PKL facility. Photo: FRAMATOME, Germany
The Primärkreislauf-Versuchsanlage (Primary Coolant Loop Test Facility [PKL]) is a facility owned and operated by Framatome GmbH (formerly AREVA NP) in Erlangen, Germany, to perform experiments on the thermal-hydraulic behaviour of pressurised water reactors (PWRs) during operational transients in order to try to solve PWR safety issues.
For a number of years, Framatome GmbH has conducted experiments on reactor thermal hydraulics at the PKL facility, including earlier experiments carried out in the framework of the SETH project (2001‑2003). Complementary tests have also been performed in some PKL phases at the PMK test facility of the Centre for Energy Research (CER), formerly MTA-EK, in Budapest, Hungary, and at the PWR-PACTEL test facility at the LUT University, Lappeenranta, Finland.
A significant number of tests from the PKL project have been performed as counterpart tests to tests of the ROSA/LSTF and ATLAS projects and have been the subject of comparative benchmark exercises.
PKL-1 investigated pressurised water reactor (PWR) safety issues, specifically:
In the first category of tests which dealt with inherent boron dilution during a small break loss-of-coolant accident, the key issue was whether there were plant thermal-hydraulic conditions that could produce reactivity insertion into the core, and thus a potential accident situation. The experiments tried to reproduce different plant and system configurations, especially those that were believed to be potentially the most serious, thus encompassing an envelope of conservative cases. Measures that could remedy the boron dilution issue were also investigated.
The second category of tests was to assess accident management operations of the primary circuit after a loss of residual heat removal capability during mid-loop operation. Tests with closed reactor circulation system explored safe procedures for re-establishing heat removal and avoidance of significant reactivity insertion into the core. Tests with open circulation systems aimed to explore measures for preventing fuel damage and maximising safety margins provided by different means of coolant injection.
Two tests were performed in 2004 and two in 2005. A workshop was also organised in 2005 covering an analytical exercise with code predictions related to the PKL tests. The 2005 tests focused on the loss of RHR in a three-quarter loop operation with the reactor cooling system closed and on the effect of pressuriser temperature on the RCS inventory distribution. The two tests were carried out to address the following scenarios:
Three final tests for phase one were performed and reported on in 2006. The first phase of the project ended with a final meeting in May 2007.
Project data package
PKL-2 investigated safety issues relevant for current PWR plants as well as new PWR design concepts. It also focused on complex heat transfer mechanisms in the steam generators and boron precipitation processes under postulated accident situations.
The first category of tests included tests addressing the heat transfer mechanisms in the steam generators (SGs) in the presence of nitrogen, steam and water, in both vertical and horizontal steam generators. Also covered were cool down procedures in the case where steam generators had partly dried out on the secondary side. An additional test addressed heat transfer in the steam generators under reflux condenser conditions (e.g. fast secondary side depressurisation). Fast cool down transients (with a water-filled reactor coolant system) such as main steam line break, completed by tests that mixed hot and cold water in the reactor pressure vessel (RPV) downcomer and the lower plenum were also considered in this phase. Further investigation addressed boron precipitation processes in the core following large break loss of coolant accidents (LB-LOCA).
The program included eight integral experiments at the PKL test facility covering the following topics:
* The tests on the heat transfer mechanisms in the SGs in the presence of nitrogen were complemented by tests in the PMK test facility in Hungary for horizontal SGs.
** The tests on fast cool down transients were completed with tests at the Rossendorf Coolant Mixing Model (ROCOM) test facility in Germany on mixing in the RPV downcomer and the lower plenum.
A concluding joint workshop with the ROSA-2 Project was organised from 15-19 October 2012 at the OECD Conference Centre. 45 presentations were given covering the general overview of PKL and ROSA projects, analyses of the counterpart test at the PKL and ROSA/LSTF facilities, the results and analyses related to PKL-2/ROCOM tests, the results and analyses related to other PKL and ROSA tests, analytical studies on core exit temperature (CET) behaviour and general analyses related to PKL-2 and ROSA-2 tests.
The final summary report of the PKL-2 project is available here.
Project data package
PKL-3 began in 2012 and investigated safety issues relevant for current PWR plants as well as for new PWR design concepts by means of transient tests under postulated accident scenarios and systematic parameter studies on thermal hydraulic phenomena.
