UJD SR, in its report dated 26 August 2019 (Final evaluation of hot hydrotest of Unit 3 of NPP EMO3&4) provided a detailed opinion on the reasons for requesting reheating of Unit 3 on its website.
In the preparatory phase before reheating, UJD SR inspectors carried out inspections of the preparedness of Unit 3 of NPP Mochovce with emphasis on the following areas, in particular:
The result of all inspections carried out confirmed compliance with the conditions of Unit 3 preparedness for reheating according to the approved program.
During the reheating itself, UJD SR inspectors and its external contractual support specialists performed inspections at Unit 3 on a daily basis, attended the most important tests and performed preliminary evaluation of their results.
Program of reheating of Unit 3 Mochovce was realized from 14 December 2019 till 13 January 2020.
Time course of the most important milestones of reheating:
Preparatory stage of reheating (before starting to increase the temperature of Unit 3 primary circuit):
11 Dec. 2019
12 Dec. 2019
14 Dec. 2019
Start of Reheating:
14 December 2019 at 11:36am, start-up of the first main circulation pump, start of the primary circuit temperature increase, initial temperature of primary circuit of 30°C
Course of Reheating:
16 Dec. 2019
17 Dec. 2019
18 Dec. 2019
26 Dec. 2019
27 Dec. 2019
28 Dec. 2019
29 Dec. 2019
30 Dec. 2019
5 Jan. 2020
6 Jan. 2020
7 Jan. 2020
9 Jan. 2020
11 Jan. 2020
13. Jan. 2020
End of reheating
13 January 2020, at 3:50pm – the primary circuit cooled down to 38°C, completed implementation of the reheating program of Unit 3.
Based on the knowledge gained from the inspections carried out during reheating, the results of the tests carried out and other documents, the following can be stated:
a) All scheduled tests have been carried out.
b) The strength pressure test of the primary circuit with an overpressure of 16.8 MPa was successfully carried out.
c) The leak pressure test of the primary circuit with an overpressure of 13.7 MPa was successfully realized. This pressure test was performed on 27 December 2019 after removal of minor leaks on the separating plates of the primary circuit valves that were detected during the failed first leak test of the primary circuit performed on 16 December 2019.
d) Pressure tests of all steam generators with an overpressure of 5.0 MPa were successfully performed.
e) The program of reheating was interrupted from 17 December 2019 until 26 December 2019. The reason for the interruption was the cooling of the Unit, its preparation for repair of detected leaks on the valves of the primary circuit and the repair itself.
f) Testing of automated gradual loading of diesel generators on all three safety systems – program of loading diesel generators at the primary circuit temperature lower than 140°C. Preliminary evaluation of the test is satisfactory. During the test, a large range of electric parameters of diesel generators was captured based on a request from ÚJD SR. Reading of these parameters was performed by non-standard apparatus, the results are being evaluated. The purpose of these measurements is to prove the proper operation of the excitation and power controllers of diesel generators and their power margin in the given mode.
g) Testing of automated gradual loading of diesel generators on all three safety systems - program of loading diesel generators at the primary circuit temperature higher than 140°C. Preliminary evaluation of the test is satisfactory. During the test, a large range of electric parameters of diesel generators was captured based on a request from ÚJD SR. Reading of these parameters was performed by non-standard apparatus, the results are being evaluated. The purpose of these measurements is to prove the proper operation of the excitation and power controllers of diesel generators and their power margin in the given mode.
h) During the tests of automated gradual loading of diesel generators, the flow rate of essential service water through the spraying system coolers was measured on all three safety systems (flow rates achieved in accordance with the success criteria).
i) The normal operating mode of the HVAC system of the hermetic zone and the airtight zone (rooms that make up the enclosure of the hermetic zone) was set. During 6 days, measurements of temperature and negative pressure in the hermetic zone were taken, the operation parameters of HVAC systems were recorded and also the impact of their configuration on the temperature and negative pressure in the hermetic zone. Preliminary evaluation of these measurements is satisfactory.
j) During the reheating, data for validation of the operating procedures for the personnel were obtained. It has been proven that the operating procedures are developed at a very good standard and are fully applicable to the Unit heating and cooling stages. All identified shortcomings in the documentation are duly registered and will be used for further improvement of the procedures.
k) Data were obtained for validation of the automatic reactor protection system and the safety assurance system. During reheating, these systems run fully in accordance with the design.
The following deficiencies were identified during Unit reheating:
l) Stated reduced insulation resistance of 4 electric heaters of the pressurizer – the failure is being analysed by experts of Slovenské elektrárne in order to take necessary action to prevent its recurrence.
m) Detected reduced air quality in the hermetic zone -probably due to vapours from applied coatings. A sample of air mass was taken and is being analysed in a specialized laboratory. Appropriate action will be taken based on the results of the analysis.
Slovenské elektrárne, a. s., and its contractors are currently working on detailed evaluations of individual tests of the reheating of Unit 3, analysing the failures and detected deficiencies and taking corrective actions.
After submitting the test results (in particular the tests referred to in paras f, g, h, i, j, k), submitting a cause analysis and appropriate corrective actions to the deficiencies found (as stated under paras l) and m), and evaluating the submitted documents, UJD SR will issue its final assessment of the reheating of Unit 3 of NPP Mochovce.
Modified: 7.2.2020 13:17