1

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

INES 1: Anomaly

Impact on Defence-in-Depth
  • Overexposure of a member of the public in excess of statutory ­annual limits.
  • Minor problems with safety components with significant defence-in-depth remaining.
  • Low activity lost or stolen radioactive source, device or transport package.
(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 1

REACTOR SCRAM AND COOLDOWN BECAUSE OF LEAKAGE IN A PRIMARY CIRCUIT MEASURING SYSTEM

The event took place during the start up of the unit after refuelling. Due to a leak in the reactor pressure measuring system steam blew out in a room where transmitters of measuring systems were installed. Some transmitters failed, among others those measuring water level in the steam generators no. 1, 2 and 3 for protective purposes. The reactor protection shut down the reactor. The unit was cooled down to investigate the cause of the failure and to begin the repair work. During cooldown the leak was located and climated by closing out the affected section.

Category: Power Reactor Hungary Paks »

INES-event
INES 1

DROPPING OF SPENT FUEL BUNDLES OF CHANNEL P-09 IN SOUTH SIDEFUEL TRANSFER CAVITY

Dropping of spent fuel bundles of channel P-09 in South side fuel transfer cavity.
BASIS FOR RATING: 1. Problem was caused by drift in calibration of a potentiometer. Hence it falls in expected category.
2. Full safety system availability was there.
3. Since event is of expected frequency and postulated and event is large scale contamination of system it should be classified below zero. But as event was caused by operator inattention it is classified in category one.

Category: Power Reactor India »

INES-event
INES 1

FIRE IN LOW LEVEL RADIOACTIVE WASTE STORAGE


The storage is situated east of the on-site station switchgear, far away from the reactor buildings. The fire was extinguished by plant fire protection forces before it caused significant damage. The causes of the fire are being investigated. No on-site or off-site releases.

Category: Power Reactor Bulgaria Kozloduy »

INES-event
INES 1

EARTHQUAKE IN CENTRAL EUROPE

An earthquake (5.5 on Richter Scale) with the epicentre in Romania occurred on 18.7.91. The setpoint of the special reactor protection was not reached and therefore did not lead to reactor shutdown.
BASIS FOR RATING: Level 1 was justified acc. p.4.4C and Table. 1 of the user's manual.
DIFFICULTIES IN RATING:

Category: Power Reactor Bulgaria Kozloduy »

INES-event
INES 1

MG-TRIPPING ON UNDER/OVER FREQUENCY PROTECTION

Motor generator set MG no. 1 tripped on 30-2 relay indication. EMTR was initiated and class II and class III tie breaker 5231 CB 8 closed as per design intent and supply was restored to class II bus. The unit continued to operate at 145 MWe.

BASIS FOR RATING: A-2R. In this event the tie breaker between Class II and Class III closed restoring supply to class II bus-S. There was only 300 m/sec interruption of supply to Bus-S. Had the power supply to class II bus not been restored by EMTR, there would have been degradation of defence in depth. Hence level I is selected.

Category: Power Reactor India »

INES-event
INES 1

SHUT DOWN OF MAPS UNITS 1 AND 2 FOLLOWING INABILITY TO MEET MINIMUM STAFF REQUIREMENT

During power operation, the supervisors and tradesmen of the incoming
crew of I shift on 8.1.91 did not turn up for duty and the supervisors and tradesmen of the III shift on 7.1.91 left their locations. Units were manned with engineers and planned shutdown effected.

Category: Power Reactor India »

INES-event
INES 1

HEAVY WATER SPILL FROM MODERATOR SYSTEM

During unit shutdown, a flange joint in Moderator heavy water line started leaking resulting in spillage of heavy water and resulted in tritium in air concentration in Moderator room (inside containment) going up. Plant emergency had to be declared. Heavy water was drained below the level of the flange and the leak was attended.

Category: Power Reactor India »

INES-event
INES 1

MISGRAPPLING OF FUEL BUNDLE MB-140 IN THE CORE OF UNIT NO. 2

While catching the bundle MB-140 in the core with fuel grapple, the nose of the hook went inside the bail, and hook open-close operation was not taking place. After giving 'Open' signal to the grapple the grapple was lifted up and the operator found the fuel bundle hanging on the nose. To provide additional support and to secure the bundle in its position, the bundle was caught on the bail with a 'J' hook and was lowered on the channel stripping machine in the fuel pool.

Category: Power Reactor India »

INES-event
INES 1

FAILURE OF FUEL OIL LINE IN RUNNING DG-2

DG-2 of unit 2 was running on isolated, Class III bus in view of ACVR-2 shut down as per Technical Specifications. At 02.00 hrs. of 3.5.91, fuel oil leak was observed in the fuel oil cylinder supply line ferrule joint of the running DG-2. Since the leak was heavy, DG-2 was stopped after connecting 5231 Bus-Q to Class IV source through 5231-TR-2.
BASIS FOR RATING: According to Table I, C-2P, level 1 or 2 can be selected. Since the problem was attended quickly and back up from diesel generator of the other shut down unit was available, level I is selected.
DIFFICULTIES IN RATING:

Category: Power Reactor India »

INES-event
INES 1

FUEL ASSEMBLY TILTED OVER DURING CORE LOADING

During core loading a fuel assembly was not properly seated on the lower core plate. Zero load was obtained with the assembly standing on top of the two guide pins which are supposed to enter the foot piece of the fuel assembly. The gripper of the manipulator was released and at this moment the fuel assembly fell over towards the baffle. No damages were caused to neighbouring assemblies or reactor internals and no activity release was observed.

Category: Power Reactor Ringhals Sweden »