Design & Built New Decay Tank Syatem For Ir-131 @ IPPT.
||A) Design & Built New Decay Tank Syatem For Radioiodine 131 (Ir-131) @ IPPT.
I. ) Low Level Radioactive Waste Management :
- Work Order. Click HERE
- Decay Tank Contract Documentation : -
- Radioiodine 131 Treatment In IPPT
In Radioiodine treatment, a patient is given Radioiodine 131 (Ir-131) in a drink or capsule form. The average activity is 150mCi per patient. The patient is expected to stays in one of the 3 isolation rooms for 3days. Urine and feces are highly radioactive and 70% of the 150mCi is expected to be excreted. A system of decay and delay is necessary to allow a safe discharge to the main sewer.
- Legislative Infrastructure and Radioactive Waste Management In Malaysia.
Atomic Energy Licensing Act requires that we manage radioactive waste. Atomic Energy Licensing Board has issued legislations on radiation protection, which also cover radioactive waste management. However, a new legislation, substituting the old one, covering the discharges of radioactive effluents from the licensed establishments is to be legislated in the near future. It is therefore prudent that the system in IPPT be in line with this new discharge limit for Ir-131.
- Liquid Radioactive Wastes
The liquid radioactive wastes from IPPT can be discharged to the sewage system according to the concentration limits of 27micro curies per meter cube. Short-lived radionuclide such as Ir-131 with half-lives of about 8.4 days can be discharged to the sewage system at this discharge limit. The legislation requires monitoring of Ir-131 discharges for hospital.
II.) Design Foundamentals For IPPT Decay Tank System.
- Waste Volume Calculation;
3 rooms will have a maximum of 6 patients/ week.
And each patient stays for 3 days with 8 flushes per day then :
Based on 1.5 liters / flush.
1 day for 1 patient : 8 x 1.5 liters = 12 liters
For 3 days stay per patient : 3 x 12 liters = 36 liters
In a week, there will be a total of 6 patients using the 3 rooms.
For 6 (MAX) patients per week = 6 x 36 liters = 216 liters/week.
For 1 month : 216 liters x 4 weeks = 864 liters per month of radioactive waste will be discharged to the tank.
For the capacity of a septic tank, the size of the tank should follow as below:
1 liters is equal to 0.001m3.
For decay tank to hold 864 liters of wastes, each of the 5 tanks shall have a minimum capacity of : 864 x 0.001m3 = 0.864m3 per tank.
In practise an extra capacity of 20% is included ie : therefore the tank capacity shall not be less than 1.1m3 per tank capacity.
Based on the formula below formulated a new Ir-131 decay chart, suitable for the new discharge limits for decay process calculation. This is due to the fraction of remaining activity available in there decimal points for the old decay chart. Our decay process calculation for Ir-131 needs to be correct to at least six decimal points for more accuracy since the 'soon to be released' discharge limit is 27uCi per m3. The earlier discharge limits calculation was based on 10 half life. However, the tolerance included in our design using 5 tanks allows us to accommodate and satisfy the new discharge limits even in a worse case scenario.
A(t) = A(0) 2 - (t/hl) ( Source from I-131 Decay Chart - DEHS, UMN )
A(0) : activity at time t = 0
t : elapsed time
hl : half time
Ir-131 half life : 8.04 days
Table 1 : Fraction of Original Radioactivity Remaining after t Days
- Design Criteria for 6 Patients - Radioactivity;
Average activity is about 150mCi ( as confirmed by end user ) for one patient. 6 patients are treated in a day. All calculation is based on the Table 1.
150mCi x 6 patients per day = 900mCi
30% of the activity is absorbed and 70% is excreted in 72 hrs ( 3days) = 23.33% per day Assuming that the Decay Tank is filled in one month with 864 liters and every patient stays for 3 days. 6 new patients start therapy every fourth day throughout the month unless it's a Sunday.
Total activity after one month in receiving tank = 640.354mCi ( refer decay chart 2 ).
Total activity in 1st Decay Tank
- 30 days : 640.354 mCi x 0.0752929 = 48.2141mCi
- 60 days : 48.2141 mCi x 0.0752929 = 3.6302 mCi
- 90 days : 3.6302 mCi x 0.0752929 = 0.3722 mCi
- 116 days : 0.2733 mCi x 0.1062967 = 0.0291 mCi
During the transfer from receiving tank to decay tank we assume 200 liters of water from rinsing being diluted with 864 liters of waste. Total waste volume is 1064 liters.
