Following discharge from the reactor core, spent fuel assemblies of Light Water Reactors are stored in pools linked to the reactor via a transfer tunnel. Reactor spent fuel pools are never used up to their design capacity because of the need for operational buffer capacity during core reloads. In addition to the reactor pools, utilities have therefore often additional storage, which can be a spent fuel pool in a different building (wet storage) or a building that hosts casks in which fuel elements are stored under inert gas (dry storage). Since many years, Belgium and Germany have experience with dry storage facilities based on dual use casks (storage and transport) (Survey of Wet and Dry spent fuel storage, IAEA-TECDOC-1100 (IAEA, Vienna, 1999) ISSN-1011-4289).
Until today, only intact fuel rods are stored under dry conditions although there are no scientific reasons for rejecting dry storage for non-intact fuel rods, especially not if such defective rods are properly dried and stored under inert gas in a sealed capsule. Technological solutions for the safe and reliable encapsulation of damaged fuel rods either exist already today or are being developed for on-site application, but the issue of drying a defective fuel rod that has been stored for an extended period of time under water, has not been solved yet.
The WETFUEL project (Water Extraction Tests on nuclear FUEL) aims to fill this knowledge gap and provide scientific and technological data on the removal of water from damaged spent nuclear fuel.
The wetting and drying tests will be performed in SCK•CEN's laboratory for high and medium level activity
- A device will be developed to insert water in a true spent fuel column and subsequently apply different drying techniques: direct vacuum drying, heat or gas assisted drying etc.
- For the tests, segments will be taken from a defective fuel rod, irradiated in the Belgian NPP Tihange I, which has been sent for R&D purposes several years ago, and which was made available for the WETFUEL studies. One or more segments of around 500 mm will be taken for a series of wetting and drying tests.
- During each drying sequence, the dynamics of each of the method will be investigated on-line.
- It is expected to derive quantitative information on the drying process of a real spent fuel segment and to derive the principles for a reliable test that can be used to prove dryness.
The entire project (device development, installation, tests and interpretation) is carried out by SCK•CEN.
Results & Future work
The project is expected to provide its first results during the year 2014.
SCK•CEN contact: Marc Verwerft