Nuclear data propagation with burnup : impact on SFR reactivity coefficients
Abstract
For the next generation fast reactor design, the
Generation IV International Forum (GIF) defined global
objectives in terms of safety improvement, sustainability,
waste minimization and non-proliferation. Among the
possibilities studied at CEA, Sodium cooled Fast Reactor
(SFR) are studied as potential industrial tools for next
decade’s deployment. Many efforts have been made in the
last years to obtain advanced industrial core designs that
comply with these goals. Concerning safety issues,
particular efforts have been made in order to obtain core
designs that can be resilient to accidental transients. The
“safety” level of such new designs is often characterized
by their “natural” behavior under unprotected transients
such as loss of flow or hypothetical transient over power.
Transient analysis needs several accurate neutronic input
data such as reactivity coefficient and kinetic parameters.
Beside estimation of the level of “absolute” values,
associated uncertainties have also to be evaluated for the
whole set of relevant data. These estimations have to be
performed for different core state such as end of cycle
core for feedback coefficient. This means that
uncertainties have to be obtained not only a fixed time but
also have to be propagated all through irradiation.
To do so, we need to couple Boltzman and Bateman
equations at sensitivities level. The coupling process
could be done with the help of the perturbation theory
which gives adapted framework suited for deterministic
calculation codes. This coupling is currently in progress
in ERANOS code system. The actual implementation gives
access to estimation of sensitivities for both reactivity
coefficients and mass balance.
After a brief theoretical description of Boltzman/Bateman
coupling capabilities in ERANOS, the study presented in
this paper focuses on sensitivity and uncertainties
estimation for the main feedback coefficients involved in
fast reactor transients: the thermal sodium expansion
coefficient and the Doppler Effect. Using these
sensitivities, a global evaluation of impact of the fuel
depletion can be quantified for these reactivity effects at
core scale for end of cycle state. An illustration is given
for a GEN IV SFR industrial core design (SFR V2B). A
first glance at preliminary uncertainty level is presented
using current covariance matrices available at CEA.
Origin : Files produced by the author(s)
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