/if STUK-B-YTO 135 Operation of Finnish nuclear power plants Quarterly report 1st quarter, 1995 Kirsti Tossavainen (Ed.) SEPTEMBER 1995 STUK-B-YTO 135 SEPTEMBER 1995 Operation of Finnish nuclear power plants Quarterly report 1st quarter, 1995 Kirsti Tossavainen (Ed.) Nuclear Safety Department FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY P.O.BOX 14, FIN-00881 HELSINKI FINLAND Tel. +358 0 759881 Translation. Original text in Finnish. ISBN 951-712-062-1 ISSN 0781-2884 Painatuskeskus Oy Helsinki 1995 FINNISH CENTRE FOR RADIATION STUK-B-YTO 135 AND NUCLEAR SAFETY TOSSAVAINEN, Kirsti (ed.). Operation of Finnish Nuclear Power Plants. Quarterly Report, 1st quarter. 1995. STUK-B-YTO 135. Helsinki 1995, 24 pp. + apps. 2 pp. ISBN 951-712-062-1 ISSN 0781-2884 Keywords PWR type reactor, BWR type reactor, NPP operating experience ABSTRACT Quarterly Reports on die operation of Finnish nuclear power plants describe events and observations related to nuclear and radiation safety which the Finnish Centre for Radiation and Nuclear Safety (STUK) considers safety significant. Safety improvements at the plants and general matters relating to the use of nuclear energy are also reported. A summary of the radiation safety of plant personnel and of the environment, and tabulated data on the plants' production and load factors are also given. Finnish nuclear power plant units were in power operation in the first quarter of 1995, except for two shutdowns at Loviisa 2, and shutdowns at both TVO units. The shutdowns at Loviisa 2 were due to an abnormal rise in the coolant outlet temperatures of certain fuel bundles. The shutdowns at TVO plant units were due to problems caused by the formation of frazil ice in sea water. Also, electricity generation at both TVO plant units was discontinued for a short period to repair a generator cooling system water leak. The load factor average of all four plant units was 93.9%. The following events during the first quarter of 1995 were classified level 1 on the International Nuclear Event Scale (INES): At Loviisa 1, one of two isolation valves in the nuclear fuel storage pool cooling system pipeline were found to have been leaking since the 1994 annual maintenance outage. This valve is in a pipeline penetrating the containment building wall. In a potential accident, there would have been only one isolation valve to prevent the release of radioactive substances to the atmosphere via the pipeline in question. Impurities were observed in certain fuel bundles at Loviisa 2, resulting in abnormally increased coolant outlet temperatures in the bundles in question. Six such bundles were replaced. The impurities might have compromised the cooling of the fuel bundles during certain transients. In January, frazil ice accumulating in the filters of TVO Is cooling water screening plant caused the plant unit's shutdown by its automation systems. Later the same day, with die plant unit in shutdown state, die filters were again clogged up by ice. Supply of cooling water to systems important to safety is ensured by taking half of die service water required by die TVO plant units from the outlet side in die cold season. If die need arises, even die intake of the other half can be reversed. The reversal was not fully successful this time since some gates in die sumps of the service water pumps could not be opened. The removal of decay heat was ensured the whole time, however, since enough service water was drawn from die outlet side. Also, die service water was cold. 3 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-B-YTO 135 During back-up diesel loading tests at TVO plant units in February it was snowing heavily and the air intake channel filters of the diesels were blocked by snow. A decision not to continue the test was made at TVO I. This event disclosed deficiencies in the supply of suction air for the back-up diesels. Other events in this annual quater were classified level 0 on the INES. Occupational doses and radioactive releases off-site were below authorised limits. Radioactive substances were measurable in samples collected around the plants in such quantities only as have no bearing on the radiation exposure of the population. 