The APR-1400 (for Advanced Power Reactor 1400 MW electricity) is an advanced pressurized water nuclear reactor designed by the Korea Electric Power Corporation (KEPCO). Originally known as the Korean Next Generation Reactor (KNGR), this Generation III reactor was developed from the earlier OPR-1000 design and also incorporates features from the US Combustion Engineering (C-E) System 80+ design. Currently there is one unit in operation (Shin Kori unit 3) and seven units under construction, four in the United Arab Emirates at Barakah and three in South Korea: one at Shin Kori and two at Shin Hanul. Two more units are planned with construction yet to commence at Shin Kori.
Contents
History
APR-1400 design began in 1992 and was awarded certification by the Korean Institute of Nuclear Safety in May 2002. The design certification application was submitted to the Nuclear Regulatory Commission in December 2014 and in March 2015, it was accepted for technical review to determine if the reactor design meets basic US safety requirements.
South Korea
The first commercial APR-1400 reactors at Shin Kori were approved in September 2007, with construction starting in October 2008 (Unit 3) and August 2009 (Unit 4). Shin Kori-3 was initially scheduled to commence operation by the end of 2013, but the schedules for both Units 3 & 4 were delayed by approximately one year to replace safety-related control cabling, which had failed some tests. Construction of two more APR-1400 units at Shin Kori, Korea (Units 5 and 6) had been expected to begin in 2014, but as of December 2016 plans had not been finalised.
Construction of two new APR-1400s, Shin Hanul Units 1 & 2, began in May 2012 (Unit 1) and June 2013 (Unit 2), with Unit 1 expected to be completed in April 2017. Two more APR-1400s at Shin Hanul were approved in 2014, with construction to start in 2017.
United Arab Emirates
In December 2009, a KEPCO-led consortium was awarded the contract to build four APR-1400 reactors at Barakah, United Arab Emirates. Construction of Barakah Unit 1 started in July 2012, Unit 2 started construction in May 2013, Unit 3 started construction in September 2014 and Unit 4 started construction in September 2015.
Design
The APR-1400 is an evolutionary Advanced Light Water Reactor which is based on the previous OPR-1000 design. Under Korean conditions, the reactor produced 1455 MW gross electrical power with a thermal power capacity of 3983 MW (4000 MW nominal).
The design was developed to meet 43 design requirements, with the main developments being evolution in capacity, increased lifetime and enhanced safety. The design improvements also focus on meeting economic objectives and licensing requirements. Compared to the OPR-1000, the key features are:
Several other changes were incorporated such as moving to complete digital I/C and implementation of new systems in the Safety Injection System (SIT).
Core
The reactor core of the APR-1400 consists of 241 fuel assemblies, 93 control element assemblies, and 61 in-core instrumentation assemblies. Each fuel assembly has 236 fuel rods in a 16 x 16 array (some space is taken up by guide tubes for control elements) containing Uranium dioxide (average enrichment of 2.6 w/o), which is capable of producing an average volumetric power density of 100.9 W/cm^3. Up to 30% of the core can also be loaded with Mixed Oxide fuel with minor modifications. The core is designed for an 18-month operating cycle with a discharge burnup up to 60,000 MWD/MTU, with a thermal margin of 10%. For the control element assemblies, 76 Boron carbide pellets rods are used in the full strength control rods, while 17 Inconel-625 is used in the part strength control rods.
Primary
Like the OPR-1000 and preceding C-E designs, the APR-1400 has two reactor coolant loops. In each loop, heated primary coolant leaves the reactor pressure vessel (RPV) through one hot leg, passing through one steam generator (SG), returning to the reactor vessel through two cold legs, each equipped with a reactor coolant pump (RCP). In loop 2, there is one pressurizer (PZR) on the hot leg, where a steam bubble is maintained during operation. The loops are arranged symmetrically, so the hot legs are diametrically opposed on the RPV's circumference. Because the SGs are elevated relative to the RPV, natural convection will circulate reactor coolant in the event of RCP malfunction. The PZR is equipped with a pilot-operated relief valve which not only protects against Reactor Coolant System over-pressure, it also allows manual depressurization in the case of a total loss of feedwater.
Secondary
Each SG has 13,102 Inconel 690 tubes; this material improves resistance to stress corrosion cracking compared to the Inconel 600 used in prior designs. Like the late-evolution System 80+ design, the SG design incorporates an integral feedwater economizer, which pre-heats feedwater before it is introduced into the SG. Compared with the OPR-1000 design, the SG features a larger secondary feedwater inventory, extending the dry-out time and affording more time for manual operator intervention, should it be needed. The design tube plugging margin is 10%, meaning the unit can operate at full power with up to 10% of the SG tubes plugged. Each of the two main steam lines from the SG contain five safety valves, a main steam relief valve and one isolation valve.
APR+
The APR-1000 has been further developed into the APR+ design, which received its official type certification on August 14, 2014 after seven years in development. The reactor design features improved safety and among others "a core damage frequency an entire order of magnitude lower than that calculated for the APR1400 design that it supplants". The APR+ core uses 257 fuel assemblies (16 more than APR-1400) to increase output to 1550 MW gross electricity. Certain safety features, such as backup generators, have been increased from two to four independent, redundant systems.