Journal of Nuclear Energy最新文献

The energy spectra of neutrons transmitted through iron, lead and perspex slabs were measured for 0·5, 1·0, 1·5 and 1·8 incident neutron energies, using a helium-3 spectrometer. The energy spectra were obtained as a function of the thickness of the scatterer.

The energy dependent cross-section for the ¹¹⁵In(n, n′)^115mIn reaction was measured in the neutron energy region from 3·37 to 4·89 MeV with a 2 MeV van de Graaff accelerator. A pair of semiconductor proton recoil counters composed of a polyethylene radiator and a silicon detector was used for the absolute measurement of the neutron flux at the indium sample.

A comparison of the average cross section, 175 ± 6 mb, which was measured with a fission plate, with the average cross-section calculated with the energy dependent cross-section and the Maxwellian fission neutron spectrum is presented and discussed.

A simple method has been used to estimate mean beta and gamma decay energies of the short lived fission products, for which only half-life measurements and total decay energy estimates are available. This has enabled calculations to be made of beta and gamma decay heating from fission products which are in agreement with experimental results to better than 10 per cent for decay times as short as 1 s. Calculated beta and gamma decay energy following a long irradiation of 335U (thermal fission), is found to reproduce to better than 3 per cent a currently accepted curve of beta + gamma decay energy (SHURE, 1961) following an infinite irradiation of ²³⁵U, for decay times 1 ≤ t ≤ 10⁸ s. These calculations also gave values $\text{B (∞, 0)=6·60}\text{Me/fission}$, $\text{G (∞, 0)=6·56}\text{Me/fission}$, $\text{D (∞, 0)=21·44}\text{Me/fission}$for the total beta, gamma and total kinetic energy release respectively, from thermal neutron fission of ²³⁵U. A study of the calculations of ENGLAND (1970) and comparisons made, do not support his suggestion that the data of SHURE (1961), which is widely used in industry, underestimates beta + gamma decay energy by ∼ 20 per cent. This suggestion would have serious implications on reactor design criteria; however, it is implied on the basis of comparisons presented in this paper, that the results of ENGLAND (1970) over-estimate by ∼ 15–20 per cent the beta + gamma decay energy following fission for decay times 10 < t ≤ 10⁶ s.

Therefore the results of the present work reject the idea, implicit in the results of ENGLAND'S calculations, that reactor systems have been underdesigned with respect to decay heat removal.

In addition, the present calculations show that the code FISP, together with its data library, provide a reliable means of estimating fission product decay energy release at all decay times after fission.

Informations on the ⁹³Nb(n, 2tn)⁹²Nb reaction at 14·6 MeV have been obtained from measurements of neutron emission spectra and its analysis taking into account the compound nucleus emission and emission during the precompound phase of the reaction. The result is a value of ≈ 1200 mb for σ_{n, 2n} confirming recent analysis that the activation cross-section of ≈ 450 mb should be considerably increased with important consequences for design of fusion reactor blankets, where Nb is a preferred material.

The neutron spectrum resulting from a monoenergetic source in an infinite medium, composed of atomic hydrogen gas and a 1/v absorber, is evaluated by series methods applied to integral and differential equations. The properties of the series that make up a fundamental set of solutions are examined. The classic analysis of Wigner and Wilkins is extended by determining the Green's function for thermalization, a new interpretation is provided for the relationship of asymptotic and small argument series, and calculations are reported for a variety of physical situations.