Spent Fuel Pool liner repair on the nuclear power plant BN-350 NPP

The K1.01/96 B project was a specific nuclear safety related project implemented in the framework of the On Site Assistance (OSA) for the Aktau BN350 NPP, Republic of Kazakhstan. Its object consisted in restoring the water tightness of the spent fuel storage pool of the above mentioned NPP. Since end of 70s, a water leakage from this facility had been detected by the plant operator and had been, as well as possible, managed by collecting the water leaking from the pool in a confined volume, under the pool’s bottom level. From this confined volume, the collected water was then pumped again into the pool after filtering. Nevertheless, considering the average increasing trend of the leak flow rate and the fact that pool was, at the time, used for storage of all the spent fuel assemblies unloaded from the reactor following its definitive shutdown, this situation was considered uncomfortable and potentially dangerous.

Manufacturing, delivering, on site training, instructions in the use, transfer of know-how and operational qualification to the plant operators at Aktau Nuclear Power Plant of the following supplies:

1. repair workshop laying out equipment,
2. workshop personnel safety equipment,
3. liner surface preparation equipment,
4. workshop air conditioning and lighting equipment,
5. coating products, coating preparation, application and testing tools,
6. cleaning solvent and accessories.

The following services were also included in the supply:

7. execution of coating products qualification tests,
8. elaboration of workshop management plan,
9. elaboration of procedures for liner preparation for coating,
10. detailed design, operation and maintenance procedures of workshop air conditioning system,
11. elaboration of procedures for application of coating onto the liner,
12. elaboration of liner coating test and repair procedures,
13. delivery of the provided equipment to Aktau BN350 NPP,
14. training of End User operators to the utilisation of the provided equipment,
15. qualification of End User operators to on site execution of the above listed procedures.

The contract for this TACIS project was given to the French company PREZIOSO, under supply contract 30311, signed on 30 April 2003. Below are the main milestones during the implementation of the project:

Factory acceptance of equipment on 15 October 2003;
Equipment shipment and delivery completed in December 2003;
Assistance to repair of items damaged during transportation, completed in February 2004;
Completion of BN350 NPP operators training and qualification for the liner repair works, by end February 2004;
Provisional Acceptance Certificate signature for the equipment provided by the project, in March 2004;
Workshop preparation for the spent nuclear fuel (SNF) storage pool repair workshop inside the pool’s basin 06/3, under the responsibility of the End User and with the supervision of PREZIOSO begun in June 2004;
During the setting up of the workshop in the SNF pool basin 06/3 some unexpected concerns appeared in relation with operators protection, that led to a temporary suspension of works.
Works in the 06/3 basin started again, in protected conditions, in August 2004, with the scaffolding of the basin’s walls. The Supplier achieved his supervision services foreseen in the supply contract;
Sandblasting of basin’s metallic liner was a heavy work, due to the confined working space (the SNF has a roof that complicates materials and operators access). Some unexpected difficulties (excess “powders” from used sandblasting medium) were solved with the support of the Supplier. At end November 2004 liner sandblasting was completed in the basin 06/3. Defects that could reasonably be pointed out as the origin of water leak from the SNF pool were detected in several points of the liner;
In December 2004 the coating of liner with the epoxy-glass fibre reinforced resin started. The area of the 06/3 basin (walls and bottom) amounts to about 450 m2. Basin 06/3 basic layer of liner coating was finally completed. The final coating layer was applied after the satisfactory verification of adherence of the basic layer.