Dry storage system

Just over 20% of the electricity generated in the United States is produced by nuclear power plants. In 1995, 32,200 metric tons of spent fuel, with a total activity of 30,200 MCi, was stored by the electric utilities at 70 sites (either in pools or in dry storage systems) (Ahearne 1997, Richardson 1997). By 2020, the projected inventory will be 77,100 metric tons of heavy metal (MTHM) with a total activity of 34,600 MCi. Although the volume of the spent fuel is only a few percent of the volume of HLW, over 95% of the total activity (defense-related plus commercially generated waste) is associated with the commercially generated spent nuclear fuel (Crowley 1997). At present in the United States, none of the spent fuel will be reprocessed all is destined for direct disposal in a geological repository at Yucca Mountain, Nevada (Hanks et al. 1999). 

BROOKS, P.,SINDELAR,R.L., Characterization of FRR SNF in basin and dry storage systems , Proc. 3rd Topical Mtg on DOE Spent Fuel and Fissile Materials Management, Charleston, SC, 1998, USDOE, Washington, DC (1998) 542-549. 

To ensure that these criteria are met, the total amount of decay heat stored in the system must be limited. Dry storage systems currently available allow as much as 45 kW of decay heat to be stored. The canister cavity is backfilled with helium gas to ensure an inert environment and to further facilitate heat transfer. 

The principal source of radiation in the dry storage system is gamma rays and neutrons. The gamma source is the result of decay of radioactive fission products, secondary photons from neutron capture, and activation of fuel assembly components during in-core irradiation. The neutron source originates from spontaneous fission, alpha-neutron reactions in the fuel, secondary neufrons from subcritical fissions, and gamma-neutron reactions. 

Criticality safety of a dry storage system is ensured by the following design parameters ... 

Additionally, criticality safety of fhe dry storage system includes the following conserva-five assumptions ... 

For dry storage systems, heat removal from the fuel occurs by conduction, radiation, and natural or, in some cases, forced air convection. For these facilities operational controls should consist of verifying that there are no impairments to air flow. If heat removal requires forced convection, additional operational controls and maintenance will be required on air moving systems. 

Figure 228 shows the examples of liquid and solid open sorption storage systems. In both cases the Desorption is activated by an hot air stream carrying the heat of desorption. For the solid a packed bed of adsorbent pellets and for the liquid solution a reactor are blown through, leaving the packed bed dry and the solution concentrated. 

Fixed systems may be fixed nozzles or hand hose line systems. They usually range in capacity from 68 to 1,360 kgs (150 to 3,000 lbs.). Most use a high pressure nitrogen cylinder bank to fluidize and expel the dry chemical from a master storage tank. Where immediate water supplies are unavailable, fixed dry chemical systems may be a suitable alternative. 

A number of observations help to understand the mechanism of hematite formation from ferrihydrite in aqueous systems i. e. under conditions essentially different from those for solid-state transformation by dry heating (see 14.2.6). Air-dry storage of ferrihydrite containing 100-150g H20/kg of water (found by weight loss) at room temperature for 20.4 years in closed vessels led to partial transformation to fairly well crystalline hematite with a little goethite (Schwertmann et al., 1999). In contrast, no hematite was formed from ferrihydrite if the content of adsorbed water was substantially reduced (Stanjek and Weidler, 1992 Weidler, 1997) as seen from the following examples ... 

In stationary storage systems, the hydroxide waste will be stored as a slurry with excess water. It will be held in closed containers with active mixing and will be pumped into tank trucks or railroad cars and transported to a regeneration plant where it will serve as the raw material for the production of the hydride slurry. For vehicular storage the hydroxide will be carried as a dry powder that will be mixed with water to form a slurry as it is removed from the vehicular. 

Fire protection is another critical safety concern. Automatic fire detectors are located throughout the plant. Sprinkler systems supplied from a large storage tank come on automatically in the event of a fire in the unloading and unpack areas. In other areas, dry chemical systems are deployed. Halon systems protect the control room and power supply room. 

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