Passive safety system

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). 

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. 

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... 

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. 

In China, the Nuclear Power Institute (Chengdu) is developing the AC-600 advanced PWR, which incorporates passive safety systems for heat removal. 

HICKEN, E.F., Passive Safety Systems, a Possibility of Enhancing Reactor Safety, Kemtechnik 61 (1996) 207-209. 

As described in the previous chapter, the MRX copes with anomaly including accidents by help of the engineered passive safety system The core is flooded by the water-filled containment and the decay heat is removed by the EDRS and the CWCS. To view the function and the transient behavior, the LOG A analysis using RELAP5/mod2[ll] and COBRA-IV[12] codes is presented here as followings. 

The functions of the engineered passive safety systems of the MRX which are significantly simplified are evaluated with the safety analyses. The LOCA analysis as an example presented in the previous chapter shows that core flooding is kept and decay heat removal is performed successively. Corresponding to the Japanese governmental PWR licensing safety review guideline , the analyses of the accidents and the anticipated transient events are conducted. The... 

The MRX simplified passive safety system can ensure safety of the reactor, which is confirmed by the safety analysis. It is noteworthy that the MRX never uncover the core by help of the water-filled containment even in a LOCA. 

A passive safety system is one that brings an out-of-control condition back to a safe state without any action required from equipment, instruments, or facility personnel. 

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. 

Changes to passive safety systems such as the firewater and flare headers can lead to covert safety problems. As additional equipment is installed, these systems can be overloaded. The capacity of the flare system should be checked, but, if it is not, and since such systems are passive, there are no indications that they have become overloaded until they are called upon to operate. 

Hence, attention focused on passive safety systems and on inherent or intrinsic safety systems. These needed fewer auxiliary systems, they were simpler, with a lower number of parts which could potentially fail, and they did not require as much operator intervention as active systems. 

Some passive safety systems for nuclear plants... 

Passive plant reactors (e.g. the AP600W) are proposed future reactors that use the technology of current reactors, but include also significant changes in plant design and layout. Safety, in the event of an accident, depends on truly passive safety systems and on safety systems which are passive in operation although started up by a simple action such as valves opening. 

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. 

Passive safety systems Passive safety systems are defined as the operating safety features of structures and devices designed to counteract specific events without the reliance on mechanical and/or electrical power, forces or intelligence signals external to the same structures and devices. 

E.g. the results of the new advanced nuclear power plants equipped with passive safety systems may indicate that the core damage frequency is assessed below the lE-06/ry, which is for orders of magnitude smaller than core damage frequency of existing plants. 

Ricotti, M. et al. 2002.The REPAS study reliability evaluation of passive safety systems. In Proceedings of the 10th International Conference on Nuclear Engineering (ICONE 10), Arlington, Virginia, April 14—18, 2002, paper no. 22414... 

Passive safety systems similar to gas-cooled and liquid-metal-cooled reactors engineered in the 1980s and 1990s, especially the Super Power Reactor Inherently Safe Module (S-PRISM) design developed by General Electric (GE). ... 

The next evolution of the method presented by Busch is called PreEffect-iFGS. It is a prospective method for evaluating the field effectiveness of integral pedestrian protection systems [21]. The main procedures of Busch, i.e., selection of relevant accidents, simulation with/without system, translation into injury severity, and calculation of the effectiveness, stayed the same with some additions. The improvement is an incorporation of test results for active and passive safety systems derived from hardware testing [54]. The initial version also includes an automated backwards simulation of each accident based on the values available in GIDAS. The results are then transferred into the commercial software PC-Crash and are then simulated forward with and without the measure in question. 

Under a technical cooperation agreement among ENEL, ENEA, ANSALDO and WESTINGHOUSE, an integral test of AP-600 passive safety systems has been performed at the SIET facility in Piacenza. 

The low-tech system, i.e., a donkey system, is the opposite. It requires less manpower, although it still needs more than natural reactors. Because of needing little maintenance and having potential for a continuous operation for a decade without fuel replacement, it can be sited in an isolated island or in a remote area. Of course, it would be necessary to design the reactor to be robust to disturbance and less dependent on control system operations. It maybe easier to understand it as a typical passive safety system. For example, reactor control against disturbance does not require a rapid response as in the case of control rods but expects reactivity feedbacks, such as the Doppler effect to work. Additionally, natural circulation, which is driven by buoyancy force generated by difference in coolant temperature, should be employed in such reactors rather than pumps. 

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