THE OBJECTIVE OF THIS RESEARCH IS TO STUDY THE LONG-TERM PERFORMANCE OF STRUCTURES COMPRISING NUCLEAR POWER PLANTS. THE TIME PERIOD OF INTEREST FOR THIS STUDY IS 140 YEARS (THIS FIGURE IS BASED ON MAXIMUM PERIODS OF 40 YEARS FOR OPERATION AND 100 YEARS OF STORAGE). PARTICULAR ATTENTION WILL BE GIVEN TO THOSE PARTS OF THE PLANT FOR WHICH LEAK TIGHTNESS AND STRUCTURAL INTEGRITY ARE REQUIRED, BOTH DURING OPERATION AND FOR LONG PERIODS AFTER FINAL SHUTDOWN.
THIS RESEARCH WILL BE EXECUTED IN CLOSE CO-OPERATION WITH ZERNA, SCHNELLENBACH UND PARTNER GMBH.
THE SPECIFIC AIM OF THIS RESEARCH IS TO PREDICT FUTURE DETERIORATION OF NUCLEAR POWER STATION BUILDINGS, DUE TO CORROSION OF REINFORCEMENT AND PRESTRESSING STEEL. THE STATE AND RATE OF DEGRADATION OF EXISTING BUILDINGS WILL BE ASSESSED TP PROVIDE QUALITATIVE DATA AND TO IMPROVE EXISTING KNOWLEDGE OF THE FACTORS CONTROLLING THE AGEING PROCESS OF NUCLEAR PLANT BUILDINGS. RELEVANT PLANT MATERIALS WILL BE IDENTIFIED AND PROPOSALS MADE FOR MONITORING PROCEDURES, PREVENTIVE MEASURES AND RECOMMENDATIONS FOR FUTURE DESIGNS.
BUILDINGS TO BE INVESTIGATED WILL BE TYPICAL OF POWER STATIONS OF THE UNITED KINGDOM. HOWEVER, THE RESULTS WILL BE APPLICABLE ALSO TO PLANTS SITED IN OTHER EUROPEAN COMMUNITY COUNTRIES DUE TO THE NATURE OF THE SPECIFIC PROBLEMS POSED. THE SURVEY OF STATION BUILDINGS WILL BE CARRIED OUT ON A RANGE OF NUCLEAR POWER SITES IN THE UNITED KINGDOM, SELECTED TO PROVIDE A RANGE OF EXPOSURE CONDITIONS, VARIOUS DEGREES OF DETERIORATION AND A RANGE OF CONCRETE TYPES. THIS SURVEY WILL INCLUDE THE SHUT-DOWN GAS-COOLED REACTOR STATIONS OF CHINON-AL AND MARCOULE-G2 IN FRANCE.
Investigations were undertaken into the likely durability of reinforced concrete components of buildings and structures at nuclear power stations over the currently envisaged period of up to 100 years for the completion of decommissioning. As sites for the studies, 4 United Kingdom (UK) nuclear power stations were chosen, 3 of the Magnox type, and one advanced gas cooled reactor (AGR) type. Information was also obtained from 3 other Magnox type plants and from French plants at Chinon and Marcoule.
The principle deterioration mechanism examined was reinforcement corrosion, and in particular the 2 main processes which can lead to corrosion initiation on reinforcement, ie chloride ingress and carbonation penetration. Based on information gathered from literature, these processes were examined in relaiton to the prevailing climatic environmental conditions at nuclear power stations and in particular those selected for this project.
Based on the processes concerned in the reinforcement corrosion mechanism, and the environmental factors of relevance, techniques for on site measurements were selected. Surveys of selected available components at the 4 UK nuclear power stations were then undertaken, utilizing the inspection, testing and sampling techniques identified principally for reinforcement corrosion appraisal.
The reinforcement corrosion process, and in particular the corrosion initiation stage, was studied to identify means for predicting the likely timescales of such events, in relation to the 100 year decommissioning period; the data gathered in site surveys were then analysed to estimate whether or not reinforcement corrosion should be expected at the stations examined. Monitoring techiques are proposed for observing the progress of the deterioration mechanisms in the future, as well as options which should be considered for arresting or retarding the deterioration.
1. SELECTION OF SITES AND CONCRETE TYPES;
2. LITERATURE SURVEY INCLUDING THE ASSESSMENT OF THE IN-SITU STATE OF THE CONCRETE AND STEEL AND THE DETERMINATION OF THE CAUSES FOR CONCRETE DETERIORATION AND CORROSION OF STEEL;
3. IN-SITU TESTING OF THE MATERIALS, USING NON-DESTRUCTIVE TECHNIQUES, INCLUDING THE MEASUREMENTS OF ULTRASONIC PULSE VELOCITY, REBAR POTENTIAL, CONCRETE RESISTIVITY, ETC;
4. LABORATORY TESTS ON SAMPLES REMOVED FROM SAFE AREAS (CONCRETE STRENTGH, DEPTH OF CARBONATION, WATER PERMEABILITY, OXYGEN DIFFUSION, ETC.);
5. USE OF THE TEST RESULTS, TO DEVELOP A COMPUTER PROGRAM PREDICTING RATE OF DETERIORATION, ONSET AND RATE OF CORROSION, EXTENT OF CRACKING AND SPALLING, DAMAGES, SERVICE LIFE OF THE STRUCTURE, ETC.
6. RECOMMENDATIONS FOR DAMAGE PREDICTION AND FOR REDUCING CORROSION RATES.