Q & As about reactor safety screenings

July 19, 2014

News Navigator: How are nuclear plants determined to be safe?

http://mainichi.jp/english/english/perspectives/news/20140719p2a00m0na006000c.html 

The Mainichi answers common questions readers may have about the safety of nuclear power plants as Sendai Nuclear Power Plant takes a step toward reactivation as it clears a provisional safety assessment.

Question: It appears Kyushu Electric Power Co.'s Sendai Nuclear Power Plant is going to be the first power station to clear the Nuclear Regulation Authority's new safety regulations. How are nuclear power plants evaluated for safety?

Answer: Based on lessons from the Fukushima nuclear disaster, in July 2013 the Nuclear Regulation Authority (NRA) created new safety regulations that incorporate beefed-up earthquake and tsunami measures, as well as anti-terrorist measures. The NRA assesses whether power companies' safety measures meet the new criteria, and if they do, the power station is given a green light.

Q: Is a power plant safe if it meets the criteria?

A: For the first time, the new regulations require that measures against severe disasters such as core meltdowns be implemented in all nuclear plants. If the contents of the criteria are updated, they will be retroactively applied to existing nuclear plants.

However, even NRA Chairman Shunichi Tanaka has said, "We cannot say that a disaster will never happen. The regulations cannot guarantee safety."

Q: So there's no way to make nuclear plants completely safe?

A: In the case of Fukushima No. 1 Nuclear Power Plant, there were many opportunities to adopt anti-disaster measures, but both the regulatory authorities and plant operator Tokyo Electric Power Co. kept postponing doing so. Since the disaster broke out, however, the idea of "defense in depth" has gained more traction, and more efforts are being made to prevent disasters, and to keep damage at a minimum in the case of a disaster.

Q: What is defense in depth?

A: It's a way of thinking about the safety of nuclear facilities set forth by the International Atomic Energy Agency. Safety measures are divided into five successive levels of defense, based on the degree of an incident's severity. Regulatory authorities in Japan prior to the Fukushima disaster only required utilities to clear three levels of defense: prevention of abnormal operation and failures, control of abnormal operation and detection of failures, and control of accidents within the design basis. Since the Fukushima disaster, however, level 4 -- control of severe plant conditions including prevention of accident progression and mitigation of severe accident consequences -- has been made part of the criteria. However, level 5 -- mitigation of radiological consequences of significant off-site releases of radioactive materials -- has not been incorporated into the NRA's regulations.

Q: Is the NRA responsible for checking everything?

A: In the safety assessments, the NRA primarily checks the facilities to determine whether level 1-4 measures have been implemented. Meanwhile, the Basic Act on Disaster Control Measures stipulates that municipalities lay out their respective disaster prevention plans, so they are not subject to the NRA's assessment.

Q: Not having an evacuation plan is worrisome, isn't it?

A: The NRA's new guidelines on nuclear disasters expanded the zone required to have evacuation plans in place from areas within eight to 10 kilometers of a nuclear power plant to areas within up to 30 kilometers of a nuclear plant. Many municipalities have yet to finish devising evacuation plans according to the new rules, and this is recognized as a problem. Even if nuclear power plants are given the go-ahead according to new NRA regulations, we still face many challenges in ensuring the safety of the plants. (Answers by Shimpei Torii, Science & Environment News Department)

July 19, 2014(Mainichi Japan)