On March 11, 2011, the strongest earthquake in Japan’s recorded history triggered a 15-meter tsunami, which swept over the Fukushima nuclear power plant’s 5-meter seawall in what soon came to be known as the world’s worst nuclear disaster since Chernobyl.

A decade has passed, but areas around the Fukushima plant remain off-limits and worries about radiation levels persist. The decommissioning of the crippled plant will take decades and billions of dollars, experts say.

South Korea, observing the struggles of its neighbor, has made extensive efforts to upgrade the safety features of its 24 nuclear reactors operating, while the government has drawn up a road map to phase out the reactors.

“After the Fukushima crisis, Korea Hydro & Nuclear Power has set 56 short and long-term safety goals and accomplished 54 of them. The remaining two will be completed by 2024,” said an official at the country’s sole operator of nuclear power plants.

The company has reinforced, replaced and validated all 38,500 parts comprising nuclear reactors so that they can withstand earthquakes with a magnitude of 7.0, the official added.

All nuclear power plants have completed stress tests based on European Union standards.

Unlike Japan, South Korea is considered relatively safe from earthquakes. Since 1978, earthquakes with a magnitude greater than 5.0 -- sufficient to damage buildings -- occurred only 10 times in Korea, compared to 4,400 such cases in Japan.

However, reflecting on the lessons from the Fukushima crisis, KHNP is not letting its guard down.

To protect the Kori nuclear power plant located on the southeast coast, KHNP has built a concrete seawall that is 10 meters high and 2.1 kilometers long, to protect it in case of a tsunami.

According to KHNP, the Fukushima plant safety’s mechanism halted operations after sensing the earthquake. However, it was the tsunami that caused the plant to lose all power and cooling capabilities, which triggered the meltdowns and hydrogen explosions.

To be further prepared for flooding, KHNP installed independently developed waterproof doors on all nuclear power plants last year in December. The doors have passed authorities’ earthquake, waterproof and fire resistance tests and are currently also installed at a nuclear power plant in the United Arab Emirates.

In case of emergency generator failures, it has mobile generators and mobile coolant pumping systems ready. For a worst-case scenario in which the cooling system fails and a meltdown begins, a passive hydrogen removal system that functions without electricity to prevent hydrogen explosions will be mobilized. Also, KHNP will equip firetrucks with coolant and keep cooling systems operational no matter what, it said.

“KHNP has put safety first in the construction, operation and management of its nuclear reactors, and has made improvements in safety by recounting the Fukushima crisis. We will continue to secure the technological safety of reactors and innovate the safety level to the extent Korean people can rest assured,” KHNP President and CEO Chung Jae-hoon said.

Despite the reassurance, however, safety concerns persist.

Last summer, Maysak, the ninth typhoon of the season, caused issues with power transmission lines and four reactors at the Kori nuclear power plant were shut down, drawing concerns over the nuclear power plant’s susceptibility to natural disasters.

In October, Democratic Party of Korea Rep. Lee Jang-sub revealed data that showed that containment buildings encapsulating Kori reactor Nos. 3 and 4 and Shin Kori reactor No. 3 had 20 small cracks or holes.

A containment building is a structure made of five layers of reinforced steel, concrete or lead enclosing a nuclear reactor. The structure acts as a fail-safe to contain the escape of radioactive steam or gas if accidents occur.

In case of Shin Kori reactor No. 3, though it was constructed just five years ago in 2016, a crack 49.5 centimeters deep was found.

The Moon Jae-in administration’s road map for a nuclear phase-out, announced in 2017, has also faced setbacks recently.

Three officials from the Ministry of Trade, Industry and Energy are currently on trial for disturbing the state auditors’ examination of the decision-making process behind the closure of the Wolsong-1 reactor. The Board of Audit and Inspection earlier concluded that the shutdown decision was based on biased research to undervalue the reactor’s economic viability.

By Kim Byung-wook (kbw@heraldcorp.com)