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Ydinturvallisuusinsinööri Julia Virtanen

Internal hazard analyses examin how threat situations occurring inside a nuclear power plant would affect its safety, tells Nuclear Safety Engineer Julia Virtanen.

Hazard analyses help us tackle safety threats

We ensure that the various internal and external threats to a nuclear power plant's safety and electricity production are duly considered in the plant design.

I work in Fennovoima's Nuclear Safety Department in a team responsible for probabilistic risk analyses (PRA) and hazard analyses. I am responsible for the internal hazard analyzes and their methodology.

Internal hazard analyzes are research into how various threat situations occurring inside a nuclear power plant, such as a fire, a heavy load drop, or a pipe rupture, would affect its safety. Working on hazard analyzes is interesting because there is plenty of analyzes that are all very different in content.

In practice, there are two types of internal hazard analyzes: functional and structural. With functional analyses, we look at the physical separation at the plant, i.e., the fact that the redundant trains of the plant's safety systems are located in different rooms so that the plant's safety can be ensured if one of system trains fails in a threat situation. With the help of structural analyzes, we find out what consequences different threat situations can have on structures, and that they are designed to endure the impact of hazards and in such a way that we have enough time to act in the event of a hazard. For example, we study what a fire would cause to buildings' walls and doors, how the fire would spread inside the building, and what kind of area and equipment we would practically lose due to fire.

We received functional hazard analyzes from the plant supplier for evaluation last year. In September, we have received more hazard analysis reports, which are currently being reviewed. In terms of physical separation, in particular, we have made clear progress, and the plant supplier has corrected most of the open points in the design in line with our findings. Of course, there are still open issues, especially in system-level design, but plant level physical separation is in good shape.

However, we also noted that our and the plant supplier's views on the analyses assumptions and the acceptance criteria for the analyses results differ. We considered it necessary to develop the harmonized general methodology for internal hazard analyses, which determines the assumptions for the different hazard types and components, and how the hazard analyses are performed. The methodology is currently under our review.

Once we have approved the methodology, the plant supplier will provide us with updated functional analyzes and a structural fire analysis of the nuclear power plant reactor building, one of the essential internal hazard analyzes. Inside the reactor building, the physical separation is implemented with distance and limited amount of protective structures. Therefore, it is necessary to demonstrate through structural analyzes that in case of a hazard we can shut the plant down immediately if necessary. The reactor building is also the most complex of all the nuclear power plant's buildings in terms of design. For other buildings critical or important for safety and availability, we look forward to receiving the missing hazard analyses on the course of the fall in line with our stage-wise approach.

Julia Virtanen 
Fennovoima's Nuclear Safety Engineer 

Julia Virtanen works as a nuclear safety engineer at Fennovoima. Julia has a master's degree in energy technology from Aalto University and a degree in mechanical engineering from Metropolia University of Applied Sciences. Julia's career choice in nuclear safety has been greatly influenced by the fact that her father once worked as a reactor physicist at the fifth unit of Chernobyl, which was never completed due to the fourth unit's accident. As a nuclear safety engineer, Julia does her part to contribute to the Hanhikivi 1 nuclear power plant's safe design and operation. Julia, an active practitioner of Ashtanga Yoga, also loves traveling, photography, and hiking in the mountains.

Julia Virtanen työskentelee Fennovoimalla ydinturvallisuusinsinöörinä.

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