On April 26, 1986 at 1:23 a.m. (Moscow time), an accident occurred at the Chornobyl Nuclear Power Plant in Ukraine.

On April 26, 2006 several ceremonies were held to mark the 20th Anniversary of the accident. In Kyiv, bells tolled 20 times, marking the time of the explosion at Reactor No. 4 at the Chornobyl nuclear power station. Ukrainian mourners carried single red carnations and flickering candles during a solemn ceremony to remember the 1986 Chornobyl explosion. Orthodox priests led the mourners in a somber procession.

In Slavutych the commemorations began an hour earlier to coincide with Moscow time, which was used at the time of the accident. Residents laid flowers and placed candles at a monument dedicated to Chornobyl as sirens blared.

In Moscow a ceremony for survivors honored those who cleaned up after the tragedy. Memorials, exhibitions and scientific conferences were held throughout the international community.

To commemorate the 20th anniversary of the Chornobyl accident and acknowledge the close connection between Chornobyl and the Pacific Northwest National Laboratory, Battelle Memorial Institute provided a gift that demonstrated our respect and friendship developed over 20 years of collaboration. $5,000 was gifted to the City of Slavutych for the purpose of repairing the Chornobyl Memorial. Plaques were presented to both the City of Slavutych and Chornobyl NPP. Adhering to each plaque was a piece of graphite originally intended for use in the Hanford production reactors.

PNNL Involvement in DOE-Sponsored Post-Chornobyl Activities

Accident Investigation: PNNL’s Grumman Gulfstream I aircraft collected air samples of fallout from the Chornobyl nuclear accident immediately following the event in 1986. PNNL scientists measured radioactivity in samples taken within weeks after the accident and authored a paper which was presented to IAEA members at a meeting in Vienna. Later in 1986, a PNNL scientist worked with scientists from Sweden to collect and analyze samples in that country and in the Chornobyl exclusion zone. Additionally, a PNNL manager chaired an IAEA committee studying how to deal with such accidents in the future.

Shelter Implementation Plan: The Shelter Implementation Plan (SIP) was approved by Ukraine and the G-7 nations in June 1997. PNNL scientists and engineers worked to establish the SIP Project Management Unit and develop bid packages for 17 urgent, early-start projects. These early bid projects included stabilization design, shielding design, geotechnical and seismic investigations, emergency preparedness, dust management, nuclear criticality monitoring, water management designs, characterization of the fuel mass, strategies for radiological protection and industrial safety, and the development of strategies and technologies for removing and confining the fuel mass.

Stack Stabilization: A ventilation stack mounted on the common auxiliary building between Unit 3 and the Unit 4 Shelter was heavily damaged during the accident, making the stack vulnerable to collapse. Stabilization of the stack was necessary to reduce risk to workers. Calculations indicated damage to external braces that support the 210 foot high stack had reduced its stability by 75% and failure was indicated under credible seismic and high wind condition. PNNL engineers assisted Chornobyl management and the Ukrainian contractors in stabilization of the vent stack.

Radiation dose reduction:

• Because stack stabilization was urgent, the Chornobyl Shelter Organization developed a plan for stack stabilization and committed to performing the work during the summer of 1997. The initial plan projected a completion time of 4200 man-hours and worker exposure of 4600 man-rem. At the request of the Shelter Organization, a team of PNNL scientists and engineers reviewed the repair plan and helped identify an alternative approach that reduced worker exposure to 400 man-rem and the completion time to 1700 man-hours. In response, Chornobyl management made the review methodology a standard for all future high exposure jobs at the Shelter.
• To reduce the radiation dose and minimize contamination to workers, PNNL provided dosimetry equipment, dose-tracking software, portable survey instruments, radiation protection clothing, and respirators. Radiation protection technicians also received expert mentoring and standards-based training from their PNNL counterparts.
• PNNL worked with Sandia and Oak Ridge National Laboratories to improve worker safety by developing a tele-robotic unit for remote visual evaluation and monitoring of areas inside the Shelter that were too radioactive for routine human access. A radiation-hardened robotic unit was shipped to Chornobyl in December 1998. In 1999, the Pioneer Mobile Robot crawled on tracks at the Chornobyl Shelter and inspected and mapped contamination areas.

