Filtered Containment Venting Systems

Transcription

1 Swiss Federal Nuclear Safety Inspectorate ENSI Filtered Containment Venting Systems at Swiss NPPs and KKL in particular January 15, 2014, Ft. Lauderdale J. Hammer, ENSI, and A. Ritter, KKL

2 Agenda Swiss Nuclear Power Plants Filtered Containment Venting Systems (FCVS) Current Venting Systems in Swiss NPPs KKB, KKG and KKM The FCVS at Leibstadt NPP FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 2

3 The four Swiss NPPs FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 3

4 Nuclear Installations in Switzerland NPPs Research Reactors Interim Storage FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 4

5 Mühleberg Nuclear Power Plant (KKM) BWR Start of commercial operations: 1972 Net electrical output: 355 MW el Copyright KKM End of operations scheduled for 2019 FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 5

6 Gösgen Nuclear Power Plant (KKG) PWR Start of commercial operations: 1979 Copyright KKG Net electrical output: 985 MW el FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 6

7 Beznau Nuclear Power Plant (KKB 1 & 2) PWR Start of commercial operations: KKB 1: 1969 KKB 2: 1971 Net electrical output: 380 MW el each Copyright KKB FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 7

8 Leibstadt Nuclear Power Plant (KKL) BWR Start of commercial operations: 1984 Net electrical output: 1220 MW el Copyright KKL FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 8

9 May 2011: No nuclear new build! KKL KKB EKKB KKG KKN KKM EKKM FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 9

10 Filtered Containment Venting

11 Philosophy of Filtered Containment Venting i. Filtered Containment Venting (FCVS) is a measure for beyond design basis accidents. ii. iii. iv. The FCVS is in general passive and does not depend on any external input such as actuation, mechanical movement or supply of power. The FCVS is important to safety; its malfunction could lead to radiation exposure of members of the public. The FCVS serves mitigate the consequences of a severe accident. v. IAEA NS-G-1-10, says: Where containment venting systems are installed, the discharge should be filtered to control the release of radionuclides to the environment. Typical filter systems include sand, multi-venturi scrubber systems, HEPA or charcoal filters, or a combination of these. HEPA, sand or charcoal filters may not be necessary if the air is scrubbed in a water pool. vi. In case of a severe accident we have to deal with wet and hot gas and air mixtures. Therefore, the FCVS must resist temperatures up to 160 C and high vapor concentration. vii. The important nuclides are 131 I, 134 Cs and 137 Cs. viii. The FCVS should be designed for heat removal of several MW th during 3 to 5 days FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 11

12 New Guidelines for FCVS (ENSI, preliminary) The FCVS is a Safety Relevant System In addition to the FCVS, ENSI demands a passive ventilation system without operator action The FCVS is always ready during power operation Remote and Local operation, RP-conditions Simple and passive design, no AC power need The gas flow has to be adjustable Exhaust via stack, two valve closing system Exchange of water and chemicals in the filter during operation should be possible FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 12

13 Design Basis for FCVS (ENSI, preliminary) Retention factor >1000 for aerosols >100 for elementary Iodine to be proven by experiments in the range of 30 to 100% of nominal flow Filter loading up to 150 kg aerosols Probability for containment rupture < 0.1% Operating time >100 hours, self-sufficient Earthquake resistant as the containment building Resistant to pressure peaks as in case of hydrogen deflagration FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 13

14 Venting Systems at Swiss NPPs

15 SIDRENT the FCVS of KKB 1 & 2 Technical Data max. containment pressure: 3.1 bar nominal, 6.2 bar break down Rupture Disk nominal pressure: 4.2 bar Nominal flow rate: 4.5 kg/s Filter: Air-Lift-Effect Diameter: 3.5 m Height: 7 m water capacity: 30m 3 max. Filter loading: 150 kg max. Temperature: 166 C Retention factor: >1000 for aerosols >100 for Iodine (elementary) Self-sufficient operating time: 24 h FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 15

16 SIDRENT the FCVS of KKB 1 & 2 FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 16

17 KKG Filtered Containment Venting Technical Data max. containment pressure: 5.89 bar abs. nominal, Rupture Disk nominal pressure: 6.5 bar Nominal flow rate: ~2 m 3 /s Filter: Venturi Scrubber System Diameter: 3.0 m Height: 6.0 m water capacity: 15 m 3 max. Filter loading: 200 kg max. Temperature: 160 C Retention factor: >1000 for aerosols >100 for Iodine (elementary) Self-sufficient operating time: 24 h FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 17

18 KKG Filtered Containment Venting Scheme 18

19 KKM Filtered Containment Venting CDS Technical Data max. containment pressure: 9.5 bar Rupture Disk nominal pressure: 6.2 bar Nominal flow rate: 25 kg/s Filter: Multi Venturi Scrubber System Outer torus water capacity: 1000m 3 Retention factor: >1000 for aerosols >100 for Iodine FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 19

