This document discusses the requirements to manage sites entering the Care and Maintenance stage of decommissioning (sometimes called deferred dismantling in IAEA documents and SAFESTOR in the USA) where mos
t of the quick wins in terms of cleaning out components have been achieved and the sites waits for several decades for radiological decay to reduce dose rates to more manageable levels before final dismantling of the reactor core and buildings in completed. It is estimated that about 50% of the nuclear facilities that have been shut down are in safe store and that learning from these sites is increasing. This document was written to allow the benefits of that experience to be shared. It was drafted and reviewed by consultants managed by the IAEA
The document discusses the length of time a site may wait before dismantling based on the half-lives of the isotopes giving most of the dose on the one hand and the deterioration of the structures and containment on the other. It concludes that 15 – 20 years is often a sensible duration provided that there is a suitable waste repository for the final waste arisings.
Section 2 of the document talks about the facilities that are required in safestore, the options to repurpose existing buildings during safestore and the removal of unnecessary buildings. It provides reports of experiences and photographs. Several of the examples are based on the experience of Magnox, which as an ex-employee, pleases me.
Section 3 is about the preparations for safestore. This includes the recording of the hazard inventory and a hazard management plan (remove it or make it safe for the duration of safe store), clean up and deplanting, decontamination, drainage and protection.
In a section on firefighting it states that the risk of fire can be reduced by removing as much of the combustible material and as many ignition sources as practical in the preparations for Care and Maintenance phase. However, it states that a firefighting plan is still required and should be developed and agreed with the local fire fighters and the regulators.
Where external firefighters are the first responders familiarisation training, fire plans, exercising and testing are recommended. For unmanned sites there is a need for automatic alarms that reach the firefighters and the site’s management and access arrangements for the local firefighters. These firefighters must have the appropriate security training and classification to enter the site unescorted.
Security measures are required to keep people off the site to avoid vandalism, damage and theft and also to reduce damage by vermin.
The continuing need for environmental monitoring of radionuclides is discussed in Section 6.6. This is likely to be a regulatory requirement but at a lower level that when the site was operating. It is suggested that it would be sensible to taper off monitoring after a period of about five years by which time a workable baseline understanding of the site would have been achieved. There is a warning that new release pathways may be revealed in time.
The interesting bit of this document for me is the section on emergency planning.
The document (Section 7.5) states that “emergency planning and preparedness (EPP) is necessary for a safe enclosure as it contains large amounts of radioactive materials due to structures, systems or components activation and contamination in various parts of the facility”.
As the risks of the facility reduce the operator should review and rewrite emergency plans to ensure that they remain fit for purpose. Off-site measuring equipment can be reduced but is still required and must be maintained. I assume this is referring to off-site radiation detection. In my experience this is sensibly reduced to perimeter monitoring equipment because of the small releases feasible from such structures do not give a sufficient signal very far downwind.
The document admits that it might be difficult to get the local authorities to agree on the need to maintain and test emergency plans for a site in safestore and suggest that the need to be able to deal with protestors and intruders might be one selling point.
There are sections on the management and regulation of sites, the costing of decommissioning activities (including an introduction to a system called the International Structure for Decommissioning Costing).
Section 12 and several of the annexes of the report give outlines and experiences of decommissioning projects around the world including Magnox’s lead and learn process which has been used to ensure that learning is shared between the different sites and that the process becomes more effective and cheaper with each subsequent site.
This publication does not represent in-depth guidance on care and maintenance of decommissioning nuclear sites. It provides a high level review of the aims of care and maintenance and some of the key considerations. Several examples are discussed. As such it makes interesting reading and may be useful as an introduction to the field for those in operating facilities that are coming to the end of their design life.