Methodology for a Large Gas-Cooled Fast Reactor Core Design and Associated Neutronic Uncertainties

International audienceA feasibility study of a 2400 MWth gas-cooled fast reactor using neutronic and thermo-hydraulic constraints has been performed. Previous feasibility studies [1, 2] were performed on 600 MWth cores. Considering larger cores do not imply any change in the safety approach but relax some of the design constraints on the fuel technology, on the fuel residence time and on the power density. These changes allow an enhanced economy competitiveness. The reference core has a 100 MW/m3power density, is based on a dispersed fuel with a fuel-to-matrix volume ratio of 50/50 and achieves a breeding ratio of 1.0 without fertile blankets. This concept possesses enhanced safety features due to a large Doppler effect owing to the presence of carbon in the SiC matrix. The possibility to remove the decay heat out of the core by natural circulation of the gas under a minimum back-up pressure is kept by limiting the core pressure drop. Numerical validation of deterministic calculations by comparisons with Monte-Carlo results are presented and uncertainties due to nuclear data are quantified. It is shown that the specificities of gas-cooled fast reactors keep bias and uncertainties within reasonably limits which are sufficient for current pre-design studies. Definite uncertainties for detailed design studies will be available after the dedicated experimental program ENIGMA in the MASURCA facility be completed

Fine 3D neutronic characterization of a gas-cooled fast reactor based on plate-type subassemblies

International audienceCEA neutronic studies have allowed the definition of a first 2400 MWth reference gas-cooled fast reactor core using plate-type sub-assemblies, for which the main neutronic characteristics were calculated by the so-called ERANOS 'design calculation scheme' relying on several method approximations. The last stage has consisted in a new refine characterization, using the reference calculation scheme, in order to confirm the impact of the approximations of the design route. A first core lay-out taking into account control rods was proposed and the reactivity penalty due to the control rod introduction in this hexagonal core lay-out was quantified. A new adjusted core was defined with an increase of the plutonium content. This leads to a significant decrease of the breeding gain which needs to be recovered in future design evolutions in order to achieve the self breeding goal. Finally, the safety criteria associated to the control rods were calculated with a first estimation of the uncertainties. All these criteria are respected, even if the safety analysis of GFR concepts and the determination of these uncertainties should be further studied and improved

Neutronic benchmark on the 2400 MW gas-cooled fast reactor design

International audienceThe 2400 MWth Gas-Cooled Fast Reactor (GCFR), with plate-type carbide/SiC CERCER fuel, is an innovative design exhibiting many attractive features among which sustainability achieved with an internal breeding gain close to zero and feedback coefficients enabling an excellent behavior under some safety transients. This paper summarizes the analytical results of an international benchmark exercise being set up within the European Union to verify the neutronic tools and associated nuclear data libraries currently used for helping in finalizing the design of the GCFR within the European Union. A rather simple homogenized 2D model has been specified for the first phase of this benchmark. The computational tools being used in the analysis include both a stochastic and a deterministic code, MCNP and ERANOS, respectively, with nuclear data essentially based on the JEF-2.2 data library. The overall results indicate that the agreement of the solutions provided by the different participants is satisfactory. The most significant discrepancy, which can be partly attributed to different ERANOS options, is observed in the case of the end of life reactivity and amounts to a few dollars. The rather positive outcome of this initial phase of the benchmark has allowed identifying deficiencies in the analytical tools and serves as a basis for the definition of subsequent phases. It might also help to identify potential ways to improve the design

Oscillation experiments techniques in CEA MINERVE experimental reactor

International audienceThe CEA is deeply involved in a research program (Material Testing Reactors, Zero Power Reactors) concerning the nuclear fuel advanced studies (actinides, plutonium), the waste management, the scientific and technical support of running French PWR reactors and EPR reactor, and innovating systems. In this framework, specific neutron integral experiments have been carried out in the critical facilities of the CEA Cadarache, such as MINERVE, EOLE and MASURCA. This paper deals with experiments in the MINERVE pool Zero Power Reactor. MINERVE is mainly devoted to neutronics studies, in view to improve the calculation routes by reducing the uncertainties of the experimental databases for nuclides arising in plutonium and wastes management. MINERVE experimental measurement programs are performed by using the oscillation technique. This experimental technique consists in a periodic insertion and extraction of samples containing the nuclide of interest in a well characterized neutron spectrum. The reactivity variation of the sample is compensated by a calibrated rotary automatic pilot using cadmium sectors. The normal accuracy for measurements of small-worth samples in MINERVE by using such a technique is about 3% for absolute reactivity worth, including the uncertainties on the material balance and on the calibration step. Reactivity effects of less than 1.5 cent can be measured. The OSMOSE and the OCEAN programs have been carried out since 2005 and will last until 2011. These programs aim at improving, in different neutron spectra, the absorption cross sections of respectively a majority of the separated heavy nuclides from 232Th to 245Cm appearing during the reactor and the fuel cycle physics, and of current and future types of absorbers as Gd, Hf, Er, Dy, Eu

Combined-modality therapy for clinical stage I or II Hodgkin's lymphoma: long-term results of the European Organisation for Research and Treatment of Cancer H7 randomized controlled trials.

