A new LFR design concept for effective TRU transmutation
Jae-Yong Lima, and Myung-Hyun Kim
Department of Nuclear Engineering, Kyung Hee University, SeoCheon-dong, Kiheung-gu, Yongin-shi, Gyeonggi-do 446-701, Republic of Korea
One of the lead-alloy cooled fast reactors, PEACER (Proliferation-resistant, Environment-friendly, Accident-tolerant, Continuable-energy, and Economical Reactor), has been designed by a university research team in Korea. This reactor is a medium-size modular fast reactor of 850 MWt (300 MWe) rated power with lead–bismuth coolant loop. A square lattice fuel assembly with large pitch size might be favorable to ensure sufficient mass flow rate not only in normal operation but also in natural cooling under accidents. A metal fuel of (U,TRU)10%Zr is chosen in this study for the advantage of high thermal conductivity. Multinational energy complex with a closed fuel cycle facilities should provide proliferation resistance with an institutional barrier. Under the material control safeguards, all fuel isotopes and radioactive material should be confined in a complex but as low-level radioactive waste. In order to achieve this goal, efficient transmutation of long-lived minor actinides (LLMAs) and long-lived fission products (LLFPs) should be completed in an LFR core.
An energy complex, PEACER-Park, consists of four PEACERs and two collocated pyro-processing plants. Only low-level waste from spent fuel reprocessing plant is designed to be transported out of PEACER-Park. Recovery factors in reprocessing plant, therefore, should be high enough to make low-level tail satisfy US NRC class C classification. However, an interim storage should be collocated in PEACER-Park for storing radioactive fission products having short half-life such as Cs-135 and Sr-90.
Parametric studies have been done for a core design to maximize its transmutation capability within safety criteria.
■ When a pitch to diameter ratio (P/D ratio) was increased, the transmutation capability of each LLMA isotope changed in different ways.
■ When neutron leakage was increased by making core shape flat, the transmutation enhanced.
■ It was confirmed that longer cycle length was favorable to transmutation.
■ In the case of feed fuel composition and coolant operation temperature, there were no significant effects on transmutation performance.
The final optimized core was designed as follows: a flat core shape with 50 cm of active core height and 5 m core diameter, pitch to diameter ratio of 2.2 which could be compromised between different transmutation tendencies of Np-237 and Am-241 and three different enrichment zones with 1-year cycle length. This design could achieve a sufficient transmutation capability with a support ratio of 2.085. Maximum pin power peaking was less than 1.5. Large negative radial expansion feedback coefficient and a sufficient shutdown margin could also be guaranteed.