Zainus Salimin
Radioactive Waste Management Technology Center
National Atomic Energy Agency of Indonesia

The prime function of the Interim Storage for Spent Fuel of Indonesian Multi-Purpose Reactor 30 MW ( ISFSF of MPR-30 ) is to receive and store, underwater, spent fuel arising from the operation of MPR-30. The capacity of the ISFSF is to be sufficient to store the fuel arising over 25 year reactor operation and 1 core unload, specified as 1,448 elements in which 8 fuels exchanges per cycle for 7 cycles per year on the reactor operation. Spent fuel from reactor contain at of 47.590 Watts per fuel element which is stored temporary in reactor pool for about 100 days to decay heat into 377.2 Watts, and than transferred to ISFSF through the Transfer Channel. Spent fuel heat on the maximum capacity of the ISFSF is 35 kW, heat generating by light system and other heat source are 5 kW. The pond cooling system of ISFSF is designed to remove heat from the stored fuel assemblies by water circulation of 6 m³/hr. The system has primary and secondary loop circuits through primary and secondary plate type heat exchangers to avoid contamination to the chilled water. For maintaining the water quality, a mix bed of normal anion-cation exchange resin will be used. In case of Caesium contamination the system is also equipped with a special mix bed to catch Caesium. The circulation flow rate is 6 m³/hr. The mix bed ion exchange units will treat the water which is taken from the deep section of the pond and returned to the far end of pond beyond the fuel storage along the same line as the cooling water. The radioactive drainage for the facilities will be a separate system feeding to waste storage tanks adjacent to the ISFSF building. The capacity of tank collection is 2.5 m³ made of stainless steel SS-304, either for liquid and spent resin slurry, this tank is to be emptied when necessary by waste handling and collection services in existence. The air continuos monitoring system will be located at the ISFSF building. Hand and foot monitor will also be provided.

The primary objectives of irradiated fuel handling is that it must be stored in a safe, economical, and environmentally acceptable manner until it is transferred to a repository for final disposal or to a reprocessing plant for recovery of U and Pu.

In the method of spent fuel storage, the basic function of facilities required here are:

• Removal of heat from the fuel, which means to carry away the heat produced by radioactive decay of fission product and transuranium element. Heat removal is accomplished by use of cooling medium, such as water or air.
• Radiation shielding, i.e. to maintain acceptably low level of radiation in working areas. Shielding against radiation is obtained by storing the fuel well below water in an appropriate depth or by containing the fuel in cavity surrounded by solid material, such as concrete or earth sufficiently thick to prevent significant levels of radiation from penetrating it. The primary concern for shielding is to comply with established regulation for maximum radiation exposures to personnel involved with the operation of the facility. Design allowing good biological shielding would, in general, provide for an average surface radiation exposure between 2 and 5 mRem/h (the maximum permissible surface radiation is normally 200 mRem/h for transport casks).
• Containment of radioactive materials that is to prevent the potential release of radionuclides in the working area and the general environment, containment is accomplished by storing the fuel under water, in a voult, or in container which prevents the release of significant quantities of radioactive material even during accident condition of damage of cladding. The fuel pellets which contain more than 95 % of the fission product, are enclosed in cladding; this represent the first safety barrier for containment the fission product and actinides produced in the fuel roads during irradiation. The three major considerations are physical damage of cladding during fuel handling, chemical attack, and control of maximum cladding temperature, which may cause failure by distortion or melting of the cladding.

The choice of aluminium alloy for cladding material in currently designed MTR was made because of its attractive neutron cross-section, resistance to irradiation damage, and chemical and mechanical properties. Aluminium alloys are normally quite stable at room temperature; neverless at 100°C they can react rapidly with oksigen, a protective oxidation layer is built up and oxidation process stops. Should the temperature continue to increase at mote than 150°C the protective oxidation layer will flake off. The design of spent fuel storage should include measures to control the purity and temperature of the cooling medium, as both the chemical and physical influence on cladding properties may be affected by the parameters.

The external fuel cladding temperature should remain under 100°C providing the fuel remains covered by water which is not allowed to boil. System are generally designed to operate normally at less than 40°C. For abnormal operation the maximum designed temperature is 67°C.

The ISFSF building consist of three floors. Basement was designed for filter room, pond and water treatment plant. Ground floor was designed for plant room, decontamination room, component storage and vehicle bay. First floor was designed for change room, toilet, health physics room, control room and storage room. The pool storage area has a dimension of 14 m long x 5 m width x 8 m depth.

The prime function of the ISFSF is to receive and storage, under water, spent fuel arising from the operation of MPR-30. The design capacity of the ISFSF is to be sufficient to store the fuel arising over 25 years reactor operation and 1 core unload, specified as 1,448 elements in which 8 fuels exchange per cycle for 7 cycles per year on the reactor operation. The ISFSF will also be used for storing experiment fuel, other irradiated materials from adjacent laboratories, and 125 standard cans for irradiated scrap.

Movement of all radioactive materials to the ISFSF will be carried out under water by means of the Transfer Channel (TC) which connect the ISFSF to the MPR-30 Installation, Radioisotope Installation (RII), and Radio-metallurgy Installation (RMI) buildings. The TC and the pond of ISFSF are built with 3 mm of thickness stainless steel liner, and 6 mm of thickness pond floor. The pond itself is provided with secondary mild steel containment which equipped with a leakage monitoring system in the inter space. The sluice gates isolate the water in the ISFSF and MPR-30 Installation ponds from the main TC. They are there as back-up as in all normal circumstances there will be water at the same level in the ponds and the TC. They will retain water in the ponds with no water in the TC with a very high degree of integrity and leak-tightness.

