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摘要
In order to keep the reactor criticality, chemical shim is universally used for the control of pressurized water reactors (PWRs). In other words, it is vital to maintain the boric acid concentration uniformly distribution in the primary cycle. Otherwise, if the low-borated water is injected into the reactor core, it will result in a reactivity excursion. Because it is difficult to measure boron concentration in the process of transient by means of experiment, numerical simulation is adopted to study these phenomena. Moreover, the CRUD known as a type of deposit on fuel cladding, which sources from corrosion products and contains high concentrated boron solutes, would be noticed in the boron dilution transient. The hidden boron should be regarded as an implicit source term in the boron transient scenarios. This scenario is not considered in the existing boron tracking model which is implemented in several system codes (e.g. RELAP5, TRACE) and subchannel codes (e.g. CTF). The paper presents an advanced boron tracking model implemented in subchannel code COBRA-IV. It is noted that the capability of boron tracking was not considered in the current version of COBRA-IV code. @@@ This paper is divided into several steps: Firstly, a new field equation is supplemented to the original COBRA-IV code's equations for the boron concentration conservation. The Modified Godunov Scheme is applied to solve the axial transport equation and the results are verified with the analytical solution. Secondly, the lateral boron transport involves diversion crossflow and turbulent mixing phenomenon is considered in this code. Finally, the model includes an advanced CRUD module, with an interface with the main code and a function of simulating the boron hiding amount. @@@ The results illustrated that CRUD layer contains small amount of boron, which can delay boron dilution in specific transient. Although the effect is quite small, according to the parameter study in Section 3.1, this phenomenon may be considerable in severe accidents. Moreover, boron dilution transient is simulated in a 3 x 3 rod bundle and a widely used 17 x 17 assembly. The results show that the boron dilution speed is positively correlated with channel's hydraulic diameter.
- 出版日期2018-11
- 单位上海交通大学
