Worker Protection - Stabilization of the Ventilation Stack

An auxiliary equipment building connects Chornobyl's reactor Unit 3, which is still operational, to the shelter over Unit 4. Mounted on the auxiliary building is a ventilation stack that depends on external braces for support. These braces also secure the stack to the building.

The 1986 accident at Chornobyl severely damaged the braces in approximately 30 places. Because of the damaged bracing, the ventilation stack could topple in an earthquake or high winds. Chornobyl plant personnel and international experts have called stack stabilization a "necessary and urgent" short-term measure for worker and nuclear safety. If the stack were to fall on the shelter, it could damage the shelter's roof, perhaps collapsing the structure and sending a cloud of radioactive dust across the site. The dust would increase risks during all future work at the site. If the stack were to fall on reactor Unit 3, which is operational, it could injure workers, shut down the reactor, and possibly lead to damage of nuclear systems.

Early in 1997, the Chornobyl Shelter Organization developed a plan for replacing the damaged bracing and asked U.S. experts to review it. A team from the Pacific Northwest National Laboratory and contractors concluded that the plan was reasonable and prudent but involved excessive radiation exposure to workers. The U.S. team recommended an alternative approach that reduced the completion time from 4,200 to 1,700 worker hours, the radiation exposure from 4,600 to approximately 400 person-rem, and the projected cost from $3.6 million to $1.8 million. The approach included the development of repair equipment and a parts-delivery system. It also uses the "as low as reasonably achievable" or ALARA principle to plan personnel movements and routes through radiation areas.

Chornobyl managers accepted the U.S. recommendation and made similar reviews standard for future high-exposure jobs at the shelter. The Chornobyl Shelter Organization signed the $1.8 million task order in December 1997, with the United States and Canada funding the work. Ukraine will provide an additional $450K in U.S. funds to the project. A Ukrainian contractor will replace the damaged bracing under the technical management of the Shelter Organization. The two-month project will begin in spring 1998, as soon as weather permits.

| The 1986 Disaster/The Unstable Shelter | Closure of the Chornobyl Plant | Preventing Collapse of the Shelter | Worker Protection | Additional Safety Projects |