Rafael Juarez

Development of the R2SUNED Code System for Shutdown Dose Rate Calculations

R2SUNED is a code system implementing the mesh-based Rigorous-two-step method for shutdown dose rates calculations, making use of MCNP and ACAB codes. In addition to the most relevant features of state-of-the-art R2S systems, novel and unique features have been implemented in R2SUNED to overcome limitations common to the current mesh-based R2S implementations. One of particular interest is the cell-under-voxel approach intended to address most of the issues associated with the conventional averaging technique used in the neutron flux determination. The underlying idea is to identify the cells enclosed in each voxel and calculate the average value of the neutron flux within each cell fraction. Subsequently, the activation of each material, filling the cell delimited by the voxel, is calculated using the neutron flux evaluated in the corresponding cell. This capability enables to properly resolve the strong spatial gradients of the neutron flux independently of geometrical considerations. Another relevant feature is that a flexible decay gamma source sampling has been incorporated to assure an efficient decay gamma transport in a vast diversity of problems. A verification of R2SUNED has been addressed on the ITER computational shutdown dose rate benchmark. It is highlighted both the limitations of voxel averaged neutron flux standard approach, and the ability of R2SUNED to overcome this issue. The excellent agreement of the results with those obtained using a mesh matching perfectly the geometry tells that R2SUNED performs correctly. Finally, a description of the most representative applications carried out with R2SUNED is provided for fusion relevant facilities.

Silica final lens performance in laser fusion facilities: HiPER and LIFE

Nowadays, the projects LIFE (Laser Inertial Fusion Energy) in USA and HiPER (High Power Laser Energy Research) in Europe are the most advanced ones to demonstrate laser fusion energy viability. One of the main points of concern to properly achieve ignition is the performance of the final optics (lenses) under the severe irradiation conditions that take place in fusion facilities. In this paper, we calculate the radiation fluxes and doses as well as the radiation-induced temperature enhancement and colour centre formation in final lenses assuming realistic geometrical configurations for HiPER and LIFE. On these bases, the mechanical stresses generated by the established temperature gradients are evaluated showing that from a mechanical point of view lenses only fulfil specifications if ions resulting from the imploding target are mitigated. The absorption coefficient of the lenses is calculated during reactor startup and steady-state operation. The obtained results reveal the necessity of new solutions to tackle ignition problems during the startup process for HiPER. Finally, we evaluate the effect of temperature gradients on focal length changes and lens surface deformations. In summary, we discuss the capabilities and weak points of silica lenses and propose alternatives to overcome predictable problems.

HiPER laser reference design

HiPER (High Power laser Energy Research) is the first European plan for international cooperation in developing inertial fusion energy. ICF activities are ongoing in a number of nations and the first ignition experiments are underway at the National Ignition Facility (NIF) in the USA. Although HiPER is still in the preparatory phase, it is appropriate for Europe to commence planning for future inertial fusion activities that leverage the demonstration of ignition. In this paper we shall detail some of the key points of the laser design. Some of the main topics of the laser architecture are presented and discussed.

Lifetime of silica final lenses subject to HiPER irradiation conditions

The goal of the European laser fusion project, is to build an engineering facility for repetitive laser operation (HiPER 4a) and later a fusion reactor (HiPER 4b). A key aspect for laser fusion energy is the final optics. At the moment, it is based on silica transmission lenses located 8 m away from the chamber center. Lens lifetime depends on the irradiation conditions. We have used a 48 MJ shock ignition target for calculations. We have studied the thermo-mechanical effects of ions and X-rays on the lenses. Ions lead to lens melting and must therefore be mitigated. On the other hand, X-rays (~1% of the energy) does not produce either a significant temperature rise or detrimental stresses. Finally, we calculated the neutron flux and gamma dose rate on the lenses. Next, based on a simple model we studied the formation of color centers in the sample, which lead to optical absorption. Calculations show that simultaneous neutron and gamma irradiation does not significantly increase the optical absorption during the expected lifetime of the HiPER 4a facility. Under severe conditions (HiPER 4b), operation above 800 K or lens refreshing by thermal annealing treatments seem to assure adequate behavior.