Total activity end of 116 days in decay tank per total waste volume in liters :
= 0.0291 mCi / 1064 l
= 0.0000273 mCi / l
Total activity end of 116 days in decay tank per total waste volumn in cubic meter :
= 0.0000273 mCi / l x 1000
= 0.273 mCi / cubic meter.
Total activity for 1m3 is 27uCi / m3
Discharge activities comply with the discharge requirement of 27 uCi / m3.
Radioiodine 131 Decay Chart ( 6 Patients ).
|Day||Activity = 150mCi x 6 patients per day. 30% absorbed and 70% excreted in 72hrs i.e. 23.33%/day||Fraction of remaining activity as per Ir-131 decay Chart||Remaining Activity mCi||Total monthly activity in Tank|
- Functional Design Brief ;
Basic Diagram of Decay Tank System
As one of the best available technique, waste tanks are used to collect and decay radioactive waste before the discharge of effluents into the sewage system. The single waste tank system makes use of the "decaying while filling" principle. Therefore, by the time that the tank is filled, the total activity in the waste tank is many times lower than the total input so that the overall capacity requirement can be greatly reduced. The use of multiple waste tanks resolves most of the problem of single waste tank system. However, it is important to design waste tank system with optimum tank number and capacity.
Designed a system using a five tank systems, tow tanks receiving the discharge from the toilets while other three tanks will be used as decay tanks. The design is based on three rooms with six patients a week. It will collect all the waste from the toilets of the rooms and store it in the receiving tank 1 for the first month or 30 days. Once the receiving tank 1 is filled up with waste for 30 days, it will be transferred to decay tank 1. Waste in decay tank 1 will be kept for 116 days before it being discharged into the sewage system. This is to satisfy the discharge concentration limits of 27 micro curies per meter cube.
The receiving tank 2 will start to be filled up with waste for the second month. After 30 days, the waste from receiving tank 2 will be transferred to decay tank 2 and the waste from the toilet will continuously start to fill up the receiving tank 1 again for the third month. Once the receiving tank 1 is filled up with waste for the whole month, it will be transferred and kept in decay tank 3. All the waste in three decay will be stored for 116 days before it being discharged into the sewage system, Each tank will have at least 1 month time gap for washing and maintenance purpose.
I. Level Detectors to measure the level of all tanks to automatically stop overflow and to inform operator the status of tank level at the remote computer display.
II. Radiation Detectors to measure the radiation levels of all decays tanks and to inform operator the status of tank radiation level at the remote computer display.
- Mixers in each tank to keep particles suspended.
- Aerators in each tank to eliminate odour.
- Venting of foul gas from tank and bunker area.
- Sampling Points for decay tank before discharge.
- Tank rinsing cycle for each tank.
- Shunting of sewage to and from each of the five tanks shall be built into the system capability.
- Graphical display to display the status of all measurement parameters and conditions.
- Computerized control of all valves, pumps, motors and switches.
Radioactive Waste Management system shall be fully automatic system with manual override system and to minimise the Physicist to enter the Decay Tank housing.
Type : Wall Mounted Vacuum Toilet
Quantity : 3 nos
Type : FRP or HDPE
Quantity : 5 nos
Volume : Minimum of 1300 Litres
Level : Millimeter. To be monitor by level sensors suitable for sewerage purposes.
Radiation : mCi. To be monitor by radiation sensors probe at each of Decay Tank.
Computer system : System is to provide supervision of radioactive waste management at Physicist room and also would provide operator wit information and database required for the ease of operation.
PLC System : PLC system to logically control for all the equipments, sensors and indicator.
Receiving tank : The radioactive sewerage shall transfer from the toilet to the receiving tank by using vacuum pumps.
Decay tanks : The collected radioactive sewerage at receiving tank shall be transferred to Decay Tank by using grinder / cutter pump once it has reached 30 days or the highest level of sewerage in the tank or whichever earlier.
Computer guided : The controls of discharge process are via the Local Control Panel ( LCP). PLCs are to be provided in the LCP for the automatic control of discharge process. Signals and status of Decay Tank are linked back to the Physicist room.
