Retention of radionuclides

The retention of radionuclides within the containment was little accounted for by the RSS, but ranges from little to very substantial because of agglomeration and deposition. This leads to a large over prediction of the iodine risk, but substantial agreement with RSS for some other isotopes. 

Hutchins DA, Stupakoff I, Fisher NS. 1996a. Temperature effects on accumulation and retention of radionuclides in the sea star, Asterias forbesi Implications for contaminated northern waters. Mar Biol 125 701-706. 

The absorption, bioavailability, and retention of radionuclides in mammals are modified by ... 

Surface complex models (SCMs) are now finding widespread application in the fields of pollutant retention behaviour (Zachara etal., 1989,1992), the soil chemistry of plant nutrient retention (Goldberg and Sposito, 1984 Goldberg and Glaubig, 1986 Goldberg and Traina, 1987) and the retention of radionuclides by sediments and transport of pollutants by colloids (Davis and Kent, 1990 Dzombakand Morel, 1990 Goldberg, 1992). 

Mathematical models are used to describe the various processes involved in the internal deposition and retention of radionuclides and the associated radiation doses received by various organs and tissues in the body. In models of this type, the body is viewed as a series of compartments into which the radioactive materials enter and exit at various rates, ultimately being removed from the system by some form of excretion, by radioactive decay, or both. 

The laboratory experiments showed the influence of the total concentration of ballast non-active salts on decontamination factors. As the concentrations of total solute in permeate from the first and third stages were very low a decrease of retention of radionuclides was observed. To improve the efficiency of radioisotopes removal additional salt injection took place before the second stage. 

Discrepancies between nonsorptive dye and radionuclide movement were observed. In some experiments where 90-100% of Rhodamine B passed through the flume after one day from release, only 5-25% of 65Zn, 58Co, 137Cs, and 85Sr added at the inlet was detected in the exit flume water. The retention of radionuclides was primarily owing to surface concentration by sediments and biomass (1, 2, 3, 4, 5, 6, 7, 8). 

The manufacturing and handling of radiopharmaceuticals is potentially hazardous. The types of radiation emitted and the half-lives of the radioactive isotopes are parameters contributing to the level of risk. Particular attention must be paid to the prevention of cross-contamination, to the retention of radionuclide contaminants, and to waste disposal. Special consideration may be necessary with reference to the small batch sizes made frequently for many radiopharmaceuticals. Due to their short half-life some radiopharmaceuticals are released before completion of certain Quality Control tests. In this case, the continuous assessment of the effectiveness of the Quality Assurance system becomes very important. 

The absorption, bioavailability, and retention of radionuclides in mammals are modified by the age, sex, species, and diet of the organism season of collection the chemical form of the radionuclide in tissue and blood residence time in the digestive tract preferential accumulation by selected organs and tissues and many other variables. 

Second, the philosophy requires control of releases by the retention of radionuclides within the coated fuel particle rather than reliance on secondary barriers (such as the primary coolant boundary or Reactor Building). The judgement made here is that the proof of containment is dramatically simplified if arguments can center on issues associated with fuel particle coating integrity alone. 

Step 1 specifies that, for each DBE, classify as "safety-related" those design selections chosen for compliance with the lOCFRlOO region dose criteria. More specifically, for each DBE, various functions can be identified which must be performed if the consequences of the event are to remain within those allowed by the dose criteria. For the Standard HHTGR, these functions, as discussed previously in Section 3.2.2, are the retention of radionuclides in the fuel and, to maintain the fuel within its design conditions to assure such retention, the removal of core heat, control of the core heat generation rate, and prevention of chemical attack on the fuel. Step 1 requires that a set of SSCs which are capable of performing these functions for all DBEs for which they are required be classified as "safety-related."... 

In order to control radionuclide release from the core, the RS must function to control radionuclide transport from the core which, in turn, requires the retention of radionuclides in the coated fuel particles while limiting fuel temperatures to ensure that the required graphite attenuation of radionuclides outside of the coated fuel particle is accomplished. 

Studies of the transfer, uptake, and retention of radionuclides in foodstuffs have been mainly concerned with Cs, °Sr, H, C, and because these nuclides have relatively long half-lives and represent biologically important elements. 

Preparation of filters in slabs or in powders suitable to be placed on air channels in fluidized beds or else as selective adsorbants on process lines. In recent years we made interesting approaches at COGEM A in this field using freeze-dried silica and alumina for the retention of radionuclides, acid droplets, and contaminants in the ventilation ducts of nuclear plants. Besides their great efficiency and low pressure drop the most interesting feature of these freeze-dried filters is that they can withstand extreme pH conditions and high temperatures. 

Without either spray droplets or flooded pathways, substantial fractions of radionuclides released from the degrading reactor fuel can be retained within the reactor coolant system. Results of some example calculation for radionuclide retention in the reactor coolant systems for various types of accidents are shown in Table III-l. The natural retention of radionuclide vapors oeeurs because the vapors either condense on surfaces or react with these surfaces. Depending on the surface temperature and the duration of its exposure to high temperature steam, the surface material is either ehromium oxide (Cr203) or iron oxide (Fe304 y). Both of these materials are expected to be reactive toward cesium-bearing vapours and strontium or barium vapors. Stainless steel lead screws above the core at Three Mile Island were found to have captured cesium by reaction with silica impurities in the steel. Metallic nickel inclusions in the oxide films on surfaces within the reactor coolant system are reactive toward tellurium whether it is in the metallic state or present as TeO or SnTe. 

Table III-1. Retention of Radionuclides in the reactor coolant system by natural deposition processes in selected accidents [V-2]... 

This report provides a comprehensive survey of experimental data and models available to predict the retention of radionuclides within the reactor coolant system during severe accidents. 

Tightness of the containment over a longer period of time is an important factor in the retention of radionuclides in support of natural deposition processes and engineered safety features. To this end, facilities for controlled depressurization of the containment have been installed in many plants (see Section 7.3.4.4.). 

The short lived wastes are essentially those which contain predominantly radionuclides having a half-life of not more than about 30 years (although limited quantities of longer-lived nuclides may be present ). The approach for the management of these wastes essentially involves retention of radionuclides for sufficient period to allow decay to itmocuous levels. Depending upon the volumes and the half-lives of the radionuclides, the retention may be in the as generated form or after volume reduction and conditioning. 

High level radioactive wastes to be emplaced in a repository shall be in a solid form with chemical and physical properties favouring the retention of radionuclides and appropriate to the disposal system. 

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