LOW-AND INTERMEDIATE-LEVEL RADWASTE DISPOSAL IN CHINA

Wang Xian De
Beijing Institute of Nuclear Engineering (BINE)
P.O. BOX 840, Beijing, China, 100840

ABSTRACT

The present development and relevant policy of waste disposal in China are briefly presented. The characteristics and package of waste are also described. Regional disposal was determined as the national policy for low-and intermediate-level radwaste because of the nuclear facilities and owners of radwaste are distributed centrally in several regions of China. Disposal of wastes in under ground and above ground have been adopted as the main manner for low-and inter mediate-level radwaste. Two repositories named Northwest and Beilong are under construction. Main features of those repositories are described in the paper.

INTRODUCTION

At the beginning of 1980s, radwaste management was focused on the disposal of waste. Since then some policies, programs, standards and technical criteria have been worked out to meet the requests of radwaste disposal, the siting and construction of repositories have also been consideration.

By the end of 1990s, two repositories of low-and intermediate-level radwaste will be operated at the northwest and south area of China. Along with the development of nuclear energy and application of nuclear technology, siting of disposal facilities is being conducted at the east or other area. Four or five repositories will be constructed in order to dispose the accumulated waste of nuclear industry, the waste generated by the decommissioning of early nuclear facilities or the operation of nuclear power plants in accordance with the national program.

Near surface disposal is adopted for low-and intermediate-level radwaste in China. Solidification is demanded for existing liquid waste as early as possible. The duration of interim storage is not longer than five years for new produced waste of facilities and it is should be delivered to the repositories after their operation. The fund of construction for repository is supported by national investment and partial budget of nuclear power plant. The operation expense is relied on disposal charges from customer. China National Nuclear Corporation (CNNC) is responsible for the siting, construction and operation of repositories, but the approval of environmental impact assessment, issue of standards, inspection of disposal activities are performed by National Environmental protection Agency (NEPA) and its local administration.

WASTE CHARACTERISTICS

Wastes are divided into two kinds, which are wastes of nuclear industry and nuclear power plant based on their origin.

• Wastes of nuclear industry cover abandoned equipments, components, pipings, valves, filters, clothings and construction materials. Dominant radionuclides in waste of nuclear industry are ¹³⁷Cs and ⁹⁰Sr, which are about 90% and 10% of total radionuclides and the others such as ⁶⁰Co, ⁶³Ni, ¹⁴C, ¹²⁹I, ⁹⁹Tc exist in trace amount. The specific activity of low-and intermediate-level radwaste are 7.4(breve)10¹⁰Bq/kg.
• The waste of nuclear power plant in operation consists of spent filters, clothings, immobilized resin & filter and solidified waste. Radionuclides containing in waste of nuclear power plant are ⁶⁰Co, ¹³⁷Cs, ⁶³Ni, ¹⁴C, ⁹⁰Sr. Among them, ⁶⁰Co, ¹³⁷Cs, and ⁶³Ni are approximately 58%, 20% and 20% of total radionuclides respectively. The specific activity of waste is about 9.0(breve)10⁶ to 7.5(breve)10⁸Bq/kg.

WASTE PACKAGE

• Carbon steel drum with the volume of 200 liters is used for the package of low-level waste produced from nuclear industry. Intermediate-level waste is placed in two kinds of reinforced concrete container with the volume of 200 and 400 liters. Those containers have the same outer diameter of 1400 mm and height of 1300 mm but their thickness are different.
• The same drum is used for the package of low-level waste in nuclear power plant. Four kinds of reinforced concrete container are applied to the placement of intermediate-level waste based on the waste characteristics. The dimension, volume and weight of containers are shown in Table I.

SITE FEATURES

• Northwest repository is located at Gebi desert, where is dry and sparsely populated, neither valuable resources nor historic spot are present there. The average annual precipitation and water table are 61.5 mm and 30 to 35 meters. Thick clay layer with strong adsorbability to ⁹⁰Sr and ¹³⁷Cs exists at the site. The distance between the nearest river and site is over 2.5 kilometers.
• Beilong repository is situated at the coastal area where is wet, rainy and slow economy in development. The average annual precipitation is 1900 mm, which is more than Northwest repository and its water table is 19 to 31 meters. The site is 100 to 300 meters from the rivulets.

