a method of locating leakage of heavy water using ratio of tritium to heavy water

Wolsong NPP II KHNP

JASON SHINKorea Hydro & Nuclear Power co.

Wolsong NPP II KHNP

CANDU reactorsCANDU reactorsCANDU : Canada Deuterium UraniumCANDU : Canada Deuterium Uranium

(Pressurized Heavy Water Reactor)(Pressurized Heavy Water Reactor)Heavy water(D2O) coolantHeavy water(D2O) coolantHeavy water moderatorHeavy water moderatorNatural uranium fuelsNatural uranium fuels

Wolsong NPP II KHNP

Two systems containing heavy waterTwo systems containing heavy waterPrimary Heat Transport System(PHT system)Primary Heat Transport System(PHT system)

Coolant : 190 tonCoolant : 190 tonHigh temperature : 266 ~ 310 High temperature : 266 ~ 310 ooCCHigh pressure : 100 barHigh pressure : 100 barTritium concentration : Tritium concentration : ~ 2 Ci/kg~ 2 Ci/kgUsual leakage rate : ~ 10 kg/dayUsual leakage rate : ~ 10 kg/day

(Wolsong Unit 3 & 4)(Wolsong Unit 3 & 4)

Wolsong NPP II KHNP

Moderator System(MOD system)Moderator System(MOD system)Moderator : 260 tonModerator : 260 tonLow temperature : 46 ~ 69 Low temperature : 46 ~ 69 ooCCLow pressure : 0.2 barLow pressure : 0.2 barTritium concentration : Tritium concentration : ~ 40 Ci/kg~ 40 Ci/kgUsual leakage rate : ~ 1 kg/dayUsual leakage rate : ~ 1 kg/day

(Wolsong Unit 3 & 4)(Wolsong Unit 3 & 4)

Two systems containing heavy waterTwo systems containing heavy water

Wolsong NPP II KHNP

Features of a PHWRFeatures of a PHWRHigh tritium concentrations in coolant or High tritium concentrations in coolant or

moderatormoderatorInevitable leakage of coolant and Inevitable leakage of coolant and

moderator (not only at a PHWR)moderator (not only at a PHWR)High tritium concentration in air of High tritium concentration in air of

reactor buildingreactor buildingHigh concern about internal dose by High concern about internal dose by

tritiumtritium

Wolsong NPP II KHNP

What happens during sudden heavy What happens during sudden heavy water leakage?water leakage?Tritium concentration in air soars highTritium concentration in air soars highAmount of tritium release increasesAmount of tritium release increasesAmount of heavy water recovery increasesAmount of heavy water recovery increasesWide survey for leakage is neededWide survey for leakage is neededInternal dose of workers increaseInternal dose of workers increase

Wolsong NPP II KHNP

If we know which system heavy If we know which system heavy water leaks from...water leaks from...Survey time will shortenSurvey time will shortenWe can reduceWe can reduce

Heavy water leakageHeavy water leakageTritium releaseTritium releaseInternal dose of workersInternal dose of workers

Wolsong NPP II KHNP

Tritium & heavy water in airTritium & heavy water in air

Heavy water : X+YTritium : AX+BYPHT heavy water : X

PHT tritium : AX

MOD heavy water : YMOD tritium : BY

PHT system MOD system

Wolsong NPP II KHNP

System Equation for X & YSystem Equation for X & YEquations for PHT & MOD heavy waterEquations for PHT & MOD heavy water

AX + BY = TAX + BY = T X + Y = HX + Y = H

X = (T - BH) / (A - B)X = (T - BH) / (A - B) Y = (T - AH) / (B - A)Y = (T - AH) / (B - A)

where A is tritium concentration in PHT heavy water where A is tritium concentration in PHT heavy water (known)(known)

B is tritium concentration in MOD heavy water B is tritium concentration in MOD heavy water (known)(known)

T is tritium in the sample (measured)T is tritium in the sample (measured) H is heavy water in the sample (measured)H is heavy water in the sample (measured) X is PHT heavy water in the sample (unknown)X is PHT heavy water in the sample (unknown) Y is MOD heavy water in the sample (unknown)Y is MOD heavy water in the sample (unknown)