Discharge Limits : The discharge shall be manually opened by the Physicist
Manual override : All motorised valve had equipped with manual override mechanism. In the event of power failure, UPS system ( 10 min ) shall be provided as back up power supply for the PLC in the control panels while the awaiting the essential supply from the hospital generator.
This document should be read on the whole and fully understood by the vendor who is bidding for the decay tank system.
The vendor must accept full and complete responsibility of the efficient functioning of the system as it is designed to do base on this document.
the vendor is expected to work closely with the Radiation Consultant to achieve the planned discharge limits.
Decay Tank Layout
Decay Tank Layout
1. Decay Tank Layout ( Preliminary For HUSM, Kepala Batas )
2. Decay Tank ( Preliminary ) Sewerage Line ( Incoming Route ) For HUSM, Kepala Batas.
3. Decay Tank ( Preliminary ) Sewerage Line ( Outgoing Route) For HUSM, Kepala Batas.
PROJECT : CADANGAN PEMBANGUNAN PROJECT INSTITUT PERUBATAN DAN PERGIGIAN TERMAJU UNIVERSITI SAINS MALAYSIA DI SEBERANG PERAI UTARA, PULAU PINANG.
CONTRACT : Design, Built & Commissioning of New Decay Tank System for Iodine - 131 Room Toilets
Radioactive Waste Decay Tank is also called as decontamination plants which are individually designed according to the requirements of the respectively hospital. In the era of new technology whereby the Radioactive Waste Decay Systems will be equipped with modern central process control system including process visualization regulates the plant and guarantees a high safety standard.
When thyroid diseases are treated with radio iodine ( I-131) in the nuclear medical departments of hospitals, a large quantity of radioactive isotopes is deposited. The radioactive wastewater may not be discharged into public sewer, but it must be stored until radioactivity has decayed below the legally defined value.
Due to the quite long retention time of the wastewater in the decay tank, an anaerabe process must be prevented to avoid biogas generation. Therefore, an aerobic process takes places when the wastewater is periodically aerated. Consequently, it had replaced the neutralization process which had been used in former decay plants.
The scale of above plant is mainly depending on the daily water volume discharged from the water closet. However, with the new technology of vacuum toilets system, the daily sewage discharge into recipient tanks is reduced by 50% compare to the conventional type and in the other words, the quantity of storage versus the numbers of days for decaying process had been increased.
The Radioactive Waste Decay Systems consists of the following systems : -
- Vacuum Toilet Systems
- Holding Tank Systems
- Decay Tank Systems
- Sump Pit Discharge Systems
- Aeration Systems
- Rinsing Systems
- SCADA Systems
A. Vacuum Toilets Systems
I ) Introduction
Vacuum technology is used for collecting and conveying wastewater in domestic, commercial and industrial areas, for both outdoor and indoor systems. It also offers innovative solutions in both economic and ecologic respects for the discharge of wastewater from buildings.
In terms of flexibility and cost saving, the vacuum toilets system required a minimal usage of water i.e. approximately 1.2 litres per flush compare to conventional toilet system because air is used as transport medium instead of precious water. In addition to that, the pipe works laying does not have any restriction on slope or building structural. Wastewater can even lifted up to a height of 4.50m.
II ) Functionality
The pneumatic vacuum toilet is hooked into vacuum sewer line, which may consist of a single or multiple series of sewer lines. The vacuum sewer line are connected to the vacuum station where vacuum pumps create the required negative pressure ( approximately - 0.3 bar ). Therefore, once patient uses the toilet and flushes it, the flushing actions opens a valve in the toilet water closet, and the vacuum sucks the contents of the toilet out and transfers it to Holding Tank for next process.
- Closed systems with no leakage or smell.
- Low water usage per flush compare to conventional water closet.
- Reduce the scale of the plant
- Small diameter pipelines.
- Flexible pipeline construction.
B. Holding Tank System
I ) Introduction C. Decay Tank System
Holding Tank Systems is used to collect the continuous waste water and store the wastewater up to designed numbers of days or high level of the tanks before transfer to designated tank for decaying purpose. In additional to that, an aerobic process will takes place by periodically aeration to avoid any biogas generation to the tanks.
II ) Functionality
Holding Tank System consists of 2 nos FRP/HDPE tanks ( 1 duty and 1 standby ) to receive the continuous Radioactive waste from the vacuum system until for the extension of 37 days or the designated High-Level whichever come earlier. It also equipped with Motorized Ball Valve with manual override and Cutter pump which acts as macerator and transfer pumps.
