INTERIM STORAGE OF HIGH-LEVEL WASTE IN BELGIUM

J.P. Boyazis and M. Demarche
ONDRAF
Belgium

ABSTRACT

A new facility for the receipt and storage of radioactive waste, known as Building 36, was built on the Belgoprocess site in Belgium. This facility is intended to receive and store intermediate and high radioactive waste originating from the reprocessing by COGEMA of spent fuel from Belgian nuclear power plants.

The facility consists of :

Storage modules can be added in the future, without interfering with the operational area of Building 36. The storage capacity can thus be extended eight to ten fold.

Building 36 is designed to withstand earthquakes, external explosions and airplane crashes.

The duration of storage depends on the development of final disposal facilities. The design life is planned for a period of 75 years, although 100 years or more are possible.

INTRODUCTION

The seven nuclear reactors in Belgium will have consumed, until their closure, an approximative total quantity of 4000 tons of uranium. In order to recover the recyclable elements (uranium and plutonium), agreements have been entered into between Synatom and the French reprocessing company Cogema. The existing contracts provide for the reconditioning of 670 tons of uranium and the return of the waste products to Belgium. This waste consists of economically uninteresting, but highly radioactive elements. The spent fuel elements are reprocessed by Cogema in La Hague, France. The waste products will be conditioned in this facility into an inert matrix and packaged in standard containers. The return of the waste to Belgium will commence in 1997 and the last shipment is expected to arrive ten years later.

The Belgian National Agency for Radioactive Waste and Enriched Fissile Materials, NIRAS (ONDRAF), has built a new storage facility for the receipt and storage of the above-mentioned waste products. It is located on the Belgoprocess site close to Mol in the northeast of Belgium and is referred to as "Building 36". Belgoprocess is a subsidiary of NIRAS and is in charge of storing radioactive waste products taken over by NIRAS. The storage facility can, if necessary, also handle or store radioactive waste products from other origins.

The duration of the storage will depend on the development of final disposal facilities. The design life of Building 36 is 75 years, although 100 years or more are possible.

RADIOACTIVE WASTE

Radioactive waste from the reprocessing of spent fuel elements at Cogema, La Hague is classified in the following five categories :

  1. Very highly radiating and heat producing waste : vitrified solutions of fissile materials, residues from the purification of solvents and residues of solutions.
  2. Highly radiating waste : structural waste from workshops where the used fuel elements are cut and dissolved (hulls, ends, frames, etc.).
  3. Intermediate radiating waste : bituminized process sludge.
  4. Low or intermediate alpha radiating waste : technological alpha waste (parts of equipment and materials from the reprocessing workshops and laboratories).
  5. Low radiating non-alpha waste : technological non-alpha waste (parts of equipment, clothing and different packing materials from the reprocessing workshops).

The first three categories and the intermediate alpha radiating waste of category 4 will be stored in Building 36. Low alpha radiating waste and waste of category 5 will be stored in another building, Building 51, on the Belgoprocess site.

The characteristics of the above-mentioned waste categories and of the standard containers that will be stored in Building 36 are presented in Table I.

Table I Characteristics of the Residues from Cogema (La Hague, France)

WASTE STORAGE AND RECEIPT

Building 36 is designed for the storage of waste from the categories 1, 2 and 3 and for part of the category 4 waste (intermediate radiating alpha waste). Once the waste has reached a sufficiently low level of radiation and heat production, it can be transferred to a final disposal facility.

Building 36 can also serve as a receiving and loading station for road transport containers, including those with a weight of 112 ton, in the following cases :

  1. For the receipt of category 5 waste intended to be stored in Building 51.
  2. For the dispatch of waste types similar to category 1 waste, which will be vitrified in the Pamela installation on the Belgoprocess site.

LAYOUT CONSIDERATIONS

Building 36 consists of storage modules (cells and bunkers) for the different categories of waste. These modules are positioned around a common receiving station. This station consists of a receiving hall, a lock, an unloading cell and a transfer corridor.

Due to the important heat production, category 1 waste will be stored in special storage cells. The waste from categories 2, 3 and 4 will be stored in a storage bunker.

The building is designed in such a way that it can easily be extended in order to meet the storage requirements of the total national reprocessing program (approximately 4000 tons of uranium). Construction work for additional cells or bunkers can be executed without interfering with the operational use of the existing facilities. The storage capacity of Building 36 can easily be extended to 8 to 10 times its original capacity.

The total cost of the building in its actual configuration (two storage cells of each thirty pits and one storage bunker) is of the order of eighty-five million US Dollars.

GENERAL LAYOUT

The general layout of Building 36 is shown on Figs. 1, 2 and 3 and consists of the following areas. The numbers and letters in brackets indicate the reference of the area or the equipment as shown on the figures.


Fig. 1. Level 0.00 m.


Fig. 2. Level 4.50 m.


Fig. 3. View 1-1 and 2-2.

