vessel Neutron Fluence Calculations

The methodology used to prepare the source for neutron fluence calculation at the reactor pressure vessel is examined, and its effect on the calculated cavity dosimeter reaction rate is evaluated. ...

Evaluation of the uncertainties in the source distribution for pressure vessel neutron fluence calculations

Monte Carlo calculations of pressure vessel (PV) neutron fluence have been performed to benchmark discrete ordinates (S{sub N}) transport methods. These calculations, along with measured data at the ex-vessel cavity dosimeter, provide a means to examine various uncertainties associated with the S{sub N} transport calculations. For the purpose of the PV fluence calculations, synthesized 3-D deterministic models are shown to produce results that are quite comparable to results from Monte Carlo methods, provided the two methods utilize the same multigroup cross section libraries. Differences between continuous energy Monte Carlo and multigroup S{sub N} calculations are analyzed and discussed.

Bojan G. Petrovic

Papers

Analysis of Inherent Oscillations in Multidimensional SN Solutions of the Neutron Transport Equation

Monte Carlo Transport Calculations and Analysis for Reactor Pressure Vessel Neutron Fluence

Effects of SN Method Numerics on Pressure Vessel Neutron Fluence Calculations

Evaluation of the uncertainties in the source distribution for pressure vessel neutron fluence calculations

Benchmarking of synthesized 3-D S{sub N} transport methods for pressure vessel fluence calculations with Monte Carlo