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Report to OAH-NBI. Investigation report on the fuel damage occurred on 10-11 April within the Cleaning Equipment of FANP (2003)

AuteurPaks NPP Ltd
Datum2003
Classificatie 2.28.9.90/01 (HONGARIJE - REST INSTALLATIES)
Voorkant

Uit de publicatie:

Investigation report on the fuel damage occurred on 10- 11 April within 
the Cleaning Equipment of FANP

NBI 03.11.
B20301

REPORT TO OAH- NBI
(OAH- NBI =Hungarian Atomic Energy Agency- Nuclear Safety Inspectorate)

1. Event description: Damage of fuel assemblies occurred on 10 - 11 April 2003
inside a cleaning tank designed, manufactured and operated by Framatome ANP 
(hereinafter called as FANP).
2. Number of the Unit involved: 2
3. Event initiating time: 22:00 hours on 10th April 2003.
4. Event classification by INES Scale: Classified to Level 2 on 11 April 2003.
Finally classified to Level 3 on 17 April 2003.
5. Technical Specification requirement violated during the event: 5.5.1.1.2.a
6. During the event the Unit has been classified according to the following section
of Technical Specification: 6.2.2.5./d
7. Event brief summary:
On 10th April 2003 during the Unit 2 had been shut-down for scheduled maintenance.
The fuel assemblies were cleaned within the Shaft No.l and, at the same time, the 
cleaning of the reactor internal components was also performed. The 6th charge of 
fuel assemblies loaded into the cleaning tank was completed by 16:55 while the 
cleaning of reactor internal components was still going on. The cooling of the 
cleaning tank at 37°C was continuously maintained by FRAMATOME (FANP) 
specialists by circulating the coolant using a submergible pump. At 21:53 hours 
activity was detected by the workers on the krypton measurements installed in the 
cleaning circuit, and at the same time, the 'emergency' level was reached by the 
noble gas activity concentration monitors within the reactor hall, and then the 
operational dosimetry systems installed in the ventilation stack indicated abrupt 
increase of noble gas activity (max. 0,2x1013 Bq/10 min). The Plant Supervisor 
ordered to terminate the work carried out in the reactor building and to evacuate the 
area. An extraordinary Maintenance Working Commission has been called upon in 
order to evaluate the event and to take necessary actions. As highest priority, it was 
decided to open the cleaning tank, to carry out its visual inspection, if possible, to 
separate the leaking fuel assembly and also to analyse the water quality in the decay 
pool and the Shaft No. 1. The first results of water chemistry analysis were obtained 
at 04:00 hours on 11th April 2003. The following fission products Csl34,137, J131, 
132, Xe133, Kr85 have been identified in the samples at activity level of 104-107 
Bq/kg. The hydraulic locking pins of the cleaning tank lid were unlocked by FANP 
at 02:15 hours. Immediately after this, a staggering activity increase was observed 
in the dosimetry control and monitoring system and, at the same time, the water 
level in the decay pool lowered by app. 7 cm. During the cleaning tank lid removal 
operation, one of the three cables of the lifting tackle has broken thus the lid 
removal failed. It was observed during the inspection performed with the use of a 
video camera on 16 April 2003 after the lid lifting that the damage of the fuel 
assemblies was more severe than assumed before.

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