Effective energy management design of spent fuel dry storage based on hybrid control rod‐heat pipe

Abstract

Spent fuel dry storage cask, which stores the spent fuel from wet storage facility to final processing, has been developed and managed. Even though thermal management mechanisms of dry storage casks secure the thermal integrity of the cask, improvement of thermal management capacity of dry storage cask would enhance thermal margin against unforeseen off-normal conditions with increasing specific storage capacity. Ulsan National Institute of Science and Technology (UNIST) CANister (UCAN) utilizing the new-type thermosyphon heat pipe, is under development as an advanced design of spent fuel dry storage cask. Hybrid control rod-heat pipe, which is an annular thermosyphon by containing neutron absorber, is a key component of UCAN. Heat removal performance of the hybrid control rod-heat pipe was analyzed bya series of experiment withtest facility simulating single fuel assembly with full height. The UCAN fuel assembly showed the reduced structural and fuel temperatures compared to bare fuel assembly of conventional cask designs, exhibitingimproved thermal margin. According to experimentally observed heat removal rate of the hybrid control rod-heat pipe, UCAN design could extend manageable thermal capacity from 13.3% to 33.8%. The removeddecay heat through hybrid control rod-heat pipe could be reused in electricity generation with stirling engine and thermoelectric devices improving energy management efficiency. Intermittent boiling accompanying geyser phenomena was frequently occurred inside the test section, and the boiling behaviors according to fill ratios (FRs) and operating pressures dominated the heat removal performances. The hydrostatic pressure owing to large aspect ratio affected differentiated thermal-hydraulic behaviors compared to conventional thermosyphons. To develop heat transfer and hydraulic models of the hybrid control rod-heat pipe, geyser phenomenon inside the test section wasdiscussed physically. This workexhibited the feasibility of UCAN design and provides fundamental physics on intermittent boiling of thermosyphon operating at sub-atmospheric pressures.

Energy Analysis and Verification of a Constant-Pressure Elastic-Strain Energy Accumulator Based on Exergy Method

“…The discharging process is similar to the above expression, and only the corresponding integral limit needs to be modified. The ratio of the discharging energy to the charging energy is the energy storage efficiency of the airbag during the charging/discharging process, as shown in Equation (2).…”

“…The energy loss during the charging/discharging process is mainly caused by three factors: (1) the rubber material's mechanical properties (such as the Mullins effect, hysteresis effect, etc. which can cause material deterioration); (2) the friction between the airbag and rigid shield during the charging/discharging process, causing energy loss; (3) pressure loss due to thermal changes. The impact of these three factors on the rubber airbag is directly reflected in the value of its contraction pressure, which is lower than the expan- The stress-strain curve in Figure 3 was divided into four regions.…”

“…The airbag-type hydraulic accumulator is often used as an energy storage device in hydraulic hybrid systems to recover the energy generated when a car is braked and supply power when the car is restarted [1]. Studies have shown that when hydraulic hybrid technology has been applied to vehicles, fuel savings of 12-25% can be achieved in urban areas and fuel savings of 6-10% can be achieved during long-distance driving [2,3]. However, because the airbag type hydraulic accumulator cannot store and release energy at a constant pressure, the energy is often not fully recovered and is released due to the mismatch with the system pressure during the working process, resulting in energy waste [4].…”