In-core irradiation

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. 

An irradiation position of 2 or 3 cm in diameter and 15 to 20 cm long is sufficient. Usually this will be an in-core irradiation position. 

The initial investment for a facility to perform dating irradiations involves the in-core irradiation facilities. Most reactors already have such irradiation positions. For the analysis of older rocks, a Cd lined facility is not required. For the analysis of young rocks, it is essential. If such a facility is not available, it could be installed for a few thousand dollars or less. The only recurring expense is for irradiation capsules and shipping materials. 

SOf in solid H20 acid rain and Antarctic ice core. The signal intensity at g — 2.0036 and g = 2.0020 is enhanced considerably in y-irradiated solid H20 doped with S032. One can detect the concentration down to 10-100 ppm of S032- in irradiated solid H20. 03 radicals are stable after OH radicals are annealed out.120... 

A solid sample (under vacuum) is irradiated with a monochromatic beam of x-rays. Electrons in core-and valence-region orbitals are ejected. The kinetic energies of these ejected electrons are analyzed in an energy spectrometer and, after correction for the energy of the incident radiation and for instrumental effects, give the binding energies of core and valence electrons in the solid... 

The relatively low overall yields of radicals were attributed to the high recombination rate of closely spaced base ion radicals in the densely ionized track core. The proximity of these radicals coupled with Coulomb attractions facilitates fast core ion radical-ion radical recombination. However, neutral sugar radicals in the core are not affected by Coulomb attractions, thus they do not recombine as readily. Therefore, most of the neutral sugar radicals stabilized at 77 K are presumed to form in the core. On the other hand, most of the base radicals that are stabilized at 77 K are assumed to form in the isolated, low LET-like spurs formed by delta-rays. The similarity in the behavior of the base radicals in argon ion-beam irradiated samples and in y irradiated samples lends support to this picture.In this model C(N3)H is in equilibrium with C and is found to act as an ion-radical. 

Fast breeder reactor fuel rods consist of stainless-steel-clad mixed oxide (U,Pu)02 fuel however, more stable alloys for cladding and in-core structural materials, with resistance to swelling and embrittlement under fast neutron irradiation, and more efficient fuels (carbide see 17.3.12.1.2) or nitride (see 17.3.12.3)] are needed h The mechanical, metallurgical, and chemical processes in fuel element irradiation are depicted in Figure 1. Figure 2 shows the PFR (U.K.) fast breeder fuel element, and Figures 3 and 4 illustrate the Fast Flux Test Facility (FFTF) fuel system. 

The other full-scale applications of the Thorex process have been to separation of from thorium irradiated at the U.S. Atomic Energy Commission s production reactors at Savannah Rivet and Hanford. As the object of these irradiations was to produce of high isotopic purity for use in the first core of the LWBR, the bumup to which the fuel was exposed was low, and the concentrations of uranium and fission products in the irradiated thorium were much lower than will exist in power reactor fuel irradiated to full bumup. Nevertheless, the successful separation of uranium and thorium from each other and from fission products is significant confirmation of the workability of the Thorex process. 

Figure 10.28 Principal head-end steps in preparing irradiated LMFBR core and blanket assemblies for Purex process. F.P. = fission products S.S. = stainless steel.

Emission measurement from the excited states is also a powerful method to investigate the ion beam radiation chemistry because a very sensitive time resolved photon-counting technique can be applied. In 1970s, temporal behavior of the emission from benzene excited states in 40 mM benzene in cyclohexane irradiated with pulsed proton and He ion particles was measured and compared with UV pulse irradiation. It was found that immediately after the irradiation there is a short decay (< 10 ns) followed by a longer decay corresponding to the life-time of the benzene excited states (26-28 ns). The fraction of the shorter decay component increases with increasing LET of the particle. This was explained by a quenching mechanism that radical species formed in the track core attack and quench the benzene excited states, which would take place only shorter period less than 10 ns after irradiation [69]. 

Wolf 1. R. 1979. Linear variable differential transformer and its uses for in-core fuel rod behavior measurements. International Colloquium on Irradiation for Reactor Safety Programmes. Petten, Netherlands 23. 

Nominal thermal and flow parameters were used in the fuel performance analysis except that the thermal power was increased to 102 percent of nominal full power per NRG Regulatory Guide 1.49 to account for uncertainties in core power measurements. The major thermal parameters used in the analysis are listed in Table 4.1-1. Nominal values of material properties were used in the analysis. The design correlations for the material properties of the H-451 graphite and the fuel rods account for thermal expansion, and the effects of fluence and temperature on thermal conductivity and irradiation-induced shrinkage. These thermal and flow parameters and... 

Allowable impurity levels additional requirements for materials in core sheiis and welds subjected to neutron irradiation... 

Design Basis Accident analysis codes PREDIS and VENUS have been validated against European LOFA benchmark problems. Fuel subassembly worths at different radial positions in core during initial fuel loading were calculated. A study was made on the possibility of recriticality of molten fuel dropped in the core catcher from the core following an accident. Calculations of neutron irradiation dose for the reactor assembly out of core componets both in radial and axial locations were completed and indicated that the dose values are negligible ( ldpa). 

From a measured value of R(, O Eq. (57.9) allows one to calculate the mean reaction cross section for the respective nuclide. Correspondingly, one may determine the integral of the unmoderated neutron flux cj)fi if the mean reaction cross section is known. Values of fl varies as a function of the location in the reactor core (irradiation position) but is constant for a well-defined location at a given reactor power. 

The safety analysis should cover all the sources of radioactive material in the plant. In addition to the reactor core, this includes irradiated fuel in transit, irradiated fuel in storage and stored radioactive waste. 

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