Beneficiary Organisation: Energoatom
1) Background
EC (Erosion corrosion) of secondary circuit piping is a serious problem in VVER plants. Some leakages have been observed and even two dangerous guillotine breaks have occurred (Loviisa NPP). The EC has also been a serious problem in western light water reactors. In Surry in the USA, 3 workers were killed in a pipe burst in the 1980's. The reason for the pipe break was EC. The EC can be managed by different preventive actions at the plant. One way of reducing EC is changing the water chemistry by using morpholine additions to the secondary circuit.
This project was a continuation of a former Tacis -95 project "Assistance to NPP to Morpholine treatment". Under this feasibility project a test was conducted to prove the satisfactory performance of the morpholine based treatment for the secondary system chemistry control, as far as the corrosion products transportation and resins behaviour is concerned. This test had to be postponed due to new licensing requirements requested by the NRA (Nuclear Regulatory Authorities of Ukraine). The NRA gave its final acceptance for the test implementation to be performed in March 1998. From March 23rd to June 27th, 1998, the test was performed and good results were achieved. A Final test report, was issued in July 1998 and was approved by the NRA in August, so the complete morpholine conditioning system implementation could take place. In this project, which started in August 1998 after finishing of the first project, the application of morpholine water chemistry was studied in more detail and trial runs were carried out.
2) Objectives
To implement a secondary side water chemistry control based on a mixed addition of morpholine and hydrazine as in the original chemistry strategy, instead of only hydrazine. This will slightly increase the pH of the water and reduce the corrosion rates and therefore improve safe operation and ensure long term reliability of secondary circuit components.
3) Project results–achievements
The Procurement Specifications for the supply of morpholine and Ion Exchange Resins, necessary for the morpholine conditioning were issued. Based on these specifications the Procurement Agent (PA) prepared the contract for the morpholine and resins purchase. The calibration, preoperational and operational procedures was completed, based on the preparatory work performed under the a.m. Tacis 95 project.
A plant walk-down took place on December 1998 to check the plant lay-out regarding implementation of the new water chemistry. Morpholine and required resins were delivered to plant the same time. The NRA requested that in order to obtain a permission to operate in morpholine conditions, it was necessary to qualify the secondary water chemistry procedures presented as regards morpholine, hydrazine, iron, copper micro content in accordance to the Ukrainian requirements. Chemistry Procedures qualification and Technical Conditions development could be performed only by qualified Ukrainian organisations. As the above NRA request came after the completion of the related Tacis 95 project and was completely unexpected, it could not be included in Tacis 96 budget (this project). Therefore EC was requested to provide funding means in order to help the Plant efforts to improve the Plant Safety.
A special report requested by the NRA on the Environmental Impact of the morpholine was issued in June 1999. The main additional requirement of the NRA licensing of the morpholine water chemistry was weekly monitoring of the water chemistry. The plant needed to send water samples weekly to the Ukrainian Oil Treatment Institute for analysing the chemistry. For the licensing studies, a contract was signed between the OSA Utility and Ekna in December 2000.
Ekna, once the contract had been signed, started with the licensing studies, consisting on an engineering solution for development of scientific-technical products on the subject of Development and metrological certification of the procedures for measurement of copper, iron, hydrazine and morpholine mass concentration in SU NPP secondary process water. With this activity the project was completed successfully. The Plant Units have been operating using morpholine conditions with very good results, and a long term study between consecutive outages performed by plant confirmed that the corrosion rate was decreasing due to the introduction of the new water chemistry. This could be seen in less magnetite in filters and resins as well as in wall thickness measurements on selected pipes and components.
4) Comments
From the finalisation of this Specific Project, about two years and a half passed. It means that a period between consecutive outages has been studied. From the results of these long-term studies, it is possible to say that the erosion-corrosion rates of the secondary circuit components significantly reduced and consequently the objectives in which this Project was defined was achieved.
Further Information
Further information on the project results could be sought from the beneficiary organizations.