Fuel lifetime

To achieve a fuel management scheme with the lowest fuel cycle cost consistent with the current thermal and material performance limits, the following parameters are selected (l)a fuel cycle incorporating uranium/thorium (2) a fuel lifetime of four years (3) an average power density of 8.4 W/cm3 and (4) a refueling frequency of once a year. 

Periodically, a portion of the fuel in a nuclear reactor is removed and replaced with fresh fuel. In the past, the average lifetime of fuel in the reactor was 3 years with one-third of the fuel being removed each year. More recently, attempts are being made to extend fuel lifetimes. 

The very first NS with LMC (design 645) was equipped with two-reactor Power Reactor Installation (PRI). After the port-side-reactor accident during the second fuel lifetime (1968), the NS was kept afloat for some period. Then, after filling of free reactor cavities and the whole Reactor Compartment (RC) with preservative agents, the NS was dumped in the Kara Sea close to the Novaya Zemlia (New Land) archipelago at 50-m depth (1981). Some characteristics of NS, design 645, are given in Table 2. 

The NS 900 put into operation in 1970 was the very first vessel of designs 705 and 705K. In 1972 because of failure of NS primary circuit s auxiliary pipelines and impossibility of their repair, the NS was taken out of service after expiration of only 10% of fuel lifetime in the reactor. The RC was cut out of NS, and free cavities of the primary circuit were filled with preservative agents on furfurol basis. A bitumen-layer of about 1000 mm was laid over the whole surface of the upper deck of RC including the reactor upper head. Under such condition the RC is to be stored with nuclear fuel for long within the waterborne storage center. Some characteristics of NS, design 705, are demonstrated in Tables 3, 4 and 5. 

LMFR core orificing is important because fuel lifetime strongly depends on maximum cladding temperature, which is determined primarily by the core coolant temperature rise (AT) and inlet temperature. 

It is known that fuel claddings experience radiation hardening and embrittlement in an operating reactor. Over the fuel lifetime the yield strength can increase twofold while the ductility can be reduced by one half. 

Fuel lifetime/period between refuellings in effective full power days (EFPD)... 

Fuel lifetime, mass balances offuel materials, design basis lifetime of reactor core, vessel ... 

The fuel lifetime/bum-up characteristics and economic characteristics of the ELENA-NTEP plant are given in Table III-4. 

TABLE m-4. FUEL LIFETIME/BURN-UP CHARACTERISTICS AND ECONOMIC INDICATORS... 

Fuel lifetime (without reloading and shuffling of the fiiel) 190 000 hours... 

To realize a core design with extended fuel lifetime, R D is necessary on lifetime characteristics of fuel elements and fuel assemblies under low power density and extended operation interval (compared with WER type reactors, the power density has been decreased by a factor of 2.5-3, the linear fuel heat rate - by a factor of 4). 

Fuel lifetime between refuellings, effective hours 70 000... 

The low core power density (33 kW/1), mild conditions of fuel operation and reduced fuel heat loads increase thermal margins and contribute to an extended fuel lifetime. 

To provide a maximum fuel lifetime at a given fuel loading and to meet the selected criteria on power peaking, a scheme of the operating reactivity margin compensation by central group of absorbing rods, previously developed for icebreaker reactor cores, was applied. 

The most important areas of further research and development (R D) are development and validation of fabrication technique for cermet fuel development of a long-life once-at-a-time refuelled core and validation of its safe and reliable operation over the whole fuel lifetime ... 

The fuel lifetime and the period between refuellings are both about 1800 effective full power days (EFPD), or more than 5 years. From the viewpoint of the neutronics, a 10-year (about 3650 EFPD) refuelling interval is possible but the integrity of the fuel cladding is not confirmed for more than 5 years of operation in the conditions similar to those of a PWR core. 

The target for the fuel lifetime is about 10 years but the integrity of the fuel element cladding for such period of continuous operation has not been confirmed so far. All components including cassettes can be replaced at the site, so the concept of an increased lifetime of the reactor vessel and structures is not applicable to the Package-Reactor. 

The fuel lifetime is targeted to be more than 10 years, depending on considerations of plant economy and energy security requirements. It could be easily achieved by adequate dimensioning of the reserve fuel chamber. Within the fuel lifetime, the reactor is assumed to operate with a weld sealed vessel. 

The fuel elements of the FBNR are confined in the fuel chamber, which could be sealed by the authorities and inspected at the end of fuel lifetime. 

Core and fuel lifetime 30 years (no refuelling during the whole lifetime) ... 

The 4S operation without on-site refuelling is one of the keystones for the reactor application in rural areas, for a variety of reasons. The core and fuel lifetime as well as the plant lifetime would be approximately 30 years the fuel in the 4S does not need to be reloaded or shuffled during the plant lifetime. The fuel is just installed when the 4S is constructed at a site. Therefore, the concept of annual flow of fuel and non-fuel materials is of somewhat limited meaning for the 4S. 

Interval between fuel shuffling, years 1 Selected to support long fuel lifetime and low peaking factors... 

The fuel lifetime is 10 years, coinciding with the period of reactor operation without on-site refuelling. 

Different variants of the core load differ in temperature and coolant density reactivity coefficients, but their sign and the void reactivity effect are always negative. The bum-up reactivity swing for the fuel lifetime varies from -7.0 Pefifto 0 (for UN fuel). 

The fuel lifetime is equal to the period between refiiellings and constitutes 1750 effective full power days. 

The BN GT-300 design employs a high grade of standardization, factory fabrication and transportability. The main equipment lifetime could be prolonged by the duration of one additional fuel lifetime, assuming that present day safety requirements would be valid and would not become stricter during the whole projected period of plant operation. In this aspect, a better approach may be to use two reactor modules with the state-of-the-art safety and economy characteristics and a 45-year lifetime, than to try to build reactors capable of meeting safety standards that would be valid in the second half of the 21 century. 

Whole core refuelling, which is performed at the end of each fuel lifetime the discharge of fuel is performed cassette-by-cassette fresh fuel is loaded as a single cartridge with the help of a refuelling equipment set common to all reactor modules within a given NPP ... 

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