Radioactivity source term

In assessing the source term, it is necessary to take into account the operational experience and specific design features of RBMKs such as on-line refuelling. Long operational experience shows that the reference (initial) activity of the radionuclide 1 in the coolant is normally well below the operational limit. It is obvious, however, that there is no direct relation between the number of leaking fuel rods and the operational limit for the radioactivity. On the basis of operational experience with RBMK reactors, it can be stated that  

Rare surges of activity in the coolant beyond the operational limit were caused by the appearance of individual rods with a direct fuel-coolant contact, rather than by a large increase in the number of leaking fuel rods. 

Not a single case has ever been observed throughout the operation time of any RBMK in which more than one rod at a time developed a leak with direct exposure of its fuel to the coolant (an event with I activity in excess of the operational limit). 

Any fuel assembly with a leaking rod is promptly detected by the system for fuel cladding integrity monitoring and is immediately removed from 

It has been repeatedly shown in previous RBMK safety analyses that none of the DBAs would lead to MPTRs. Should analysis of any BDBA encounter a sequence of events with the possible rupture of more than one fuel channel, the extent of the MPTR should be determined and the maximum capacity of the reactor cavity venting system analysed in order to assess the likely structural and mechanical consequences of this BDBA, including the reactor cavity integrity. 

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Assessment of the radioactivity source term should be made with regard to the operational limit for leaking fuel rods, plus one rod with direct exposure of fuel to the coolant. 

Potential radioactive source terms, and doses to the population from direct radiation fields and from airbome/aqueous pathways ... 

The results obtained prove that FP vapor deposition in the core region could significantly affect the radioactive source term. MELCOR predictions evidence that core baffles could melt and relocate quite early after core uncovery core atmosphere would, then, become into direct contact with the bypass atmosphere as a consequence, vapors and aerosols released from the core region could be retained on the inner wall of the core barrel. Thus, it was finally decided to consider this fact when modeling FP behavior and transport in the scenarios considered. 

FIRAC is a computer code designed to estimate radioactive and chemical source-terms as.sociaied with a fire and predict fire-induced flows and thermal and material transport within facilities, especially transport through a ventilation system. It includes a fire compartment module based on the FIRIN computer code, which calculates fuel mass loss rates and energy generation rates within the fire compartment. A second fire module, FIRAC2, based on the CFAST computer code, is in the code to model fire growth and smoke transport in multicompartment stmetures. 

At any one instant, only a very small proportion of the total number of unstable nuclei in a radioactive source undergo decay. A Poisson distribution which expresses the result of a large number of experiments in which only a small number are successful, can thus be used to describe the results obtained from measurements on a source of constant activity. In practical terms this means that random fluctuations will always occur, and that the estimated standard deviation, 5, of a measurement can be related to the total measurement by ... 

In K-Ar or zircon U-Pb dating, modeling the loss of radiogenic isotopes by volume diffusion is important. If P0 is the local concentration at t = 0 of a radioactive element decaying with constant X, a source term exists in the transport equation of the radiogenic element which is the local rate of accumulation AP0e Xt. For dual decay,... 

TU any of the less-understood phenomena leading to the observed fall-out distribution resulting from a nuclear explosion occur on a relatively short time scale (a few tens of seconds or less). These short term phenomena lead to an initial distribution of radioactive material referred to as the source term in a fallout study. Many predictive calculations are based on an assumed source term, which of necessity has been quite oversimplified. Two typical simplifications made for purposes of model development are (1) that the radiochemical composition of fallout is well defined and uniform (2) that the particles comprising the initial debris are uniform with respect to settling rate in the atmosphere. The latter assumption has received considerable attention elsewhere, notably in the work of Miller (2). However, the former assumption concerning the radiochemical uniformity of the debris has received far less systematic attention. 

Waste form leach rates in a geologic repository will be affected by unknown water flow rates and by extensive cracking of the waste form monolith. An understanding of these effects is important in predicting the geochemical behavior of disposed radioactive waste forms over the full range of possible scenarios. The dependence of the waste form source term on the rate of renewal of aqueous solution is first established for the simple but important case of solubility-limited network dissolution control. 

Since 1990 extended radioecological monitoring based on radiation mapping has been implemented into the radioecological survey practice [2]. Completeness of the environmental contamination information has been attained through generation of radiation field maps with simultaneous indication of source-term location areas, boundaries of radioactive substance spreading, identification of radiation-hazardous zones with indication of the most probable man-caused radionuclide transfer paths. 

In many cases due to unknown or uncertain parameters of the release, the estimation of source term characteristics, based on environmental pollution monitoring, is a very important issue for emergency response systems. For example, after the Algeciras accident in Spain (30 May 1998) many European monitors measured peaks of air radioactive contamination, but during several days the reason was unknown. Similar situations had happened after the Chernobyl and many others man-made accidents. After 11 September 2001 this problem became potentially more important due to the risk of possible terrorist actions followed by atmospheric releases of dangerous NBC matters. 

Commercial facilities are closely regulated in terms of release of facilities and equipment for unrestricted use. The radioactive materials license has specific requirements for disposal of radioactive sources and trace materials, even when the useful life of these radioactive materials has been exceeded. 

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