Cladding failure

Nuclear Applications 10.6.8.1 Cladding Failure in Oxide Fuel Pins of Nuclear 394... 

I0.6.8.I Cladding failure in oxide fuel pins of nuclear reactors. The long-term operational performance of nuclear fuel pins is critically governed by the reactions that occur in the gap between the fuel and its cladding. Ball et al. (1989) examined this for the cases of (1) Zircaloy-clad pellets of U02+, in a pressurised water reactor (PWR) and (2) stainless-steel-clad pellets of (U, P)02+, in a liquid-metal-cooled fast-breeder reactor (LMFBR). In particular they were interested in the influence of O potential on Cs, I, Te and Mo and the effects of irradiation on the gaseous species within the fuel-clad gaps. 

The chemical properties of a fuel are also important considerations. A fuel should be able to resist the wholesale change in its properties, or the destruction of its mechanical integrity, that might take place if it is exposed to superheated coolant water through a cladding failure. On the other hand, certain chemical reactions are desirable. 

Resistance to radiation damage so that physical properties are not degraded Chemical stability with respect to coolant in case of cladding failure Physical and mechanical properties that permit economical fabrication... 

Operational limitations such as rate of power increase and power for a given power ramp rate are imposed to lessen the effect of PCI. PCI appears to be more likely to occur during initial power increase and can be very costly if cladding failure occurs. 

To minimize the effects of fuel densification, plant procedures limit the maximum permissible rate at which power may be increased to ensure that the temperature will not exceed 1200 C during a loss of coolant accident. This allows the fuel pellets to shift slowly, with less chance of becoming jammed during the densification process, which in turn reduces the chance of cladding failure. 

PCI may lead to cladding failure and subsequent release of fission products into the reactor coolant. 

Embrittlement is caused by hydrogen diffusing into the metal. Cladding embrittlement can lead to cladding failure. 

High fuel burnup rate can cause the reactor to be refueled earlier than designed. Swelling can cause excessive pressure on the cladding, which could lead to fuel element cladding failure. 

The thermohydraulic features of lead-bismuth and lead coolants are high boiling temperatures and the relative inertness compared with sodium. The melting and boiling points of sodium are respectively 98°C and 883 C. For lead-bismuth eutectic the respective figures are 123.5°C and 1670°C and for lead 327 C and 1740°C at atmospheric pressure. The boiling points are well above cladding failure temperatures. The specific heats per unit volume of lead-bismuth and lead are similar to those of sodium but the conductivities are about a factor of 4 smaller. 

The effectiveness of delayed neutron detectors for detecting clad failure was tested by operating the reactor with vented fuel SA in the core. The void coefficient of reactivity at various core locations were measured using two special SA fabricated for this purpose. The void coefficient was found to be negative. 

Cutting the sodium inlet and outlet pipes and clad failure detection lines ... 

The primary system includes four primary pumps and eight intermediate heat exchangers connected with four secondary loops. The total amount of sodium in these four secondary loops is 1500 tons. The core of SPX is made of fuel elements (mixed UO2-PUO2), breeder elements, rods plus complementary control rods (pins containing pellets of boron carbide B4C). The power of SPX reactor was 3000 thermal MW converted to 1242 electric MW. At the date of the decision of the final shutdown of the reactor, SPX was in operation only 320 Equivalent Full Power Days. During this time there was no cladding failure. Therefore it can be assumed that SUPERPHENIX has a very low residual activity and minor contamination in the primary sodium. Thus the residual activity of the primary sodium was measured. The values in 2000 were ... 

Release of sodium sulphate into the Rhone river. Considering the low activity of the primary sodium and absence of fission products (no fuel clad failures), release into the Rhone river of the equivalent of 2.5 tons of sodium treated per day is possible within the framework of current release authorizations (250 GBq/year of liquid effluent excluding tritium). Studies of the environmental impact have been carried out, they have shown it would be very low (0.1 mSv) and... 

As no clad failure happened the radioactivity of this sodium is relatively low, thereby simplifying the problems of pollution and radiation protection. 

Lennox, D. H., Danger of Fuel Assembly Cladding Failure with Natural Convection Cooling, ANL-EKF-18, January 5, 1950. 

To study the p>ossibilities of fuel ejection under the following conditions the induction of a clad failure during a slow ramp rate when a low melt fiaction (around 10 %) is obtained RBI test to be performed in CABRI. 

Barrier number one is the fuel element cladding, which contains and confines the nuclear reaction products, and whose leak tightness is continually monitored. In the event fuel cladding failures occur, radioactivity thresholds are exceeded, the installation is shut down, and the damaged elements are removed and replaced. 

Visual control of the pool elements is performed regularly during scheduled preventive maintenance. During 30 years of operation, there have been no problems related to pool equipment or FA cladding failure during FA storage in the cooling pool. 

BCFl Bej ond clad failure Ramp effect (3% Pn/s) VIGGEN-4... 

Different ways of these criteria minimization were used the search of low-level activated materials, new design approaches, cladding failures reduction, deep decontamination, recycling and re-use of activated materials under specific clearance levels. Two steps of optimization have been done. 

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