Accident Prevention through System Design

TABLE 4.1 Samples of Behavior Patterns That Must Be Considered During System Design 

People do not USUALLY consider the effects of surface friction on their ability to grasp and hold and article. 

MOST people do not watch where they place their hands and feet, especially in familiar surroundings. 

People OFTEN utilize the first thing available as an aid in getting where they want to go or to manipulate or fix something. 

People SELDOM anticipate the possibility of contact with sharp corners or edges. 

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Since water of the reactor pool is important for the KAMADO safety concept, loss of water from the reactor pool should be prevented through appropriate design measures, such as double walls of the reactor pool, a monitoring system of water leakage, etc. Location of the reactor pool below ground level could inherently prevent accidents with the loss of pool water. 

The simplest types of accident models for use in the design of SHE Information Systems are the causal-sequence models. An early and historically very important example is the Chain of Multiple Events or Domino theory . Figure 5.1. In this model, an accident is described as a chain of conditions and events that culminate in an injury. A link in this chain is an unsafe act or unsafe condition at the workplace. It is suggested that accidents be prevented through the reduction of unsafe acts and conditions. 

The Savannah River Site (SRS) reactors are designed with an airborne activity confinement system (AACS) rather than a containment system. The AACS is an active ventilation system that continuously exhausts air from prescribed zones in the reactor building through a set of filters in order to prevent unattenuated release of contaminated air to the environment under accident conditions. The system is designed such that air flows from areas of least expected radioactive contamination to areas of higher potential for radioactive contamination. This is achieved by maintaining the process areas at negative pressures by the operation of fans and dampers. 

The atmosphere is the ultimate heat sink for the AP600 reactor system. Computer calculations have shown that under design basis accident scenarios the containment steel structure would provide sufficient cooling to prevent exceeding the containment design pressure. In performing this function, the heat is transferred through the containment vessel to the... 

The containment isolation system (CIS) provides the means of isolating the various fluid systems passing through the containment walls as required to prevent the release of radioactivity to the outside environment. Design bases of the CIS consider several factors. Subsequent to an accident which may release radionuclides within the containment, there must be a barrier in all pipes or ducts that penetrate the containment. Leakage from the containment through these pipes or ducts which penetrate the containment is minimized by a double barrier. This double barrier ensures that failure of a single active... 

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