Nuclear Reactor

In: Science

Submitted By Shrek
Words 635
Pages 3
연쇄핵분열반응의 결과 순간적으로 방출되는 다량의 질량결손(質量缺損) 에너지가 방출되도록 연쇄반응을 제어하여 핵분열에서 발생하는 열에너지를 동력으로 사용하도록 하는 장치이다. 최초의 원자로는 1942년 이탈리아 출신의 물리학자 페르미(Enrico Fermi, 1901~1954)가 미국의 시카고대학교 실험실에서 만들었다.
크게보기원자로

원자로(Nuclear Reactor)는 원자력 발전소의 중심 부품으로 사진의 원자로 왼쪽의 바늘처럼 나온 것이 제어봉구동장치이다.

원자로의 원리
핵폭발 때 순간적으로 방출되는 다량의 에너지가 목적하는 바에 따라 서서히 방출되도록 조절함으로써 핵에너지를 실생활에서 활용할 수 있다.

보통의 화력로가 물질의 연소열을 이용하는 데 반해 원자로는 핵분열반응의 결과 발생하는 질량결손(質量缺損) 에너지를 이용하는 점에서 차이가 있다. 즉, 연소열에 의해 자동으로 연소가 확대되는 화력로와 달리 원자로는 연료의 핵분열 때에 방출되는 중성자(中性子)를 매개체로 하여 핵분열(원자로의 경우에도 연소라 한다)을 지속하게 된다.

따라서, 원자로에서는 핵연료에 흡수되는 중성자수를 제어함으로써 핵연료의 연소를 조절하는데, 원자로 내의 핵분열을 지속시키기 위해서는 핵분열시 방출되는 중성자 중에서 다시 핵연료에 흡수되어 재차 핵분열을 일으키는 수가 최소한 1개 이상이어야 한다. 만약 그 수가 1일 때에는 핵분열반응은 감소하지도 증가하지도 않고 일정하게 유지되며, 이 상태를 원자로의 임계(臨界)라고 한다.

또한 그 수가 1을 초과할 때는 핵분열반응의 수도 점점 증가하게 되는데 이를 초임계상태(超臨界狀態)라 하며, 그 반대의 경우를 미임계상태(未臨界狀態)라 한다. 일반적으로 원자로를 일정한 출력으로 운전할 때는 이를 임계상태로 두거나 약간의 임계초과상태로 하여 여분의 중성자를 적당한 물질(제어봉)에 흡수시키는 방법을 취한다. 1회의 핵분열에서 방출되는 중성자수는 우라늄 235의 경우 평균 2개 정도이지만, 이들 모두가 재차 핵분열에 기여하는 것은 아니고 원자로 외부로의 누설, 또는 비핵분열성 물질에의 흡수 등에 의해 그 수가 감소하므로 원자로를 계속 운전하기 위해서는 이러한 중성자 손실을 최소로 해야만 한다.

그 방법으로는 핵분열성 물질의 양을 증가시키거나 핵분열시 방출되는 고속중성자를 열중성자준위로 감속시켜 흡수확률을 높이는 방법, 노심외부(爐心外部)로의 누설량을 최소화할 수 있도록 원자로의 크기를 충분히 크게 하는 방법, 그리고 다른 비핵분열성 물질에의 흡수를 최소로 하는 방법 등이 있다. 핵분열의 순간에 방출되는 중성자는 에너지가 높은 고속중성자로서 핵연료에 흡수될 확률이 극히 낮으므로, 이를 감속시켜 흡수확률을 높여 주는 것이 중요한 문제이다. 원자로의 제어는 카드뮴·붕소 등과 같이 중성자 흡수 단면적이 큰 재질(보통 막대 형태)을 노심 내에 집어넣거나 빼냄으로써 중성자수를 조절하여 제어하게 되며, 또한 반사체(反射體)나 감속재의 양을 변화시키는 방법을 사용하기도 한다.

원자로의 구조
원자로는 핵연료와 감속재, 냉각재, 제어재, 구조재로 구성되어 있으며 이용 목적에 따라 실용로, 개발시험로, 생산로, 연구로 등으로 구분할 수 있다.

원자로의 중앙에는 연료체가 격자 형태로 배열되어 있고, 그 사이 및 주위에 감속재가 있는 노심부가 있다. 연료체와 잠속재로 구성된 노심부에서 연쇄반응이 일어난다. 그 바깥으로 중성자 누설을 방지하기 위한 중성자 반사체가 배치되어 있으며, 가장 바깥측은 노 내에서 발생하는 강한 방사선인 감마선과 중성자선의 누출을 막기 위한 차폐체가 있다.

노 내에서 발생한 열을 외부로 빼기 위해서 냉각계가 이를 관통하여 설치되어 있다. 감속재의 종류에 따라 냉각계의 형태에 차이가 있다.

제어봉장치는 일반적으로 노의 위쪽 또는 아래쪽에 설치되며 중성자 흡수체로 만든…...

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