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Steel Structure Shelters Sarcophagus at Chernobyl

31 years after the world's worst nuclear disaster

In the early morning of April 26, 1986, when darkness still cloaks the land, operators at the Chernobyl Nuclear Power Plant conducted what is typically a routine safety test which instead went wickedly wrong.

The plant's Unit 4 graphite-core reactor's power surged and quickly raced out of control. Cooling water flashed into steam and blasted apart nuclear fuel rods. The roof ripped wide, as if someone was using a can opener, scattering the internals of the reactor around the exterior of the building and igniting a raging fire in what was left of the nuclear core.

Unit 4 Plant after the explosion

For 10 days, the reactor blazed, disgorging 400 times the radioactivity released by the Hiroshima bomb. It drove 116,000 people from their homes—one of which eventually made his way to Richland, Wash. and Pacific Northwest National Laboratory.

During the years leading up to the Chernobyl nuclear disaster, Andrei Glukhov was a reactor operator and then a safety specialist at the plant. The morning of the explosion, he telephoned the Unit 2 control room from his home located a few miles from the plant. An operator told him they were increasing the power level after the outage. "What happened to Unit 4?" Andrei recalled asking.

"Look out the window," the man replied.

"I went to my balcony," Andrei said. "I saw smoke coming out of the plant." Telling his family to stay indoors, Andrei left to offer help.

Once the fire was eventually squelched, roughly 700,000 liquidators, civilian and military persons quickly went to work to help eliminate the consequences of the accident. They decontaminated the plant; immediately upgraded safety to Units 1, 2 and 3; and built a steel structure over the top of what remained of the Unit 4 plant to entomb the highly radioactive debris.

PNNL Brings Nuclear and Engineering Expertise

In the early 1990s, Andrei joined Battelle, operator of PNNL, where a team of scientists and engineers were employed to look at the long-term safety and containment of Chernobyl Nuclear Power Plant Unit 4. Through 2014, our researchers have been applying their expertise in nuclear science, safety, remediation and engineering to help Ukrainians. The consortium comprised Bechtel, Electricite' de France and Battelle. Some highlights included:

  • Improved the safety of the highly contaminated sarcophagus, a structure hastily built after the meltdown to contain the radiation.
  • Awarded funding through the international Shelter Implementation Plan (SIP) to address rising safety concerns of the rickety sarcophagus. The SIP was a joint effort between the U.S., Ukraine and the G-7 nations. The $1.5 billion total effort included site safety projects, decommissioning facilities and constructing a new shelter to cover the existing sarcophagus.
  • Led, through SIP, early designs for the arch structure called the New Safe Confinement (NSC) that would be built and then slid over the top of the contaminated hull. The effort was billed as the world’s largest moveable structure—steel arch 257 meters (843 feet) across, 108 meters (355 feet) high, and 150 meters (492 feet) in length.

An Engineering Wonder

Battelle's recently retired Eric Schmieman led the early designs for the NSC. For Eric and his team, the effort was an engineering wonder that mandated stretching beyond conventional practices. Among the challenges:

  • Ground-level radiation from buried materials
  • Reflections from the sky down onto the top of structure
  • No condensation on the inside to prevent corrosion of the steel frame
  • Minimizing air movement to ensure no radioactive dust exposure for the workers
  • Modeling effort challenged the limits of computational capacity available even at the U.S. national laboratories
  • Biggest challenge: pick apart and permanently entombing what remains within the existing shelter
  • Using remotely operated cranes to take down the sarcophagus
  • Fuel-containing masses would remain
  • Having to develop new technology.

"During the design and construction of NSC, I have frequently been asked what our greatest challenge was. Most people expected a technical response from me, such as this is a first-of-a-kind design, the unknown subsurface conditions, or scaling up the tensile truss, etc.," Eric recalled. "But, my answer was always the same: our biggest challenge was communication. Design works were carried out simultaneously in multiple locations in the United States, Ukraine and France by engineers of different cultures, different educations, different design codes and standards and different expectations."

New Safe Confinement

Though Battelle withdrew from the project in 2014, a few employees remained "on loan" to Bechtel at Slavutych to oversee construction and movement of the arch to its final destination over the sarcophagus. In 2010, construction began on the nearly 40,000-ton structure—roughly the size of two Manhattan blocks and tall enough to enclose the Statue of Liberty. The massive arch was delicately slid into place in November 2016 over the sarcophagus and will safely and securely contain the radioactive materials for 100 years.

"The technical complexity of the project is beyond measure, and I've been impressed by how well the teams of engineers, designers and workers from dozens of countries have been able to progress so well toward a single goal. It's been very rewarding to contribute to a project that is as equally important to the local community as it is to the larger international community," said Michael Smith, a Battelle researcher who has spent nearly six years in Slavutych overseeing design aspects related to radiation safety and managing the biophysical and biomedical monitoring of over 2,000 workers.

Leaving a Lasting Legacy

For Andrei, who also remained on loan to Bechtel, seeing the commissioning of the NSC was especially monumental. "This step demonstrated the success of tremendous efforts undertaken by Ukraine and the international community within 30 years after the accident to bring the existing shelter into environmentally safe conditions for workers and the public. This accomplishment commends those who have spent the largest parts of their careers helping to mitigate the consequences and honor those who sacrificed their lives," Andrei said.

From 1994 through 2014, more than 200 staff members contributed to help to improve safety at the Chernobyl Nuclear Plant. Joel Hoyt worked at the Chernobyl site between 2005 and 2009, where he managed the $70-million SIP project effort until he returned to the U.S. "PNNL staff played a crucial role within the SIP consortium," said Joel. "We routinely brought our world-class science, engineering, safety and project management expertise to bear in solving first-of-a-kind problems faced at Chernobyl. This was expertly achieved by embedding key staff within the in-country SIP team and then leveraging all of PNNL's capabilities via reach-back support."

Several researchers uprooted entire families, relocating them from the Tri-Cities to Slavutych to be closer to where the solutions were needed. In addition to contributing scientific research and engineering, they introduced to Slavutych one of the U.S.'s favorite games—baseball.

Diane Strong coordinated travel and the relocation of families to Slavutych. The Ukrainians were so grateful for her efforts, the mayor of Slavutych awarded her with a letter of commendation.

Three decades later, much has been accomplished to safely contain the radiation that once ravaged the surrounding land under and near the Chernobyl Nuclear Power plant. Today, for many Ukrainians, daily life is routine.

"Living through this unprecedented accident is something I'll never forget, but I'm proud I was part of the international team dedicated to help overcome consequences of this tragedy," said Andrei, who has dedicated his life's work to helping his country.

Actual Unit 4 Emergency Shut Down Switch on Display

The actual emergency (KOM) shutdown switch is be on display in one of PNNL's lobbies. The switch, courtesy of Andrei, was used by the Unit 4 reactor operator in a last attempt to shut down the reactor. If the regular shutdown mode isn't functioning, regulations require operators to use an emergency switch to deactivate electrical power to control rod drive brakes which then allows the rods to fully drop—under gravity—into the reactor core.

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