Nuclear Decommissioning: The Three Approaches


This is the first in a Forum on Energy series on nuclear decommissioning. The series will cover the history of decommissioning and assess the current state of decontamination in key countries.

iStock_000017116815SmallNo energy plant, whether it is coal, gas or nuclear, is designed to last forever. They will all shutter one day. The first nuclear energy plants, conceived and built in the nascent years of the energy source, were designed to run for about 30 years. Modern reactors have lifespans closer to 40-60 years.

When they do come to the end of their service, it’s not as simple as flipping an “off” switch. Under the strict observance and guidance of regulators, nuclear licensees must demolish their facilities while also removing and safely storing the radioactive materials that are the byproduct of electricity generation. Decommissioning must be completed within 60 years of a plants closing in the United States. The  end result is the release of the property and the termination of the Nuclear Regulatory Commission (NRC) license.

Licensees have three options (or, as a fourth option, can mix and match the three into an approach that suits them best):

DECON (Decontamination)
This is the fastest approach. It allows plants to terminate their licenses in as little as five years, and can begin mere months after a plants closes down. Decontamination or removal of nuclear fuel rods and equipment (99 percent of the facility’s radioactivity) quickly reduces the radiation levels, making it safe for workers to complete the rest of the decommissioning process.

Advantages

  • Knowledgeable personnel from operation are available
  • Operating history is well known
  • Time scale and costs are well defined
  • Existing infrastructure can be used
  • No further consideration of duration of life are needed
  • Current laws and guidelines

Disadvantages

  • Higher collective dose
  • Greater complexity if shieldings or remote controlled systems are used
  • Final repository is needed
  • Intermediate storage of radioactive waste is needed if no final repository exists

SAFSTOR (Safe Storage)
This approach allows the passage of time itself to turn the radioactive elements into stable elements. The shuttered plant is kept untouched and in protective storage for as many as 60 years. Fuel is drained from the reactor vessels and kept in on-site fuel pools, while the NRC provides oversight, maintenance and security. Once radioactivity has decayed to the appropriate levels, the facility is dismantled in the same way as with the DECON approach. In fact, licensees can halt the SAFSTOR approach at almost any point and shift to the DECON approach.

Advantages

  • Activity is reduced (for Cobalt-60, or C-60, by a factor of 64 after 30 years), “decay storage”
  • Lower collective dose
  • A greater part of the material can be reused (clearance)

Disadvantages

  • Loss of Co-60 as a key nuclide
  • Loss of knowledge and experience
  • Preliminary work must be done under same dose rates like immediate decommissioning – no benefit
  • Control must be established for 30 years
  • Safety relevant parts must be checked for 30 years additional lifetime
  • Infrastructure like cranes and ventilation has to be assessed for 30 years

ENTOMB (Entombment)
Entombment is not a true alternative to DECON or SAFSTOR. The International Atomic Energy Agency recommends it only under exceptional circumstances, such as in the wake of a severe accident. The area of radioactivity is reduced as much as possible and then encased (such as with concrete) for an indefinite period. No NRC-licensed facility has ever requested entombment.

Advantages

  • Fast
  • Less expensive than other methods
  • Only little material goes to final repository (no big storage capacity needed)

Disadvantages

  • Preliminary work must be done under same dose rates like immediate decommissioning, but less work needed
  • Material cannot be reused and is wasted
  • Site cannot be reused
  • Unwanted legacy for future generations
  • Local final repositories are created
  • Public opinion