Upon receiving Radioactive Waste from the vacuum Toilet System, the waste will be stored in the either one of FRP/HDPE tanks which will be act as 1 duty and 1 standby. All the waste will be store at FRP/HDPE tanks for 37 days limited or high permitted level whichever come earlier.
Simultaneously the filled Holding Tank will transfer to Decay Tank System thru a cutter pump which also acts as a macerator to the radioactive waste.
III ) Advantages
- To ease the sequencing process and also to acts as additional standby tank for any unforeseen circumstances.
- The combination of macerator and transfer pump will eventually reducing the maintenance cost for operation of the plant.
I ) Introduction D. Sump Pit Discharge System
Decay Tank systems is used to receive the wastewater from the Holding Tank and store the wastewater up to designed numbers of days or radioactivity has decayed below the legally defined value before it can be discharge to public sewer.
In additional to that, an aerobic process will takes place by periodically aeration to avoid any biogas generation to the tanks.
II ) Functionality
Decay Tank System consists of 3 nos FRP / HDPE tanks to receive and store the wastewater accumulation for 37 days or High - Level from the Holding Tank system to the extension of 111 days or the radioactivity has decayed below the legally defined value.
This system will be equipped with Motorized Ball Valve with manual override and Radioactivity sensor for the continuous monitoring purposes.
Upon receiving Radioactivity Waster from the Holding Tank System, the waste will be stored in the one of FRP /HDPE tank for additional 111 days or radioactivity has decayed below the legally defined value whichever comes earlier.
Once the above criteria is meet, the Medical Physicist are required to take a sample from the Decay Tank to double confirmation of the radioactivity has decayed below the legally defined value before it permitted to proceed to discharging process.
III ) Advantages
- Continuous monitoring and recorded trending for decaying process.
- Additional safety feature designed for user to carry put sampling and double confirmation the radioactivity reading before discharging to public sewer.
I ) Introduction E. Aeration System
Sum Pit Discharge System is used to collect and transfer back any wastewater collected during abnormal criteria and also as a pre-discharge tank before the discharge of permitted radioactivity waste water to public sewer.
II ) Functionality
Sump Pit Discharge System consists of 1 no of Return Pump to transfer back any radioactive wastewater which flowing to the sump bit back to Holding Tank system when in abnormal conditions. Besides that, there is also 1 no of manual gate valve at the outlet of sump pit for Medical Physicist to open upon confirmation of sampling is ready to discharge and also to control the flow rate of discharging.
Upon detection of high-level at Sump Pit and all of Decay Tank's discharge still in CLOSED mode ( abnormal condition ), the return pump will be activated and pump the radioactive waste back to Holding Tank System.
During Normal Condition where one of the Decay Tank discharge valve is in OPEN mode,
the return pump will be deactivated and the Medical Physicist shall open the manual gate valve upon confirmation to discharge.
III ) Advantages
- To ensure all un-permitted radioactive waster not been discharge
- To enable Medical Physicist to control the flow rate of discharge manually.
I ) Introduction F. Rinsing System
Since the wastewater is a biodegradable waste, an aeration system is used to create aerobic process by periodically aeration to the wastewater in order to prevent any anaerobe process and avoid any biogas generated. Further to that, the aeration system will also preventing any possibility of sludge creation and reduce to odor in the tank.
II ) Functionality
Aeration System consists of 1 no of Air Blower and 2 nos of submerged coarse bubble diffuser which will be install at each of Holding Tank and Decay Tank.
III ) Advantages
- Odor removal.
- Prevent of biogas generation.
- Prevent of sludege sedimentation.
I ) Introduction G. Scada System
Rinsing System is used for tank cleaning before receiving the new batch of wastewater.
II ) Functionality
Rinsing System consists of 1 no of Water Pump and 5 nos of solenoid valve which will be installing at each of Holding Tank and Decay Tank. It had designed for the purpose of tank cleaning after radioactive waste had been transferred.
When the process of transferring / discharging of radioactive waste, the rinsing system will be activated and the rinsing process will start when the radioactive waste in the tank remained 20% of volume and stop after one ( 1 ) minutes of rinsing.
III ) Advantages
- To remove or ensure all radioactive waste had been transferred / discharged to the next process.
