Operational wet storage

Research reactor RECH-2 is in the condition of permanent shutdown, and during its short operation period it did not generate any spent fuel. Nevertheless, the reactor pool has four operational storage racks with the capacity to store 10 fuel assemblies on each of them. Besides, the facility has an operational wet storage pool, separate from the reactor pool, with a capacity to store 256 spent fuel assemblies. Figure 11 shows details of the spent fuel storage pool of RECH-2. 

According to the present spent fuel inventory, and due to the high water quality in both reactors, the Chilean spent fuel assemblies can be maintained in operational wet storage for many years. 

Current planning considers that the operational wet storage will be followed by interim wet storage in a 16 m deep pool at LAPEP at the Centro Atomico Ezeiza, currently under construction. As regards the spent fuel currently stored at the facility with underground tubes, they will be sent to the storage pool at LAPEP. 

For the reasons mentioned above, the need for maintenance of operational wet storage as the first phase of any spent fuel management strategy is easily understood, and the main issues that should be taken into account in this phase of the spent fuel storage programme are as... 

Materials compatibility shall be taken into account because different materials will be present in the operational wet storage pool, depending on the construction materials used. In particular, contact between cladding and any dissimilar metal, such as stainless steel racks or pool liners, should be avoided. Furthermore, many additional materials, which can play an important role in initiating localized corrosion, could be introduced into the pool throughout the reactor lifetime due to the experimental activities and/or maintenance or construction activity in the vicinity of the pool. 

In 1980 the construction started for an underground interim storage for all SNF from the Swedish NPPs. It was taken into operation in 1985. It is a wet storage and is located close to the Oskarshamn NPP. 

While wet storage has operational advantages, it imposes extra loads on the con-finitig vessel. The mass is heavier because of the interstitial brine, and the fluidity of the contents adds a horizontal thrust on the walls. Also, when the vessel is used to accumulate... 

Plant design must also cater to the shutdown of one line of cells. If the diaphragm cells are shut down, the mercury cells can operate on stockpiled evaporator salt or purchased salt. If neither is available, the mercury cells will be forced to shut down. In the case of a mercury-cell shutdown while evaporator salt is still being produced, the salt can be stockpiled in a resatmator (see Section 1.22.2 for a discussion on wet storage of salt) or used to produce new brine. The latter approach probably involves curtailment of production from the diaphragm cells. 

The factors promoting corrosion of aluminium alloys are complex and interrelated. They often operate synergistically, making prediction of corrosion difficult. In wet storage of aluminium clad spent fuel, there are a number of corrosion mechanisms involved. The most important mechanisms as related to spent nuclear fuel are briefly discussed here. Other details and definitions related to aluminium corrosion can be found in the normative publications and ISO standards provided therein. 

Research reactors in Latin America have several common features. The first one is that with the exception of some critical facilities, all of them are water cooled, either Material Testing Reactor (MTR) or Training Research Isotope production General Atomic (TRIGA) reactor types, and, with the exception of the critical facilities and very low power reactors, wet storage is the form used for operational storage of spent fuel. 

It is an alternative that, once it is selected, can easily be implemented within the reactor building. It requires less modification than the wet storage option and, if properly planned, can be implemented while maintaining the reactor in operation, without having to stop the production of radioisotopes, which could generate problems in fulfilling commercial contracts. 

For the aluminium based RRSF, currently in operational and interim wet storage, interim dry storage of the processed spent fuel is being considered. 

Currently, aluminium based spent fuels from research reactors are in operational and interim wet storage. However, for an eventual extended storage as well as for disposal, there are some concerns about the suitability of the aluminium as a matrix resistant to water corrosion. Therefore, the preferred alternatives are extended storage in dry conditions and disposal of the derivatives from spent fuel processing instead of its direct disposal. 

Due to the low nominal power and short operation cycles, the research reactors RA-1 (40 kW) at Centro Atomico Constituyentes in Buenos Aires and RA-6 (500 kW) at Centro Atomico Bariloche in San Carlos de Bariloche do not generate spent fuel. Nevertheless, both installations have a facility to store all the fuel of the reactor core. In RA-1 the irradiated fuel is dry stored in 24 underground concrete tubes located inside the reactor building, and in RA-6 a separate decay pool, physically independent of the reactor pool but located inside the reactor building, is used for wet storage of the fuel assemblies. Figure 2 shows the decay pool of RA-6. 

There are several features of pool management which contribute to the safe operation of wet storage facilities. These include operations that maintain design parameters and minimize corrosion for pool structures, systems and components, and promote radiation protection, such as shown in Table I ... 

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