Yoshiharu Nagao

In-situ Tritium Recovery Experiments of Blanket In-pile Mockup with Li2TiO3 Pebble Bed in Japan

Lithium titanate (Li2TiO3) is one of the most attractive tritium breeders for breeding blanket in fusion reactor from view points of low tritium inventory, high chemical stability and so on. The data on the performance of a blanket mockup with pebble bed under neutron irradiation is needed for the design of breeding blanket. To obtain such data, two kinds of the blanket in-pile mockups with Li2TiO3 pebble bed were developed and the in-situ tritium recovery experiments were carried out in the Japan Materials Testing Reactor (JMTR). In these studies, effects of various parameters, i.e., irradiation temperature, sweep gas flow rate, etc., on the tritium recovery behavior from Li2TiO3 pebble bed were evaluated. It was found that the tritium recovery (R) to tritium generation (G) ratio (R/G) increased with increasing the temperature of Li2TiO3 pebble bed and was saturated when the temperature of Li2TiO3 pebble bed at the outside edge exceeded 300°C. Additionally, the sweep gas flow rate in the range of 100 to 900 cm3/min affected very little the tritium recovery from Li2TiO3 pebble bed. A good prospect for the design of breeding blankets using Li2TiO3 pebble bed was obtained from these results of in-situ experiments.

Integrated experiment of blanket in-pile mockup with Li2TiO3 pebbles

Abstract Lithium titanate (Li 2 TiO 3 ) is one of the candidate tritium breeding materials for breeding blanket of the fusion reactor. Therefore, tritium release experiments from Li 2 TiO 3 packing region were carried out to evaluate the effects of various parameters, i.e. sweep gas flow rate, irradiation temperature, and hydrogen content in sweep gas, etc. on tritium release. As for the shape of the Li 2 TiO 3 , a small spherical form (pebbles) is preferred to reduce the induced thermal stress in the breeding material. The diameter and total weight of Li 2 TiO 3 pebbles were 1 mm and ∼135 g, respectively. And the integrated experiment of blanket in-pile mockup with Li 2 TiO 3 pebble bed was carried out at the Japan Materials Testing Reactor (JMTR). The tritium released from Li 2 TiO 3 pebble bed was swept by the helium gas with hydrogen. The total tritium concentration (HT+HTO) and gaseous tritium concentration (HT) of tritium released from Li 2 TiO 3 pebbles were measured, and HT/(HT+HTO) ratio was evaluated under various conditions.

Preliminary neutronic estimation for demo blanket with beryllide

Abstract In preliminary neutronic assessment was conducted for the design of the DEMO blanket with neutron multiplier and tritium breeder materials packed in a multi-layered area of a blanket container. Beryllium metal and beryllides (Be 12 W, Be 12 Ti, Be 12 V, etc.) are suggested as candidate neutron multiplier materials and material property evaluations of each candidate neutron multiplier materials under neutron irradiation have been carried out. This study estimates the effect of neutron multiplier materials and the effect of the packing configuration on the TBR of the SSTR-based blanket. This work shows that the tritium-breeding ratio (TBR) in a mixed type blanket is about 1.2 times greater than that of separated type blanket. This study shows that TBR of mixed type blanket using Be 12 Ti or Be 12 V will be about 1.2 (required TBR is about 1.3), which is 90% of the TBR for a mixed type blanket using Be. It is concluded that Be 12 Ti and Be 12 V are the most promising neutron multipliers from the view of the tritium breeding.

In-pile test of Li2TiO3 pebble bed with neutron pulse operation

Abstract Lithium titanate (Li 2 TiO 3 ) is one of the candidate materials as tritium breeder in the breeding blanket of fusion reactors, and it is necessary to show the tritium release behavior of Li 2 TiO 3 pebble beds. Therefore, a blanket in-pile mockup was developed and in situ tritium release experiments with the Li 2 TiO 3 pebble bed were carried out in the Japan Materials Testing Reactor. In this study, the relationship between tritium release behavior from Li 2 TiO 3 pebble beds and effects of various parameters were evaluated. The ( R / G ) ratio of tritium release ( R ) and tritium generation ( G ) was saturated when the temperature at the outside edge of the Li 2 TiO 3 pebble bed became 300 °C. The tritium release amount increased cycle by cycle and saturated after about 20 pulse operations.

Characterization of hybrid self-powered neutron detector under neutron irradiation

Abstract To evaluate the irradiation behaviour of a blanket mock-up on in-pile functional test, it is necessary to measure the neutron flux change in the in-pile mock-up by a neutron detector, such as the self-powered neutron detector (SPND). With its small-sized emitter, which has high sensitivity and fast response time, SPND is an indispensable tool in order to measure the local neutron flux change. In the case of an in-pile functional test, it is necessary that response time is less than 1s and ratio of SPND output current is more than 0.3 of output current of SPND with Rh emitter. Therefore, a hybrid SPND with high sensitivity and fast response time was developed. This hybrid SPND used a hybrid emitter, i.e. Co cladded Pt-13%Rh.

Neutronic and thermal estimation of blanket in-pile mockup with Li2TiO3 pebbles

Abstract To evaluate exactly temperature distribution in large volume of tritium breeding materials during the blanket in-pile tests with the JMTR, neutronic and thermal calculations were conducted by using Monte Carlo code ‘MCNP’ with nuclear cross section library of ‘FSXLIBJ3R2’ and the transient and steady-state distribution code ‘TRUMP’. From the results of preliminary estimation of temperature distribution in the blanket in-pile mockup, the calculated values were 24–28% higher than the measured values. One of the reasons is due to overestimation of calculated thermal neutron flux.

Neutronic Design of Pulse Operation Simulating Device for In-pile Functional Test of Fusion Blanket by MCNP

The pulse operation of a fusion reactor can be simulated in a fission reactor by controlling the neutron flux entering a test section by using a rotating “hollow cylinder with window” made of hafnium. The rotating cylinder is installed between the test section and the fixed outer neutron absorber cylinder and is also made of hafnium with an opening in the direction to the core center. For gathering engineering data for the tritium breeding blanket such as characteristics of temperature change, tritium release and recovery, etc., it is desirable that the ratio of minimum to maximum thermal neutron fluxes is greater than 1:10. Design calculations were performed for the test assembly which considered local neutronic effects and the mechanical constraints of the device. From the results of these calculations, the ratio of minimum to maximum thermal neutron flux under irradiation would be about 1:10 using a pulse operation simulating device which has a thickness of 6.5 mm and a 150° window angle for the rotating hollow cylinder and 5.0 mm in thickness of fixed neutron absorber.

Revised Procedure for Determining Large Excess Reactivity of Reactors

Existing experimental methods for determination of large positive reactivity, the fuel addition method and the neutron absorption substitution method were analyzed. It is found that both the experimental methods are possibly affected to the substantially large systematic error, when the value of potential excess multiplication factor comes into the range close to 20%Δk. To cope with this difficulty, a revised procedure is validly proposed. The revised procedure evaluates the value of the excess multiplication factor as the accumulation of the consecutive increases of the effective multiplication factor in a virtual core, which are converted from those in an actual core multiplied by a calculated conversion factor f. The conversion factor f is to be determined in principle by calculation. Numerical experiments were done on a slab reactor with one group diffusion model. The systematic errors observed in the existing methods are mostly swept out in the proposed revised procedure. Influence of the uncertainti...