AQUEOUS HOMOGENEOUS REACTORTECHNICAL PANEL REPORT

Considerable interest has been expressed for developing a stable U.S. production capacity for medical isotopes and particularly for molybdenum- 99 (99Mo). This is motivated by recent re-ductions in production and supply worldwide. Consistent with U.S. nonproliferation objectives, any new production capability should not use highly enriched uranium fuel or targets. Conse-quently, Aqueous Homogeneous Reactors (AHRs) are under consideration for potential 99Mo production using low-enriched uranium. Although the Nuclear Regulatory Commission (NRC) has guidance to facilitate the licensing process for non-power reactors, that guidance is focused on reactors with fixed, solid fuel and hence, not applicable to an AHR. A panel was convened to study the technical issues associated with normal operation and potential transients and accidents of an AHR that might be designed for isotope production. The panel has produced the requisite AHR licensing guidance for three chapters that exist now for non-power reactor licensing: Reac-tor Description, Reactor Coolant Systems, and Accident Analysis. The guidance is in two parts for each chapter: 1) standard format and content a licensee would use and 2) the standard review plan the NRC staff would use. This guidance takes into account the unique features of an AHR such as the fuel being in solution; the fission product barriers being the vessel and attached systems; the production and release of radiolytic and fission product gases and their impact on operations and their control by a gas management system; and the movement of fuel into and out of the reactor vessel

Design Methodology for Fuel Debris Experiment in the New STACY Facility

International audienceThe new criticality experiments facility STACY will be able to contribute to the validation ofcriticality calculations related to the fuel debris. The experimental core design is in progress inthe frame of JAEA/IRSN collaboration. This paper presents the method applied to optimize thedesign of core configurations of the new STACY to measure the criticality characteristics ofpseudo fuel debris focused on Molten Core Concrete Interaction (MCCI) debris. To ensure thata core configuration is relevant for code validation, it is important to evaluate the reactivityworth of the main isotopes and the keff sensitivity to their cross sections. If the sensitivitiesprofiles are similar to those of the configuration to be validated, it is potentially feasible toprovide relevant feedback on its nuclear data. In the case of MCCI debris described in this study,silicon is the nucleus that has the highest keff sensitivity in the concrete. Therefore, someparameters of the core configuration, as for example the lattice pitch or the core dimensions,were adjusted using optimization algorithm to research efficiently the optimal coreconfigurations to obtain high sensitivity of silicon capture cross section. This method allowsexploring a large space of possibilities by limiting the number of calculations. Two examples ofdesigns tested using this approach are presented in this paper. The first study was performedon a simple square core configuration with ideal conditions. In the second study, the core wasdivided in two zones to investigate the interest of having both an experimental zone and a driverzone. Based on these results, realistic series of experiments for fuel debris in the new STACYcould be defined to obtain an interesting feedback for the MCCI

Criticality configuration design methodology applied to the design of fuel debris experiment in the new STACY

International audienceThe new critical assembly STACY will be able to contribute to the validation of criticality calculations related to the fuel debris. The experimental core designs are in progress in the frame of JAEA/IRSN collaboration. This paper presents the method applied to optimize the design of the new STACY core to measure the criticality characteristics of pseudo fuel debris that simulated Molten Core Concrete Interaction (MCCI) of the fuel debris. To ensure that a core configuration is relevant for code validation, it is important to evaluate the reactivity worth of the main isotopes of interest and their keff sensitivity to their cross sections. In the case of the fuel debris described in this study, especially for the concrete composition, silicon is the nucleus with the highest keff sensitivity to the cross section. For this purpose, some parameters of the core configuration, were adjusted using optimization algorithm to find effciently the optimal core configurations to obtain high sensitivity of silicon capture cross section. Based on these results, realistic series of experiments for fuel debris in the new STACY could be defined to obtain an interesting feedback for the MCCI. This methodology is useful to design other experimental conditions of the new STACY

Aqueous Homogeneous Reactor Technical Panel Report

Considerable interest has been expressed for developing a stable U.S. production capacity for medical isotopes and particularly for molybdenum- 99 (99Mo). This is motivated by recent re-ductions in production and supply worldwide. Consistent with U.S. nonproliferation objectives, any new production capability should not use highly enriched uranium fuel or targets. Conse-quently, Aqueous Homogeneous Reactors (AHRs) are under consideration for potential 99Mo production using low-enriched uranium. Although the Nuclear Regulatory Commission (NRC) has guidance to facilitate the licensing process for non-power reactors, that guidance is focused on reactors with fixed, solid fuel and hence, not applicable to an AHR. A panel was convened to study the technical issues associated with normal operation and potential transients and accidents of an AHR that might be designed for isotope production. The panel has produced the requisite AHR licensing guidance for three chapters that exist now for non-power reactor licensing: Reac-tor Description, Reactor Coolant Systems, and Accident Analysis. The guidance is in two parts for each chapter: 1) standard format and content a licensee would use and 2) the standard review plan the NRC staff would use. This guidance takes into account the unique features of an AHR such as the fuel being in solution; the fission product barriers being the vessel and attached systems; the production and release of radiolytic and fission product gases and their impact on operations and their control by a gas management system; and the movement of fuel into and out of the reactor vessel