Sixth International Informational Sixth International Informational Exchange Forum Exchange Forum Kyiv, Ukraine, April 2002 Kyiv, Ukraine, April 2002 Use of Main Loop Isolating Valves Use of Main Loop Isolating Valves Investigation in Case of SGTR for Investigation in Case of SGTR for VVER440/V230 VVER440/V230 Presented by: Presented by: PAVLIN P. GROUDEV & ROSITSA V. GENCHEVA PAVLIN P. GROUDEV & ROSITSA V. GENCHEVA Institute for Nuclear Research and Nuclear Energy Institute for Nuclear Research and Nuclear Energy Bulgarian Academy of Sciences Bulgarian Academy of Sciences 1 1
Sixth International Informational Exchange Forum Sixth International Informational Exchange Forum Kyiv, Ukraine, April 2002 Kyiv, Ukraine, April 2002 During the development of Symptom Based Emergency During the development of Symptom Based Emergency Operating Procedures for VVER 440 units at Kozloduy NPP a Operating Procedures for VVER 440 units at Kozloduy NPP a number of analyses have been performed using the number of analyses have been performed using the RELAP5/MOD3.2 computer code. RELAP5/MOD3.2 computer code. In this report are discussed advantages and disadvantages of In this report are discussed advantages and disadvantages of Main Loop Isolation Valves (GZZs) use in case of Steam Main Loop Isolation Valves (GZZs) use in case of Steam Generator Tube Rupture (SGTR) accident. Generator Tube Rupture (SGTR) accident. The results demonstrate that sometimes GZZs could provide The results demonstrate that sometimes GZZs could provide safety function but sometimes their closing and re- -opening opening safety function but sometimes their closing and re could make the situation worse. could make the situation worse. The reference power plant for this analysis is Unit 4 at The reference power plant for this analysis is Unit 4 at Kozloduy NPP. This plant is a VVER 440/V230 pressurized Kozloduy NPP. This plant is a VVER 440/V230 pressurized water reactor that produced 1375 MW thermal power and water reactor that produced 1375 MW thermal power and generates 440 MW electric power. generates 440 MW electric power. 2 2
Sixth International Informational Exchange Forum Sixth International Informational Exchange Forum Kyiv, Ukraine, April 2002 Kyiv, Ukraine, April 2002 A model of VVER 440/V230 was developed and A model of VVER 440/V230 was developed and validated at the INRNE validated at the INRNE - - BAS. The model includes six BAS. The model includes six coolant loops, each one including one main coolant pump coolant loops, each one including one main coolant pump and one horizontal steam generator. and one horizontal steam generator. The transient scenarios and acceptance failures are The transient scenarios and acceptance failures are designed with the participation of leading specialist from designed with the participation of leading specialist from Kozloduy NPP. The The following following acceptance criteria acceptance criteria are used are used to to Kozloduy NPP. analyse SGTR SGTR for VVER for VVER– –440/V2 440/V23 30 0: : analyse Fuel claddin ladding temperature g temperature – – not more than 1200 not more than 1200 o C. . Fuel c o C Safe and steady end state. Safe and steady end state. In this analysis it has been also investigated ability In this analysis it has been also investigated ability for fast depressurization using different systems for fast depressurization using different systems – – Spray in the pressurizer or Pressurizer PORV opening. Spray in the pressurizer or Pressurizer PORV opening. 3 3
Sixth International Informational Exchange Forum Sixth International Informational Exchange Forum Kyiv, Ukraine, April 2002 Kyiv, Ukraine, April 2002 Base Case, Variant A – Base Case, Variant A – Isolation the damaged SG #6 by closing Isolation the damaged SG #6 by closing Main Loop Isolation Valves (GZZs), Depressurization by Spray in Main Loop Isolation Valves (GZZs), Depressurization by Spray in the pressurizer and consequent GZZs re- the pressurizer and consequent GZZs re -opening opening. . Base Case, Variant B – – RCS cooling to reaching 14 RCS cooling to reaching 14 0 C under the Base Case, Variant B 0 C under the temperature of saturation in SG #6, Depressurization by temperature of saturation in SG #6, Depressurization by pressurizer PORV PORV opening opening, GZZs re , GZZs re- -opening, SG #6 cooling down opening, SG #6 cooling down pressurizer to 155 0 C to 155 0 C Fail Case, Variant C – Fail Case, Variant C – GZZ #1 on the hot leg fail to re GZZ #1 on the hot leg fail to re- -open, open, supporting of 60 0 supporting of 60 0 C primary subcooling margin C primary subcooling margin Fail Case, Variant D - - GZZ #1 on the hot leg fail to re GZZ #1 on the hot leg fail to re- -open, open, Fail Case, Variant D supporting of 40- -45 45 0 C primary subcooling margin supporting of 40 0 C primary subcooling margin Fail Case, Variant E - - GZZ #1 on the hot leg fail to re GZZ #1 on the hot leg fail to re- -open plus open plus Fail Case, Variant E Loss of AC power simultaneous with the reactor SCRAM Loss of AC power simultaneous with the reactor SCRAM 4 4
Sixth International Informational Exchange Forum Sixth International Informational Exchange Forum Kyiv, Ukraine, April 2002 Kyiv, Ukraine, April 2002 The broken tube is located in the middle layer of The broken tube is located in the middle layer of the tube bundle in SG #6 close to the cold collector. the tube bundle in SG #6 close to the cold collector. In the initial state of the transient it is assumed: In the initial state of the transient it is assumed: Reactor power to be nominal. Reactor power to be nominal. Burn up status – Burn up status – corresponding to the end of life. corresponding to the end of life. Primary pressure and temperature to be nominal. Primary pressure and temperature to be nominal. Initial secondary pressure is assumed to be nominal Initial secondary pressure is assumed to be nominal too. too. Pressurizer level is assumed as nominal Pressurizer level is assumed as nominal - - 5.2 m. 5.2 m. Steam Generator water level is assumed to be nominal Steam Generator water level is assumed to be nominal – – 2.12 m. 2.12 m. 5 5
Sixth International Informational Exchange Forum Sixth International Informational Exchange Forum Kyiv, Ukraine, April 2002 Kyiv, Ukraine, April 2002 Scenario: Scenario: 1. The double ended break of one pipeline in SG #6 close to the col 1. The double ended break of one pipeline in SG #6 close to the cold d collector. collector. 2. The operator starts one Makeup pump (6 m 2. The operator starts one Makeup pump (6 m³ ³/hr ) to inject in primary /hr ) to inject in primary loop. loop. 3. 3. Switching on pressurizer heaters due to primary side pressure Switching on pressurizer heaters due to primary side pressure decreasing down to 120 kgf/cm decreasing down to 120 kgf/cm² ² 4. 4. Actuation of Emergency Protection Actuation of Emergency Protection – – I (AZ I (AZ- -1) according to the set 1) according to the set point “Pressurizer water level < < < < < 2.6 m”. < < < point “Pressurizer water level 2.6 m”. 5. 5. Switching off all Pressurizer heaters due to Pressurizer water Switching off all Pressurizer heaters due to Pressurizer water level level became less than 2.0 m. became less than 2.0 m. 6. 6. Actuation of only Actuation of only one system for automatic step by step loading one system for automatic step by step loading Pressurizer water level < < < 2 m < < < < < (AASSL) according to the set point “ (AASSL) according to the set point “Pressurizer water level 2 m ”. ”. Only HPP #1 starts to inject borated water with concentration of Only HPP #1 starts to inject borated water with concentration of boric boric acid 39 g/kg. acid 39 g/kg. 6 6
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