Active safety systems

Efforts to develop nuclear power reactors have been focused on the enhancement of safety and reliability by using active safety systems with redundancy and diversity while improving economy through scale factor. Although the goals have been fairly achieved, traditional power reactors can be used only under the prerequisites and are thus usable for a limited area of application. 

Active safety systems require a mechanical or instrumentation system to take action on identification of an unsafe or out-of-range condition. Pressure relief valves are a standard example if they... 

Because active safety systems rely on action being taken they are liable to failure. Therefore, they should only be used when the system cannot be made inherently safe or when passive safety systems cannot be used. 

Human factors incorporate both active and passive safety. For example, placing a valve so that it is easy to identify and operate is a passive design feature however, an operator control panel is more of an active safety system. 

The best form of fire protection is passive, i.e., it is effective regardless of actions taken by individuals or active safety systems. Fire protection generally includes the following items ... 

No active safety system Seismic design as required... 

Active safety systems Systems which need energy and/or intelligence signals to operate. See also Passive safety systems , which are the contrary of active systems. 

The active safety systems consist of the safety injection system (SIS), safety depressurization and vent system (SDVS), in-containment refueling water storage system (IRWST), auxiliary feedwater system (AFWS), and containment spray system (CSS). 

A comparative cost analysis was performed for the AHTR by scaling individual subsystem costs for either the GT-MHR or the S-PRISM. The result is that the AHTR overnight capital cost (without contingency) is estimated to be approximately 820 /kW(e) (2002 dollars), which is 50-55% of the S-PRISM and GT-MHR costs for similar total output. This is a consequence of economy of scale. The AHTR electrical output is approximately four times that of these other reactors but with a similar plant size and complexity. Relative to light-water reactors, the AHTR should be more economical because of the higher power conversion efficiency, low-pressure containment, and absence of active safety systems. 

High-pressure helium has not been used for safety, performance, and cost reasons. If helium is allowed, active safety systems with very fast acting valves dumping to atmosphere will be required for rapid depressurization in the event of an accident before the chemical plant is pressurized and disperses hazardous chemicals. 

Effective active safety systems usually require a well-coordinated interaction of all elements of the control loop. The primary driving task can be supported at any level of the following three-level hierarchy [1] ... 

The driving state is normally continually monitored (by the driver and/or a system) in order to make corrections on any or all of these levels if required. Detailed applications, variations and refinements of this model can be found in the literature [4, 10-12]. Classically, active safety systems, e.g.. Dynamic Stability Control (DSC), have been designed to provide support at the stabilization level. At this level, the target quantities are generally well defined in terms of vehicle physics. Preventive pedestrian protection, which is in the focus of this thesis, addresses primarily the maneuvering level and thus involves additional eomplexities in control—particularly those involving the interpretation of driver behavior and the interaction of system actions with the driver. 

The approval process for braking assistance can be regarded as a prerequisite for active safety systems. The requirements formulated by the Directive 2003/102/EG, Phase 2, of the European Parliament and of the Council [53] could nearly not be fulfilled by means of passive safety. As a consequence, an evaluation regarding the effectiveness of different measures of pedestrian protection has been carried out [54, 55]. The commitment of the European Automobile Manufacturers Association (ACEA) European Automobile Manufacturers Association to implement brake assist, an active safety system, in every new car, led to a reduction of the requirements... 

Testing procedures and evaluation schemes for passive safety are defined and standardized in the regulations cited above and have reached a rather advanced stage of development. However, objective, reliable, representative and reproducible methods for evaluating the effectiveness of active safety systems, especially preventive pedestrian systems, have yet to be developed. 

The objective of this thesis is the advancement of knowledge in order to enable the development of a method for evaluating active safety systems. The example used is vehicle-based preventive pedestrian protection. 

As many active safety systems do have a human-machine interface, the driver can also be in the focus of evaluation. The surroundings of the vehicle constitute... 

The presence of the measure in a vehicle must be identifiable in accident data [16] in order to group the accidents. The information as to whether an active safety system was active during an accident is rarely available in nearly all accident data sets (this applies only to measures which can be deactivated by the driver). (The limitations of accident data bases in general are discussed further below.). 