FACILITY DESCRIPTION

• The capacity of Northwest repository is 200,000 m³ of waste and its first phase is 20,000 m³. Beilong repository can dispose 240,000 m³ of waste but the capacity of first phase is 14,500 m³.
• Repository is divided into controlled and non-controlled areas. The controlled area includes disposing, buffer and operating zones and the non-controlled area consists of administrative, auxiliary buildings and utility. The functions of operating and disposing zone are reception & inspection or emplacement of waste, the buffer zone acts as the isolation area between the disposing zone and adjacent field. The disposing zone covers several disposal units.
• The options of under ground and above ground disposal are adopted for Northwest and Beilong repositories according to their natural conditions.

Northwest Repository

In Northwest repository, disposal units comprise several concrete vaults without bottom slab, concrete blocks and cover of 2 meters. The inside dimension of vault is 135(breve)23(breve)5.3 or 5.7 meters(L(breve)W(breve)H), the thickness of wall and cover of 2 meters. The inside dimension of vault is 135(breve)23(breve)5.3 or 5.7 meters (L(breve)W(breve)H), the thickness of wall and concrete blocks are 300 and 200 mm. The bottom of vault is laid of rammed soil, which should be strong enough to stand the loading of waste. The cover consists of five layers , they are soil, clay, grit, soil and gravel from bottom to top. The cover has a slop of 0.5% in order to drain off rainwater. The manner of mixed emplacement is applied to dispose wastes in vault. It means the canisters and drums with wastes are placed in the same vault. In general, canisters are laid on the bottom of vault and drums are put on them. Five layers of canisters and drums in which one or two layers are canisters are settled in vault based on their weight.

Beilong Repository

In Beilong repository, the outside dimension of vault is 17(breve)17(breve)7 meters (L(breve)W(breve)H) and the vault has a concrete bottom slab and a cover of 5 meters. A mobile shelter is installed on the disposal units to prevent rainwater entering into the vaults during disposing of waste. Figure 1 and Fig. 2 show the mobile shelter of vault.

The cover includes several layers, which are soil, sand, clay, sand, gravel, soil and plantation. The cover of vault in Beilong repository is shown in Fig. 3.

WASTE DISPOSING

The procedure of waste disposal includes inspection of waste, reception and registration, emplacement of waste ( or temporary storage ), backfill, casting of concrete block, covering of top.

When the vault is filled up with waste, the cement grout is poured into the gap of canisters or drums in Beilong repository, but the gap is filled with sand in Northwest repository. The waste could be stored in storage temporarily when the bad weather condition influences waste disposal.

SAFETY MEASURES

Several measures have been adopted in designing repository to protect environment from the potential pollution of radionuclides. The main aspects are as follows:

• The suitable site should be considered.
• Multibarrier of disposal units can isolate waste effectively and prevent human, animals or plants from inadvertent access to the waste.
• In Beilong repository, drainage system is installed to discharge rainwater and ground water probably entering the vault. The bottom slab of vault is sloped from sides to center and a drain pipe which is connected with the drainage system is set at the lowest spot of slab. A drain channel is arranged at the top of cover to discharge rainwater on it.
• Monitoring of radiation dose, sampling of air, water, soil, animals and plants are stipulated for the activities of waste disposal and adjacent area of repository.

CONCLUSION

Near surface disposal is widely applied on low-and intermediate-level radwaste in the world based on its safety, economy. The options of under ground and above ground disposal have been considered according to the different site conditions in China. Although the experience originated from Northwest and Beilong repositories will be beneficial to the construction of repositories in the other areas late on but there isn't much knowledge in the operation. The further studies on the institutional control in the long period are still proceeding.

REFERENCES

1. NEPA, China National Environmental Protection Agency, "Environmental Policy of China on Low-and Intermediate-Level Radwaste Disposal", June 24, 1992.
2. LI XUEQUN et al., "Strategic Review on Management and Disposal of Low-and-Intermediate-Level Solid Radwastes", Proceedings of Sino-French Seminar, April 1993, pp. 18-20.
3. GB9132, "Regulations for Shallow Ground Disposal of Low-and Intermediate-Level Solid Radwaste". The National Environmental Protection Agency, 1988.