LEADER Task 3.3 ALFRED - Primary Cover Gas System (PCGS)

1. LEADER Task 3.3 ALFRED - Primary Cover Gas System (PCGS) L. Mansani, M. Bruzzone, V. Pierantoni Karlsruhe, November20th, 2012

2. TABLE OF CONTENTS System Functions • Safety-Related Functions • Non-Safety Related Functions Cover Gas Composition Primary Cover Gas System Design Configuration • System Configuration Requirements • System Configuration System Alignments • Normal Plant Operation • Plant Shutdown before Maintenance • Nitrogen Purge and Argon Recovery TABLE OF CONTENTS

3. 1. Primary Cover Gas System Functions

4. Primary Cover Gas System Functions Safety Related Functions Primary Boundary Integrity Contribute to maintain the integrity of the Primary Boundary during all plant conditions Non-Safety Related Functions Molten Primary Coolant Inertization Maintain and control a slight argon underpressure in the primary cover gas volume and keep up the required inertization status of the molten primary coolant

5. Primary Cover Gas System Functions Non-Safety Related Functions (cont.) Containment of Radioactive Releases To maintain the radioactive releases to the Reactor Hall below the design limits by providing the mean for purification of the primary cover gas bulk mass Nitrogen Purge & Argon Recovery To purge the nitrogen flowing from Reactor Hall into the Reactor Vessel during maintenance, restore the argon atmosphere and re-establish underpressure conditions inside the Reactor Vessel before every startup

6. Primary Cover Gas System Functions Non-Safety Related Functions (cont.) Fuel Cladding Failure Detection To detect failure in fuel assemblies cladding by monitoring increased primary cover gas activity originated by fission products circulating in the primary coolant Primary Heat Exchanger Leakage Detection Timely to detect a small leak of the primary heat exchanger and provide the way to condense and collect vapor and trap the radionuclides entrained by the vapor stream

7. 2. Primary Cover Gas Composition

8. From EUROTRANS: “the volatility of all the investigated elements (Po, Cs, Sr and I) is depressed, typically by several orders of magnitude, through strong chemical interaction with the heavy metal coolant. The strong retention of fission products constitutes a considerable advantage with lead and LBE coolants”. “In lead coolant (EFIT) the production of 210Po is about three orders of magnitude smaller, and the amounts of volatilized 210Po are correspondingly lower. In both XT­ADS and EFIT, volatilization of 90Sr is completely negligible.” Molar fraction passed to the gas phase PRIMARY COVER GAS COMPOSITION

9. The activity in the Cover Gas comes from a fraction of the radionuclides present in the primary lead coolant that have vaporized into the gas phase The radionuclides in the primary lead have two different sources: The activation products resulting from the coolant interaction with the neutrons The activity released from the damaged fuel rods in case of fuel damage Due to the retention property of Lead the more significant radionuclides present in the Cover Gas are Noble Gases and Tritium • Ne 23 5,54E-11 • Ne 24 4,83E-18 • Ar 39 4,69E-05 • Ar 41 9,89E-12 • Ar 42 1,20E-10 • Ar 43 2,06E-15 • Ar 45 4,25E-17 • Xe127 1,21E-15 • Xe129m 3,75E-13 • Kr 81 5,92E-13 Preliminary activation product evaluation –Noble Gases composition after 40 years (grams) PRIMARY COVER GAS COMPOSITION

10. 3. Primary Cover Gas System CONFIGURATION

11. 3. PCGS CONFIGURATION System Configuration Requirements • Provision of two (2) piping penetrations on the Reactor Cover for PCGS gas extraction and return flow • Comply with Reactor Cover penetration Layout • Minimize the chances of preferential gas streams capable of bypass the circulation of the RV ceiling Provision of buffer tank to compensate passively for gas pressure variation due to LBE temperature transients Provision of a blowers station with the performances required by the PCGS purification function to force recirculation of the Reactor Vessel ceiling through the filtration banks

12. 3. PCGS configuration System Configuration Requirements Provision of an electrical heater in the blowers station discharge pipe to increase the gas temperature back to the current Reactor Vessel ceiling temperature, during primary cover gas recirculation and purification Provision of an argon storage tank to store and supply the amount of argon necessary to recover the primary cover gas for normal operation of the PCGS Provision of a argon supply electrical heater to support argon heat up from low temperature to a temperature high enough to prevent LBE from experiencing thermal shocks during plant startup conditions recovery via nitrogen purge and argon flushing operation Provision of a single blower to purge the nitrogen flowing from Reactor Hall into the Reactor Vessel after maintenance, restoring the argon atmosphere and re-establishing underpressure conditions inside the Reactor Vessel before every start-up

13. 3. PCGS configuration System Configuration Requirements Provision of an HIGH temperature and a LOW temperature gas coolers to reduce the primary cover gas temperature to suitable values for purification Provision of activated carbon beds to temporary entertain Xenon and Krypton, allowing that delay period significantly reduces the radioactivity of the gas flow leaving this section Provision of a Tritium treatment station to collect tritium released in the primary cover gas Provision of a fine-dust filter and an HEPA filters bank for removal of remaining fines post purification upstream of the blowers station suction

14. 4. System Alignments

15. 4. System Alignments Normal Plant Operation

16. 4. System Alignments Before Maintenance

17. 4. System Alignments Nitrogen Purge and Argon Recovery

18. Thank you for your attention