Defense-in-Depth is the basis of safety design of nuclear plants, and refined and strengthened year by year. Nowadays, the importance of it has been further highlighted triggered by the accident at Fukushima Daiichi Nuclear Power Station.

Accidents described previously have been shown it could not care enough to uncertainty related to design, construction, maintenance and operation has exposed. It’s the lessons learned of that is to say to reduce uncertainty of design is the use of risk informed is essential. Therefore, the establishment of the design approach that uses risk informed consideration of the Defense-in-Depth is an important theme.

Defense-in-Depth is a measure which prevents the increase of the event frequency and core damage in consideration of the degree of safety margins, redundancy, diversity and consideration of radiation safety due to core damage and security.

The plant designers and utilities have made efforts to ensure safety utilized conventional design technique, which means deterministic, and risk information, in order to incorporate Defense-in-Depth concepts.

To consider Defense-in-Depth in the design phase, various requirements should be taken into consideration. It has been coming to be able to perform more rational and quantitative judgment by utilization of risk information.

In that case, while the designers of various fields will work in cooperation to ensure safety, if there are common utilization schemes for risk information among designers, more efficient and rational design works can be advanced in consideration of Defense-in-Depth. However, conventionally, it is hard to say that such schemes have functioned in order that designers may advance design works in collaboration.

This research intends to generate the schemes which advance design works in sharing the same risk information databases, which mean various risk indications etc), in other words, the schemes which will become lingua franca for utilizing risk information, in case of nuclear plants designs.

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