Small Sample Reactivity Measurements in the RRR/SEG Facility: Reanalysis using TRIPOLI-4

Abstract

This work involved reanalyzing the RRR/SEG integral experiments performed at the Rossendorf facility in Germany throughout the 1970s and 80s. These small sample reactivity worth measurements were carried out using the pile oscillator technique for many different fission products, structural materials, and standards. The coupled fast-thermal system was designed such that the measurements would provide insight into elemental data, specifically the competing effects between neutron capture and scatter. Comparing the measured to calculated reactivity values can then provide adjustment criteria to ultimately improve nuclear data for fast reactor designs. Due to the extremely small reactivity effects measured (typically less than 1 pcm) and the specific heterogeneity of the core, the tool chosen for this analysis was TRIPOLI-4. This code allows for high fidelity 3-dimensional geometric modeling, and the most recent, unreleased version, is capable of exact perturbation theory. Within the framework of the CEA-DOE agreement, Andrew Hummel spent three months at the CEA Cadarache utilizing this newest version of TRIPOLI.

Experimental analysis of small sample reactivity measured in the SEG experiment by a deterministic reactor physics code system CBZ

“…The same tendency was observed in the previous work by Hummel. [8] The energy group-wise Mo-100 sample reactivity, which is normalized so as to make total reactivity unity, is shown in Figure 11. The energy group profiles of the Mo-100 sample reactivity of the different cores are similar with each other, and it seems difficult to provide reasonable explanations on the significant underestimation observed only in the result at SEG-7A.…”

“…These can be referred in the reports by Dietze [9] and by Hummel [8]. The reaction-wise contribution to the total reactivity are also omitted here since it is almost the same as those presented in these existing reports [8,9].…”

“…The SEG experiment is well summarised in the report by Hummel [8]; thus this experiment is briefly reviewed here and interested readers can refer Hummel's report.…”

Application of the EGPT methodology in the analysis of small-sample reactivity worth experiments

“…The EGPT method [7] proposes to evaluate the sensitivity of the reactivity worth Dr = r 2 Àr 1 to a given parameter p as the difference of sensitivities of the two multiplication factors k 1 and k 2 . The latter is obtained from the standard perturbation theory, by computing the adjoint flux F + and convoluting it into the balance equations (1) and (2). Then, the following equation is obtained as:…”

“…-The sample is usually fabricated from a very pure material, so it contains a limited number of elements or isotopes. -Under special spectral conditions [2], resulting from an adequate core configuration, it is possible to emphasis one type of reaction against all the possible ones (for instance: capture or scattering).…”