Emptying the MSSS

SELLAFIELD’S MAGNOX SWARF STORAGE SILO (MSSS) was built in the 1960s to store intermediate-level waste produced by magnox fuel decanning operations. The silo is made up of 22 compartments – each 16 metres deep – and It received magnox fuel cladding or swarf, which is almost 100% magnesium, from nuclear power stations until 1991. Since then that type of waste has been immobilised in concrete as it is more passive and practical to manage.

The radioactive inventory and lack of modern standards in the silo makes it one of the Nuclear Decommissioning Authority’s highest priority missions. Today, Sellafield Limited is focused on decommissioning the MSSS as part of its site hazard and risk reduction programme. The strategy involves removing the 11,000m3 of historic waste from its current condition and processing it through existing and planned facilities at the Sellafield site. Preparations for removing the wastes from the silo and placing them into safe, modern storage have been 20 years in the making.

Next year three 360t Silo Emptying Plant (SEP) machines will start reaching in to the silos and removing the waste with a hydraulic grab. The first stage involves mechanical retrieval of the bulk solid wastes into disposable skips. The waste will then be loaded into the shielded transfer packages and safely stored on the Sellafield site until a permanent geological disposal facility is constructed.

In August, the first 50t waste transfer package was lifted into the building for the first time, and safely placed onto one of the three 360t Silo Emptying Plant (SEP) machines that will begin grabbing waste out of the MSSS’s compartments from next year.

“The transfer package is the essential link in the chain to safer storage,” said Chris Halliwell, head of programme for MSSS. “It’s a big moment to see it finally being attached to the SEP machine inside the silo. Never before have these two bits of machinery met inside the place where they’ll be carrying out our biggest job in hazard reduction.”

The first transfer package to enter the silo was manufactured by Workington firm TSP Engineering and is one of nine original packages they have built and modified for Sellafield Ltd.

TSP is currently in the middle of a multi-million pound contract to modify and refurbish a fleet of high integrity shielded containers and doors that will facilitate the safe transfer of waste from the MSSS, to purpose built storage.

Its initial contract was for the modification, manufacture, testing and commissioning of 13 off units which consist of packages and gamma gates.

The gamma gate body is a bolted carbon steel assembly with top and bottom openings to enable a waste skip to pass through. The doors comprise a carbon steel slab clad with stainless steel. A driving wedge on the door connects with a package door when the package is seated on the gamma gate. This will be mounted within buildings on the Sellafield site.

The package – a shielded container – will be used to transfer nuclear waste between the Silo Facility and Silo Direct-Encapsulation Plant. Together the packages and gamma gates provide a short-term storage contingency should the Silos Direct Encapsulation Plant and Box Encapsulation Plant not be available.

As part of the project TSP Engineering manufactured a package lid, rope drum and lifting equipment. The package base was modified, along with the door locking mechanism, interface box to encompass new safety features.

The package receipt area on the gamma gates were clad with stainless steel, re-machined, and new locking mechanisms were designed and incorporated. The electrical routings and controls were modified to bring the gamma gates up to the highest specifications.

After assembly, the gamma gates were transferred to a purpose-built test rig for functional testing.

TSP Engineering is currently competing with Cavendish Nuclear to build the next batch of 15 transfer packages; an advanced manufacturing contract worth tens of millions of pounds to British Industry.  

About TSP Engineering

Following a few uncertain years, TSP Engineering is now a standalone independent subsidiary of the British Steel business. The firm has remained in profit for the last three financial years and is going from strength to strength. John Coughlan, chief executive officer, says the majority of TSP’s work is servicing the civil and defence nuclear, and industrial sectors in the UK and internationally.

Working on the Sellafield mission is a key step in the TSP Engineering journey but is not the limit of their ambitions. “Sellafield is the most iconic nuclear facility in the world and to knowing that we, as a local business, are helping to clean up the site is something that we take a real pride in,” Gareth Monkhouse, proposals manager, said, “but we also have our sights set on customers across different industries.”