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MA-VL and HA waste from irradiated fuel in nuclear power plants

One of the major challenges facingnuclear energy is the management and storage of high-level, long-lived nuclear waste. They remain dangerously radioactive for hundreds of thousands of years (generally 200,000 years) and require special treatment, regulated by the states that guarantee public safety. In France, nuclear waste is managed by ANDRA . It is classified according to two main characteristics: its hazardousness and its lifespan. These characteristics are broken down into six waste categories. In this article, we focus on the following two categories:

  • Long-lived intermediate-level waste (ILW)
  • high-level waste

Most of the LV-AM comes from nuclear fuel support structures, e.g. zircaloy fuel assembly cladding. The waste is compacted to reduce its volume, then packaged in metal or concrete containers. They represent 3% by volume of all nuclear waste produced in France.

HA comes from spent fuel processing. These are non-reusable residues such as actinides or fission products. They are charred and then vitrified. The glass-waste mixture (3% waste, 97% glass, by mass) is packaged in stainless steel packages, which are sometimes placed in a second steel container. This HA waste represents 0.2% by volume of all nuclear waste produced in France. They concentrate 96% of radioactivity.

These two categories of waste(MA-VL and HA) represent a small portion of the total mass or volume of nuclear waste. However, they have periods of several hundred thousand years, and are highly toxic. They are all derived from spent fuel. One solution under study is deep reversible storage.

MA-VL and HA waste management

The management of this waste is divided into two phases:
  1. Storage: Temporary, based on the principle of continuous thermal evacuation to cool irradiated fuel.
  2. Storage: This is definitive and is based on the principle of decreasing levels of radioactivity in irradiated fuel.
In this article, we provide an overview of these two management phases, their operating principles and their limits from a sustainable development perspective.

Temporary storage of radioactive waste

We distinguish two categories of temporary storage systems: pool and dry.
Pool storage
  • PRINCIPLE
Once discharged from the reactor, irradiated fuel elements are stored for at least five years in water pools located in the same building housing the nuclear reactor. Each of these fuel elements is stored in cells arranged in a grid at the bottom of the pools.
  • STORAGE POOL
The pools are made of reinforced concrete, with walls lined with welded steel. They are designed to prevent leaks and withstand external events. The main function of pool water is to cool irradiated nuclear fuel in the early stages of radioactive decay. This process enables the residual heat generated by the fuel to be continuously removed.
Areva - Orano storage pool
  • THERMAL INERTIA AND RADIATION SHIELDING
Thanks to the high heat transfer to the water and its high heat capacity, this system offers high thermal inertia and keeps the fuel cladding (zircaloy alloy) well below its melting point. This keeps the first containment barrier against radioactive dispersion intact. Pool water also provides good radiological shielding against the radiation emitted by irradiated fuel.

Dry storage (not used in France)
  • PRINCIPLE
Temporary storage is a medium- to long-term system designed to house spent fuel and high-level waste in the same country for a given period (up to 100 years).
  • STORAGE STRUCTURE
Waste is generally stored in metal or concrete containers, or in vaults with special heat removal systems. This is only possible after a cooling period in the pools of nuclear power plants (see above). Temporary storage facilities are located on the surface or at relatively shallow depths. They may be located on or off the plant site. In the latter case, irradiated fuel from one or more EPRs may be stored together.
  • RADIATION SHIELDING
These facilities feature a concrete structure offering radiation shielding and anti-intrusion security.
  • LIMIT
Under no circumstances can this solution be considered definitive, nor can it be extended indefinitely.

Storage
  • GEOLOGICAL REPOSITORIES
This solution involves isolating the waste by interposing a series of layers in storage facilities at depths of around 500 meters. The waste is first introduced into extremely thick metal containers, resistant to corrosion and other forms of degradation for many years. They are then evacuated in tunnels dug into stable geological formations, surrounded by low-permeability soil with a high retention capacity.
MA-VL HA storage - Cigéo scheme

The containment and isolation of waste is ensured by various elements:

  1. the container into which the waste is introduced before being placed in the final storage cell.
  2. in some cases, the overpack: an additional sealed package that transforms primary vitrified waste packages into storage or disposal packages.
  3. the natural barrier provided by the receiving rock.
  • PRINCIPLE OF FINAL STORAGE

The defining characteristic of final disposal, as opposed to interim storage, is that the objective of waste recovery is not systematic. In other words, the waste disposal facility is closed and sealed, without the need for an additional above-ground operating facility.

  • WASTE RECOVERY IN QUESTION

In any case, it is always possible to keep the storage facility and its environment under surveillance for as long as deemed necessary. The plant can be designed so that stored waste can be recovered in the future. ANDRA envisages reversibility of the deep disposal facility for a period of 100 years.

  • LIMITS

Deep geological disposal requires safety demonstrations concerning :

  • The ageing of buried waste packages over several thousand years. The aim is to prove that the rock will retain radioactive species once corrosion has damaged the packaging.
  • Resistance to geological events such as earthquakes.
  • The memory of the landfill site. Remembering where waste is located is a key issue. This means transmitting information to many generations of individuals. It is therefore necessary to devise a means of communication that lasts beyond the language, and a communication medium that does not alter.

The different stages of radioactive waste disposal in video I The Cigéo project

INNOVATIVE PROCESSING SOLUTIONS FOR MA-VL AND HA

  • A LOW-CARBON FUTURE
At DAES, we are sensitive to the challenge of a carbon-free future. With this in mind, we are working with TRANSMUTEX to make the treatment of nuclear waste a priority and to remedy this ultimate limit of nuclear energy.

  • DAES EXPERTISE :
Thanks to our long-standing expertise in nuclear power, our teams are able to simulate the entire energy cycle, from production to restitution. We support you in the product and process design of your projects: pollution reduction/control, equipment, energy optimization, compliance with efficiency and regulatory requirements.
  • Structural analysis
  • Non-linear and contact modeling
  • Impact and explosion
  • Design optimization, noise and vibration, fatigue
  • Motion and system analysis
  • Stress and strain analysis
  • Thermal analysis and heat transfer
  • Acoustics
Contact us for more information or to schedule a technical meeting with our teams. #InSimulationWeTrust. Discover here our ANSYS APP developed for nuclear equipment dimensioning.

  • A RESPONSIBLE AND INNOVATIVE PARTNERSHIP
The Transmutex solution is a revolutionary nuclear technology based on transmutation. The latter can be performed by accelerator-driven nuclear systems. These coupled systems are known as ADSs (Accelerator Driven Systems). ADS produces fast neutron fluxes to induce actinide fission and transform long-lived nuclear species (a few hundred thousand years) into much shorter-lived species (a few hundred years). This process also generates carbon-free energy. Transmutation of actinides and fission products can be carried out flexibly and very efficiently in accelerator-driven systems.
  • TRANSMUTATION AND RADIOTOXICITY
Transmutation of irradiated fuel will reduce its radiotoxicity by a factor of 100, and shorten its storage life as nuclear waste by a factor of 1,000. Starting with a storage horizon of around 200,000 years, the TRANSMUTEX solution would reduce this to 200 years, a more than acceptable timeframe given existing, proven technologies.

  • WNE 2020 – For a Low Carbon Society

  • We’ll be taking part in the WNE 2020 trade show in the near future, to take part in the current and future challenges facing the nuclear industry, and to present a promising project alongside the Transmutex teams.

    To keep up to date with our news and other DAES events, follow our Blog and Linkedin Page.

    For more information about our solutions, please contact us.

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