US Dept. of Energy
Office of International
Nuclear Safety and Cooperation
1000 Independence Ave S.W.
Washington, DC 20585
During an emergency, nuclear power plant operators must stabilize the reactor quickly to
prevent damage to the reactor core and preclude the release of radioactive material.
Symptom-based instructions for rapid emergency response were developed in the United
States after the 1979 accident at Three Mile Island.
Previously, operators could not respond to abnormal conditions until they first identified the
problem or event--such as a steam-generator tube rupture or loss of cooling water. They then
followed procedures designed to correct the specific problem and mitigate its consequences.
These procedures, still used at most Soviet-designed
nuclear power plants, are called event-based emergency
Symptom-based emergency operating instructions, now
used at all U.S. plants and many others around the world,
enable operators to respond to emergencies without first
determining the specific cause. These instructions provide
responses to emergency symptoms--crucial changes in
plant parameters such as reactor pressure, water level, or
temperature. Operators immediately can stabilize the
reactor by responding to these symptoms, regardless of
the cause. The time saved can prevent damage to the
|New emergency operating instructions are being developed and
implemented at Soviet-designed nuclear power plants. The
instructions allow reactor operators to rapidly respond to emergency
conditions without first determining the cause of the accident.
Symptom-based procedures also inform operators which
actions to take first when two or more problems occur
simultaneously. This increases operators' ability to resolve
the problems before reactor core damage occurs.
In the countries where Soviet-designed reactors are
located, U.S. experts have completed efforts to train local
specialists in the methodology for developing the instructions. Host-country personnel now are
developing symptom-based emergency operating instructions for the four major types of
Soviet-designed reactors--VVER-440, VVER-1000, RBMK and BN. The reactors include
Balakovo, Kola, Novovoronezh and Smolensk in Russia; Chornobyl, Rivne and Zaporizhzhya
in Ukraine; Kozloduy in Bulgaria; and Ignalina in Lithuania. Specialists at several additional
sites also have undertaken work to develop symptom-based instructions.
In Russia, the Novovoronezh plant has implemented a complete set of instructions at one of its three
reactors. Staff in Russia have drafted the required instructions for plants at Balakovo, Kola and
Smolensk. In Ukraine, the Chornobyl plant has implemented its emergency operating instructions.
Instructions have been drafted but not yet implemented the Ukrainian plants at Rivne and
Zaporizhzhya. Lithuania's Ignalina plant is in the process of validating its instructions. Six reactors are
located in the Kozloduy plant in Bulgaria, where instructions are in draft form awaiting the completion
of supporting analyses.
U.S. experts are working with specialists in each host country to validate instructions before they are
implemented. The specialists develop calculations and use computer models of accident scenarios to
test the instructions, ensuring that they will mitigate the consequences of an accident and prevent
damage to the reactor core.
U.S. participation in this project will be complete when host-country specialists have validated the
instructions for each type of plant and implemented them at the pilot plants. At this point, specialists in
each country will have the capabilities to develop, validate, and implement instructions for the
remaining reactors within their borders.
An example from the Zaporizhzhya plant in Ukraine demonstrates that the training is having the
desired effect. Even before management formally implemented emergency operating instructions at
Zaporizhzhya, training in their use on a simulator in the United States made a difference for Chief
Engineer Yuri Kovorskin during a 1996 crisis. During routine testing of a pressurizer safety valve, the
valve failed in the open position and could not be closed. The plant rapidly depressurized, and the core
began heating up. Approved methods to restore core cooling failed. Calling into play his simulator
training, or symptom-based emergency operating instructions, Yuri Kovorskin drafted a temporary
procedure that initiated actions to cool the reactor core. The forced cooling stabilized plant conditions.
Operators were then able to cool down the plant, close the safety valve, and restore the plant to a
stable shutdown condition.
Another example of the value of symptom-based emergency operating instruction training is
reported, in his own words, by a shift supervisor at the Novovoronezh plant in Russia. "On June 18,
1997, the emergency feedwater supply of the primary circuit was actuated. As a result, for the first
time the control room #3 personnel under my charge have used the emergency operating instructions
to restore safety, including monitoring of critical safety functions. Thus, we can claim a significant
help to the personnel due to use of the emergency operating instructions."
In a related project, the United States is working with Ukraine and Russia to develop safety
parameter display systems, which work hand-in-hand with the symptom-based emergency operating
instructions. The display systems quickly provide control room operators with the status of key plant
conditions. When an emergency occurs, the system allows the operator to rapidly determine which
conditions--or symptoms--within the plant are abnormal. The operators then use the symptom-
based emergency operating instructions to stabilize the plant.
Safety parameter display systems developed with U.S. cooperation are operating at Russia's Kursk
and Novovoronezh plants, and at Ukraine's Chornobyl plant. Scheduled to come on line in 1999 are
systems in Ukraine (Khmelnytskyy, Zaporizhzhya and South Ukraine). Six more systems are
scheduled for installation in the years 2000 to 2003.