IFE plant technology overview and contribution to HiPER proposal

HiPER is the European Project for Laser Fusion that has been able to join 26 institutions and signed under formal government agreement by 6 countries inside the ESFRI Program of the European Union (EU). The project is already extended by EU for two years more (until 2013) after its first preparatory phase from 2008. A large work has been developed in different areas to arrive to a design of repetitive operation of Laser Fusion Reactor, and decisions are envisioned in the next phase of Technology Development or Risk Reduction for Engineering or Power Plant facilities (or both). Chamber design has been very much completed for Engineering phase and starting of preliminary options for Reactor Power Plant have been established and review here.

Waste Management Assessment of Candidate Materials for HiPER Reaction Chamber

Abstract One of the critical decisions in the HiPER project is to select the most appropriate material for the reaction chamber. Within this framework, we investigate the performance of different steel alloys with respect to waste management. The capabilities of commercial steels, both austenitic and ferritic/martensitic, compared to reduced-activation ferritic/martensitic steels are evaluated as for different waste management strategies (near surface burial, clearance, hands-on and remote recycling). The examined materials are: SS304, SS316, mod.9Cr-1Mo and HT9 and EUROFER. Real impurities concentrations are taken into account, and their impact is analyzed. In the study, we have assumed the most exigent HiPER 4a irradiation scenario. Commercial steels revealed to be a suitable choice for the HiPER reaction chamber, as far as their waste management options do not differ significantly from those of the reduced activation ferritic steel case. We found that for mod.9Cr-1Mo and EUROFER hands-on recycling is already possible after a cooling time shorter than 50 years and that shallow-land burial is practicable for all the steel alloys studied. The impurities present in the real heats affects the cooling time for manual recycling but not significantly. Shallow-land burial feasibility is not perturbed by the presence of impurities in the real commercial heats. Moreover, the impact of activation cross section uncertainties on the waste management assessment of the irradiated steels has been analyzed, and it is found to be of no practical significance to determine eligibility of the considered steels for the HIPER 4a reaction chamber.

Radiation In-Port Cross-Talks for ITER Port Diagnostics

Abstract This paper emphasizes the need of estimation of the mutual influence, called “cross-talk,” for neutronic analyses of neighboring diagnostics systems shared by the same ITER port. Using examples of several diagnostic systems inserted inside the ITER Equatorial and Upper Port Plugs, we have demonstrated this mutual influence. Cross-talk effects have been shown by examining the radiation environment inside the port plug in terms of neutron energy spectra and Shut-Down Dose Rate (SDDR) inside the Port Interspace (PI) area. In-port cross-talk was investigated for the diagnostic systems deployed in two Equatorial Port Plugs (EPP) #17 and #8, and for the components of Upper Port Plug (UPP) #3. One example of in-port cross-talks is a gamma shadow effect of the Tritium and Deposit Monitor (TDM) shield block, which affects the SDDR inside the PI of EPP#17. Where the gamma radiation originated from the dominant radioactive sources of the irradiated structures of Core-Imaging X-ray Spectrometer (CIXS) is blocked by the TDM shield. Another example is an influence of neutron streaming along the Fast Ion Loss Detector (FILD) channel on the neutron energy spectra calculated in the Tangential Neutron Spectrometer (TNS) in EPP#8. For the example of UPP#3 with Charge eXchange Recombination Spectroscopy (CXRS-core), performed neutronic analysis identified excessive neutron streaming along the CXRS shutter, which must be reduced by further design iterations.

Thermo-fluid dynamics and corrosion analysis of a self cooled lead lithium blanket for the HiPER reactor

The HiPER reactor is the HiPER project phase devoted to power production. To reach a preliminary reactor design, tritium breeding schemes need to be adapted to the HiPER project technologies selection: direct drive ignition, 150 Hz of power released through fusion reactions, and the dry first wall scheme. In this paper we address the main challenge of the HiPER EUROFER-based self cooled lead lithium blanket, which is related to the corrosive behavior of Pb?15.7Li in contact with EUROFER. We evaluate the cooling and corrosion behavior of the so-called separated first wall blanket (SFWB) configuration by performing thermo-fluid dynamics simulations using a large eddy simulation approach. Despite the expected improvement over the integrated first wall blanket, we still find an unsatisfactory cooling performance, expressed as a low outlet Pb?15.7Li temperature plus too high corrosion rates derived from local Pb?15.7Li high temperature and velocity, which can mainly be attributed to the geometry of the channels. Nevertheless, the analysis allowed us to devise future modifications of the SFWB to overcome the limitations found with the present design.