출력증강으로 인한 노심 안전성에 미치는 영향연구

Abstract

In general, nuclear power generation is regarded as economical. However, its huge initial investment and social costs involved in site selection make it not-an-ideal solution to meet rising power demand with construction of a new plant. Under the circumstances, one of the other ways to enhance economics of nuclear power generation is the power uprate. Power uprate means increasing thermal power of the reactor core and has three methods of measurement uncertainty recapture power uprates(MURPU) by decrease in measurement inaccuracy, stretch power uprate(SPU) by changing the set point, and extended power uprate(EPU) by change of BOP equipment. Using the above three method, respectively 2%, 7% and 20% power can be increased. In the US, unit 1 of Calvert Cliffs Nuclear Power Plant was the first one to enhance thermal power by 5.5% with adjustment of equipment set point in 1977. As of October 2009, a total of 5,726MWe in installed capacity was increased from 129 times of power uprate and other 29 sites are in the process of or planning power uprate. In korea, there are 20 nuclear power generation units and they produce a combined 50,773 MWt in thermal output. Only a 5% of power uprate could have the similar effect of constructing an additional unit. Required cost for power generation is considerably lower compared to required cost for constructing a new power plant. In order to evaluate core safety of Yonggwang Nuclear Power Unit 1&2, the power uprated core of Kori Nuclear Power Unit 3&4 with similar furnace type is analyzed on the base of the design criteria. For the evaluation of power uprated core margin of safety, thermal hydraulic design, nuclear design and fuel rod & structure design are evaluated after power uprate, and all the design criteria are satisfied in power uprate. And, all of the practical data(Heat flux hot channel factor, nuclear enthalpy rise hot channel factor, Activity of RCS nuclide, RCS average temperature, Axial offset, Critical boron concentration) of Kori Nuclear Power Unit 4 cycle 19 - after power uprate - are also satisfied with the design criteria. Some items with decrease in safety margin also meet the limits. So core safety items of Yonggwang Nuclear Power Unit 1&2 after power uprate are expected to be satisfied the limit But power uprate applied to Kori Nuclear Power Unit 3&4 (WH type) does not increase fuel concentration or new fuel loading amount, and as a result cycle period of 22EFPD(Effective Full Power Day) is reduced on a 4.5 w/o enrichment, 64 bundles of new fuel and equilibrium core basis. Reduced cycle period drives up power generation unit cost and therefore undermines a portion of economic gains acquired from power uprate. So, in order to maximize economics of power uprate and to ensure optimal cycle period of 18 months, enrichment or new fuel loading amount should be increased. And a little mount of safety margin decreased also are optimized by high performance fuel assembly and 3D core monitoring system. Power uprate is a more effective way where the country have low public acceptance of nuclear energy or site selection problem as in Korea. And it is an economical and efficient way of power generation and capacity increase compared to construction of new units. A recent research trends for the development of improved fuels and core management system are expected to have a positive effect on power uprate. Therefore, in the near future, Optimized power uprate technology will be maximize safety & economics of power uprate.