I ) Introduction
SCADA systems are typically used to perform data collection and control at the supervisory level. Some SCADA systems only monitor without doing control, these systems are still referred to as SCADA systems.
The supervisory control system is a system that is place on top of a real-time control system to control a process that is external to the SCADA system. This implies that the system is not critical to control the process in real-time, as there is a separate or integrated real-time automated control system that can respond quickly enough to compensate for process changes within the time-constants of the process. The process can be industrial, infrastructure or facility based as described below :
- Industrial processes include : manufacturing / production / power generation / fabrication / refining - continuous, batch repetitive or discrete.
- Infrastructure processes may be public or private and include : water treatment and distrubution, wastewater collection and wastewater treatment, oil & gas pipelines, electrical power transmission and distribution and large communication systems.
- Facility processes in private or public facilities including : buildings, airports, ships or space stations in order to monitor and control : HVAC, access control , energy consumption management.
The SCADA systems for these applications all perform Supervisory Control And Data Acquisition, evne though the use of the systems are very different.
II ) Functionality
When the Physicist selected all equipments in the LCP to 'Remote' mode, the whole equipments in the Decay Tank System will be run as automatically based on written PLCs. Any alarms, trending and reading which required will be display in the workstation in the physicist room and it had been set up for three types of user as a security features as below :
III ) Advantages
- Admin Level ( High ) - the user can control and print reports for all the Decay Tank system in their workstation.
- Engineer Level ( Medium ) - the user can control only for any related to engineering works in the Decay Tank System thru their workstation.
- Technician Level ( Low ) - the user can on view the Decay Tank systems and NOT allow to control any of the Decay Tank System.
- To automate, retrieving and record all activities happen in the Decay Tank System during operation.
- To facilitate the user to do reporting purposes.
2. Operational of the Radioactive Decay Tank System
The radioactive waste discharges from the ward goes into one of the holding tanks, HT1 or HT2, i.e. one is on duty and one on standby. (Say HT 1)
After receiving radioactive waste discharges for 37 days, the waste is pump through a cutter pump which acts also as a macerator to one of the decay tanks, DT 1 or DT 2 or DT 3. ( Say DT 1 )
HT 1 now goes on standby. HT 2 starts receiving another 37 days discharge from the ward.
Once HT 2 has received discharges for 37 days, the waste is pump through a cutter pump which acts also as a macerator to one of the two other decay tanks, DT 2 or DT 3. ( Say DT 2 )
The waste that was already in DT 1 is now 74 days old.
HT 2 now goes on standby. HT 1 starts receiving another 37 days discharge from the ward.
After HT 1 has received discharges for 37 days, the waste is pumped through a cutter pump which acts also as a macerator to the remaining decay tank DT 3.
Waste in DT 1 is now 111 days months old and can now permit to be discharged into the public sewer.
Waste in DT 2 is now 74 days old and will be discharged to the public sewer in another 37 days time.
3. Leakage and Structural Failure of Tanks.
The possibility of leakages cannot be discounted and this has been taken into account. Structural failure of the tanks is very remote but has been designated to be replaced with ease.
During operations, one of the receiving tanks and one of the delay tanks are always on standby, i.e. they are empty.
Should a leak occur, say in HT 1, which can be detected, as all five tanks are equipped with level sensors, the contents are transferred to HT 2 via valves and pump. HT 1 can then be replaced or repaired.
Similarly with the DT 1, DT 2 or DT 3. The contents from the leaking DT Tank will be transferred to an empty HT/ DT tank.
The floor of the reinforced concrete bunker containing the tanks are sloped to one corner, where a small sump collects spillages. Surrounding of bunker will be facialites with water hose for rinses the floor and water from this goes into the sump.
A small pump empties the sump into the incoming pipeline from the ward. This will go into either HT1 or HT2.
1. Proposed RC Plinths And Sump Pit Layout.
2. Proposed Equipment & Piping Layout. 3. Process & Instrumentation Diagram. 4. Proposed Equipment & Piping Layout. 5. Proposed Equipment & Piping Layout.
6. Proposed Equipment & Piping Layout.
. Proposed Equipment & Piping Layout.
8. Main Control Panel Layout.
9. Main Control Panel - Front Layout.
10. Mimic Diagram Layout.
11. Single Line Diagram 1.
12. Single Line Diagram 2.
13. Single Line Diagram 3.
14. Single Line Diagram 4.