Wolsong NPP II KHNP

Contribution to the leakageContribution to the leakageX & Y show how much PHT heavy water X & Y show how much PHT heavy water

and MOD heavy water exist in the sampleand MOD heavy water exist in the sampleThese are found by comparing the ratio of These are found by comparing the ratio of

tritium (T) to heavy water (H) with the the tritium (T) to heavy water (H) with the the ratios of tritium to PHT heavy water and MOD ratios of tritium to PHT heavy water and MOD heavy water (A & B)heavy water (A & B)

B is much bigger than AB is much bigger than AIf T/H is very close to A, most of heavy water If T/H is very close to A, most of heavy water

and tritium must come from PHT systemand tritium must come from PHT systemIf T/H is a little close to A, most of heavy water If T/H is a little close to A, most of heavy water

comes from PHT system but most of tritium comes from PHT system but most of tritium comes from MOD systemcomes from MOD system

Wolsong NPP II KHNP

Wolsong Power Plant II’s experience 1Wolsong Power Plant II’s experience 1(Unit 3, Dec. 2008)(Unit 3, Dec. 2008)

Tritium concentration in air in the reactor Tritium concentration in air in the reactor building suddenly rosebuilding suddenly rose

Wolsong NPP II KHNP

Wolsong Power Plant II’s experience 1 Wolsong Power Plant II’s experience 1 (Unit 3, Dec. 2008)(Unit 3, Dec. 2008)

Water vapor sampling from the air in the Water vapor sampling from the air in the reactor building using gas washing bottle reactor building using gas washing bottle Tritium in 1g (T) = 25.9 kBqTritium in 1g (T) = 25.9 kBqHeavy water in 1g (H) = 26.4 mgHeavy water in 1g (H) = 26.4 mgHeavy water compensated forHeavy water compensated for

natural deuterium in 1g (H) = 9.7 mgnatural deuterium in 1g (H) = 9.7 mg

※※Tritium concentration in PHT (A) = 1.714 Ci/kgTritium concentration in PHT (A) = 1.714 Ci/kg

Tritium concentration in MOD (B) = 37.92 Ci/kgTritium concentration in MOD (B) = 37.92 Ci/kg

Sampling & analysisSampling & analysis

Wolsong NPP II KHNP

Calculation resultCalculation result85% of leaked heavy water was from PHT 85% of leaked heavy water was from PHT

system,system,

and 15% from MOD systemand 15% from MOD system

20% of tritium in air was from PHT system,20% of tritium in air was from PHT system,

and 80% from MOD systemand 80% from MOD system

※ ※ Ordinarily, more than 90% of tritium in air Ordinarily, more than 90% of tritium in air hadhad

been from PHT systembeen from PHT system


Wolsong NPP II KHNP

Follow-up actionsFollow-up actions


An intensive survey on MOD systemAn intensive survey on MOD systemFinding out the leakage point at a junction Finding out the leakage point at a junction

near a pressure instrument of the MOD near a pressure instrument of the MOD systemsystem

Delay Delay TankTank

Callandria

To MOD Purification To MOD Purification SystemSystem

PumpPump

Wolsong NPP II KHNP

Follow-up actionsFollow-up actions


The tritium concentration in air in the The tritium concentration in air in the reactor building decreased after repairreactor building decreased after repair

Wolsong NPP II KHNP

Wolsong Power Plant II’s experience 2Wolsong Power Plant II’s experience 2(Unit 4, Apr. 2009)(Unit 4, Apr. 2009)

Tritium concentration in air in the reactor Tritium concentration in air in the reactor building jumpedbuilding jumped

Wolsong NPP II KHNP

Water vapor sampling from the air in the Water vapor sampling from the air in the reactor building using gas washing bottle reactor building using gas washing bottle Tritium in 1g (T) = 50.3 kBqTritium in 1g (T) = 50.3 kBqHeavy water compensated forHeavy water compensated for

natural deuterium in 1g (H) = 93.0 mgnatural deuterium in 1g (H) = 93.0 mg

※※Tritium concentration in PHT (A) = 1.513 Ci/kgTritium concentration in PHT (A) = 1.513 Ci/kg