20 KKM - CDS FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 20

21 KKL-FCVS Actual Filtered Containment Venting System Layout Efficiency Radiological Impact Planned Improvements Hydrogen Problem Radiation Monitor Filter Long Term Retention FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 21

22 Filtered Containment Venting System Scheme FCVS Reactor Pressure Vessel Shield Wall Weir Wall Drywell PI 21YY00P011 PI 11YY10P011 XK10 N010 Containment PRP 21YY10P011 PI 21YY10P011 PIP 11YY10P011 PI 11YY10P011 M 11XK10 S001 XK11 B001 XK20 N001 M LC 11XK10S002 XK12 B001 XK10 N001 XK10 S206 Stack Roof of Reactor Auxiliary Building ZC22R140 FIP 11XK10F002 FT 11XK10F002 Room ZC22R103 XK10 S207 XK10 B001 VENT XK10 S301 Stack XK10Z006 UD70 S098 Exhaust Chimney ZQ00B100 Sodium thiosulfate is flashed Make-Up into filter Fire tanks Water Water System System on system initation due (UD) (UJ) to pressure difference UJ70 S067 Suppression Pool LO XK11S004 XK11 S002 LO XK12S004 XK12 S009 XK10 S107 XK10S007 XK10S006 LC XK10 S005 TC70 S034 Room ZC10R126 Local Operating Position ZC24R102 Suppression Pool Cleaning System Scrubber construction ensures 5 sec residence time allowing for Iodine reaction to complete 12 radial branches equipped with nozzles (92 nozzles per filter) expand the gas-steam mixture into aerosol-carrying bubbles FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 22

23 Clean gas to stack Layout Shielded local control room Drain to Radwaste Designer: Sulzer / EWI Rupture Disc Pressure [bara]: 3.1 Operating Pressure [bara]: 2.55 Gas from Containment Filter Tanks Comissioning: 1993 Max Flow [kg/s]: Nominal flow [kg/s]: FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 23

24 FCVS Efficiency Activity release ( source term ) after postulated core melt accident Without Filter ( Fukushima ) With FCVS Filter ( KKL ) Noble gases Cesium + Iodine Noble gases Decon Factor Iodine: 100 Decon Factor Aerosols: 1000 Cesium + Iodine Temporary Iodine Resuspension FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 24

25 Simulation: 1 Year Committed Dose Without Filter ( Fukushima ) With FCVS Filter ( KKL ) 1 msv limit 1 msv limit 10 msv limit 100 msv limit 10 msv limit FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 25

26 Radiological Impact of Loaded Filters: Direct radiation very well shielded by surrounding buildings. Filter Inventory: 1E18 Bq ( 3E7 Ci) Skyshine related Exposure on Site: <10 msv/h (1 % of Stack Exhaust Exposure) Operator Control Room: 30 msv/h FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 26

27 H 2 H 2 H 2 H 2 Stack Flow Direction Exhaust «Plume» Problems with Existing Configuration: Possible Hydrogen Explosion Hazard of Explosion due to Hydrogen Input into Stack Calibration of Rad Monitor not easy due to difficult Geometry Radiation Monitor Exhaust Line from Filters to Stack FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 27

28 Difficulties with Source Term Estimation Sampling not possible, very high Dose Rates of Samples and inside Stack Radiation Monitor is measuring Dose Rate [msv/h], resp. [R/h] Conversion Factor Dose Rate to Source Term [msv/h] [Bq/h], resp. [R/h] [Ci/h] Conversion Factor is depending on Energy of Nuclide- Mixture and Stack Ventilation Rate: Depending on Accident Conditions and elapsed Time (rad. Decay). Conversion Factor is averaged for many different Accident Conditions over first 8 hours: 5E11 (Bq h/sv m 3 ) Stack Flow my be not well defined under Accident Conditions Radiation Monitor needs to be relocated FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 28

29 New Pipe Routing outside Stack, new Rad Monitor Location No Hydrogen Input into Stack: No Explosion Hazard New Location of Rad Monitor (inside or outside of Stack Wall) Easy Calibration due to well defined Geometry FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 29

30 Filter Long Term Retention Activity release ( source term ) after postulated core melt accident Change in Filter Chemistry under Consideration: Long Term Retention of Organic Iodine (CH 3 I) possible With FCVS Filter ( KKL ) Noble gases Cesium + Iodine Temporary Iodine Resuspension With proposed Additives (Aliquat) FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 30

31 Conclusions Filtered Containment Venting System were implemented 20 years ago in all Swiss NPP FCVS turned out to be very helpful in the Post-Fukushima Safety Evaluations Improvements concerning Hydrogen, Earthquake Resistance, and Source Term Evaluation under way FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 31

32 for more information please visit: FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 32

33 Thank you for your attention! FCVS 2014 ALARA Symposium J. Hammer and A. Ritter 33