A series of studies on determining optimal quantities of CSP(concurrent spare parts) were conducted by many researchers. but most of them are focused on system availability model. On this study we'll introduce the weighting rate of each CSP to find a solution to optimal quantities of CSP which are acquired for using considerably long time. As the weighting rate, the concept of NORS(Not Operationally Readiness Supply) was used. To solve the problem, this paper proposes a new CSP model which can be used in permitting backorder flexibly. Through the simple experiment, we validated the mathematical model which was suggested in this paper. Also, we determined the purchasing quantities of each item minimizing total system costs under an available budget constraints.

Abstract
 1. 서론
 2. 기본 가정사항
 3. 수학적 모형
 4. 실험결과
 4. 결 론
 참고문헌

• 홍인섭(연세대학교)
• 김경섭(연세대학교)