Hot Leg Pipe Research Articles

実用化戦略調査研究でのNa炉の1次主冷却系設計(液体金属冷却炉,革新型原子炉の開発および多目的利用技術,原子力要素技術開発)

In the "Feasibility Study on Commercialized Fast Reactor Cycle Systems", an innovative concept of a sodium-cooled loop-type reactor to pursue high economic competitiveness has been developed by adopting several innovative concepts. For one of the concepts, 12Cr-steel with high strength and low thermal expansion rate has been employed as a structural material of the primary piping. As a result, the diameter is enlarged and length is shortening and the cooling system has been remarkably simplified. For the design concept of the hot leg piping, it is designed as a simple L-shaped top-entry type piping selected on the view point of economical and technical issues. And the structural integrity against a thermal stress and the instability of the vibrations of primary piping are evaluated.

Prediction of counter-current flow limitation at hot leg pipe during a small-break LOCA

The possibility of hot leg flooding during reflux condensation cooling after a small-break loss-of-coolant accident in a nuclear power plant is evaluated. The vapor and liquid velocities in hot leg and steam generator tubes are calculated during reflux condensation cooling with the accident scenarios of three typical break sizes, 0.13, 1.02 and 10.19% cold leg break. The effect of initial water level to counter-current flow limitation is taken into account. It is predicted that the hot leg flooding is precluded when all steam generators are available for heat removal. It is also shown that both hot leg flooding and SG flooding are possible under the operation of one steam generator. Therefore, it can be said that the occurrence of hot leg flooding under reflux condensation cooling is possible when the number of steam generators available for heat removal is limited.

Dynamic characteristics of KALIMER IHTS hot leg piping system conveying hot liquid sodium

In this paper, the dynamic characteristics of the KALIMER (Korea Advanced LIquid MEtal Reactor) IHTS hot leg piping system conveying hot liquid sodium are investigated to eliminate the pipe supports for economic reasons. To do this, a 3-dimensional straight pipe element and a curved pipe element conveying fluid are formulated using the dynamic stiffness method of the wave approach and coded to be applied to any complex piping system. Using this method, the dynamic characteristics including the natural frequency, the frequency response functions, and the dynamic instability due to the pipe internal flow velocity are analyzed. As one of the design parameters, the vibration energy flow is also analyzed to investigate the disturbance transmission paths for the resonant excitation and the non-resonant excitations.

Experimental Study on PORV Break LOCA in PWR Plants

Small break loss-of-coolant accident (LOCA) tests simulating a pressurizer power operated relief valve (PORV) break LOCA were performed using the EOS (Emergency of System) test facility. The break sizes were 0.25 and 0.88% of a guillotine break of a primary piping. The following major conclusions were obtained and the useful data and information for the verification of a computer code were obtained: (1) The pressurizer was almost full of water due to flooding limitation in the surge line of the pressurizer, when no water was in the hot leg piping. (2) The core was kept completely covered with two-phase mixture during the small break LOCA. (3) The core was sufficiently cooled down by reflux condensation in the steam generator even after the primary system natural circulation stopped. (4) After the depressurization of the primary system was stopped or when the depressurization rate of the primary system was small, the operator action to bleed the steam in the secondary system could steadily depressurize the primary system. (5) This operator action could resume the natural circulation in the primary system.

Experimental study on PORV break LOCA in PWR plants.

Small break loss-of-coolant accident (LOCA) tests simulating a pressurizer power operated relief valve (PORV) break LOCA were performed using the EOS (Emergency of System) test facility. The break sizes were 0.25 and 0.88% of a guillotine break of a primary piping. The following major conclusions were obtained and the useful data and information for the verification of a computer code were obtained: (1) The pressurizer was almost full of water due to flooding limitation in the surge line of the pressurizer, when no water was in the hot leg piping. (2) The core was kept completely covered with two-phase mixture during the small break LOCA. (3) The core was sufficiently cooled down by reflux condensation in the steam generator even after the primary system natural circulation stopped. (4) After the depressurization of the primary system was stopped or when the depressurization rate of the primary system was small, the operator action to bleed the steam in the secondary system could steadily depressurize the...

Consideration of Cesium and Iodine Chemistry and Transport Behavior during the Three Mile Island Unit 2 Accident

Data from the Three Mile Island Unit 2 (TMI-2) accident have shown that only small amounts of iodine and cesium escaped the plant, on the order of tens of curies. To assess the chemical and physical processes responsible for such a limited release, a detailed investigation of iodine and cesium chemical and transport behavior during the core degradation phase of the TMI-2 accident was initiated. Analyses indicate elemental iodine and cesium release from fuel, which subsequently reacts with the high-temperature steam/hydrogen effluent to produce the gaseous species Csl and CsOH. Partial condensation and chemisorption of CsOH in the upper reactor plenum and on hot-leg piping is also predicted, where loss of the CsOH molecule from a mixture of H2O, Csl, CsOH, and HI gases in chemical equilibrium can result in destabilization of the Csl molecule to replace CsOH, forming HI in the process. Likewise, Csl reaction with borated water is predicted to have resulted in partial conversion of Csl to cesium borate and HI. A combination of Csl, HI, and CsOH is therefore assessed to be the principal form of iodine and cesium transport leaving the reactor vessel during core degradation. These species were subsequently dissolved in water, resulting in large-scale retention of fission product iodine and cesium.

64. ROSA-IIによるPWRの冷却材喪失事故模擬試験,(IV)

Experimental results of the ROSA-II hot leg break tests with ECCS injection were compared with these of cold leg break tests. Adequacy of the RELAP-3 prediction of extremely severe break configuration for core cooling during blowdown was confirmed by parameteric tests on the conditions. The major conclusions are as follows:(1) In a large break of hot leg piping, downward core flow at the early stage of blowdown process is weak and almost stagnant. Therefore fuel temperature begins to rise at early time after break due to exposure to steam void under free water level.(2) Since upward steam flow in downcomer is weak, accumulator injection results in remarkable water accumulation in pressure vessel. Therefore core cooling during reflooding process is better. Injection location of low pressure coolant injection system is less sensitive to core cooling.

ＲＯＳＡ‐ＩＩによるＰＷＲの冷却材喪失事故模擬試験 Ｉ

ROSA-II Test Program is intended to clarify thermal and hydrodynamic behavior in a primary cooling system of pressurized water reactor during a postulated loss-of-coolant accident by an integral test facility, ROSA-II. Thirty eight test runs were performed from February, 1974 to September, 1975.The present report gives the purpose of the test program, the qualitative investigation of fluid behavior, a description of the test facility and some experimental results of a cold-leg break test. The results are as follows.(1) Stored heat of the broken and the unbroken loop steam generators has considerable effect on flow behavior in the primary system.(2) Accumulator water injected into the cold-leg piping flows out through the break. However, the coolability of injected water from low pressure coolant injection system into the hot-leg piping is enhanced by the preceded injection of accumulator water.