INES Levels
INES N/A 
INES 4
INES 0
INES 5
INES 1
INES 6
INES 2
INES 7
INES 3

INES 0: Deviation

No safety significance

(Arrangements for reporting minor events to the public differ from country to country. Also, it is difficult to ensure precise consistency in rating events between INES Level-1 and Below scale/Level-0)

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INES-event
INES 0

Reactor trip due to degradation of photoresistic cell in the main feedwater control system

Ulchin unit 1 was operated at full power. During normal operation, one of the main feedwater control valves was opened and reactor was tripped by steam generator level high-high signal. Investigation revealed that photoresistic cell in the feedwater control system, which gave certain value to consider the influence of feedwater temperature in comparing steam generator level and programmed feedwater flow, was degraded by the effect of heat generated in nearby resistance. Plant was returned to normal operation after replacement of failed control circuit.

Category: Power Reactor South Korea »

INES-event
INES 0

REACTOR COOLANT SPILLAGE DURING OVERHAUL

Plant was under the 1st refueling operation. Under the reactor vessel situation of 30 deg. C in coolant temperature and 115 feet in coolant level, reactor protection system was tested according to the schedule of overhaul. Soon after removal of the power supply of train "B", Engineered Safety Feature Actuation Signal was generated. All the components related to this signal were actuated. Twelve valves of the safety injection system were opened as designed.

Category: Power Reactor South Korea »

INES-event
INES 0

Reactor trip due to actuation of sensitive relay influenced by starting current

This unit was escalating the power after overhaul. At 48% power, as soon as operator made one main feedwater pump start to raise reactor power, Restricted Earth Relay (RER) which was designed to protect Unit Auxiliary Transformer (UAT) was actuated. Then turbine was tripped and caused reactor trip. After investigation, it was revealed that the setpoint of RER was 0.1A and was exceeded by influence of starting current of main feedwater pump. Setpoint of RER was adjusted from 0.1A to 0.2A as other units in Korea and plant was returned to operation.

Category: Power Reactor South Korea »

INES-event
INES 0

Reactor trip due to improper operation of main feedwater bypass valve

This unit experienced steam generator "A" level fluctuation during re-startup in reactor power of 16%. Operator changed the operation mode of feedwater level control from automatic to manual control. However, steam generator level was not stabilized. Reactor was tripped by steam generator level low-low signal. Investigation revealed that extension rod and hand jack guide plate of main feedwater bypass valve were damaged and bent because their position was not adjusted.
There was no release of radioactive materials outside the reactor building and no unplanned exposure to employees.

Category: Power Reactor South Korea »

INES-event
INES 0

TURBINE TRIP AND REACTOR SCRAM DUE TO TO AG WATER LEVEL HIGH-HIGH

The unit was in stable operation with a load of 290 MWe on December 15, 1995. Because some tubes of no. 3 high pressure heater leaked seriously, at 10:18 a.m. control room operator isolated the leaking no. 3 high pressure heater. The Main feedwater automatic regulation could not meet the requirement of water level control of SG and then manual control failed, which led to turbine trip and reactor scram because of "SG water level high-high" at 10:26:50 a.m.

Category: Power Reactor China »

INES-event
INES 0

REACTOR SHUTDOWN BY THE FAST-ACTING SCRAM SYSTEM DUE TO SPURIOUS SIGNALS OF INCREASED PRESSURE IN THE ISOLATION CONTROL VALVES ROOM

On 9 February 1996 Ignalina NPP Unit 1 was under normal operation at the thermal power of 4100 MW. Electrical power of Turbogenerators TG-1/2 was 620 MW/680 MW respectively.
At 12:32 p.m. the reactor was shut down by the fast-acting scram system (FASS AZ-1) due to the signals of increased pressure in the isolation control valves room (Reactor Building Room 209). The signals were actuated by 2 of 4 pressure sensors.

Category: Power Reactor Ignalina Lithuania »

INES-event
INES 0

WRONG SWITCH-OFF OF THE OIL-SYSTEM OPERATING SECONDARY COOLANT PUMP

After long time period of outage (since April 1995) for realisation of the life time prolongation program the reactor BN-350 was switched on and operated with power 420 MW since 05/01/96.
At 17/01/96, during routine switching, oil-system operating secondary coolant pump has been wrongly switched off by operator.
Automatically reactor power has been decreased to 300 MW. After 14 hours according to a routine procedure reactor power had been recovered to 420 MW.
There was no damage of equipment or radiation leakage in the plant or exposure to the plant employees.

Category: Power Reactor Kazakhstan »

INES-event
INES 0

LEAKAGE OF THE FEEDWATER OF RECIRCULATION PIPELINE

At 05.50 a.m., on 22/01/96 during routine surveillance the operator discovered steam in the steam-generator box no. 513/5. The primary main coolant pump has been switched off by hand, automatically reactor power has been decreased to 300 MW and steam generator has been drained.
After 45 minutes reactor power had been recovered to 420 MW with 3 loop.
As inspection showed the steam generator recirculaion feed water pipeline was damaged.
There was no radiation leakage in the plant or exposure of plant employees.

Category: Power Reactor Kazakhstan »

INES-event
INES 0

CRACKS IN THE REACTOR CORE SHROUD IN THE LID OF THE SHROUD AND IN REACTOR VESSEL INTERNALS

A major overhaul was made during the past two years at Oskarshmn-1. Visual and ultrasonic testing revealed cracks in the core shroud and in some connected components and also in the feed water riser pipe.
Based on metallurgical tests and inspections the failure mechanism was determined as thermal fatigue.
The oxidation found in the end of the cracks indicate that the propagation had stopped. Stress calculations show that none of the cracks will grow to critical length at least within five years.

Category: Power Reactor Oskarshamn Sweden »

INES-event
INES 0

SMALL RADIOACTIVITY RELEASE

During the annual calibration of the pressure sensors on the waste gas system a small amount of radioactive gases was released to the waste gas compressor room, and through the plant vent to the environment. The investigation showed that the impurities on the sealing surface of the instrumentaion isolation valve of the waste gas system were a probable cause of its leakage. The leak consisted only of noble gases: Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m. The release in excess of the alarm setting was in the duration of 5 minutes.

Category: Power Reactor Krško Slovenia »