In this context, not only the driver in view of his actions and decisions is of interest, but also regarding his acceptance of different measures [39] (see Sect. 4.3 for more on acceptance and its connection to safety). During the use of a system of active or integral safety, changes in behavior due to adaption or compensation effects can occur and must be accounted for when evaluating safety benefits [32]. To draw a conclusion, a full forecast of their [i.e., active safety systems author s note] potential is only possible with respect to the complete relation of driver-vehicle-system-environment [9] (see also [40]). These and various other aspects of evaluation of active safety systems have also been subject of discussion in European Union funded projects an overview is, for example, given in [41]. 

The secondary impact is not assessed, but is assumed to improve with decreasing impact speeds [73, 74]. The actual performance of an active safety system together with the driver (if a driver-relevant component is included) is estimated by weighting the different VERPS+k indices for different speeds according to the performance of the active safety system (including avoided accidents and the probability of avoided head impact on the vehicle). Averaging over all drivers in the population in question and all relevant accident situations, the resulting VERPS+ index is able to quantify the effect of an active safety system [73, 74] once the primary effect of the active safety system (i.e., the reduction of vehicle speed) has been assessed properly. An example for the use of the VERPS index as well as an addition for leg injuries can be found in [75]. 

Each, M., Ockel, D. (2009). Evaluation methods for the effectiveness of active safety systems with respect to real world accident analysis. In 2Ist International Technical Conference on the Enhanced Safety of Vehicles (ESV 2009), No. 09-0311. 

WUle, J. M., Zatloukal, M. (2013). rateEFFECT effectiveness evaluation of active safety systems. In 5th International Conference on ESAR Expert Symposium on Accident Research , No. F 87 in Fahrzeugtechnik, Bundesanstalt flir StraBenwesen, Fachverlag nw. 

Ebner, A., Samaha, R. R., Scullion, R, Helmer, T. (2010). Methodology forthe development and evaluation of active safety systems using reference scenarios Application to preventive pedestrian safety. In Proceedings of the International Research Council on Biomechanics of Injury (IRCOBI) (pp. 155-168). 

Helmer, T., Ktihbeck, T, Gruber, C., Kates, R. (2012). Development of an integrated test bed and virtual laboratory for safety performance prediction in active safety systems (F2012-F05-005). In FISITA 2012 World Automotive Congress-Proceedings and Abstracts (2012). ISBN 978-7-5640-6987-2. 

The driver and his behavior are of high relevance for the genesis of an accident (see Sect. 1.1, p. 1) as well as for the evaluation of changes in traffic safety by means of simulation (see Chap. 3). The change in driver behavior (e.g., particular reaction times) due to an active safety system can be derived by comparing use versus non-use of a system and serves as input for simulations as described in the previous chapter. To this end, driver behavior in response to a preventive pedestrian protection system (short system) and his acceptance of specific system actions (especially false-positive responses) are investigated. The contents of this chapter are also partly included in [1, 2]. 

This thesis has focused on the development of a methodology for representative and reliable evaluation of active safety. The practical example studied was preventive pedestrian protection. Active safety systems act within a complex, dynamic... 

As a possible positive safety effect is evident mainly within accidents (instead of non-accident situations), common approaches rely on reconstructed accident data and simulate the effect of an active safety system. However, there are several well-known limitations False-positive system actions (and consequently an important component of overall functional costs ) cannot be adequately assessed, as no representative sample of situations in which the system would be triggered (including non-accident situations) can be generated. Also assessment based on accidents can be sensitive to details of the accident reconstruction, which are indeed subject to uncertainties. However, a particular instance of a reconstmcted accident may not be entirely representative, particularly regarding the effectiveness of a proposed assistance system. 

Helmer, T., Neubauer, M., Rauscher, S., Gruber, C., Kompass, K., and Kates, R. Ilth International Symposium and Exhibition on Sophisticated Car Occupant Safety Systems. Fraunhofer-Institut fiir Chemische Technologic ICT, 2012, ch. Requirements and methods to ensure a representative analysis of active safety systems, pp. 6.1-6.18. ISSN 0722-4087... 

Passive safety features simplify the design and attain the required safety objective in a different way compared to large plants with more active safety systems. This could reduce cost and facilitate the presentation of the safety of the reactor to both regulatory authorities and the public. 

The design of QP300 uses the active safety system to mitigate accidents. 

---