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General description

General description of the nuclear unit

The nuclear unit is composed of only one civil engineering structure supporting two zones with different containments: the reactor building (RB) and the nuclear auxiliary building (NAB). The objective of this single structure is to contain all the radioactive materials in one place.

The reactor is a pool type reactor. The maximum thermal power is 100 MW. This power is dissipated via the primary and the secondary circuit to the external cold source during irradiation ; the core, the primary circuit and experimental rigs, are completely enclosed in the RB. The Reactor pool is connected to several storage pool and hot cells located in the NAB through a water block



The reactor core

The core (600 mm fuel active height) is cooled and moderated with water. It will be operated, as a reference solution with a high density low enriched fuel (U enrichment lower than 20%), density 8 g.cm-3, requiring the development of UMo fuel.

The fuel element is of circular shape (set of curved plates assembled with stiffeners) and comprises a central hole. The reference UMo fuel, is under development within an international collaboration (UMo/Al dispersion solutions and monolithic UMo solution) and is not at the time being an industrial product. Consequently, as a back-up solution, the JHR will start with an U3Si2 fuel with a larger enrichment (typically 27%).

The core area is surrounded by a reflector which optimizes the core cycle length and provides intense thermal fluxes in this area. The reflector area is made of water and beryllium elements.

Irradiation devices can be placed either in the core area (in a fuel element central hole or in place of a fuel element) or in the reflector area.

In core, experiments will address typically material experiments with high fast flux capability up to 5.1014 n.cm-2.s-1 perturbed fast neutron flux with energy higher than 1 MeV.

In reflector, experiments will address typically fuel experiment with perturbed thermal flux (lower than 0.625 eV) up to 5.1014 n.cm-2.s-1.

Experiments can be implemented in static locations, but also on displacement systems as an effective way to investigate transient regimes occurring in incidental or accidental situations.

This provides a flexible experimental capability able to create up to 16 dpa/year for in-core material experiments (with 260 full power operation days per year) and 600W.cm-1(on 1% 235U enriched fuel) for in reflector simple fuel experiments.

The JHR facility will allow performing a significant number of simultaneous experiments in core (~ 10) and in reflector (~ 10).


Typical Loading


The JHR Experimental Capability

JHR is a 100MW tank pool reactor. The core area is inserted in a small pressured tank (section in the order of 740 mm diameter) with forced coolant convection (low pressure primary circuit at 1.5 MPa, low temperature cooling, core inlet temperature in the order of 25°C). Reactor primary circuit is completely located inside the reactor building.

The reactor building is divided into two zones. The first zone contains the reactor hall and the reactor primary cooling system.

The second zone hosts the experimental areas in connection with in pile irradiation (eg., typically 10 loops support systems, gamma scanning, fission product analysis laboratory etc.).

The Fission Product Laboratory will be settled in this area to be connected to several fuel loops either for low activity gas measurements (HTR, …) or high activity gas measurements (LWR rod plenum, …) or water measurements (LWR coolant, …) with gaseous chromatography and mass spectrometry.

The hot cells   The NAB/RB Interconnexion  
The hot cells
The NAB/RB Interconnexion

Bunkers and laboratories in the experimental area will use 300m² per level on 3 levels.

Pools in the reactor building are limited to the reactor pool (including neutronography for experiments) and an intermediary deactivation pool (for temporary storage of fuel elements, reflector elements or replaced core mechanical structures).

During reactor shutdown, experimental devices can be temporarily stored in a dedicated rack in the reactor pool.

Hot cells, laboratories and storage pools are located in the nuclear auxiliaries building.

The experimental process will make use of two hot cells to manage experimental devices before and after the irradiation. Safety experiments are an important objective for JHR and require an “alpha cell” to manage devices with failed experimental fuel.

A fourth hot cell will be dedicated to the transit of radioisotope for medical application and to the dry evacuation of used fuel.

Three storage pools are dedicated respectively to spent fuel, experimental devices and mechanical components management.

Revision : 2009-03
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