As written in previous articles, the United States Nuclear Regulatory Commission (USNRC) has strict rules governing nuclear power plant decommissioning. The USNRC states clearly on its decommissioning backgrounder that “before a nuclear power plant begins operations, the licensee must establish or obtain a financial mechanism – such as a trust fund or a guarantee from its parent company – to ensure there will be sufficient money to pay for the ultimate decommissioning of the facility….Decommissioning must be completed within 60 years of the plant ceasing operations. A time beyond that would be considered only when necessary to protect public health and safety in accordance with NRC regulations.”
There are three different ways that decommissioning can be accomplished: DECON, SAFSTOR, and ENTOM.
- DECON (Decontamination): Dismantling or removing all radioactive materials above acceptable limits. This step reduces the radiation level in the plant and minimizes the potential exposure to workers during subsequent decommissioning operations.
- SAFSTOR (Safe storage): Leaving the reactor intact but in a safe state. Highly radioactive components such as spent fuel are removed and placed in on-site storage while the surveillance and monitoring continue. This low initial cost process allows time for decay of radioactivity and the plant is dismantled in future years following steps like the DECON ones.
- ENTOM (Entombment): Permanently enclosing the facility on site into a condition that will allow the remaining radioactive material to be on-site without ever removing it.
According to the USNRC, DECON and SAFSTOCK are often used together, while ENTOM is a rarely used option. So what steps are involved in these decommissioning actions? The requirements for power reactor decommissioning activities may be divided into three phases: transition, major decommissioning and storage; and license termination activities. You can read about Phases of Decommissioning on the USNRC website.
Generally, there are eleven main activities involved in these phases, which include:
- Pre-decommissioning actions
- Facility shutdown activities
- Procurement of general equipment and material*
- Dismantling activities*
- Waste processing, storage, and disposal*
- Site security, surveillance, and maintenance
- Site restoration, cleanup, and landscaping*
- Project management, engineering, and site support
- Research and development
- Fuel and nuclear material*
Those tasks that contain an asterisk* mean that radiation monitoring and measurement is needed. The radiological properties of the waste (e.g. activity and composition of radionuclides, dose rates from the waste) are measured using radiation monitoring instruments. These radiation monitoring instruments include personnel contamination monitors and personnel dosimeters as well as general-purpose instruments.
Their use is highly critical since the decommissioning of facilities must be conducted in a safe and environmentally acceptable manner in accordance with regulatory practices.
The radiological properties of the waste (e.g. activity and composition of radionuclides, dose rates from the waste) are measured using when radiation monitoring and measurement instruments. Here are some of the tasks from the list above where instruments are used.
- Upgrading general radiological protection systems and health physics equipment every 10-15 years, depending on instrument type, wear, and age, is generally advised.
- Periodic radiation and environmental surveys are needed, but the frequency and scope of inspections currently are not regulated in most countries.
- It is fair to skip the R&D activity since all technologies and equipment that are necessary to decommissioning an NPP are currently available and could be purchased on the market.
Read about these technologies and more by downloading the ebook:
A Practical Guide to Radiation Safety During Nuclear Power Plant Decommissioning
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