Tritium concentration in MOD (B) = 36.99 Ci/kgTritium concentration in MOD (B) = 36.99 Ci/kg

Sampling & analysisSampling & analysis

Wolsong Power Plant II’s experience 2 Wolsong Power Plant II’s experience 2 (Unit 4, Apr. 2009)(Unit 4, Apr. 2009)

Wolsong NPP II KHNP

Calculation resultCalculation result100.14% of leaked heavy water was from PHT 100.14% of leaked heavy water was from PHT

system,system,

and -0.14% from MOD systemand -0.14% from MOD system

103.7% of tritium in air was from PHT system,103.7% of tritium in air was from PHT system,

and -3.7% from MOD systemand -3.7% from MOD system

※ ※ This irrational result was thought as due to anThis irrational result was thought as due to an experimental error but such results were experimental error but such results were

repeatedrepeated in more samplesin more samples


Wolsong NPP II KHNP

Further InvestigationFurther InvestigationThe ratio of tritium to heavy water in the The ratio of tritium to heavy water in the

water vapor samplewater vapor samplewas supposed to be between the tritium was supposed to be between the tritium

concentrations in the PHT heavy water and concentrations in the PHT heavy water and MOD heavy water, that is, between 1.513 Ci/kg MOD heavy water, that is, between 1.513 Ci/kg and 36.99 Ci/kgand 36.99 Ci/kg

but, was measured as 1.46 Ci/kg.but, was measured as 1.46 Ci/kg.We started to think about the possibility of We started to think about the possibility of

leaking of another heavy water which has leaking of another heavy water which has lower tritium concentration.lower tritium concentration.


Wolsong NPP II KHNP

Further InvestigationFurther InvestigationStagnant heavy water in the PHT systemStagnant heavy water in the PHT system

isolated for a long time from circulating coolantisolated for a long time from circulating coolanthad a little less tritium concentration than main had a little less tritium concentration than main

PHT heavy waterPHT heavy waterlike one in Coolant Storage Tank and more like one in Coolant Storage Tank and more

Tritium concentration of heavy water in Coolant Tritium concentration of heavy water in Coolant Storage Tank was measured as 1.40 Ci/kgStorage Tank was measured as 1.40 Ci/kg

This result could explain the ratio of tritium to This result could explain the ratio of tritium to heavy water in the water vapor sample from the heavy water in the water vapor sample from the reactor building, 1.46 Ci/kgreactor building, 1.46 Ci/kg


Wolsong NPP II KHNP

Follow-up actionsFollow-up actionsA careful survey on isolated systemsA careful survey on isolated systemsFinding out the leakage point on Degas Finding out the leakage point on Degas

Condenser Tank, a semi-isolated systemCondenser Tank, a semi-isolated system


Heavy Heavy Water Water

Storage Storage TankTank

Degas Degas CondenseCondense

r Tankr Tank PressurizerPressurizer

Main PHT SystemMain PHT System

Wolsong NPP II KHNP

Follow-up actionsFollow-up actionsThe tritium concentration in air in the The tritium concentration in air in the

reactor building decreased after repairreactor building decreased after repair


Wolsong NPP II KHNP

ConclusionsConclusionsYou can discriminate which system heavy You can discriminate which system heavy

water leaks from, the PHT system or the water leaks from, the PHT system or the MOD system.MOD system.

You can also know how much one of these You can also know how much one of these systems contributes the heavy water leakage systems contributes the heavy water leakage or the increased tritium concentration in air or the increased tritium concentration in air in the reactor building.in the reactor building.

Using this information, you can locate the Using this information, you can locate the leakage point more quickly.leakage point more quickly.

If it works, you can reduce the inner dose of If it works, you can reduce the inner dose of the workers.the workers.

Wolsong NPP II KHNP

Thanks for your Thanks for your attention.attention.

Do you have any Do you have any questions?questions?

a method of locating leakage of heavy water using ratio of tritium to heavy water

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