R4.08/93 REMEDIATION LEPSE FLOATING-BASE

From 1962 to 1985 the LEPSE was used as a service vessel for replacing and storing spent fuel assemblies from three nuclear powered icebreakers: Lenin, Arktika and Sibir. During that period 645 spent fuel assemblies were accumulated aboard, located in two storage containers.

In 1967, fuel elements from the Lenin, which had been damaged during a loss-of-coolant accident (LOCA), were transferred to Lepse. These elements had swollen and were overheated and distorted during the accident, and have been partially forced into the channels, or emplaced at random in the larger channels called caissons. In addition to the spent fuel, there are a number of tanks for liquid radioactive waste and casks for solid radioactive waste.

The Lepse was constructed in 1934-1936, sunk in 1941, salvaged after the war and then modified for nuclear service purposes. It is in a bad condition, heavily corroded, highly radioactive and contaminated, containing a subtotal of 750000 Ci activity in fuel elements. This constitutes, as it is now, a major ticking, floating threat to the environment. Without urgent remediation measures the vessel might constitute a source of an extensive radioactive release and contamination catastrophe. The JSC Iceberg in St. Petersburg was the ship builder. The LEPSE Project (De-fuelling) in total comprises 10 stages, called Work Plans.

The present project covers Preparatory Investigation and Engineering Concept for Remediation at the LEPSE Floating Base.

The project produced basic data on:

• Storage containers, cooling;
• Fuel characteristics like fuel status, geometrical characteristics, logical status, criticality calculations and technical specifications for fuel acceptance at Mayak;
• Canister buffer storage and transport characteristics;
• Data related to the LEPSE ship;
• A report on video inspection and measurements made on the ship;
• Engineering concept on fuel retrieval, where 3 scenarios have been developed;
• A basic design on equipment to be manufactured for various work to remove the SNF safely;
• Review of the safety issues;
• A time schedule for fuel retrieval has been set up;
• Cost assessment;
• Storage of removed fuel Dismantling of the LEPSE after removal of SNF.