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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.
 INES 1 |
WRONG POSITIONING OF THE FUEL ASSEMBLY WHILE PERFORMING FUEL ROD CLADDING INTEGRITY TEST |
While performing fuel rod cladding integrity test of the removed fuel, the fuel assembly was erroneously placed in the abnormal position on the plate of the testing system flasks and disconnected from the refueling machine telescopic beam. Later the above fuel assembly was placed in the testing system flask. Inspection of the fuel assembly did not reveal any damage.
BASIS FOR RATING: Initiator - fuel assembly handling in the wrong position.
Criterion - degradation of defence-in-depth.
INES 1 |
UNIT SHUTDOWN DUE TO SG-4 PULSE LINE RUPTURE |
Unit shutdown occurred due to the rupture of the pulse line measuring pressure in SG-4 steam header. Pulse line damage occurred because of design deficiency in the routing and fixing the pulse line during SG replacement.
INES 1 |
TURBINE SJAES STEAMING DUE TO PLANT PERSONNEL ERROR |
The unit was operating at nominal power. Thermal Instrumentation and Controls Service (TICS) shift personnel admitted TICS maintenance personnel to perform work on hydrogen content monitoring sensors at the outlet of moisture separator of the hydrogen reburn facility without informing Turbine Service operating personnel and plant deputy shift supervisor. While performing work on one of the sensors spurious signal of hydrogen concentration increase to 0.4% was formed.
INES 1 |
PRESSURIZER DISCHARGE TANK MEMBRANE RUPTURE |
On 5 February 1991 at 12.00 pm during the routine survey of the reactor compartment a ruptured membrane of the pressurizer discharge tank was discovered. The gas-aerosol activity near the discharge tank was measured 3 x 10-8 Ci/l, and the activity in the hermetic steam generator box was measured 8 x 10-9 Ci/l. A possible reason for the rupture of the membrane is a routine blowing away of the hydrogen in the pressurizer by means of low-pressure nitrogen.
INES 1 |
REACTOR COOLANT LEAKAGE DUE TO FAILURE OF SEALING OF MAIN REACTOR FLANGE |
On 21 December 1990 a leak was discovered from the first two (inner) out of four nickel sealing rings of the main reactor flange. The gas-aerosol activity of the air under the reactor protective cap was measured 2.7-3 x 10-9 Ci/l (100 Bq/l).
The reactor was shut down manually by the operator due to a violation of the limits and conditions for safe operation.
BASIS FOR RATING:
DIFFICULTIES IN RATING:
INES 1 |
FAULTY WELD DETECTED ON PRIMARY CIRCUIT |
BASIS FOR RATING:
DIFFICULTIES IN RATING:
INES 1 |
LOSS OF POWER SUPPY TO REACTOR COOLANT PUMPS DUE TO 6 KV CABLE FIRE |
While testing automatic activation of 6 kV auxiliary power bus standby source of Unit 1 which was in maintenance and due to switching overvoltages, standby boiler's 6 kV cable insulation was damaged resulting in cable short-circuiting and burning. This resulted in the damage to Unit 2 cables laid nearby, deenergizing of two 6 kV auxiliary power buses, loss of power to two reactor coolant pumps causing the actuation of reactor scram. Breach of safe operation limits and conditions did not occur. Radiation situation remained normal. No injuries occurred while extinguishing the fire.
INES 1 |
DEGRADATION OF NATURAL CIRCULATION |
Refuelling of Unit 4 was commenced on 18 June 1988. Operating personnel performed a planned switchover to natural circulation from loops 4 and 6 to loops 1 and 3 on 30 June. Meanwhile, the effectiveness of core cooling by natural circulation decreased sharply for about a 3 hour period. After switching over the natural circulation among the llps, the operating personnel isolated loops 4 and 6 and started to drain them. Nitrogen used to drain the water got into the loops in operation and most of the water was pushed from the SG primary side into the reactor vessel.
INES 1 |
REACTOR COOLANT LEAK ON REACTOR TEMPERATURE DETECTOR |
Reactor coolant System Leakage of 280 Lit/H Upper Technical Specifications Limit (227 L/H). The leakage was located in a flowmeter on the reactor temperature detector (RTD) Line (loop A). The leakage was initatied at 21.15 hrs. (July 7) and isolated at 20.30 hrs (July 8). The plant remained in hot shutdown operation mode. The total leakage was 7.000 litres.
BASIS FOR RATING: Initiator frequency: Expected, real
Safety function availability: full
Insignificant on site impact inside containment. No off-site impact.
DIFFICULTIES IN RATING:
INES 1 |
FEEDWATER TUBE RUPTURE DUE TO EROSION CORROSION |
One pipe of the feedwater system of Loviisa 1 broke. The ruptured tube was situated in the turbine hall of the unit. Water and steam flew into the turbine hall. The operation of the Unit was stopped by a manual reactor scram immediately after trip of all feedwater pumps. Both auxiliary feedwater pumps started as planned and the transient in the steam generator level was small. The leak was isolated in about twenty minutes. The local damages to nearby cables and smaller pipelines were significant but no important functions were lost besides the main feedwater system.
