IN THE COMMUNITY'S FIRST FIVE YEAR (1979-83) PROGRAMME OF RESEARCH ON DECOMMISSIONING OF NUCLEAR POWER PLANTS, WORK WAS CARRIED OUT TO IDENTIFY FEATURES WHICH COULD BE INTRODUCED TO FUTURE PLANTS TO FACILITATE THEIR EVENTUAL DECOMMISSIONING AND DISMANTLING.
AMONG THE FEATURES IDENTIFIED WAS THE POSSIBILITY OF CONSTRUCTING THE ACTIVATED REGION OF A PRE-STRESSED CONCRETE REACTOR VESSEL (PCRV) OR THE BIOLOGICAL SHILED IN BLOCKWORK WHICH COULD LATER BE REMOVED EASILY IN PREDETERMINED REGULARLY SHAPED PIECES. ALTHOUGH THIS FEATURE WOULD GIVE RISE TO A NUMBER OF PLANES OF WEAKNESS IN THE INNER REGIONS OF THE STRUCTURE, PRELIMINARY ANALYSES SHOWED THAT SUCH PLANES OF WEAKNESS DO NO SIGNIFICANTLY AFFECT THE OVERALL PERFORMANCE OR INTEGRITY OF THE STRUCTURE.
THE OBJECTIVE OF THE PRESENT RESEARCH IS TO CARRY OUT SUPPLEMENTARY, MORE DETAILED ANALYSES FOCUSING AS NECESSARY ON PROBLEM AREAS, AND THEN TO VERIFY THE ANALYTICAL RESULTS BY MEANS OF SIMPLE, SMALL-SCALE MODELS OF PCRVS WITH BUILT-IN PLANES OF WEAKNESS.
THE RESEARCH WILL BE DIRECTED MAINLY AT PCRVS TYPICALLY AS USED IN THE CURRENT ADVANCED GAS-COOLED REACTOR SYSTEMS. THE ANALYSES WILL BE CONFINED TO SUCH STRUCTURES AND THE MODELS WILL ALSO RELATE TO THEM. HOWEVER, IT IS CONSIDERED THAT THE RESULTS OF THE RESEARCH WILL BE EQUALLY APPLICABLE TO THE CONCRETE BIOLOGICAL SHIELDS USED IN CURRENT LIGHT WATER REACTOR SYSTEMS.
A review of previous analyses of prestressed concrete reactor vessels (PCRVs) was carried out to identify regions of the PCRV which might be particularly sensitive to the introduction of planes of weakness. Two 1/20th scale models of a single cavity PCRV were designed, one without and the other with planes of weakness. Computer representations of the vessel models were formulated to take account of any significant indications derived from the review of the previous analyses. Analyses were made of the vessel models, with and without planes of weakness, for a selection of load cases. Two concrete models based on the above design were constructed, one with and one without planes of weakness. These structural models were pressure tested.
The overall conclusion of the study is, firstly, that the analyses indicate that the planes of weakness have no significant effect on the behaviour or integrity of the PCRV. Secondly, it may be said that the common regions of the models unaffected either by the wate leakage or by the suspected mismatch arising from the scaling effect of the weakness plane material behaved in an essentially similar manner. To this extent, therefore, the model tests would appear to give support to the analytical results. On the basis of the work done to date, therefore, it would appear that the planes of weakness feature could provide an acceptable means of facilitating the dismantling of the activated regions of concrete in PCRV, biological shields and similar structures.
B.1.- REVIEW OF THE PREVIOUS ANALYSES TO IDENTIFY REGIONS OF THE PCRV WHICH MAY BE PARTICULARLY SENSITIVE TO THE INTRODUCTION OF PLANES OF WEAKNESS.
B.2.- CONSTRUCTION OF A COMPUTER MODEL, OF VESSEL MODELS TO TAKE ACCOUNT OF ANY SIGNIFICANT INDICATIONS DERIVED FROM THE REVIEW OF THE PREVIOUS ANALYSES.
B.3.- ANALYSES OF MODEL VESSELS WITH AND WITHOUT PLANES OF WEAKNESS, FOR A SELECTION OF LOAD CASES.
B.4.- CONSTRUCTION OF TWO CONCRETE MODELS OF SINGLE CAVITY PCRV STRUCTURES AT SCALE 1-20, WITH AND WITHOUT PLANES OF WEAKNESS.
B.5.- PRESSURE TESTING OF THESE STRUCTURAL MODELS.
B.6.- CONCLUSIVE ASSESSMENT OF RESULTS IN RELATION BOTH TO PCRVS AND LIGHT WATER REACTOR SYSTEM BIOLOGICAL SHIELDS.