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

INADVERTENT STEAM RELEASE INTO THE REACTOR HALL DUE TO STOP OF PUMP IN RESIDUAL HEAT REMOVAL SYSTEM

During shutdown both residual heat removal pumps stopped inadvertently. The reactor was shut down for the yearly outage and the pump stop was not discovered until four hours later when the pressure vessel lid was dismantled. During the pump stop the water temperature increased to 98 degrees C.
BASIS FOR RATING: Level 1, Table 1 A-1R, chapter 4.5
DIFFICULTIES IN RATING:

Category: Power Reactor Barsebäck Sweden »

INES-event
INES 1

DEVIATION FROM OPERATING INSTRUCTIONS

During outage a search light fell into the main recirculation loop. To be able to examine the bottom of the RPV three control rod guide tubes had to be removed from the reactor core. An exemption from the regulatory body, SKI, for doing this was necessary as the rods belonged to three different scram groups. This was granted on the condition that an extra independent verification was made by use of a TV camera. This extra control though included in the operation instruciton was not executed.
BASIS FOR RATING: Level 1. Table 1 A - 1R, Chapter 4.5
DIFFICULTIES IN RATING:

Category: Power Reactor Oskarshamn Sweden »

INES-event
INES 1

NEW RADIOACTIVE "HOT SPOTS" DISCOVERED AT KOZLODUY NPP

On 6th August 1991, two new contaminated spots on Kozloduy NPP where discovered. The location of the spots is south-west of the administrative building, inside the NPP fence. The surface of each spot is about 100 cm2. Samples of soil are taken for investigation. The gamma activity of the samples is 0.5 to 1.5 (mR/h) at contact. After the samples were removed the gamma-activity of the spots decreasaed to the level of the natural background activity.

Category: Power Reactor Bulgaria Kozloduy »

INES-event
INES 1

CONTAMINATION OF SOIL ON SITE

During the period from July 22 to August 6, 1991, several hot spots have been discovered at Kozloduy NPP. One being a leak of radioactive water (from the tunnel linking the reactor building Unit 1 and the auxiliary building) which has contaminated one square meter of the ground on site. This leak is probably due to a crack in the concrete through which the recent rains transported active particles. The activity of the soil was 2.5m rem/hour at contact. Investigation of the causes and implementation of corrective actions are in progress.

Category: Power Reactor Bulgaria Kozloduy »

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

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

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

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 »