Competitive Outage Lengths When Servicing the Liquid Relief Valves of the Heat Transport System

Abstract

Conservative engineering judgement has been frequently used to decide how early into an outage certain type of maintenance work for key elements of the Heat Transport System (HTS) can be conducted. The immediate consequence of this approach is that the length of the outages is increased unnecessarily because this maintenance work often becomes the critical path and, in an environment of competition such as the up coming open market for electricity in Ontario, short duration outages provide great strategic advantages. This paper presents the work done to relax the 30-day waiting period to block closed the LRVs. A detailed model of the HTS which includes the SDCS and the LCH piping connection to the D70 Storage Tank was developed for the state-of-the-art Two Unequal Fluids (TUF) computer code. The results of the simulations with the TUF code have shown that the LCH can be credited as the overpressure relief path as early as two days after unit shutdown in case of loss of forced circulation (e.g., loss of Class 111 Power to the SDCS pumps). The financial savings and the additional flexibility in planning outage work due to the reduction of the waiting period by a factor of 15 are apparent.