The State Office for Nuclear Safety in the Czech Republic (SUJB) has published the report concerning the degradation of the Westinghouse-made fuel elements in the Temelin NPP.

Inter alia, the Czech regulatory body states that "throughout the recent days we have experienced, once again, a surge of interest some domestic and foreign media took in the issue of geometric degradation of fuel assemblies at the Temelin Nuclear Power Plant."

The core of each of two Temelin's VVER-1000 reactors is loaded by 163 fuel assemblies. Each of the fuel assembly contains the 312 fuel pins. During the reactor operation, one monitors the leaks in the fuel elements as well as its mechanical deformation.

Summary data for leaks being detected in the Temelin NPP

Temelin-1 unit

• cycle 1 - not diclosed;
• cycle 2 - 2 assemblies removed;
• cycle 3 - 4 assemblies removed and 1 assembly repaired;
• cycle 4 - 6 assemblies detected;
• cycle 5 - 6 assemblies detected.

Temelin-2 unit

• cycle 1 - not diclosed;
• cycle 2 - 4 assemblies detected and 1 removed;
• cycle 3 - 10 assemblies detected;
• cycle 4 - 5 assemblies detected.

Summary data for geometric degradation influence on the nuclear safety of the Temelin NPP

The SUBJ states: "The mechanical deformations of fuel rods and assemblies, i.e. the deviations from their ideal geometric shapes and the elongation of fuel assemblies (radiation growth), come as a natural phenomenon accompanying the production of energy inside the cores of nuclear reactors."

"The deformation figures themselves are irrelevant, since the nuclear safety will depend on the proper performance of the mechanical control of the reactor, i.e. on the clusters possibly affected by the deformation. The safe function of clusters is defined by the A.3.1.4 Limit Condition requiring that the clusters are capable of gravity dropping to the core, and that the time needed to elapse between the moment when the clusters are released in their top end positions and the moment when they enter the hydraulic dampers of guide tubes is 3.5 seconds or shorter."

Temelin-1 unit

Number of cluster failing

Temelin-2 unit

Number of cluster failing

Not so optimistic experience of the Westinghouse-made fuel assembly operation has forced the Czech nuclear companies to ask for replacement of some structural materials, e.g. the Zircaloy-4 alloy has been replaced by the ZIRLO and Alloy 718.

SOURCE: AtomInfo.Ru

DATE: April 03, 2008

Topics: NFC, East Europe, Czech, Westinghouse