Enzo Tachikawa

The characteristics of the prompt gamma-ray analyzing system at the neutron beam guides of JRR-3M

Abstract A reactor-neutron-induced prompt γ-ray analyzing system was constructed at JRR-3M. The system can be set at cold and thermal neutron beam guides with a neutron flux at the sample position of 1.1 × 10 8 and 2.4 × 10 7 n cm −2 s −1 , respectively. The system was designed to achieve the lowest γ-ray background. This is done by using lithium fluoride tiles as neutron shielding, by placing the samples in a He atmosphere, and by using a Ge-BGO detector system for Compton suppression. The γ-ray spectrometer is equipped to acquire three modes of spectra simultaneously: single mode, Compton suppression mode, and pair mode in an energy range of up to 12 MeV. Due to the cold neutron guide beam and the low background system, sensitivities and detection limits better than those in other PGA systems have been achieved. For typical elements such as H, B, Cd, and Gd, analytical sensitivities with the cold neutrons are 10 to 18 times higher, and detection limits are lowered by factor of 6 to 8, compared to the case with thermal neutrons under the same geometrical condition. Detection limits down to a range of 2 to 7 ng were recorded for B, Cd, Sm, and Gd by the cold neutrons. Hydrogen, one of the most important elements in material studies, could be detected down to 1.0 and 2.8 μg by cold and thermal neutrons, respectively.

A thermal desorption study of the surface interaction between tritium and type 316 stainless steel

The thermal desorption of tritium from a type 316 stainless steel exposed to gaseous tritium (HT-gas) was studied. In the desorption spectra of tritium, four distinct peaks appeared at about 430 (peak HT-1), 540 (peak HTO), 750 (peak HT-II) and 970 K (peak HT-III). The activation energies for the peaks HT-I, HTO and HT-II were determined as 20 ± 4, 27 ±7 and 55 ±9 kJ/mol, respectively. It is presumed that the tritium leading to the peak HTO forms tritoxyl ion (OT−) by combining with surface O2− ion or by the isotopic exchange with the protium of surface OH− ion on the sorption process. The OT ion combines with the OH− ion or the dissolved protium into HTO at the desorption process. The tritium leading to both peaks HT-II and HT-III is sorbed and dissociates into atomic species which diffuse into the bulk, while that leading to the peak HT-I is very weakly held on the topmost surface of stainless steel in the form of a molecule or HT+ ion.

Chemical decontamination of the tritium-sorbing surface of Type 316 stainless steel

The chemical decontamination of Type 316 stainless steel surfaces exposed to gaseous tritium has been examined by using a technique of combined thermal desorption and chemical treatment with corrosive solutions. With the finding that the tritium sorbed at the various sites on the stainless steel surface can selectively be eliminated by treatment with a particular corrosive solution, the distributions of sites and their properties have been elucidated. On the basis of the results, it has been demonstrated that a two-step chemical treatment, i.e., the dipping in dilute HCl for the whole surface corrosion and then in a CuSO4-H2SO4 solution for intergranular corrosion, leads to an almost complete removal of tritium sorbed on the stainless steel surface with minimized dissolution of the bulk. It is also shown that the non-oxidizing acids like HC1 accelerate the sorbed tritium to release in the form of HT, while the oxidizing acids like HNO3 allow it in the form of HTO.

PROMPT GAMMA-RAY ANALYSIS USING COLD AND THERMAL GUIDED NEUTRON BEAMS

A permanent and stand-alone neutron-induced prompt γ-ray analysis (PGA) system, usable at both cold and thermal neutron beam guides of JRR-3M has been constructed. The characteristics of the system, including neutron beam and γ-ray spectrometer were measured. Owing to the absence of fast neutrons and the low γ-ray background, analytical sensitivities and detection limits better than those in other PGA systems have been achieved. Analytical results of ten elements in Standard Reference Material of Coal Fly Ash agreed well with those obtained by other methods. Isotopic analysis of Ni and its application to accurate and precise determination of Ni by stable isotope dilution method were performed.

Effect of surface treatments on the sorption of tritium on type-316 stainless steel

Abstract The effect of surface treatments on the interaction between tritium and type-316 stainless steel was studied by a thermal desorption technique. The surface treatments caused changes in intensity for all of the four desorption peaks of tritium. The chemical passivation resulted in a decrease of the peak at 540 K (peak HTO) as well as the peak at 430 K (peak HT-I). The vacuum bake-out at 773 K led to a decrease of the peak at 750 K (peak HT-II) and an increase of the peak at 970 K (peak HT-III). The sputter-etching resulted in an increase of the peaks HTO and HT-I. These changes in the behavior of thermal desorption of tritium can primarily be attributed to the variation of the surface composition. It is suggested that the peaks HTO and HT-I are given by desorption of the tritium of which sorption is related to iron on the surface, while the peaks HT-II and HT-III are given by desorption of the tritium which is trapped on the sites of carbide and nickel, respectively, in the surface layer.