Nuclear (criticality) safety monitoring: PNNL engineers built and tested a prototype criticality monitoring system to determine whether a high neutron count rate was caused by fission reactions or by damage to the existing neutron monitoring equipment inside the Shelter. In June 1998, PNNL personnel provided training that covered instrument settings and calibration, software operation, neutron measurements, data interpretation, and system testing. PNNL and Chornobyl workers installed the system in November 1998.

Dust suppression: The Shelter Implementation Plan identified the need for fixatives to coat highly radioactive material throughout the Shelter and install emergency dust suppression in case of a Shelter collapse. PNNL addressed the need for equipment to support radiological cleanliness in the Shelter’s access ways and staging areas. Three portable, airless sprayers were provided to apply fixatives and decontamination solutions and two high-efficiency filtered vacuum cleaners were provided to reduce radioactive dust in access areas and other high traffic areas for personnel.

Industrial safety enhancement: PNNL delivered a variety of basic equipment to increase the safety of Shelter workers, including fall-protection devices, ladders, hard hats, ear protectors, respirators, welding gloves and curtains, chemical-resistant gloves, and emergency medical kits.

Emergency preparedness: A team from PNNL collected information about the site’s emergency plans and procedures in June 1997. This information and emergency preparedness guidelines from the IAEA were used to outline a revised emergency plan for the Chornobyl Shelter.

Fire safety: Fire safety upgrades are of particular importance to overall safety. PNNL provided fire doors, fire and smoke detectors, fire-retardant sealant barriers, and firefighting equipment, such as firefighter suits and hose nozzles to the operating Chornobyl Unit 3. The products included cable coating and penetration sealant materials, as well as confinement isolation coating materials to reduce leakage from confined spaces. Now that the Unit 3 reactor has been permanently shut down, this technology and equipment is available to protect workers at the Shelter.

Deactivation, Decontamination and Decommissioning: A survey of Chornobyl Unit 1 readiness and resources for deactivation was completed in February 1997. Experts from PNNL worked with Ukraine to establish a set of generic requirements for detailed DD&D planning and safety analysis. Ukrainian engineers will adapt these requirements to the Chornobyl plant. Transfer of the necessary DD&D software and data to the Chornobyl Center for Nuclear Safety, Radioactive Waste and Radioecology was completed in 1997. The software will enable Chornobyl's staff to estimate costs for reactor decommissioning activities and assess the radiological and chemical risks associated with various decommissioning options.

Chornobyl Heat Plant

Heat Plant: A preliminary decommissioning study of the Chornobyl site identified the need for a new heat plant. Chornobyl's heat plant provided heat to help keep the Unit 3 reactor in a safe standby condition when it was not operating. In an emergency during the winter, the heat plant also keeps the reactor coolant from freezing and breaking the pipes. The capacity of Chornobyl's existing heat plant, however, was insufficient to support all of the decommissioning activities required. The U.S. Department of Energy, with management support from PNNL, worked with Ukraine to build and commission a new heat plant in December 2001.

Cooling pond remediation: PNNL scientists and engineers completed a plan for characterizing the radiological and chemical contamination of the plant’s cooling pond in January 1998. PNNL provided RAAS-MEPAS software and related training to the Slavutych Laboratory in December 1997, enabling Ukrainian specialists to assess the radiological and chemical risks of various decommissioning and remedial options for the cooling pond.

Operational safety improvements: In order to improve safety at Chornobyl’s operating reactor, PNNL, with assistance from other DOE national laboratories, initiated operational safety projects in 1995. PNNL experts in various fields assisted their Chornobyl NPP counterparts in upgrading the site’s management procedures, normal operating procedures, emergency operating procedures, quality assurance program, fire safety program, operator and maintenance training program, nondestructive examination and safety maintenance program, and event analysis and reporting program. Methodologies inherent in these procedures and programs have been transferred in large part by the plant to the Shelter management organization.