Characterisation trial19 December 2017
Safe and cost-effective management of nuclear waste is more important than ever. Suzanne Glorie explains how new technologies can help.
Despite stringent climate goals, the closure of nuclear power plants, either planned or premature, is an important subject on some political agendas. All serious long-term climate scenarios project a firm increase in nuclear capacity, rather than a decrease.
Of all the 150 nuclear power plants in Europe, currently, there is no more than a handful that have been completely dismantled. This means that in the coming years, in Europe alone, there will be a high demand for decommissioning capacity and expertise of all sorts. Safe, reliable, and cost-effective decommissioning can furthermore contribute to enhancing the image of nuclear energy among the general public.
Spent nuclear fuel accounts for most of the legacy radioactive waste from the nuclear industry. Whilst this fuel legacy is well managed, there is still a world to win in managing a multitude of intermediate and low-level radioactive waste inventories.
It is in this area that NRG wants to be part of the solution, for example in decommissioning nuclear power plants and characterising radioactive legacies. Safe and reliable storage, and reducing radioactive waste volumes, are important goals. The decommissioning of the Grafenrheinfeld nuclear power plant, which NRG has taken part in alongside German Partner Höfer & Bechtel (H&B), is a good example of this. The innovative technique of cutting the control rods plays an important and cost-effective role.
According to the European Commission’s estimate, €250 billion must be available for decommissioning of nuclear power plants in Europe up to 2050. Within that, about €130 billion will be spent on the processing and interim and final storage of various kinds of nuclear waste. With careful characterisation, NRG believes that considerable savings can be achieved in the field of processing and storage. Among other things, this includes cutting and advanced characterisation of control rods.
Advanced characterisation saves cost
Responsible processing, characterisation, comprehensive registration and storage of radioactive waste are key to the successful decommissioning of nuclear plants. Different standards are used to classify radioactive waste in various countries. An international harmonisation of laws and regulations would contribute to efficiency and safety. NRG has built a wealth of experience in characterising and sorting high to low radioactive legacies. Advice on specialised transport is also part of this service.
Characterisation and sorting is performed based on nuclide identification with a segmented Vinish (Visual Inspection Nuclide Identification System High Active Waste) gamma scanner for radioactive waste containers. The scanner, developed by NRG, displays the activity of a number of nuclides very accurately. The big advantage is that the container of radioactive material remains closed.
NRG has also developed the Hirarchi gamma scanner, which generates a ‘radiation map’ of legacies, consisting of complex and mixed-waste inventories, on the basis of which the correct sorting and separation of the waste categories can be carried out. In this way, ‘hot’, unsorted and mixed legacies can be transformed into largely ‘cold’ legacies. The small amount of remaining ‘hot’ volume is safely separated and stored. Result: lower radioactive volume and lower storage costs.
NRG, Höfer & Bechtel-Decommisioning services took part in the complete decommissioning of the Grafenrheinfeld nuclear power plant in Bavaria, Germany as a contractor for Preussen Elektra. Grafenrheinfeld is a 1275MW pressurised water reactor, which operated from December 1981 to June 2015. The decommissioning is taking place under supervision of Preussen Elektra GmbH, TUV Sud and the Bavarian government.
The specific assignment, for decommissioning of more than a hundred control rods, is interesting in several respects. The approach is innovative; among other things, a bridge was designed that spans the reactor basin. From that bridge, the control rods are cut into pieces using remote equipment developed especially for the project. The cutting occurs from two workstations on the bridge, which enables parallel working.
Cutting the control rods minimises the amount of sawdust or other contamination in the reactor basin – a major difference compared with sawing or other techniques used elsewhere.
The control rods are then safely stored in Mosaik© containers. This gives the operators flexibility to ensure that the radioactive control rods are optimally distributed, reducing the number of containers and therefore the radioactive waste volume. It also immediately provides financial savings.
Efficiency is achieved by radiological sampling of the control rods. Accurate sampling and radiochemical characterisation is a prerequisite for keeping the containers safely and sustainably stored in a geological repository. The rods have a cladding of stainless steel, while the core consists of a silver/cadmium/indium alloy. With a specially developed sampling tool, the separation of cladding and core is performed on site. The second sample analysis, the radiochemical characterisation, takes place in the laboratories of NRG in Petten, in the Netherlands.
The fact that all aspects of decommissioning – cutting, container filling and radiochemical analysis – are carried out together makes the process very efficient. The correct characterisation also reduces radioactive waste storage costs.