Keeping Kuosheng operating15 March 2018
Rai-Fong Su explains how an innovative approach to spent fuel storage is helping to prolong the operating life of Taiwan’s Kuosheng 1.
The Kuosheng nuclear power plant is a twin-unit facility owned and operated by the Taiwan Power Company (TPC) in Taiwan. Kuosheng 1 began commercial operation in 1981, and Kuosheng 2 began operating in 1983. The site is located on the northern coast of Taiwan, approximately 22km northeast of Taipei City, the nation’s capital.
Each unit of the Kuosheng plant has a boiling water reactor (BWR) nuclear steam supply system with 624 fuel assemblies in its core, and is currently licensed to generate 3001MWt and an electrical output of more than 1000MWe. The nuclear steam supply system was designed by General Electric Company and is designated as a BWR/6 unit with a Mark III containment.
Each unit of the Kuosheng plant also has a spent fuel pool (SFP) in the fuel storage building, located outside the containment area. To facilitate the shipment of spent fuel, a small cask loading pool is annexed to the SFP, together with a cask washdown pool.
Above the reactor, within the containment area, there is an upper containment pool with racks for holding both new fuel that will be placed in the reactor and irradiated fuel that has been removed from the reactor during refuelling. All irradiated fuel is transferred from these racks to the spent fuel pool for storage after refuelling is completed and before reactor startup.
The original fuel racks of the SFP and the upper containment pool were replaced with high density fuel storage racks (HDFSRs) in 1992. In 2005, these replacement racks were retrofitted with even-higher density fuel storage racks. As a result, the SFP at each unit of the Kuosheng plant was re-commissioned with a maximum storage capacity of 4398 fuel assembly cells. An additional storage capacity of 663 cells exists in the upper containment pool, but that pool’s capacity is only utilised during refuelling outages and is not currently commissioned for spent fuel storage during normal operations.
TPC attempted to undertake the construction of a new independent spent fuel storage installation (ISFSI) at the Kuosheng site as one alternative, among other possibilities, for increasing spent fuel storage capacity. This effort has been met with nontechnical resistance from various organisations, both governmental and non-governmental. As a result, at the time of writing, actual construction work has not begun. While the design and fabrication of the Kuosheng ISFSI equipment was approved by the nuclear regulatory authority in 2015, TPC has thus far failed, despite the submission of numerous petitions, to obtain the necessary permit from the local government for the runoff wastewater pollution reduction plan.
Consequently, the SFP was nearly filled to capacity in May 2015, when 184 fuel assemblies were discharged during the end-of-cycle 24 refuelling outage at Kuosheng 1.
At that time there were only six effective storage cells remaining. Without the timely deployment of a “silver- bullet” initiative, Kuosheng 1’s EOC-25 outage, scheduled for November 2016, would have marked the end of the plant’s ability to regularly refuel the reactor core. Both Kuosheng 1&2 were faced with premature and permanent shutdown as a result of insufficient SFP capacity.
Since proposed shipments of spent fuel assemblies to either an onsite ISFSI or an overseas reprocessing facility were not likely be approved by authorities in the foreseeable future, the Kuosheng nuclear engineers began looking for an alternative.
They realised that the cask loading pool would not be used for its intended purpose – at least not for a few years to come. The notion of repurposing the cask loading pool by installing new storage racks was seen as a viable contingency measure – instead of terminating plant operation to halt the generation of spent fuel.
With the agreement of the TPC headquarters and the support of the Lungmen plant, TPC staff made a formal design change request (DCR) to install four new 11-by-10- storage-cell fuel racks, donated by Lungmen, in the cask loading pool at each Kuosheng unit. A mobilisation plan for transporting the eight 11-by-10-storage-cell fuel racks from Lungmen to the Kuosheng site – a distance of 40km – by short-sea shipping container was successfully executed on 1 April 2016. A regulatory Safety Analysis Report (SAR) was also developed in collaboration with a domestic engineering services contractor. The DCR and SAR were submitted to the nuclear regulatory authority in August 2016 and approved in April 2017. (The schematic layout of the fuel storage racks in the cask loading pool is shown in Figure 1.)
Installation of the four storage racks at Kuosheng 1 was completed in May 2017. There was then a reshuffling of 220 spent fuel assemblies from the SFP into the cask loading pool during the EOC-25 refuelling outage. The refuelling outage was successfully completed on 9 June 2017 and the reactor has been operating at full power since 19 June 2017.
The additional 440 fuel assembly storage cell capacity ensures that regular refuelling and discharging of the reactor’s fuel can be maintained at Kuosheng 1 until its current operating licence expires on 27 December 2021. This translates into an anticipated, cumulative electricity generation output of 30TWh – one-eighth of the annual electricity requirement throughout Taiwan.
A subsequent plan to install new storage racks in the cask loading pool at Kuosheng 2 has been put on hold because the unit was placed in “reserve shutdown” on 16 May 2016.
This status change occurred when the unit was being brought back on line from its EOC-24 refuelling outage. On 16 May 2016, 35 minutes after Kuosheng 2 had been re-synchronised to the network, major damage occurred to the surge arresters, capacitors, current-limiting resistors, potential transformers and flexible connectors, for all three phases of the main generator. Repair and replacement of the affected equipment was completed by the end of June 2016. Despite this, for reasons beyond the control of TPC, it seems unlikely that Kuosheng 2 will be granted permission to restart operation in the near future.