Water loading uncertainty

Shindo, J, Bregt, A. K., Takamata, T. (1995). Evaluation of Estimation Methods and Base Data Uncertainties for Critical Loads of Acid Deposition in Japan. Water, Air, and Soil Pollution, 85, 2571-2576. 

New pyrolysis vessels require conditioning before analysis. Standards should be loaded, pyrolysed and the resulting gas released for at least two runs before CO2 is collected for analysis. Repeated runs with water and cellulose standards should then be undertaken until consistent reproducibility is obtained and until accurate calibration of results can be developed. After extended periods of non-use, standards should be run in each vessel to re-establish the catalytic activity of the nickel. A water or cellulose standard should be routinely run with each sample batch, rotating the vessel in which the standard is loaded to monitor vessel performance. Analytical uncertainties of water, lake sediment and terrestrial cellulose are generally 0.5 to 1.0%o. 

Prediction. A roi rule at thunib by Pair aL (14) suggests that for random packing, the loading point will occur at a paddpg pressure dn above 0.5 in of water per foot of bed. A owrdation by KHet and Sdmltes (79) is presented bdow. Ctmsid ing the uncertainty in definite the load h point, the need for an Elaborate correlation msy be questioned. 

Extreme river discharges can be forecasted days ahead. An extreme weather or water level forecast can lead to the decision to evacuate people from a flood prone region to reduce potential loss of life. Even if such forecasts were 100% reliable, it would still be difficult to forecast the occurrence of floods in regions protected by flood defenses, such as the Netherlands. This is because flood probabilities depend not only on the uncertainty related to hydraulic conditions, bnt also on the uncertainty related to the load bearing capacity of flood defenses ... 

A Thorium-Uranium Exponential Experltnenti C. If. Skeen and W. W. Broum(AI). Because of uncertainties in the knowledge of t nuclear properties of thorium fuel and lattices containing this fuel, an experimental study was made of a thorium based fuel that is to be loaded into the Sodium Reactor Experiment (8RB) in the near future. An exponential experiment was performed with a square-celled lattice of 7-rod elements (l-in. diameter rods) spaced 9.5 in. apart in praphite. The fuel Is a Th-U-23S alloy containing 7.6% uranium by weight which is 93.13 atomic per cent U-235. The feel elements were 5 ft. long. The subcrltical lattice was placed On thd thermal column of a water boiler reactor which served as the source of neutrons for the assembly. 

A small amount of core melt and lower decay heat release determine the relatively low heat fluxes from the melt to the vessel bottom in this, the problem of keeping the melt inside the reactor vessel could be solved by external vessel cooling, i.e., by filling the reactor caisson with water in emergencies. Keeping the melted core inside the vessel reduces the consequences of accidents and eliminates some uncertainties associated with maximum loads on the protective shell. 

Implementation of a supplementary surveillance programme is being considered at some plants to reduce uncertainties due to deficiencies found. In order to prevent embrittlement, flux reduction measures (low leakage loading pattern, dummy shielding assemblies) have been introduced. To reduce PTS loads due to cold water injection, heating of ECCS water has been recommended. Annealing was conducted at the Loviisa plant in 1996. 

Partial safety factors are also applied on loads (with distinction of permanent loads and mobile loads) in order to cover the uncertainties of these loads (actions). Permanent loads also include the soil weight itself. In EC7, sometimes a model factor is introduced as well. This needs to be explicitly specified in the National Annexes to EC7 applicable for that country. Also dimensional elements (e.g. depth of excavation) and water levels may have to be increased or decreased to cover possible imcertainties. 

Critical load estimates are subject to uncertainties that arise from their method of calculation and from the accuracy of the input data. For example, empirical determinations have the virtue of simplicity and of emphasizing dose-response relationships but ignoring time related aspects (fynamic models take account of time in the response in making some of the calculations. In both methods different criteria may be adopted the critical value for lake water in relation to adverse threshold effects on biota A irles between pH 5.3 and 6.0. The outcome of such uncertainties can be seen in comparisons of critical loads arrived at for catchments using different methods of estimation fTable 1). 

The large containment water inventory would be expected to prevent DCH, so the possibility of DCH was ruled out for this evaluation. However, the conditions are conducive to ex-vessel FCIs. Evaluations performed for NUREG-1150 indicated that when only a small amount of water is present on the drywell floor (a few feet), the FCI load would not be transmitted to the containment wall. However, the evaluations Indicated that with a large water inventory present, the load could be transmitted to the containment wall and possibly fall it. The largest uncertainty for ex-vessel FCIs is the amount of debris that would actually be released at vessel breach. This uncertainty dominates the probability of containment failure from an ex-vessel FCI. We used the same probability for occurrence of an ex-vessel FCI as used for In-vessel FCIs, and considered containment failure to occur for cases with an ex-vessel FCI. 

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