The objective of stabilization of the Shelter building structures is to decrease the probability of building structures collapse for the period up to 15 years.
It is achieved by means of stabilizing the unstable building structures.
Stabilization Project was implemented in four stages:
Stage 1 – defining a list of stabilization measures
Stage 2 – conceptual stabilization decisions
Stage 3 – detail design
Stage 4 – construction, commissioning
STAGE 1 started in June 1998 and completed in May 2001.
Contractor: Consortium ICC(MK)JV consisting of Morrison Knudsen (USA), NIISK, KIEP, ISTC.
Main tasks of STAGE 1:
- Defining a number of stabilization measures;
- Conceptual decisions on stabilization measures;
- Taking decisions about required stabilization of the Shelter building structures.
Number and scope of stabilization measures to be designed are accepted by the key decision P1 “Strategy of Stabilization and Shielding”, for which 15 stabilization measures are defined, 6 ones of which depended on burdens due to tornado.
Program decision P2 “Decision on Stabilization Strategy for Roof, Supports and Structures” defines 9 measures for further implementation.
STAGE 2 started in June 2001 and completed in February 2002.
Contractor: Consortium ICC(MK)JV consisting of Morrison Knudsen (USA), NIISK, KIEP, ISTC.
Main tasks of STAGE 2: Pre-design investigations to gather initial data for development of Work Design on stabilization measures.
STAGE 3 started in September 2001 and completed in August 2003.
Contractor: Consortium КСК consisting of NIISK, KIEP and ISTC.
Main tasks of STAGE 3: Development of Work Design on stabilization measures, specification of a number of stabilization measures, approval of Work Design on stabilization measures.
STAGE 4 started in May 2004 and completed in August 2008.
Main tasks of STAGE 4: Implementation of stabilization measures.
Contractor: russian-UkrainianConsortium “Stabilization” consistingofCJSC “Atomstroyeksport”, russian(Consortiumleader), JSC “Yuzhteploenergomontazh”, CJSC “RovnoNPPConstructionDepartment” andUDETI “Atomenergostroyproekt”, Ukraine.
General contract organization JSC YuTEM performed building-assembling works on site involving 7 subcontract organizations.
Stabilization measures
Measure #14
Western support leg of “Mammoth” beam – completed on 01.11.2005
Reinforcement of the western support leg of “Mammoth” beam lies in increasing section area of existing cross braces located along edges of dimensional metal support leg. Reinforcement is provided by means of installing and welding of two angles additionally to two same angles forming T-section so that closed hollow quad of two angles is formed in section of each branch of coupling element.
The exposure dose rate (EDR) near the support leg is 400-1000 mR/h.
Measure #14А
Eastern support leg of “Mammoth” beam – completed on 20.12.2005
Eastern support leg of “Mammoth” beam is constructed as concrete abutment of 9.0 m height with 4.6x4.6 m section and metal head. The support leg basis is debris of building structures filled with concrete located at remaining cover at mark +35.500. The debris top corresponds to mark +43.050. By means of visual natural investigations, it was determined that cavities are detected within support leg basis that could impact on its stability in case of potential seismic activity.
Reinforcement is performed by embedment of support leg basis with arrangement of fixed block of metal beams secured with existing reinforced concrete columns by means of plate steel loops. Covering the support leg basis with concrete of В25 class is performed in permanent form from northern and eastern side of support leg, from mark +40,100 to mark +44,300. Metal beams of rolled sections are installed at mark 43,050 m at axis 41 between column of row “B” and column of row “Г”, and at row “Г” between column at axis 41 and column at axis 42. The maximum weight of beam is 1.5 t.
EDR values:
- near eastern support leg of “Mammoth” beam – within 300-1,200 mR/h;
- maximum value of EDR (up to 1,200 mR/h) is detected near southern-western basis of support leg between axes “В” – “Г”;
- minimum – 300-600 mR/h at axis “В” near southern support leg basis;
- the highest values of EDR (up to 1,000 mR/h) are detected near northern side of support leg, and EDR values are increasing westward and northward from support leg.
Measure #3В
Reinforcement of upper part of deaerator stack frame – completed on 27.07.2006
It was decided to reinforce the upper part of reinforced concrete frame by means of installing additional metal braces binding upper part of the column of row “Б” at mark +33,15 with cover structures at mark +24,270 near row “В”.
Metal braces are installed along column edges (axes 42-48) and are two-branch grid structure consisting of two channels combined on upper and lower booms by grid of single angles. For convenience of supplying structure elements to premise Г635/3, each branch of brace was divided into three assembling elements of length up to 6 m and of weight up to 200 kg.
EDRvalues:
- in premise Г635/3 it varies from 10 to 100 mR/h, herewith EDR values are increasing towards upper marks and towards new cover of Turbine Hall;
- local increase of EDR is detected in wall apertures near axis “Б” over Turbine Hall roof;
- maximum values of EDR (1800 mR/h) are detected near axis “Б” during measurement in wall apertures over Turbine Hall roof.
Measure #3С
Reinforcement of plates for deaerator stack cover at mark 33,70 – completed on 25.05.2005
Seven plates for deaerator stack (DS) cover at mark 33,70 are under emergency condition. To avoid their collapse and to create safe labor conditions during work performance on measure #3В, it was decided to reinforce them by means of installing pillars at mark 16,40.
