Reactors inherent safety

Station blackout Natural coolant circulation, passive safety systems, reactor inherent safety features R... 

The reactor plant safety is ensured without power supply or personnel intervention for not less than 72 hours following all possible disturbances and accidents (positive reactivity insertion, loss of heat removal, primary circuit depressurization) by means of the reactor inherent safety features and by using the complex of interconnected passive safety systems and devices. 

Takamatsu, M., et al., 2007. Demonstration of control rod holding stability of the self acmated shutdown system in Joyo for enhancement of fast reactor inherent safety. Journal of Nuclear Science and Technology 44 (3). 

Synthetic rubber latex was made by a process with a large and hazardous inventory of butadiene and styrene. In a modified process, the reactor has an initial charge of water and emulsifier. Also, the monomers are added to the reactor as one premixed stream and the emulsified aqueous sodium persulfate is added as the other stream. The improved scheme, discussed by Englund (1991a) contains less hazardous material and at a lower, more controllable temperature. It illustrates that large and established processes may be made safer by applying inherent safety. 

Forsberg, C. W., D. L. Moses, E. B. Lewis, R. Gibson, R. Pearson, W. J. Reich, G. A. Murphy, R. H. Staunton, and W. E. Kohn (1989). Proposed and Existing Passive and Inherent Safety-Related Structures, Systems, and Components (Building Blocks) for Advanced Light Water Reactors. Oak Ridge, TN Oak Ridge National Laboratory. 

Rinard dedicated his research to a detailed analysis of methodological aspects of a micro-reactor plant concept which he also termed mini-plant production [85] (see also [4, 9, 10] for a commented, short description). Important criteria in this concept are JIT (Just-in-time) production, zero holdup, inherent safety, modularity and the KISS (keep it simple, stupid) principle. Based on this conceptual definition, Rinard describes different phases in plant development. Essential for his entire work is the pragmatic way of finding process solutions, truly of hybrid character ]149] (miniaturization only where really needed). Recent investigations are concerned with the scalability of hybrid micro-reactor plants and the limits thereof ]149], Expliddy he recommends jointly using micro- and meso-scale components. 

GP 11] [R 19] Based on an analysis of the thermal and kinetic explosion limits, inherent safety is ascribed to hydrogen/oxygen mixtures in the explosive regime when guided through channels of sub-millimeter dimensions under ambient-pressure conditions [9], This was confirmed by experiments in a quartz micro reactor [9],... 

The worst hazard scenarios (excessive temperature and pressure rise accompanied by emission of toxic substances) must be worked out based upon calorimetric measurements (e.g. means to reduce hazards by using the inherent safety concept or Differential Scanning Calorimetry, DSC) and protection measures must be considered. If handling hazardous materials is considered too risky, procedures for generation of the hazardous reactants in situ in the reactor might be developed. Micro-reactor technology could also be an option. Completeness of the data on flammability, explosivity, (auto)ignition, static electricity, safe levels of exposure, environmental protection, transportation, etc. must be checked. Incompatibility of materials to be treated in a plant must be determined. 

The Inherent Safety Index (ISI) deals with both main reaction(s) and those side reactions taking place in the reactor and which are meaningful. It also deals with chemical interaction which describes unintentional chemical reactions which can take place among chemicals in the plant. 

Chemical interaction considers the unwanted reactions of process substances with materials in the plant area. These reactions are not expected to take place in the reactor and therefore they are not discussed in the side reaction subindex. The Inherent Safety Index has utilized EPA s matrix (Hatayama et al., 1980) to classify the hazards of the chemical interaction in a process. The worst interaction that appears between the substances present in the plant area is used in the calculations for the Chemical Inherent Safety Index. 

In the new designs, if coolant were lost, the nuclear chain reaction would be terminated by the reactor s negative temperature coefficient after a modest temperature rise. Core diameter of the modular units would be limited so that decay heat could be conducted and radiated to the environment without overheating the fuel to the point where fission products might escape. Thus, inherent safety would be realized without operator or mechanical device intervention. 

Forsberg, C., Reich, W., World wide Advanced Nuclear Power Reactors with Passive and Inherent Safety What Why, How and Who, ORNL/TM-11907, September 1991. 

The systematic utilization of the physical law-determined safety properties of high temperature reactors was the basis for the development of the HTR-reactor for power-heat-coupling and nuclear process heat up to 950°C in reactor sizes of 200 MWth. This reactor type was approved for industrial and public use in the Federal Republic of Germany by a nuclear-independent commission due to its inherent safety properties. 

However, the integration of PIM also creates synergy in the development of intensified processes, novel product forms, and size dependent phenomena, which in turn provides novel intensified processes. Process intensification-miniaturization is seen as an important element of sustainable development because it can deliver 1) at least a 10-fold decrease in process equipment volume 2) elimination of parasitic steps and unwanted by-products, thus eliminating some downstream processing operations 3) inherent safety because of reduced reactor volume 4) novel product forms 5) energy, capital, and operating cost reduction, and an environment friendly process 6) plant mobility, responsiveness, and security and 7) a platform for other technologies. 

The HTTR achieved the first criticality in 1998, and the full power operation was attained with reactor outlet helium temperature of 850°C in 2001. The first high-temperature operation of 950°C was conducted in April 2004. Since 2002, safety demonstration tests have been carried out to demonstrate the inherent safety of the HTGR. [2]... 

The safety demonstration tests in the HTTR are conducted to demonstrate an inherent safety feature, that is an excellent feature in Shutdown of the HTGRs, as well as to obtain the core and plant transient data for validation of safety analsis codes and for establishment of safety design and evaluation technologies of the HTGRs. The safety demonstration tests consist of Reactivity insertion test - control rod withdrawal test and Coolant flow reduction test as shown in Figure 6. In the control rod withdrawal test, a central pair of control rods is withdrawn and a reactivity insertion event is simulated. In the gas-circulators trip test, primary coolant flow rate is reduced to 67% and 33% of rated flow rate by running down one and two out of three gas-circulators at the Primary Pressurized Water Cooler without a reactor scram, respectively. 

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