Experimental Studies on : A. Bubble condenser test facility (R2.01/99) B. TKR Test facility (R2.02/99) at EREC-Elektrogorsk

R2.01/99 - Phare specific and Kola Units 3&4 specific qualification of Bubble condenser test facility at Elektrogorsk and performance of relevant tests

Objective

The project is the continuation and Kola specific completion of work performed in PH2.13/95. The results of the project shall demonstrate reliability and efficiency of the bubble condenser systems and their integrity under the design basic accident conditions.

Specific tasks for Kola NPP:

The Kola Units 3&4 have two special features which differ and demand special bubble condenser experimental support for its qualification:

twice the number of check valves are installed at Kola NPP;
there is only one corridor at Kola NPP with an area of 15.7 m2, which connects steam generator boxes and "dead" volume.
These specific features may essentially influence on the bubble condenser’s behaviour, i.e. changing water carry-over, pressure difference over the bubble condenser, etc. So an additional specific experimental qualification is necessary in this case.

The project tasks in particular:

re-mobilization work;
re-mobilization of the test facility after a 2-year conservation period.
Comparison tests shall be carried out as was performed within PH 2.13/95 (e. g. Test 1) in order to demonstrate that the conditions of the test facility have been re-established.

Kola specific tests and related pre-test and post-test analyses:

performance of 3 DBA tests (Design Basis Accident);
2 MSLB (Main Steam Line Break) tests;
1 small break LOCA test (Loss of Coolant Accident);
DBA: Tests 1, 4 and 5 (Order according to Test Matrix BC-D-ER-0006 from Project PH 2.13/95);
MSLB: Tests 7 and 9 (Order according to Test Matrix BC-D-ER-0006 from Project PH2.13/95, but with the changes derived from EREC’s calculations of MSLB accident scenario);
SB (Small Break): LOCA Test 12 (Order according to Test Matrix BC-D-ER-0006 from Project PH2.13/95);
post-test analysis;
final test report.

The results of the project have demonstrated reliability and efficiency of the bubble condenser system and its integrity under the design basic accident conditions.

R2.02/99 (contin. of R2.30/96) - Experimental verification of multiple Fuel Channel Pressure Tube rupture possibility in RBMK.

Objective

The objective of this project is to analyze the possibility of a multiple-channel tube-rupture in a RBMK caused by the rupture of one tube. The analysis is performed by forcing the rupture of one channel tube during experiments made on the largescale TKR-Test facility at EREC in Elektrogorsk.

The project is divided into the following tasks:

Task 1: Project management.

The Contractor shall work out a detailed time schedule, work plan and Quality Assurance program for the project according to ISO 9001 in agreement with the Beneficiary and Local Subcontractor.

Task 2: Experimental study of critical factors of the postulated accident process.

A range of small-scale experiments have to be carried out to achieve as far as possible "real life" parameters for the large-scale tests to be carried out under task 4 and to define the worst case scenarios and parameters. For this purpose small-scale test facilities of the following type have been established by EREC independently and separately from the TKR:

Test facility "Stand TKR-F": this test facility deals with experiments on one single technological channel of a RBMK to investigate the conditions of a thermo-mechanical rupture of a channel tube;
Test facility "Stand TKR-M": this test facility deals with experiments on mechanical reaction of a column range on static and dynamic impacts;
Test facility "Stand TKR-F (Graphite)": this test facility deals with experiments on the flow of steam-water mixture through narrow graphite gaps.
Sub-Task 2.1: Preparation.
Experimental investigations in small-scale rigs shall be performed first in order to study the factors, which are critical for accident progression.

The following subjects shall be studied:

modes and parameters of fuel channel failure;
relationship between deformation, graphite stack failure characteristics, the pattern of fuel channel failure and the parameters of the escaping coolant;
behaviour of two-phase steam-water flowing through the dynamic gaps between graphite blocks under various conditions of fuel channel failure;
effective rigidity characteristics of the stack as a whole, its local response to the static and dynamic actions;
mechanical response of individual components of the structure (steel/zirconium joints, tube attachment points, etc.) to deformation and transfer of disturbance to the loaded mechanical system;
range of critical loads causing local tube rupture (bearing strain) for specimens with different properties.
Sub-Task 2.2: Definition of the worst cases and critical factors.
The results from Sub-task 2.1 shall be analysed and the accident progression scenarios featuring the worst cases of critical factors shall be established.

Task 3: Preparatory experiments on the TKR test facility.

Sub-Task 3.1: Carrying out experiments to characterize the boundary conditions of the reactor stack module. (The full-scale TKR rig has only 25 of the 1600 RBMK channels).

These additional channels in a real reactor give additional support and resistance to coolant flow. In order to represent the stiffness and permeability to coolant flow of the missing channels a number of experiments are required to characterize them. This data will be used to design a representative boundary around the TKR channels before final experiments are executed. Using the scaled models and the partially assembled full scale TKR rig experiments shall be performed to investigate the multiple pressure tube rupture phenomenon. Scaling factors shall be derived for the small-scale rigs. Effective permeability and stiffness co-relations shall be derived.

The experiments shall be carried out with one, two and three columns in order to measure the following:

Stiffness of the fuel channel walls and graphite stack;
Strain-deformed state of the pressure tubes under various static and dynamic loads and conditions of attachment;
Dynamical characteristics of a pressure tube (containing flowing coolant) under conditions of the external and internal excitation of oscillations.
Sub-Task 3.2: Development of program and procedure for full scale tests in the TKR test facility.
The methodological experimental investigations made in the previous tasks shall be analysed and define in this way the final Program and Procedure for carrying out the full-scale experiments in the TKR test facility.

Task 4: Carrying out the full scale experiments in the TKR test facility in accordance with the developed program, parameters and procedure.

Task 5: Analysis of the experimental study results (post test analysis) analysis and classification of the experimental results.

The deduced data shall be extrapolated to real conditions in the operating reactors in order to obtain practical recommendations for upgrading and back-fitting of RBMK reactors.

Task 6: Final Report and recommendations (if any) what counter-measures are to be taken to exclude multiple tube rupture.

Result

The project has been successfully finished, demonstrating that under the specified boundary conditions, a multiple rupture of one channel cannot be triggered by the rupture of one channel.