Passive safety

Fig. 13. Proposed advanced PWR design having passive safety features (79). Courtesy of Westiaghouse Electric Corp.

The development of computer capabiUties in hardware and software, related instmmentation and control, and telecommunication technology represent an opportunity for improvement in safety (see COMPUTER TECHNOLOGY). Plant operators can be provided with a variety of user-friendly diagnostic aids to assist in plant operations and incipient failure detection. Communications can be more rapid and dependable. The safety control systems can be made even more rehable and maintenance-free. Moreover, passive safety features to provide emergency cooling for both the reactor system and the containment building are being developed. 

Nuclear Reactors. Nuclear power faciUties account for about 20% of the power generated in the United States. Although no new plants are plaimed in the United States, many other countries, particularly those that would otherwise rely heavily on imported fuel, continue to increase their nuclear plant generation capacity. Many industry observers predict that nuclear power may become more attractive in future years as the price of fossil fuels continues to rise and environmental regulations become more stringent. In addition, advanced passive-safety reactor designs may help allay concerns over potential safety issues. 

Gas-cooled, graphite moderated reactors have several significant advantages over other reactor designs by virtue of their inherent passive safety characteristics. These are the result of the large thermal mass of the graphite core, the high... 

The AP600 passive safety systems use natural forces gravity, natural circulation, and compressed gas. Simple, mostly fail-safe, s alves align the passive safety systems upon... 

The AP600 passive safety system includes subsystems for safety injection, residual heat removal, containment cooling, and control room habitability under emergency conditions. Several of these aspects are in existing nuclear plants such as accumulators, isolation condensers as natural-circulation closed loop heat removal systems (in early BWRs), automatic depressurization systems (ADS - in BWRs) and spargers (in BWRs). 

Forsberg, C. W., and Weinberg, A. (1990). Advanced Reactors, Passive Safety, and Acceptance of Nuclear Energy. Annual Review of Energy 1 h 1.33-1. S2. 

Although active safety is provided by the control systems mentioned above, passive safety is an additional important feature of a distributed plant. Due to the low inventory, even a total release of the reaction volume or an explosion would create no significant impact on the environment [139]. To prevent such scenarios, a total containment of the plant is envisaged it needs to be sealed for life . Hydrogen cyanide synthesis and chlorine point-of-sale manufacture are two examples for safety-sensitive distributed syntheses. 

Following are some examples of passive safety systems to reduce the likelihood of explosions in storage units. The use of baffles in a high-pressure storage vessel can cool the tank wall above the liquid surface via liquid pumped around by vapor bubbles, extending the time for fire fighting. Fire resistant tank insulation is also effective in delaying a BLEVE. 

These proposed passive safety systems minimize the need for active safety installations in storage, such as the provision of water cooling or water curtains. 

Intrinsic and passive safety design features are by nature more reliable than design features that depend on a consistent performance of a physical or human system.(2) Passive designs reduce the probability of an occurrence occurring or minimize the severity of the adverse consequences without the requirement for successful operation of devices, con-... 

SINTERED POLYPROPYLENE FOAM FOR PASSIVE SAFETY ON CARS... 

AP600 Passive Safety System Details, These features reduce operator responsibilities and add an extra margin of safety over contemporary PWR designs. See Fig. 37 on p. 1121. Large volumes of water stored in the containment eliminate the need for operator action to assure make-up water, either for small leaks that may occur during normal operation or for a major loss of coolant accident (LOCA). A passive plant is a system llial assures public safety even if the operators fail to act... 

Fig. 37. Schematic representation of the in-containment passive safety injection system (PS1S). 1RWST = in-containment refueling water storage tank. PRHR-HX = passive residual heat removal heat exchanger. ADS = automatic depressurization system (four stages). (Westinghouse)...

In order to achieve passive safety with reactive material, the radius of the reactor tube is designed to be small to avoid any thermal explosion inside the tube. Using the Frank-Kamenetskii approach (see Chapter 13), the radius remains below the critical radius. Thus, even assuming a purely conductive heat transfer mechanism, corresponding to a worst case, no instable temperature profile can develop inside the reaction mass. The reactor can be shut down and restarted safely. 

Because of its properties, SINCO is suitable for personal protection in passive safety systems in motor vehicles. In addition to the use of SINCO in pressure elements for seat-belt tensioners or lock tensioners, the gas mixture is also suitable for driver and passenger gas generators. In this case the mixture also performs the function of a booster charge in the igniter elements of the gas generators in addition to the main task of gas evolution. 

The double slush technique offers added service value, such as ageing resistance, passive safety, weight savings and the recycling of production waste in the same application. The Audi A2 now marks the first production car to have come onto the market with an instrument panel surface developed according to this technology. 3 refs. Translated form Kunstoffe Vol.90 No.3, 2000, p.114-7. 

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