Installation of feed water clean-up devices

One way to avoid costly fuel damages

Damages to the nuclear fuel may be caused by debris, wearing the fuel rod for the fuel pellets. In order to reduce the risk of achieving such damages, AREVA NP Uddcomb AB has developed, manufactured and installed special devices for cleaning the feed water has been installed in Swedish NPP´s.

The clean-up devices have been introduced under the name of “PARTICLE SEPARATOR”. The PARTICLE SEPARATOR is of axial centrifugal separators type, and is characterized by a robust design, high separation rate and low pressure drop. The PARTICLE SEPARATOR is intended to be installed as close to the RPV as possible to catch particles from both main feed water flow and sub-flows from systems like the RHRS. Normally the PARTICLE SEPARATOR is installed in the feed water lines inside containment, but depending on local circumstances this might vary.

PARTICLE SEPARATORS have been developed for both upward and downward flow direction, horizontal or vertical installation, with feed water flows in the range of 300 – 900 kg/s.

The development has been governed by the following requirements specification:

• High degree of separation of specified particles.
• High degree of separation also at reduced flow rates.
• Low pressure drop (typically less than 1 bar).
• Robust design with no moving or rotating parts.
• Compact design to simplify the installation.
• The trap shall not generate flow disturbances that can deteriorate the operation of components located further downstream the trap.

Typical values of separation for different types of debris that can be expected to be found in the primary systems are presented in the table below, the separation is verified in a full scale model:

The combined operational time for the PARTICLE TRAPS currently in use is approximately 18 years. The traps are easily emptied during every outage, and the collected particles are analyzed. A true sample, together with a photo of a PARTICLE SEPARATOR, recently delivered, is shown below.

The PARTICLE SEPARATOR is patented by Vattenfall, for which Uddcomb Engineering holds a license. AREVA NP Uddcomb AB takes the full responsibility of all engineering, manufacturing and installation of the PARTICLE SEPARATOR.

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