4 FINNISH CENTRE FOR RADIATION STUK-B-YTO 135 AND NUCLEAR SAFETY CONTENTS ABSTRACT 1 INTRODUCTION 7 2 OPERATION OF NUCLEAR POWER PLANTS IN IANUARY-MARCH 1995 8 2.1 Production data 8 2.2 Shutdown at Loviisa 2 to remove impurities from fuel bundles 12 2.3 Outage at Loviisa 2 to replace fuel bundles 12 2.4 Cold shutdown at TVO I due to the formation of frazil ice in sea water 12 2.5 Hot shutdown at TVO I due to a generator cooling system leak 12 2.6 Hot shutdowns at TVO II due to the fonnation of frazil ice in sea water and to a generator cooling system leak 12 3 EVENTS AND OBSERVATIONS 14 Loviisa 1 14 3.1 One of two isolation valves in the spent nuclear fuel storage pool cooling line had not been leaktight 14 Loviisa 2 IS 3.2 Impurities caused an abnormal rise in the coolant outlet temperatures of certain fuel bundles IS 3.3 Nuclear fuel cladding leak 16 TVO I 17 3.4 Supply of service water was compromised by frazil ice 17 3.5 Insufficient supply of suction air to back-up diesels during load tests due to a snow storm 18 TVO II 19 3.6 Nuclear fuel cladding leak 19 4 RADIATION SAFETY 20 4.1 Occupational exposure 20 4.2 Radioactive releases 20 4.3 Environmental monitoring 20 5 SAFETY IMPROVEMENTS AT NUCLEAR POWER PLANTS 23 No significant safety improvements 6 OTHER MATTERS RELATING TO THE USE OF NUCLEAR ENERGY 24 6.1 Regulations 24 Appendix 1: Regulatory control of nuclear facilities 25 Appendix 2: Plant data 26 5 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-B-YTO 135 FINNISH CENTRE FOR RADIATION STUK-B-YTO 135 AND NUCLEAR SAFETY 1 INTRODUCTION According to die Nuclear Energy Act (990/87), plants' production and availability factors are regulatory control of die use of nuclear energy given and die radiation safety of plant personnel belongs to die Finnish Centre for Radiation and and die environment is summarised. Safety Nuclear Safety (STUK). The Centre's functions improvements at die plants and general matters also include regulatory control of physical relating to die use of nuclear energy are also protection, emergency preparedness and of reported. The fourth Quarterly Report contains a nuclear material safeguards. The scope of nuclear summary of information reported earlier in die power plant regulatory control and inspections is year. given in Appendix 1 and general information about die Finnish plants in Appendix 2. The report is based on information submitted to die Centre by die utilities and on observations STUK publishes quarterly a report on die made by die Centre during its regulatory operation of Finnish nuclear power plants. In this activities. The events described in die report are report, plant events and observations during each classified on die International Nuclear Event quarter are described, tabulated data on die Scale ONES). 7 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-B-YTO 135 2 OPERATION OF NUCLEAR POWER PLANTS IN JANUARY-MARCH 1995 The Finnish nuclear power plant units were in power operation in the first quarter of 1995. except for two shutdowns at Loviisa 2 and shutdowns at TVO plant units. There was also a brief break in production at both TVO plant units to repair a generator cooling system leak. 2.1 Production data Detailed production and availability figures are given in Tables I and II. Nuclear's share of total electricity production in Power diagrams describing electricity generation Finland was 27.8 %. The load factor average of at each plant unit and the causes of power the plant units was 93.9 %. reductions are given in Figs 1—4. Table 1. Plant electricity production and availability. Electricity production Availability Load (gross, TWh) factor (%) factor (%) First 1994 First 1994 First 1994 quarter quarter quarter 1995 1995 1995 Loviisa 1 1.00 3.68 100.0 91.9 100.0 90.3 Loviisa 2 0.81 3.30 82.5 81.6 81.0 80.9 TVOI 1.55 6.21 97.4 96.9 97.8 96.4 TVOII 1.54 5.95 97.7 92.8 96.9 92.4 generator synchronized (h) Availability factor = •100% calendar time (h) Load factor = gross electricity production . m % rated power - calendar time (h) 8 FINNISH CENTRE FOR RADIATION STUK-B-YTO 135 AND NUCLEAR SAFETY Table 11. Nuclear energy in Finnish elearicity produaion. First 1994 1993 quarter 1994 Nuclear electricity production 4.7 18.3 18.8 (net, TWh)* Total electricity production 17.4 62.1 58.1 in Finland (net, TWh)" Nuclear's share of total 27.0 29.5 32.3 electricity production (%) Load factor averages 93.9 90.0 92.8 of Finnish plant units (%) a Source: Statistics compiled by the Association of Finnish Electric Utilities. 9 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-B-YTO 135 f5jf /. Daily average gross power of Loviisa 1 in January-March 1995. 1 The low pressure section of one of two turbines One primary circulation pump tripped from a was repaired; a turbine trip due to a controller spurious temperature signal, the reactor to 77% malfunction occurred during power raising; the power. reactor was at 51 % power. A primary circulation pump tripped again due to the same spurious temperature signal, the reactor to 75% powc. Fig 2. Daily average gross power of Loviisa 2 inJanuary-March 1995.