Through the fuel fabrication for the MONJU initial and first reload fuel, the low density MOX pellet fabrication process could be established as almost same level of high density MOX pellet fabrication. It is one of the missions given for JNC to develop and demonstrate the FBR and its related technologies for future commercial use of plutonium. Under this mission, JNC has carried out development of MOX fuel and fuel fabrication technology to reduce fuel cost.
For reducing MOX fuel cost, it is effective to introduce MOX pellet with larger diameter because the number of MOX pellets and fuel pins composing a fuel assembly could be decreased. In order to achieve same generating power per fuel assembly by decreased number of fuel pins, it is required to increase linear power for each fuel. However, linear powder for
fuel pin consisted of low density MOX pellets is limited compared to high density one because of low thermal conductivity of low density MOX pellet. Therefore, adoption of annular pellet with larger diameter is effective to realize high linear powder fuel pin for high burn up FBR fuel. Under this recognition, JNC has already started the development of annular pellet fabrication technology prepared for MONJU high burn up fuel. Now development of pressing machine with die-wall lubricating mechanism by dry method is underway for annular pellet fabrication.
Amount of Product MOX Pellets (kg) Cumulative Amount of Product MOX Pellets (ton)
Inn er Core Fue l (Init ial Lo ad) Outer Core Fue l (Initial Load)
In ner Core Fu e l (Fi rst Re load) Outer Core Fu e l (First Re load)
Production Period (Month)
Amount of Product MOX Pellets (kg) Cumulative Amount of Product MOX Pellets (ton)
Inn er Core Fue l (Init ial Lo ad) Outer Core Fue l (Initial Load)
In ner Core Fu e l (Fi rst Re load) Outer Core Fu e l (First Re load)
Production Period (Month)
JOYO 6th Re load Fuel Fabrication
FIG. 9. Amounts of MOX pellets fabricated in MONJU fuel fabrication.
5. CONCLUSION
1. Through the MOX fuel fabrication for the MONJU initial load fuel and first reloaded fuel, the low density MOX pellet fabrication process in PFPF had been established;
2. Annular pellet fabrication technology has been developed for MONJU higher burn up fuel.
REFERENCES
[1] AOKI, Y., KASHIMURA, M., YAMAGUCHI, T., “Development of Fabrication Technology of Low Density Pellet for FBR”, Future Nuclear Systems (Proc Int. Conf.
Yokohama, 1997), JNS, Tokyo (1998).
[2] ASAKURA, K., AONO, S., YAMAGUCHI, T., DEGUCHI, M., “Current Developments of Fuel Fabrication Technologies at the Plutonium Fuel Production Facility, PFPF”, MOX Fuel Cycle Technologies for Long Term Deployment (Proc. Int. Symp. Vienna, 1999), IAEA, Vienna (2000) 118.
DEVELOPMENT OF TECHNOLOGIES
OF NUCLEAR CERAMIC GRADE FUEL PRODUCTION S.A. YASHIN, A.E. GAGARIN, A.V. MANYCH
Joint Stock Company “Ulba Metallurgical Plant”
Republic of Kazakhstan Abstract
JSC “Ulba Metallurgical Plant” has developed and implemented unique technologies of fuel pellets production that allow:
- Regulating the average grain size and grain distribution by sizes within wide ranges by using methods of pellet alloying: from bimodal structure with the grain size of 1–3 µm of fine grain phase and 10–30 µm of coarse grain phase to homogeneous mono-modal structure with the average grain size about 20–50 µm. The summary boron equivalent of alloyed pellets not exceed 1.0 µg/gU;
- Regulating pore distribution by sizes (while the homogeneous pore structure is maintained) by adding special pore-forming agents: from mono-modal distribution with average pore sizes around 1.5–3.5 µm to bimodal distribution with average size of small pores around 1–3 µm and average size of large pores around 10–50 µm.
The principles of microstructure control are based on laws and mechanisms of microstructure revolution at all stages of sintering. For example, the interaction between regular pores and grain boundary is an important element in initiation of grain and pellet density increase. The control over pore mobility allows improving plasticity of pellets through increasing the amount of pores on grain boundaries and creating the conditions for plastic deformation
1. INTRODUCTION
JSC “Ulba Metallurgical Plant” (“UMP”) produces different types of uranium products for more than forty years. Today, these products include fuel pellets for nuclear reactors from uranium dioxide and uranium dioxide with burnable poisons such as erbium and gadolinium oxides. Besides, “UMP” produces uranium dioxide ceramic powders with high level of nuclear purity and powders from natural uranium.
Fuel pellets production technology at JSC “UMP” is based on conventional methods of powder metallurgy – uranium dioxide powder preparation, preliminary compaction and homogenization of its properties, preparation of moulding powder with addition of binding and lubricating substances, formation of green pellets in hydraulic and mechanical automatic presses, sintering of green pellets in hydrogen atmosphere, cylindrical grinding of sintered pellets. The high level of stability and maturity of technological processes allow producing pellets that meet high quality requirements of our customers.
At the same time, in 2000-2003 JSC “UMP” conducted a range of works focused on improving fuel pellets characteristics, that influence the operating efficiency of fuel assembly during fuel irradiation under high level of burning-out and in reactor capacity maneuvering mode. First of all, these are such characteristics of pellets as uniformity and homogeneity of microstructure, level of open porosity, pore distribution according to size, grain size, thermal stability, and plasticity of pellets.
Improvement of microstructure, morphology of which is responsible for all essential properties of pellets, was achieved by step-by-step analysis of physicochemical contents of events at each stage of technological process of uranium dioxide powder and pellets production, by searching for interconnections between those events, and finally, by defining the basic “levers” for the control of microstructure.