[en] The main subject of this invention is a nuclear reactor unit as well as an installation forming a nuclear boiler room, for instance, making use of such an unit. The invention also covers a process for setting out such an installation. But the conditions of access to the boiler room layout site are frequently difficult and, furthermore, the total weight and considerable bulk of such a boiler room make it difficult to prefabricate and to handle and move it as a single unit. For this reason, the further aim of this invention is to overcome the above drawbacks by proposing, inter alia, a nuclear facility constituted of individual prefabricated modular units that can be mutually assembled

[en] The ENHS (Encapsulated Nuclear Heat Source) is a small liquid metal lead-bismuth or lead natural-circulation cooled fast-spectrum fuel-self-sustaining (FSS) 'battery type' innovative Gen-IV reactor. Previously designed ENHS cores were fueled with either plutonium or transuranium (TRU) isotopes discharged from LWR or fast reactors. This study identifies equilibrium cycle core designs for the ENHS and examines their reactor physics characteristics. A 5 years fuel recycling period is assumed including 3 years cooling of spent fuel, 1 year reprocessing and 1 year fuel re-fabrication. The design variables are the core pitch-to-diameter (P/D) ratio and the fraction of the discharged TRU that is recycled. The study searches the combination of these variables that gives the minimum reactivity swing during the core life. The sensitivity of the optimal core design on the design power level is searched in the power range from 125 MWt to 250 MWt. It is found that the optimal equilibrium core P/D ratio tends to increase with the power level for a given discharge burnup: P/D = 1.54 for 125 MWt, P/D 1.55 for 170 MWt and P/D = 1.57 for 250 MWt. These P/D ratios are significantly larger than that of the 1.36 value for the reference core that is loaded with Pu discharged from LWR. The larger the P/D ratio, the higher becomes the power level at which the core can be operated using natural circulation cooling. The reactivity effect of the voiding of the core and fission gas plenum is negative for the equilibrium cores versus positive for the reference core. (authors)

[en] Small modular reactors (SMR) with power output below 300 MWe that strongly rely on serial, factory-based production of reactor modules are believed to have a potential for broadening the ways of developing nuclear power in the world in both connected and isolated areas. The NEA study estimated that in the high case scenario, up to 21 GWe of SMRs can be globally added in 2035, primarily in emerging economies. It is recommended that governments and industry should work together to accelerate the construction of the first SMR prototypes that can demonstrate the benefits of this technology. Collaborations concerning common research and work on national and international licensing frameworks must be launched. Another important conclusion is that SMR vendors and potential customers should work closely with the nuclear regulators in order to allow early resolution of different issues of SMR development (including validation of innovative safety features and solutions), factory assembly and deployment

[en] The current status of the neutronics design of the Nuclear Battery reactor is described. The selection of core geometry and in-core materials are discussed. The reactor safety characteristics of the Nuclear Battery are briefly presented

[en] A preliminary feasibility study of the potential application of small nuclear reactor space power systems to manned planetary surface base missions was conducted. The purpose of the study was to identify and assess the technology, performance, and safety issues associated with integration of reactor power systems with an evolutionary manned planetary surface exploration scenario. The requirements and characteristics of a variety of human-rated modular reactor power system configurations selected for a range of power levels from 25 kWe to hundreds of kilowatts is described. Trade-off analyses for reactor power systems utilizing both man-made and indigenous shielding materials are provided to examine performance, installation and operational safety feasibility issues. The results of this study have confirmed the preliminary feasibility of a wide variety of small reactor power plant configurations for growth oriented manned planetary surface exploration missions. The capability for power level growth with increasing manned presence, while maintaining safe radiation levels, was favorably assessed for nominal 25 to 100 kWe modular configurations. No feasibility limitations or technical barriers were identified and the use of both distance and indigenous planetary soil material for human rated radiation shielding were shown to be viable and attractive options

[en] After a retrospective analysis of the daily quality control results, an increasing trend on the energy resolution is observed. In this paper we propose as a reason for this phenomenon the activity variation of the "22Na source used in the daily quality controls relative to the intrinsic activity of the "176Lu present in the LYSO scintillator crystals. To this end, the relative activities of the isotopes have been measured and both spectra deposited in the LYSO crystals have been obtained using PENELOPE Monte Carlo package. The combined spectrum variation with time is obtained and the FWHM of the 511 keV peak has been measured each month for two years. An activity ratio "176Lu/"22Na = 0.057 has been measured. With this result, a variation on the energy resolution of about 1% per year has been obtained, which is in agreement with the experimental results. Anyway, the clinical implications of this effect would be negligible as soon as the FDG dose regime is high enough compared to the concentration of 0.3 kBq/ml for which the "176Lu activity has direct effect on the measurement of random events. (Author)

No abstract available

[en] The U.S. Nuclear Regulatory Commission staff is considering a more integrated, graded approach to the review of small modular reactor (SMR) pre-application activities and design applications. The concept is to improve the efficiency and effectiveness of the reviews by focusing on safety significant structures, systems, and components (SSCs). The unique design features associated with SMRs and knowledge gained reviewing other passive reactor designs present opportunities to risk-inform the SMR design certification process to a greater extent than previously employed. The review process can be modified for SMR applications by considering the aggregate of regulatory controls pertaining to SSCs as part of the review and determining those regulatory controls which may supplement or replace, as appropriate, part of the technical or engineering analysis and evaluation. Risk insights acquired from staff reviews of passive LWR designs (i.e. AP1000, ESBWR) can also be incorporated into the review process. Further, risk insights associated with integral pressurized water reactor (iPWR) design features (i.e. underground facilities impact on turbine missiles review) can be incorporated into the review process. Thus, the staff can use a graded approach to the SMR design certification process. (author)

[en] The NuScale company has recently filed a demand to NRC for the first certification of a Small Modular Reactor (SMR) in the US. This concept relies on a basis module of 50 MWe representing 160 MWt and as many modules as necessary can be added on a site to get the right power. Reactor cooling is made through natural convection so no pump is necessary, the fuel design is based on the PWR fuel and there will be 27 17*17 assemblies in the core with a 3.7% enrichment. Cycles will be 24 month long with a re-loading by third. The module will be 23.65 m high with a diameter of 4.6 m for a weight of 700 tons. These dimensions will be compatible with transport by truck or boats. The reduced size of the reactor infers a technological simplicity, no complex systems are necessary to ensure safety which will reduce the initial investment. The NuScale company expects a global cost of around 5100 dollar/kWe for a production cost of 72 dollar/MWh. (A.C.)

[en] This paper examines design variants that can improve inherent regulation in Advanced Small Modular Reactors (ASMR). It looks at the nature of unprotected upsets and then develops appropriate design measures to ensure that no upset can override a capability for safe self-regulation. This work adopts a reference sodium fast reactor (SFR) design to serve as a baseline for operational and safety performance and for comparison with variants on this design. The effect of design measures on plant stability is then examined. It is found that compared to full-power operation, the stability margin is reduced under islanded-operation. Islanded-operation is more likely for an ASMR deployed in a small regional electric grid with high penetration of renewable energy sources. The stability of core power production is a function of the inlet temperature coefficient, coolant transport times, and temperature-front attenuation in heat exchangers. The interaction of these phenomena with the control system is described