Hiroshi Sekimoto

Power flattening on modified CANDLE small long life gas-cooled fast reactor

Gas-cooled Fast Reactor (GFR) is one of the candidates of next generation Nuclear Power Plants (NPPs) that expected to be operated commercially after 2030. In this research conceptual design study of long life 350 MWt GFR with natural uranium metallic fuel as fuel cycle input has been performed. Modified CANDLE burn-up strategy with first and second regions located near the last region (type B) has been applied. This reactor can be operated for 10 years without refuelling and fuel shuffling. Power peaking reduction is conducted by arranging the core radial direction into three regions with respectively uses fuel volume fraction 62.5%, 64% and 67.5%. The average power density in the modified core is about 82 Watt/cc and the power peaking factor decreased from 4.03 to 3.43.

Preliminary engineering design of sodium-cooled CANDLE core

The CANDLE burning process is characterized by the autonomous shifting of burning region with constant reactivity and constant spacial power distribution. Evaluations of such critical burning process by using widely used neutron diffusion and burning codes under some realistic engineering constraints are valuable to confirm the technical feasibility of the CANDLE concept and to put the idea into concrete core design. In the first part of this paper, it is discussed that whether the sustainable and stable CANDLE burning process can be reproduced even by using conventional core analysis tools such as SLAROM and CITATION-FBR. As a result, it is certainly possible to demonstrate it if the proper core configuration and initial fuel composition required as CANDLE core are applied to the analysis. In the latter part, an example of a concrete image of sodium cooled, metal fuel, 2000MWt rating CANDLE core has been presented by assuming an emerging inevitable technology of recladding. The core satisfies engineering...

Study on core radius minimization for long life Pb-Bi cooled CANDLE burnup scheme based fast reactor

Fast Breeder Reactor had been interested to be developed over the world because it inexhaustible source energy, one of those is CANDLE reactor which is have strategy in burn-up scheme, need not control roads for control burn-up, have a constant core characteristics during energy production and don’t need fuel shuffling. The calculation was made by basic reactor analysis which use Sodium coolant geometry core parameter as a reference core to study on minimum core reactor radius of CANDLE for long life Pb-Bi cooled, also want to perform pure coolant effect comparison between LBE and sodium in a same geometry design. The result show that the minimum core radius of Lead Bismuth cooled CANDLE is 100u2005cm and 500 MWth thermal output. Lead-Bismuth coolant for CANDLE reactor enable to reduce much reactor size and have a better void coefficient than Sodium cooled as the most coolant for FBR, then we will have a good point in safety analysis.

Preliminary safety analysis of Pb-Bi cooled 800 MWt modified CANDLE burn-up scheme based fast reactors

Pb-Bi Cooled fast reactors with modified CANDLE burn-up scheme with 10 regions and 10 years cycle length has been investigated from neutronic aspects. In this study the safety aspect of such reactors have been investigated and discussed. Several condition of unprotected loss of flow (ULOF) and unprotected rod run-out transient over power (UTOP) have been simulated and the results show that the reactors excellent safety performance. At 80 seconds after unprotected loss of flow condition, the core flow rate drop to about 25% of its initial flow and slowly move toward its natural circulation level. The maximum fuel temperature can be managed below 1000°C and the maximum cladding temperature can be managed below 700°C. The dominant reactivity feedback is radial core expansion and Doppler effect, followed by coolant density effect and fuel axial expansion effect.

Design study of gas cooled fast reactors using natural uranium as fuel cycle input employing radial shuffling strategy

Design study of gas cooled fast reactors with natural uranium as fuel cycle input has been performed. The reactors utilizes UN-PUN as fuel, helium as coolant, and can be operated without refueling for 10 years in each batch. Reactor design optimization is performed to utilize natural uranium as fuel cycle input. This reactor subdivided into 10 regions with equal volume in radial directions. The natural uranium is initially put in region 1, and after one cycle of 10 years of burnup it is shifted to region 2 and the region 1 is filled by fresh natural uranium fuel. This concept is basically applied to all regions. To achieve criticality requirement relatively high fuel volume fraction is applied. In this study several parametric survey were performed for several parameters such as fuel-to-coolant volume fraction ratio, core radius, and core height. After some optimization process we determine a standard core with a height and a diameter of 350 cm and 240 cm respectively, and the volume fraction for this des...

Modified CANDLE Burnup Calculation System, Its Evolution, and Future Development

CANDLE Burn-up has been widely investigated during the last 15 years and give excellent possibility for natural Uranum utilization without the necessity of fuel enrchment plant and fuel reprocessing plant. Modified CANDLE burn-up scheme is a slight modification of CANDLE burn-up scheme by adopting discreet regions in the core. Modified CANDLE burn-up calculation is a complex calculations because it need accurate treatment of nuclear group constants, burn-up calculations, and multigroup diffusion calculations. Another problem come from the fact that the burn-up level of fuel is very high. Therefore the fission produc treatment have to be carried out in a highly accurate apporach and alsolarge number of energy groups is applied. Large number of Fission product is considered durng simulations. The calculations are performed under iterative scheme. For 10 regions and 10 years of burn-up period, first initial power density distributions are assumed and then multi-group diffusion and burn-up calculations are conducted. After 10 years of burn-up process the fuel in the first region is moved to the second region, the fuel in the second region was moved to the third region, the fuel in the third region is moved to the forth region, and so on. The fuel in the 10th region is then taken out. The first region is filled with the fresh fuel of natural uranium. The process is repeated till equilibrium condition achieved. Modified CANDLE burnup also has evolved to radial shuffling and combined axial-radial shuffling scheme.

The study of capability natural uranium as fuel cycle input for long life gas cooled fast reactors with helium as coolant

The objective of the present research is to assess the feasibility design of small long-life Gas Cooled Fast Reactor with helium as coolant. GCFR included in the Generation-IV reactor systems are being developed to provide sustainable energy resources that meet future energy demand in a reliable, safe, and proliferation-resistant manner. This reactor can be operated without enrichment and reprocessing forever, once it starts. To obtain the capability of consuming natural uranium as fuel cycle input modified CANDLE burn-up scheme was adopted in this system with different core design. This study has compared the core with three designs of core reactors with the same thermal power 600 MWth. The fuel composition each design was arranged by divided core into several parts of equal volume axially i.e. 6, 8 and 10 parts related to material burn-up history. The fresh natural uranium is initially put in region 1, after one cycle of 10 years of burn-up it is shifted to region 2 and the region 1 is filled by fresh natural uranium fuel. This concept is basically applied to all regions, i.e. shifted the core of the region (i) into region (i+1) region after the end of 10 years burn-up cycle. The calculation results shows that for the burn-up strategy on “Region-8” and “Region-10” core designs, after the reactors start-up the operation furthermore they only needs natural uranium supply to the next life operation until one period of refueling (10 years).