[en] Hydrogen induced delayed fraction is one of the more probable degradation mechanisms for zircaloy-clad fuel elements. This phenomenon and a mathematical model for crack propagation velocity is described. Based on the model the effect of stress intensity, temperature, yield stress and hydrogen content are discussed. Long term stress of irradiated and non-irradiated compact-tension specimens of Zircaloy-2 resulted in crack growth in about a third of the specimen. Fractographic studies, however, showed that in no case this was due to hydrogen induced delayed fraction. It is therefore hardly likely that spent zircaloy-clad fuel elements become degraded by this type of defect during long term storage in pools. (G.B.)

[en] The resonance fissions in U²³⁵ and Pu²³⁹ have been studied using cadmium and boron filters. Fission chambers were used as detectors and the experiments were performed in beam geometry. The neutron energy distribution in the beams transmitted through the different filters was determined with a fast chopper. From the cadmium filter, measurements the fission resonance integrals were determined. The values obtained were 278±9 b for U²³⁵ and 301±10 b for Pu²³⁹; 0.5 eV < E < 1 MeV. Complementary Pu²³⁹ measurements were made in which the fission events were detected from the fission product activity in irradiated foils. Contrary to what has been reported elsewhere the value of the Pu²³⁹ resonance integral, found in this way, agreed well with that obtained from the fission chamber measurement. The experiments with the boron filters yielded results which, for the thin filter, agreed well with those calculated from the cross section data given in the Karlsruhe compilation. The discrepancy was larger for the thick filter but the values did not disagree outside the common limits of error

[en] Irradiated zircaloy samples with different textures and heat treatments have been tested concerning stress corrosion. Irradiated samples of Zr-1Nb, pure Zr and beta quenched zircaloy have also been investigated. Stress-relieve annealled zircaloy is even after irradiation more sensitive to stress corrosion than recrystallized zircaloy. Zr-1Nb and beta quenched zircaloy are much more sinsitive to stress corrosion than the samples with different textures. As a rule irradiated zircaloy is sensitive to stress corrosion at stresses far below the yield point. The breaking stress decreases with the elongation rate. The extension of cracks is much faster in irradiated zircaloy than in unirradiated zircaloy. There is no simple failure criterium for irradiated zircaloy. However for a certain stress and a certain elongation rate the probability for a failure before this stress is reached with a constant elongation rate can be given. (E.R.)

[en] The resonance integrals for uranium metal and uranium oxide have been determined for a 1/E flux. The following results were obtained Metal RI 2.95 + 25.8√(S/M); Oxide RI = 4.15 + 26.6√(S/M). The oxide value agrees with the expression found earlier at this laboratory. But the result for the metal is 4. 5 % larger than the earlier one. In addition, the resonance absorption in a R1 fuel rod has been compared with that for a cadmium-covered rod placed in an approximate cell boundary flux. The former came out 3 % larger than the latter. A comparison of the fuel rod absorption with that for a 1/E flux yields a corresponding figure of 7 %. The neutron flux was monitored below the lowest resonance in uranium

[en] Sweden benefits in many ways from the reactor safety research performed in other countries. Its own activity complements this effort, but a certain fraction is oriented toward safety issues that are intimately related to the special design of the ASEA-ATOM boiling-water reactor. Through the availability of the decommissioned Marviken reactor plant, Sweden has been able to play a leading role in integral containment experiments with international participation. Joint efforts with other countries are now devoted to defining new large-scale experiments to be performed in the unique Marviken facility. The largest portion of the safety research program in Sweden is performed by Studsvik Energiteknik AB, but various universities, consultant firms, and research institutes are also involved. In addition, a substantial amount of work is done by the reactor vendor ASEA-ATOM. The overall annual budget is at present between $7 and $8 million, with three governmental authorities as the main financing bodies

No abstract available

[en] The resonance integral of niobium has been studied by both pile oscillator and activation techniques. A value of 8.15b ± 0.65 b was obtained for the infinitely dilute integral. In addition, the variation of the resonance integral with foil thickness has been measured for thicknesses in the range 0.06 mm to 1.36 mm. A separate study of the half-life of the isomeric state in ⁹⁴Nb yielded a value T_1/2 = 6.30 - 0.03 m which is about 5 % lower than the value given in literature

[en] Sweden benefits in many ways from the reactor safety research work performed in other countries. Its own activity is complementary to this effort but a certain fraction is oriented towards safety issues which are intimately related to the special design of the ASEA-ATOM boiling water reactor design. Through the availability of the decommissioned Marviken reactor plant Sweden has been able to pay a leading role in integral containment experiments with international participation. Joint efforts with other countries are now devoted to defining new large scale experiments to be performed in the unique Marviken facility. The largest portion of the safety research program in Sweden is performed by Studsvik Energiteknik AB but various universities, consultant firms and research institutes are also involved. In addition, large efforts are made by the reactor vendor ASEA-ATOM but this work is not included in the present report. The overall annual budget is at present between M dollars 7 and 8 with three governmental authorities as the main financing bodies. (author)

[en] The resonance integral for thorium metal rods of different diameters has been determined by the activation method. The irradiations took place in the central channel of the reactor R1, where the energy dependence of the neutron flux had earlier been investigated with a fast chopper up to about 1 keV. The absolute calibration was made with gold as a standard. The true resonance integral for gold was taken from the literature as 1,500 ± 35 b. The experimental values for thorium were fitted to two alternative expressions with the following results: RI = (1.70 + 15.9√(S/M)) ± 5.5%; RI 17.3√(S/M + 0.06) ± 5.5 %. The measurements were made for S/M values in the range 0.14 - 0.87 cm²/g. The main contribution to the margin of errors arises from the uncertainties in the cross sections used and in the correction for the departure of the neutron energy distribution from the 1/E form

[en] Using pile oscillator technique, the total absorption cross section for zircaloy 2 plates has been determined in the neutron spectrum of the reactor R1. The plate thickness was varied in six steps from 0. 2 mm to 6. 4 mm. The thermal cross section for the alloy was calculated from cross section data and the known composition of the alloy. By subtracting this value from the measured cross sections and dividing by the factor α=2/√(π) x r x √(T/T₀) the effective resonance integrals were obtained. After subtraction of a constant amount for resonance contributions from hafnium, tin etc., effective resonance integrals for zirconium could be evaluated. An extrapolated value of 0.85 ± 0.15 b was obtained for the infinitely dilute integral (l/v part excluded). The ratio of the resonance integral at plate thicknesses 0.2 and 6.4 mm came out as 1.65 ± 0.25