Novel UHPC Container Range

Introduction

Working alongside Frazer-Nash Consultancy Limited (FNC) and a group of UK companies, we led the detailed design, testing, manufacture, supply, and delivery of a new concept UHPC container range and concept fibre reinforced concrete mixes.

The initiative to develop a low cost UHPC Container range was born from the Sellafield Waste Container Challenge supported through the GameChanger Initiative.  This provided the ability to undertake the first steps in the journey namely:

• Develop UHPC mixes (Normal Density, High Density, Maximum Density) suitable for IP-2 waste containers
• Complete “manufacturing proof of concept” with developed mixes

The contract was awarded for Proof of Concept (POC) for Advanced Cementitious Composite ILW Containers in November 2017.

Objectives

• Create an Ultra-High Performance (Fibre-Reinforced) Concrete (UHPC) Container range suitable for a broad range of Intermediate Level Waste (ILW) and, in principle, Low Level Waste (LLW)
• To produce strong, durable containers that would meet a broad spectrum of potential end user requirements whilst adhering to the principal requirements set by national and international regulators
• Solution must be low cost but offer high integrity

Planning and implementation

This concept UHPC Container range was designed to form IP-2 transport packages but sized to fit within a Standard Waste Transport Container (SWTC-150) as a Type B transport package when outside the limits for IP-2. 

Three different densities of the UHPC were developed, a normal density (ND) UHPC, a high density (HD) UHPC and a maximum density (MD) UHPC. Wall thicknesses for the UHPC Containers are in a range of 100mm and 200mm. 

The initial phase was successful. It met all the objectives which are summarised as “meeting the UHPC target values for material properties”. These include flexural strength and demonstrating these mixes would meet the manufacturing requirements for an ILW container which was proven by the casting of a container corner. The corner mould design, the corner mould and a cast section are shown in the figure below.

Advancements continued on the benefits of fibres in concrete and with the development of a concept design based on data obtained from waste consigners. This resulted in a concept UHPC Container range comprising three variants:

• A Solid Waste (Thin) UHPC Decommissioning Concrete Container (DCC) with 100mm wall thickness
• A Solid Waste (Thick) UHPC Decommissioning Concrete Container (DCC) with 200mm wall thickness
• A Wet Waste UHPC Decommissioning Concrete Container (DCC) with a minimum wall thickness of 100mm
  
  

The two Solid Waste UHPC Containers have identical external features and dimensions, only the internal cavity is different. The Wet Waste UHPC Container has the same external dimensions but is distinguished by an additional port in the lid and, again, has a different cavity configuration. The wet waste variant can also be fitted with a metal liner.

Results

In June 2019, the UK Ministry of Defence (MOD) Submarine Decommissioning Programme (SDP) became interested in using certain variants of the UHPC Container range as part of its disposal of ILW from submarine Reactor Pressure Vessels (RPVs). MOD SDP subsequently sponsored the production of an Expert View Submission. 

This report was prepared to describe the UHPC container range in sufficient detail to allow an Expert View Assessment by Radioactive Waste Management Limited (RWM). It facilitated a container-only assessment by RWM to determine whether containers from this new range could be accepted as compliant packages in keeping with its Geological Disposal System Change Management Procedure.

The level of information provided complied with RWM WPS/908/05 ‘Generic Guidance on the preparation of submissions for the disposability assessment of packaging proposals’ (July 2016), and specifically the arrangements referenced in Section 4.3 ‘Submission for a container-only disposability assessment’. It was therefore required that RWM considered the full information provided for the UHPC container range in its Expert View Assessment. 

The report also described the proposed use by MOD SDP of certain features/variants of the UHPC Container range and included details of the waste and dose rates. This information was included so that RWM could consider the MOD SDP’s specific proposal as part of its Expert View Assessment. 

The Expert View Submission contained information at a level normally expected for a concept Letter of Compliance (cLoC) submission. 

The next stage in the programme of work was to secure a contract from a waste consigner to supply a number of containers for on-site handling and assessment.  This was achieved in early 2021 with a contract to prototype the thick-walled decommissioning concrete container (DCC) variant and supply a number of units for on-site trials to an overseas customer. This work was completed in March 2023.

The UHPC Container Range is a low cost and flexible package that provides extreme flexibility and operational scope for waste consigners, including the ability not to foreclose future waste minimisation technologies and to utilise a SWTC to allow waste to meet Type B package requirements.