SERAPH燃料要素の伝熱特性測定及び改良検討

Measurement of heat transfer characteristics of the SERAPH fuel and a study on design improvement

水野 峰雄*; 小山 和也*

Mizuno, Mineo*; not registered

高速炉安全性試験炉(SERAPH)では駆動用炉心燃料に必要とされる伝熱性能を確保する為、ペレット-被覆管ギャップの伝熱を適度な範囲に保つ事が要求されており、ギャップ部に何らかの伝熱抑制機構を設ける必要がある。本検討では、ペレット-被覆管ギャップ部におけるアルミナ織布スリーブ層及びガスギャップを設けた炉心燃料棒の伝熱性能を把握する為、下記項目の試験を実施した。(1)燃料要素の形状を模擬した体系における、織布スリーブ層圧縮状態での外面急冷/急昇温時中心温度測定。(2)円周方向に均一なガスキャップを設けた試験体による、外面急冷時中心温度測定。また、上記織布以外のSERAPH炉心燃料に要求される伝熱性能を達成し得るギャップ構造概念について検討を実施した。その結果、織布スリープ装荷ギャップ部の伝熱性には圧縮率依存性が認められた。ただし、これらの伝熱性のレベルは、先に実施した織布単体での伝熱測定データに比べて大幅に低いものとなっており、この差の原因としては「用いた織布の種類の差」などが考えられる。またギャップ幅20100mのガスギャップ型試験体での中心温度測定結果から、ガスギャップ部の伝熱性の情報を得た。さらに、織布スリーブ以外のギャップ構造に使用し得る材料技術及び使用実績を調査し、燃料要素に要求される伝熱性能を満足する新構造概念を検討した。

For the driver fuel of the FBR Safety Engineering Reactor (SERAPH), a well-controlled pellet-to-cladding heat transfer to fulfill the the requirements is necessary so that some mechanism to regulate heat transfer through the gap is indispensable. Inthis study, following experiments were performed aiming at clarification of heat transfer characteristics through the pellet-cladding gaps filled with alumina cloth or filled only with gas. (1)Measurement of center-line temperature of the test piece, in which alumia cloth sleeve in the gap is compressed simulating the real fuel element, during a rapid cooling or heating from outside. (2)Measurement of center-line temperature of the test piece, in which a constant-width gas gap is maintained along the circumference, during a rapid cooling from outside. In addition to the above experiments, a study on alternative gap concepts, which could fulfill the requirements for the SERAPH driver fuel, has been carried out. These experiments clarified that heat transfer through the alumina-cloth-filled gap is dependent on the compression level of the cloth layer. However, these experimental results with different compression levels showed that the heat transfer is much lower compared with the former experiments where pure alumina cloth layer has been tested. There are some possible elements, which could explain the difference, such as difference of the cloth type. Information on heat transfer through the gas gap has also been obtained using test elements with 20 to 100 microns of gap width. Furthermore, based on survey of existing material technology and experience, which could be utilized for realization of alternative gap concepts besides the alumina-cloth gap, potential of such alternatives to fulfill the requirements was studied.