The first category of tests addressed safety issues related to beyond design basis accident transients with significant core heat-up, i.e. station blackout scenarios or LOCAs in connection with the failure of safety systems. Without adequate accident management (AM) procedures, the postulated course of events would lead to a severe accident scenario with core damage. In the tests, the efficiency of very late initiated AM measures were established so that the safety margins could be explored. Both scenarios were connected with a perfomance assessment of the core exit temperature (CET) which is normally used as criterion for the initiation of AM measures involving emergency operating procedures and/or severe accident management measures.
With respect to current safety issues, events in cold shut down state (i.e. failure of residual heat removal (RHRS)) were also covered by the PKL-3 test phase. Findings from the the first two phases on thermal hydraulic phenomena (e.g. pressure evolution following failure of RHRS, boron dilution) were compared to the transients test conducted with an open RCS.
The second category of tests addressed some issues investigated in the previous PKL phases that could not be completed. Parameter variations from tests conducted in PKL-2 were implemented in PKL-3, either to provide an extension to already existing databases on cool down procedures under asymmetric natural circulation, or to determine the sensitivity of boron precipitation in the core following LB-LOCA for specific parameters. As with previous phases, complementary tests at ROCOM, PMK and PWR PACTEL facilities were also considered for phase three.
In 2015, two meetings were held and final tests were completed. A counterpart test was performed to compare with a test conducted at the ROSA facility in Japan. The ATLAS Project also condidered reproducing a PKL-3 test for comparison.
With all tests completed, the operating agent, Framatome GmbH, conducted analysis of the results and produced the final report in 2016. Project participants and Framatome GmbH completed discussions on a follow-up phase to cover gaps in knowledge. A workshop to discuss analytical activities related to both PKL-3 and ATLAS projects was organized in Lucca, Italy, in 2016. Main conclusions and recommendations from the workshop are presented here.
Project data package
PKL-4 investigated safety issues relevant for current pressurised water reactor (PWR) plants as well as for new PWR design concepts and focused on complex heat transfer mechanisms under two-phase flow, boron dilution and precipitation, and on cool-down procedures.
These issues were investigated by means of thermal-hydraulic experiments conducted at the PKL facility. In addition to the tests conducted at the PKL facility, additional tests were performed at the PMK facility and at the PWR-PACTEL facility. During the PKL4 phase, the PKL facility has been modified to include an EPR-like upper plenum design.
Phase four began in July 2016 and terminated in September 2020. It focused on parametric studies on thermal-hydraulic procedures for model development and validation of thermal-hydraulic system codes, and on experimental verification of cool-down procedures and operation modes for different incidents and accidents.
During the PKL-4 project phase, eight experiments – some with several test runs – were completed between June 2016 and September 2020 addressing:
A workshop to discuss analytical activities related to both PKL-4 and ATLAS-2 projects was organiSed in Barcelona, Spain, in 2018. Main conclusions and recommendations from the workshop are presented here.
Related research on thermal-hydraulics projects can be found at Integral Test Facilities and Thermal-Hydraulic System Codes in Nuclear Safety Analysis.
PKL-1: Belgium, Czechia, Finland, France, Germany, Hungary, Italy, Japan, Korea, Spain, Sweden, Switzerland, United Kingdom, United States.
PKL-2: Belgium, Czechia, Finland, France, Germany, Hungary, Japan, Korea, Netherlands, Spain, Sweden, Switzerland, United Kingdom, United States.
PKL-3: Belgium, Czechia, Finland, France, Germany, Hungary, Italy, Japan, Korea, Spain, Sweden, Switzerland, United Kingdom, United States.
PKL-4: Belgium, China, Czechia, Finland, France, Germany, Hungary, Japan, Korea, Spain, Sweden, Switzerland, United States.
PKL-1: Jan 2004 to May 2007
PKL-2: April 2008 to Sept 2011
PKL-3: April 2012 to April 2016
PKL-4: July 2016 to September 2020
PKL-1: USD 3.6 million
PKL-2: EUR 3.9 million
PKL-3: EUR 4.58 million
PKL-4: EUR 4.78 million