  1. The receiving hall (1) intended to receive or dispatch the transport containers A) which are used for road transport. Upon arrival, the 112 ton gross weight transport containers are lifted from the truck and placed vertically on the transfer wagon B). The reverse operation is applied when loading trucks for road transport.
  2. hall can also be used for loading and unloading internal transport within the Belgoprocess boundaries.
  3. The lock (2) between the receiving hall and the unloading cell is used to control the transport container (internal atmosphere, external contamination, leaktightness before road transport) and, if necessary, to decontaminate the transport container.
  4. The unloading cell (3) is the final station for the transfer wagon. Waste packages of all categories can be unloaded in this cell. Various operations are planned, for instance :
  1. The transfer hall (11) is equipped with a shielded loading machine G; H) and is destined to transfer primary packages with vitrified waste from the unloading cell (3) to the storage cell (4).
  2. The storage cell (4) consists of two modules and is equipped with a total of 60 stainless steel pits. Each pit can contain 10 primary packages. A shock absorber is installed at the bottom of the pits to prevent damage in the event of a package falling during hoisting operations. The pits are ventilated in order to discharge the product heat.
  3. The passage (9) for the transfer of primary packages with intermediate and highly radiating waste to and from the unloading cell (3) to the storage bunker (5). A mobile platform D) on rails serves as transport vehicle. This vehicle can transport waste of categories 2, 3 and 4.
  4. The storage bunker (5) for the storage of circa 1000 m3 of intermediate and highly radiating primary packages. The packages are transferred from the mobile platform, which is positioned by remote control in the passage, to the storage bunker by means of a remote controlled traveling crane I). In case of problems with the bunker crane an emergency crane will be sent into the bunker. This emergency crane can be attached to the bunker crane by remote control and pull it back into a safe position.
  5. The storage hall (12) for the temporary storage of transport containers and packages, is scheduled to be built as an extension.
  6. The central control room (10) houses the computer installation, centralized control boards, tele-monitoring screens and manipulation control panels. Lead-glass windows provide a view of the unloading cell from the control room.
  7. Utility areas (offices, locker rooms, circulation, plant rooms, etc.).

VENTILATION INSTALLATION

The ventilation comprises five independent circuits (storage cells, storage bunker, transfer hall, unloading cell and lock, building). It serves the following purposes :

  1. To provide cooling to heat producing primary packages, mainly those stored in the storage cells.
  2. To provide internal climate according to applicable Belgian standards for occupational health.
  3. To maintain lower air pressure than atmosphere pressure, in order to avoid possible radioactive air leaches.
  4. To maintain under pressure cascade to avoid a flow of contamination from areas with higher risk for contamination to areas with lower risk of contamination.

Under normal operational conditions there is no danger of internal airborne contamination. Even so, the air discharged through the chimney is filtered. Back-up extraction fans are provided.

The ventilation installation is connected to both normal and emergency supply. It is also connected to the ultimate electricity supply system. In case of complete failure of these systems, cooling is ensured through the principle of natural convection. A 37 m high chimney will provide the temperature gradient needed for cooling of the storage cells.

ELECTRICAL INSTALLATION

The electrical installation consists of three separate power supply systems :

  1. The supply by the public network, which serves all installations in the building;
  2. The emergency circuit connected to a stationary generator of the Belgoprocess site;
  3. The ultimate emergency power supply by means of a mobile generator, which provides power to the essential functions within maximum 36 hours.

A No Break serves continuously the PLC's and the radiation monitoring systems.

Fire detection systems and telephones have their own autonomous systems.

STRUCTURAL SAFETY

Building 36 is designed to resist the following exceptional events :

  1. Earthquake with a magnitude of V on the MSK-scale. During such earthquake, the structure will not only remain unaffected, but the main equipment will remain operational.
  2. Airplane crash the probability of wich is higher than 10 E-7 per annum. The resistance is based on the F16 fighter plane, which crashes with a velocity of 150 m/s. Walls and roof slabs are dimensioned in order to avoid penetration in case of direct impact and to avoid cracks. In the event of kerosine fire, it will not spread into the building.
  3. High wind velocity factor according to Belgian standards.
  4. External explosion of gas pipelines, hydrogen tankers or a static facility for hydrogen or a petrol station.
  5. The effect of flooding has been considered, but found to be negligible as the ground level is well above the maximum recorded flood levels.

RADIATION PROTECTION

Radiological safety is achieved by certain design specifications, which resulted in 1.50 to 1.70 m thick concrete wall and roof slabs. A special concrete composition was used in order to limit hydration heat production, shrinkage and formation of fissures in the concrete structure. Characteristics of this composition are : a low water content and the use of special cement, pulverized fuel ash and super plasticizer.

A radiation monitoring installation is installed to measure the following :

  1. Continuous monitoring of the ambient dose in the different areas;
  2. Regular checks by mobile monitoring on the possible presence of airborne contamination;
  3. Continuous monitoring of the exhaust air in the chimneys;
  4. Surface contamination with portable or stationary devices;
  5. Personal monitoring.

In accordance to the general rules applicable on the Belgoprocess site, the dose rate at the contact of the external walls is limited to 20 micro Sv/h.

The estimated dose rate for the population living in the immediate surroundings of the Belgoprocess site, is calculated to be lower than 10 micro Sv/year assuming the storage areas are completely filled.

The danger of contamination under normal circumstances is negligible. Nevertheless decontamination of primary packages and transport containers is possible at different locations in the building.

The possibility of criticality in the storage cells for vitrified waste has been analyzed and found to be zero.

FIRE PROTECTION AND ALARM

The construction materials are incombustible and the building is divided into fire containing areas. Around the building a 15 m wide area has been cleared of trees and bushes.

The fire fighting equipment consists of portable fire extinguishers and a static halon system in the building. Fire hydrants are installed on the periphery of the building. Fire and smoke detection systems are installed with visual and audible alarms.

All alarms are relayed to the Belgoprocess central control room.

MANIPULATIONS

All manipulations of primary packages will be remote controlled from the control room, except for the loading machine which will be served locally. Due to the high reliability of the handling systems, the primary packages can be moved without risk of incidents.

The altitude at which the packages will be transferred by the traveling cranes will be limited to avoid damage to the packages in case of fall.

The electrical power supply and the motorization of the essential handling functions are redundant to make sure that the load can be brought back to a safe position in any circumstance, even after an earthquake.

Furthermore most of the handling systems (traveling cranes, grippers, mobile platform,...) are equipped with mechanical emergency systems, which make it possible to move the loads even in case of failure of the redundant electrical system.

RELEASE TO THE ENVIRONMENT