Item does not contain fulltextPURPOSE: In early-stage Hodgkin's lymphoma (HL), subtotal nodal irradiation (STNI) and combined chemotherapy/radiotherapy produce high disease control rates but also considerable late toxicity. The aim of this study was to reduce this toxicity using a combination of low-intensity chemotherapy and involved-field radiotherapy (IF-RT) without jeopardizing disease control. PATIENTS AND METHODS: Patients with stage I or II HL were stratified into two groups, favorable and unfavorable, based on the following four prognostic factors: age, symptoms, number of involved areas, and mediastinal-thoracic ratio. The experimental therapy consisted of six cycles of epirubicin, bleomycin, vinblastine, and prednisone (EBVP) followed by IF-RT. It was randomly compared, in favorable patients, to STNI and, in unfavorable patients, to six cycles of mechlorethamine, vincristine, procarbazine, prednisone, doxorubicin, bleomycin, and vinblastine (MOPP/ABV hybrid) and IF-RT. RESULTS: Median follow-up time of the 722 patients included was 9 years. In 333 favorable patients, the 10-year event-free survival rates (EFS) were 88% in the EBVP arm and 78% in the STNI arm (P = .0113), with similar 10-year overall survival (OS) rates (92% v 92%, respectively; P = .79). In 389 unfavorable patients, the 10-year EFS rate was 88% in the MOPP/ABV arm compared with 68% in the EBVP arm (P < .001), leading to 10-year OS rates of 87% and 79%, respectively (P = .0175). CONCLUSION: A treatment strategy for early-stage HL based on prognostic factors leads to high OS rates in both favorable and unfavorable patients. In favorable patients, the combination of EBVP and IF-RT can replace STNI as standard treatment. In unfavorable patients, EBVP is significantly less efficient than MOPP/ABV

Neyman smooth goodness-of-fit tests for the marginal distribution of dependent data

Neyman’s smooth test, Goodness-of-fit, Strongly mixing process, Implied volatility,

Chemotherapy plus involved-field radiation in early-stage Hodgkin's disease.

Item does not contain fulltextBACKGROUND: Treatment of early-stage Hodgkin's disease is usually tailored in line with prognostic factors that allow for reductions in the amount of chemotherapy and extent of radiotherapy required for a possible cure. METHODS: From 1993 to 1999, we identified 1538 patients (age, 15 to 70 years) who had untreated stage I or II supradiaphragmatic Hodgkin's disease with favorable prognostic features (the H8-F trial) or unfavorable features (the H8-U trial). In the H8-F trial, we compared three cycles of mechlorethamine, vincristine, procarbazine, and prednisone (MOPP) combined with doxorubicin, bleomycin, and vinblastine (ABV) plus involved-field radiotherapy with subtotal nodal radiotherapy alone (reference group). In the H8-U trial, we compared three regimens: six cycles of MOPP-ABV plus involved-field radiotherapy (reference group), four cycles of MOPP-ABV plus involved-field radiotherapy, and four cycles of MOPP-ABV plus subtotal nodal radiotherapy. RESULTS: The median follow-up was 92 months. In the H8-F trial, the estimated 5-year event-free survival rate was significantly higher after three cycles of MOPP-ABV plus involved-field radiotherapy than after subtotal nodal radiotherapy alone (98% vs. 74%, P<0.001). The 10-year overall survival estimates were 97% and 92%, respectively (P=0.001). In the H8-U trial, the estimated 5-year event-free survival rates were similar in the three treatment groups: 84% after six cycles of MOPP-ABV plus involved-field radiotherapy, 88% after four cycles of MOPP-ABV plus involved-field radiotherapy, and 87% after four cycles of MOPP-ABV plus subtotal nodal radiotherapy. The 10-year overall survival estimates were 88%, 85%, and 84%, respectively. CONCLUSIONS: Chemotherapy plus involved-field radiotherapy should be the standard treatment for Hodgkin's disease with favorable prognostic features. In patients with unfavorable features, four courses of chemotherapy plus involved-field radiotherapy should be the standard treatment. (ClinicalTrials.gov number, NCT00379041 [ClinicalTrials.gov].)