Technology and equipment for handling non-conforming spent fuel assemblies of the service ship Lotta

Scope of work under the contract with FSUE Atomflot for safe handling non-conforming spent fuel assemblies stored in the Lotta storage tanks, their retrieval, and shipment for reprocessing was done from 2018 to 2020.

Historically, more than thirty years ago, non-conforming spent fuel assemblies of the icebreakers Lenin, Arktika and Sibir were reloaded from the reactor cores to the Lotta storage tanks for spent nuclear fuel. The Customer asked to develop the procedure and fabricate the equipment for retrieval from the Lotta storage tanks of more than thirty non-conforming spent fuel assemblies loaded into the single-cell and multi-cell storage canisters and transport them for reprocessing.

Below is the scope of work completed by Sosny R&D Company's experts under this project:

  • prepare a program to inspect the non-conforming spent fuel in the Lotta storage tanks;
  • design, fabricate and supply the equipment for inspection of non-conforming spent fuel;
  • develop a transport plan for handling non-conforming spent fuel assemblies, their retrieval from the Lotta storage tanks, and reloading into transport casks;
  • develop the process regulations, and safety justification of handling non-conforming spent fuel;
  • participate the inspection of non-conforming spent fuel under the Inspection Program using the supplied equipment and issue the inspection report;
  • prepare, approve and obtain all necessary licenses and authorizations, including the Special Requirements for delivery of non-conforming spent fuel to FSUE Mayak PA and the Certificate of Approval for transport cask design and shipment; and
  • design, fabricate and supply the equipment for retrieval and preparation of non-conforming spent fuel for shipment.

Handling non-conforming spent fuel assemblies was a specific procedure because of a need to perform all process activities in a small cargo compartment of the ship moored at a pier of FSUE Atomflot. Moreover, only a harbor crane could handle some heavy equipment, and the ship crew had to ensure the heel was as small as possible. The main problem was the worse health of spent fuel assemblies (every assembly had some mechanical damage), and some fuel assemblies also got stuck inside the storage canisters and could not be removed with the standard tools. What made the situation even worse was a variety of storage canister designs. Moreover, some canisters had suffered severe corrosion damage.

The Sosny Company developed a procedure for preparing non-conforming spent fuel for transport to the reprocessing plant that included the following stages:

  • retrieve a spent fuel assembly from the storage canister and load it into a transfer cask using a special shielding loading adapter, a vibratory hammer, a power jack, and a fuel grapple;
  • reload a fuel assembly from the transfer cask into a new thin-walled canister arranged in the transport basket using a special reloading adapter;
  • put a full transport basket inside a transport cask and prepare it for shipment.

The Sosny Company designed and fabricated a set of equipment to carry out the above-listed activities safely. Each piece of the equipment meets regulatory requirements for handling ionizing radiation sources.

Below is a description of the equipment for handling non-conforming spent fuel assemblies and some photos taken during the acceptance tests of the equipment at the Pilot Production Facility of Sosny R&D Company.

Thin-walled canister is a primary packing for a non-conforming spent fuel assembly retrieved from the Lotta storage tank. The radiation-resistant O-rings seal the lid-to-body joint. The lid has some elements to secure it onto the canister body. The lid has some elements to secure it onto the canister body and is handled using the associated lid grapple.

The Sosny Company fabricated new type ChT baskets (one thin canister per basket) to transport non-conforming spent fuel in a transport cask.

 

Thin-walled сanister for non-conforming spent fuel assembly: 1 –Body, 2 –Lid, 3 – Gripping part (a pintle)

Type ChT basket

 

Loading adapter is intended to retrieve a non-conforming spent fuel assembly from the storage canister and load it into the transfer cask. It shall be placed above the storage tank cell to be emptied. The loading adapter has a mobile CCTV camera, a light, and a manipulator. Its shielding body protects the personnel from ionizing radiation and makes support for the transfer cask. The replaceable spacers prevent displacement of the storage canister during the spent fuel retrieval and force fuel debris, if any, to spill back to the canister.

 

Loading adapter

 

Fuel grapple clutches and fixes a spent fuel assembly during handling operations using the transfer cask. The fuel grapple shall be attached to the transfer cask wire to replace the cask standard grapple.

 

Fuel grapple and a dummy fuel assembly

 

Vibratory hammer facilitates retrieval of the spent fuel assembly that got stuck inside a cell of the multi-cell storage canister. It creates a vibrating force needed to destroy sticks caused by the corrosion and enable the fuel assembly retrieval. The vibratory hammer shall be put onto the pintle of the stuck fuel grapple attached to the spent fuel assembly that got stuck inside the storage canister. A pneumatic lift generates a force needed to keep a fuel assembly from sliding down when the vibratory hammer is used.

 

Use of vibratory hammer to retrieve a stuck dummy fuel assembly

 

Power jack serves for forced retrieval of a spent fuel assembly from a cell of the multi-cell storage canister after it is free from sticking with the vibratory hammer. The power jack is placed and secured onto the loading adapter. It is also used to monitor the force applied to the stuck fuel assembly.

 

Power jack at a test facility

 

Reloading adapter serves for reloading the non-conforming spent fuel assembly from the transfer cask into a cell of the Lotta storage tank with a pre-prepared Type ChT basket and an empty canister. The bottom part of the reloading adapter has two movable plates for retaining the Type ChT basket with the canister. The reloading adapter has a mobile CCTV camera, a light, and a manipulator.

 

Insert is intended to collect fuel debris spillage if any, and reduce loose contamination inside a transfer cask while handling non-conforming spent fuel. The automated flap gate seals the insert inner cavity.

 

Reloading adapter (left) and insert (right)

 

Canister lid grapple serves for closing the thin-walled canister with the lid and the personnel radiation protection. The lid grapple shall be handled and operated vertically attached to the crane hook. The operator controls opening/closing the lid grapple.

 

Canister lid grapple

 

In May 2020, the equipment for handling non-conforming spent fuel assemblies from the service ship Lotta successfully passed the acceptance tests under the Acceptance Test Program at the Pilot Production Facility of the Sosny Company and was delivered to FSUE Atomflot, the Customer.

In the second half of 2020, the equipment was assembled, mounted and used to retrieve the non-conforming spent fuel assemblies from the Lotta storage tanks at the FSUE Atomflot’s site. The Sosny Company’s representative took part in these activities. As a result, many air-tight canisters filled with non-conforming spent fuel were prepared and transported to Mayak PA to free the spent fuel storage tanks from the non-conforming fuel stored there for a long time.

 

 

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