Halden boiling water reactor

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The  Halden  Boiling  Water  Reactor (HBWR) is a versatile tool for nuclear fuels  and  materials investigations:

REACTOR SITE

The Halden Boiling Heavy Water Reactor (HBWR) is located in Halden, a coastal town in south-east Norway near to the border to Sweden. The reactor hall is situated within a rock hillside on the north bank of the river Tista
The size of the site area is 7000 m2. The reactor vessel primary circuit system is inside a rock cavern with a net volume of 4500 m3. The rock covering is 30-60 m thick. Heat removal circuits are either placed inside the reactor hall or in the reactor entrance tunnel. Control room and service facilities are placed outside the excavation. The service buildings contain offices, workshops, and laboratories.

REACTOR SYSTEM

The HBWR is a natural circulation boiling heavy water reactor. The maximum power is 25 MW (thermal), and the water temperature is 240°C, corresponding to an operating pressure of 33.3 bars. Pressurization tests are performed at regular intervals using a pressure of 40 bars.

The reactor pressure vessel is cylindrical with a rounded bottom. It is made of carbon steel and the bottom and the cylindrical portion are clad with stainless steel. The flat reactor lid has individual penetrations for fuel assemblies, control stations and experimental equipment. 

14 tons of heavy water act as coolant and moderator. A mixture of steam and water flows upwards by natural circulation inside the shroud tubes which surround the fuel rods. Steam is collected in the space above the water while water flows downwards through the moderator and enters the fuel assemblies through the holes in the lower ends of the shroud. The steam flows to two steam transformers where heat is transferred to the light water secondary circuit. Condensate from the steam transformers returns to the reactor by gravity. An external subcooler loop is installed to provide experimental variation of void fraction in the fuel assemblies and the moderator, and is also used for heating and cooling purposes.

In the secondary circuit, two circulation pumps pass the water through the steam transformers, a steam drum and a steam generator where steam is produced in the tertiary circuit. The tertiary steam is normally delivered as process steam to the nearby paper mill, but may also be dumped to the river.

There is generally no access to the reactor hall when the reactor is operational, and therefore all control and supervision is carried out from the control room.

REACTOR OPERATING CONDITIONS

The research and development programme is based on operating the Halden Reactor.

A fuel charge consists of a combination of test fuel from organisations in member countries and driver fuel assemblies, which provide reactivity for operating the reactor.  
Light water, high pressure loops provide facilities for testing under prototypic BWR and PWR conditions.

 

CORE DESCRIPTION

DRIVER FUEL ASSEMBLIES

Currently, each driver fuel assembly consists of eight or nine fuel rods with 6 % fuel enrichment and standard fuel pellet diameter.

CORE CONFIGURATION

The core consists of about 110 - 120 fuel assemblies, including the test fuel, in an open hexagonal lattice with a lattice pitch of 130 mm. 30 lattice positions are occupied by control stations. The maximum height of the fuel section is 1710 mm, and the core is reflected by heavy water.

The central position in the core is occupied by an emergency core cooling tube with nozzles, and between eight and fourteen core positions contain pressure flasks for light water, high pressure test loops.

PLANT STATUS

The design working pressure of the HBWR pressure vessel is 40 bar with a saturation temperature of 250°C. The hydraulic acceptance pressure test was carried out at 54 bars, 35 % above the design pressure. The normal operating pressure is 33.3 bars, with corresponding saturation temperature of 240C. The stresses in the vessel are low compared with the code requirements. Thermal stresses are also normally low.

There are normally 2-3 main shutdowns per year, dictated primarily by the experimental programmes, and a few additional cooling downs for special tests. The normal heating and cooling rates are 10°C.h-1. Inspection and recertification pressure tests are performed every 3rd year at 10 % overpressure. These pressure tests are performed with water/steam at saturation temperature. According to the requirements set by Norwegian Boiler Authority, the inspection and test programmes include ultrasonic examination of vessel welds, lid, bolts, bottom nozzle and primary system piping, and evaluation of radiation induced material changes.
The bottom nozzle welds and the welds beltline region of the reactor vessel wall are being 100 % ultrasonically examined at the inspections.  Also the top lid and the flange bolt are being inspected, the bolts 100 % by ultrasonic. The primary system piping is subject to inspection by NDT methods. No defect indications in the above mentioned inspections have been found. 

The irradiation induced changes in the vessel material are being monitored by material testing every 6th year, flux evaluations and fracture analysis. The Charpy and fracture mechanics test on surveillance specimens are performed by VTT’s laboratory in Finland, using material specimens with appropriate lead factors in fluence. Flux and fluence assessments enable quantification of the fluence received by the different parts of the vessel, account taken of the changing core loading over the years.

The outcome of the material testing, fluence evaluations, inspections, and pressure testing form the basis for the assessments of vessel integrity. Internationally accepted codes, rules and recommendations are used in a consultative manner. The material tests and the analysis performed indicate that the reactor can be operated safely well beyond year 2020.

 


Revision : 2008
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