Nuclear data propagation with burnup : impact on SFR reactivity coefficients

Laurent Buiron (1) , Danièle Plisson-Rieunier (1)

1 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)

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.

Mots clés: SFR; sesnibilites en evolution; uncertitudes; COMAC

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique Nucléaire Théorique [nucl-th]

Laurent Buiron, Danièle Plisson-Rieunier. Nuclear data propagation with burnup : impact on SFR reactivity coefficients. ICAPP17, Apr 2017, Fukui-Kyoto, Japan. ⟨cea-02435062⟩