The reactions of recoil tritium atoms with water: Energetic and thermal reaction yields

Abstract In the reactions of recoil T with H 2 O or D 2 O, both containing 0·07 M LiNO 3 , hydrogen-t and water-t are formed in the ratio of 0·14 ± 0·01 for HT/HTO and 0·15 ± 0·01 for DT/DTO. Using H 2 S, acetone, and I 2 as additives, it was found that the energetic reaction yields in the reaction with H 2 O are 68% for T for H and 11% for T to HT reactions. The thermalized T atoms are mostly stabilized as HTO. The failure of a definite overall isotope effect in the energetic reaction yields results from the counterbalance of two different kinds of isotope effects, the moderator isotope effect, α H 2 O / α D 2 O , and the overall reactivity integral isotope effect, (I HT + I HTO )/(I DT + I DTO ). The ratio of acetone-t yield from H 2 O-acetone systems to that from D 2 O-acetone systems is extraporated to 0·65 ± 0·1 at zero m.f. of acetone. This means that the ratio of relative reactivities of H 2 O and D 2 O will be close to 1·5.

RAPID DETERMINATION OF SPECIFIC ACTIVITY OF NICKEL-63

For the determination of specific activity of63Ni, a method has been developed for simultaneous assessment of both stable and radionickel. The method comprises solvent extraction of Ni-dimethylglyoxime into xylene for spectroscopic measurement and liquid scintillation counting of the extractant. The application of the method has been successful for63Ni in the corrosion products accumulated on the wall surface in the primary circuiting tube of the reactor.

Diffusivity of tritium in Li-Al alloys

Abstract The diffusion coefficients of tritium in Li-Al alloys were measured. The observed diffusion coefficients were expressed by the following equations: D = 8.5 × 10 −5 exp[ −43.9± 14.8(kJ/mol)/RT] (cm 2 /s ), D = 9.3 × 10 −5 exp[ −48.5± 15.0(kJ/mol)/RT] (cm 2 /s ), and D = 5.3 × 10 −5 exp[ −62.7± 13.8(kJ/mol)/RT] (cm 2 /s ) for 0.02, 0.26 and 1.12% Li-Al alloys, respectively. Results showed that the diffusion coefficients as well as the apparent activation energy for diffusion depend upon the lithium concentration in the alloy.

Removal of radiocobalt in waste water by activated charcoal using oxine as a chelating agent

Abstract The characteristics of the adsorption of Co ion in water on activated charcoal impregnated with oxine have been studied. Impregnation of oxine largely improved the adsorption capacity of activated charcoal (AC), although the apparent initial and final adsorption rates are not influenced. Another important advantage of AC impregnated with oxine [AC(HOx)] over plain AC is that Co ion collected on AC(HOx) is not easily eluted by flowing water. Furthermore the collection of Co on AC (Hox) is not affected by the presence of Fe(III), which exists in a macroscopic amount in waste water. At the initial adsorption stage, the apparent adsorption rate of Co ion on AC (HOx) is roughly proportional to 0.91 power of the concentration of Co ion.

Diffusivity of recoil-injected or thermally-doped tritium in aluminum

Abstract Bulk diffusion coefficients of both recoil-injected and thermally-doped tritium in aluminum were measured. The temperature dependence of these diffusion coefficients was expressed by D = 2 × 10 −3 exp [−42.6 ± 2.5( kJ/mol )/RT] ( cm 2 / s ) for the recoil-injected tritium, and D = (9 ± 1) × 10 −3 exp [−51.9 ± 2.9( kJ/mol )/RT] ( cm 2 / s ) for the thermally-doped tritium. A reasonable agreement between the two sets of results is very contrasted to the results found with UO2 as a host material, in which thermally-doped hydrogen diffusion much faster than recoil tritium by several orders of magnitude. Chemical forms of recoil-injected tritium released on heating were also investigated. Both gaseous and condensable components were released. The majority of gaseous component was found as HT, and ca. 2% of CH3T and ca. 0.1% of T2 were detected in the radio-gas Chromatographic measurements.