Although the generation of both heat and radioactivity continuous, the amount of heat produced and the amount of radionuclides contained decrease with time as the decay of the fission product proceeds as shown in Fig. 1. Spent fuel from reactor contain 47,590 Watts per fuel element which is stored temporary in reactor pool about 100 days to decay heat into 377.2 Watts and than transferred to ISFSF through the TC.

Spent fuel heat on the maximum capacity of the ISFSF is 35 kW, heat generating by light system and other heat source are 5 kW, so the total heat received by cooling water is 40 kW.

The ISFSF is provided with the Ventilation and Air Condition System (VAC), Water Treatment System, and Radiation Monitoring System. The ISFSF are designed constant temperature of water about 35°C. The failure of water cooling will be increased the temperature of water in pool about 2°C per day. The failure of water cooling and VAC will be increased the temperature of water in pool about 3°C per day.

The VAC System ensures the following functions:

• To give the air change in the individual room as below:
• 8 times/hour in filter room
• 5 times/hour in normal areas
• 3 times/hour in transfer channel
• To keep the operating temperature and humidity of building at 20 - 25°C and 40 - 60 % relative humidity.
• To keep the negative air pressure at (100 + 25) Pa in filter room, pond area and TC area, the air flow pattern in TC and ISFSF flows from the lower potential radioactive contamination to areas with higher potential contamination
• To treat the contaminated or doubtful air from the TC and pond by filtration (pre-filter, HEPA and Charcoal) before release to the stack. The charcoal bed filter will only be used in case of emergency.

The flow diagram of the VAC System is shown in Fig. 2.

Water Treatment System consist of Demin Water Plant, Water Purification Plant, Water Cooling Plant, Domestic Water System and Drainage System.

Demin Water Plant was designed to make up the water for the pool and TC with a capacity 1.0 m³/h.

For maintaining the water quality of pond storage, it will be used a mix bed of normal anion-cation exchange resin. In case of caesium contamination the system also equipped by special mix bed resin to catch caesium. The circulation flow rate is 6 m³/h. The mix bed ion exchange units will treat the water which is taken from the deep section of the pond and returned to the far end of the pond beyond the fuel storage along the same line as the cooling water.

The pond cooling system was designed to circulate water with rate of 6 m³/h in the pond from the top surface near the plant room at 35°C pass through the primary heat exchanger required to remove 40 kW of heat and returned to the far end beyond the fuel storage at 28°C. The system has primary and secondary plate type heat exchanges to avoid contamination of the chilled water. The pond temperature is to be maintained at nominal 35°C by chilled water. The flow diagram of pond cooling water system is shown in Fig. 3.

The domestic water supply is taken from the existing domestic water system by intermediate of a reservoir tank.

The radioactive drainage for the facilities will be a separate system feeding to waste tanks adjacent to the ISFSF building. The capacity of tank collection is 2.5 m³ made of stainless steel SS-304, either for liquid and spent-resin.

Radiation Monitoring System is consist of gamma monitor for storage pond and TC, continuos monitoring system for ISFSF building, detector for 1-131 on the exhaust line and hand-foot monitor.

Operation in the storage pool are carried out manually under water using long tools, and aided by powered cranes and hoists. The water depth is sufficient based on shielding calculation to limit personal exposure, being the fuel elements placed in racks in the pool with at least 4 m water column above them. The dose rates one metre above pond surface on the main storage area on the maximum capacity of ISFSF for 4 m water column above spent fuel is 1.73 m Sv/h.

The storage operation consist of storage of spent fuel containing 300 g of ²³⁵U, storage of damaged fuel in cans (anticipated to be approximately 5 % of the total capacity of spent fuel to be store, i.e. 70 fuel elements), storage of special nuclear material in the form of ²³⁵U and ²³⁹Pu, storage of irradiated MPR fuel elements containing ²³⁵U and ²³⁹Pu, and storage of standard cans of scrap fuel.

Based on the above storage materials, there will be a need for 4 different racks configuration i.e. 33 spent fuel racks (42 elements per rack), 2 damaged fuel racks (36 elements per rack), 3 general purpose racks, and 11 scrap fuel cans racks (12 cans per rack).

The top view of storage material on different racks in pool storage is shown in Fig. 4.

1. ZDENEK DLOUHY, "Handling of Irradiated Fuel from Research Reactor", Czechoslovakia Nuclear Research Institute, Czechoslovakia, 1976
2. TECHNICAL REPORT SERIES NO.240, "Guidebook on Spent Fuel Storage", IAEA, Vienna, 1984.
3. SAFETY SERIES NO. 50-SGD10, "Fuel Handling Storage Systems in Nuclear Power Plants", IAEA, Vienna, 1984.
4. BATAN - IAEA ENGINEERING CONTRACT, "Transfer Channel and ISFSF for BATAN, Preliminary Design Package", November, 1992.
5. DONALD Q. KERN, "Process Heat Transfer", Mc.Graw-Hill Book Co., Singapore, 1965.
6. COULSONT, J. M., "Chemical Engineering", 4^th edition, Pergamon Press, Oxford, 1990.
7. PERRY, R. H., "Chemical Engineer's Handbook", 6^th edition, Mc. Graw-Hill International Editions, New York, 1984.

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