EDRvalues:
- in premise Г635/3 it varies from 10 up to 100 mR/h, herewith EDR values are increasing towards upper marks and towards new cover of Turbine Hall;
- local increase of EDR is detected in wall apertures near axis “Б” over Turbine Hall roof;
- maximum values of EDR (1800 mR/h) are detected near axis “Б” during measurement in wall apertures over Turbine Hall roof.
Measure #2
Reinforcement of western fragment – completed on 30.05.2008
The reinforcement of western fragment of Shelter Object is made by constructing dimensional metal reinforcing tower structure (MRS) within local zone near western buttress wall. MRS is designed as two bar support legs sized as 8.5х15 m, total height 49.2 m, with dimensional consoles outreaching up to 22.8 m eastward. The support legs are installed on reinforced concrete foundations at mark +14.000.
Stabilization of western area lies in 80% load transmission from Beams Б1/Б2, own weight of light roof and piped subfloor over Central Hall for new metal reinforcing structures to remove loads from destroyed wall at axis 50. Wall at axis 50 is reinforced by means of installing seven supporting legs at three levels.
EDRvalues:
- at height of buttress wall at axis “Л”, EDR is increasing from 20-25 mR/h at the bottom to 150 mR/h;
- EDR values at internal side of buttress wall at axes “Е” and “Н”:
- maximal – 420-620 mR/h near axes “Е” and “Ж”;
- minimal – 18-26 mR/h at axes “К” and “Л” at the bottom at mark +4,000 m.
Measure #5/11
Combining northern “shields-sticks” with northern buttress wall using fixing anchors – completed on 28.11.06
Combining northern “shields-sticks” with northern buttress wallis stipulated by means of installing and fixing “shields-sticks” at supporting traverses, by which the sticks are supported by the top of metal irremovable concrete form of northern buttress wall, specifically produced metal fixing anchors (Stabilization Measure #5), and by subsequent concreting of upper part of northern buttress wall up to designed wall top level (Stabilization Measure #11).Work area – work sites along northern buttress wall supported by its buttresses (mark +53,700 m). Welding works are performed higher the top of metal irremovable concrete form of the mentioned wall (mark +54,600 m).
EDR values:
- at mark 42,850 m at the bottom of northern buttress wall (axis “У1”), EDR values range from 6.5 mR/h (axes “47” – “49”) to 50 mR/h at axis “43”;
- the lowest EDR values are from 180 to 1000 mR/h on northern side of cover at axis “П”;
- within cover area limited by axes “С” – “Т” and “П” – “Р” and axes “41” – “49” (inclined surface of northern “shields-sticks”), EDR values range from 640 up to 2800 mR/h.
Measure #8
Combining southern “shields-sticks” with southern shields – completed on 12.12.06
Stabilization of southern part of Shelter roof is performed by combining southern “shields-sticks” with southern roof shields preventing displacement of “shields-sticks” southward. It was reached using triangulated bracing installation along row “В” between axes 41-50 at mark +57.500. The triangulated bracing is located parallel to roof surface at the distance, approximately, 500-700 mm from it and is supported by mounting hooks of southern shields and “shields-sticks” overhanging over roof surface.
Location of work area – southern area of SO cover near axis “В” between axes “41” – “50” at mark +57,600 m.
EDRvalues:
- increasing from 200-340 mR/h (axis “41”) to 1500 mR/h (axes “48”–“50”) on cover near adjoining of southern shields to southern “shields-sticks” along axis “В”;
- EDR has values 200-1000 mR/h along axis “В” and 340-1500 mR/h along axis “Г” on SO cover between axes “В”–“Г” and axes “41”–“50” at mark +57,600 m.
Measure (withoutnumber)
Local hermetic sealing (repair) of light roof – completed on 12.08.2008
The light roof is located over Central Hall and consists of six packaged units of 36 meters length. Theareaoflightroofis1405 m2. It is made of zinc-plated profiled flooring with 1 mm thickness of a plate. Since construction of Shelter Object, significant destructive impacts on roof took place leading to formation of large areas damaged by corrosion. During investigations it was revealed that along the whole roof area the profiled flooring has sections with corrosion, and in some places significant breakdowns were detected of total area from 120 to 150 m2, joint hermetic sealing is lacking, etc. Opened apertures enabled atmospheric precipitations to come easily inside the object. This resulted in destruction of building structures, influenced on condition of fuel-containing materials inside the Shelter.
The light roof repair is made by means of local hermetic sealing by stacking new plates of profiled flooring, mounting tray-like battens, recovering hermetic sealing, and arranging regulated discharge outlet.
All activities on stabilization measures were conducted under conditions of high level of radiation exposure.
Stabilization of Shelter Object structures has the importance to assure safety for personnel working today on ChNPP site, and for inhabitants of territories outside of the Exclusion Zone. It is absolutely essential for safe construction of NSC as it would enable existing Shelter to isolate the environment from the impact of fuel-containing materials enclosed inside the “Sarcophagus” until New Safe Confinement is built and accepted for operation. After this, structures of existing Shelter will be dismantled under NSC cover.