BeO, moderator

It had beryllium oxide [1304-56-9] BeO, moderator and nickel tubes, through which ran a molten salt fuel consisting of fluorides of Na, Be, and U. 

The Power Pile referred to in this memorandum is the helium-cooled, BeO-moderated, high-temperature reactor of Professor Farrington Daniels. 

The BeO moderator is similarly contained in stainless-steel cladding of the same size as the fuel. A core loading consists of about 22,000 BeO pins. 

F. A. Kloverstrom et aL, Critical Measurements on Near-Homogeneous BeO - Moderated Oralloy- Fueled Systems," UCRL-5369, Pt. 1 (1959). ... 

The design basis lifetime for the BeO moderator, BeO reflector, graphite reflector, inner, intermediate and outer vessels and all other non-replaceable components is 50 years. All fuel tubes will be changed after about 5500 EFPD (15 EFP years). It is around 18.5 years (considering about 300 EFPD of operation per year). 

The reactor core, as shown in Fig. XXIX-11, consists of nineteen prismatic hexagonal shaped beryllium oxide (BeO) moderator blocks. These 19 blocks contain centrally located graphite fuel tubes. Details of the lattice positions and fuel tubes are given in Table XXIX-5. ... 

Each fuel tube carries fuel inside 12 equi-spaced longitudinal bores in its wall. The fuel tube also serves as a coolant channel. The coolant flows through the central hole of the tube. A typical fuel bed with the BeO moderator, fuel tube and fuel compacts are shown in Fig. XXIX-12. 

Upper Plenum Downcomer Tubei Fuel Tube -Coolant -BeO Moderator... 

Beryllium Oxide (Bromellite). BeO, mw 25.01, white amorph powd, mp 2530°, bp ca 3900°, d 3.01g/cc. Sol in coned acids and alkalies. V si sol in w. Prepn is by burning BeC03 at 900° in a Pt crucible to the oxide. It is used in nuclear reactor fuels and moderators as well as in powder metallurgy, ceramics, fuel cells and coatings (see above)... 

In addition to its use as a specialized refractory, great quantities of CaO are used for the fabrication of constmction materials and the manufacture of concrete also serves as a trap for desulfurization of flue gases. CaO is obtained by the decomposition of calcite, CaC03, at 1000°C. Much of it is converted to slaked lime, Ca(OH)2-2H2o. Slaked lime is used as a whitewash for buildings. BeO is used as an admixture in nuclear fuels because of its superior properties as a neutron moderator. 

SAFETY PROFILE Confirmed carcinogen with experimental carcinogenic, neoplastigenic, and tumorigenic data. A deadly poison by intravenous route. Human systemic effects by inhalation lung fibrosis, dyspnea, and weight loss. Human mutation data reported. See also BERYLLIUM COMPOUNDS. A moderate fire hazard in the form of dust or powder, or when exposed to flame or by spontaneous chemical reaction. Slight explosion hazard in the form of powder or dust. Incompatible with halocarbons. Reacts incandescently with fluorine or chlorine. Mixtures of the powder with CCU or trichloroethylene will flash or spark on impact. When heated to decomposition in air it emits very toxic fumes of BeO. Reacts with Li and P. 

Sintered beryllia. This material exhibits an extraordinarily high thermal conductivity, only surpassed by graphite and metals — hence the high resistance to thermal shock which together with high chemical inertness is its main practically utilized property. In the application of sintered BeO in nuclear reactors, use is made of its low absorption cross section and of high scattering cross section of neutrons (moderators, reflectors). 

Beryllium oxide is used as a reflector and moderator in nuclear reactors. In addition to its low neutron-capture cross section, BeO has physical, mechanical, and chemical properties that allow its use at elevated temperatures, but its high cost and propensity to damage under irradation have limited its applications " ... 

Beryllium reacts with oxygen only at elevated temperatures and forms only the normal oxide, BeO. The other Group IIA metals form normal oxides at moderate temperatures. 

Beryllia Beryllium monoxide Beryllium oxide Beryllium oxide (BeO) Bromellete CCRIS 83 EINECS 215-133-1 Gluoina HSDB 1607 Natural bromellite Thermalox Thermalox 995. Used in manufacture of beryllium oxide ceramics, glass in nuclear reactor fuels and moderators electrically resistive catalyst for organic reactions. Electrical conductor but thermal insulator. Light amorphous powder mp = 2530 very sparingly soluble in H2O. 

Fission Nuclear fuel (UO2, UC), fuel cladding (C, SiC), neutron moderators (C, BeO)... 

This accident scenario involved the reactor being buried in Si02 with a density of 1.5 g/cc. This is a median point between the density of loose sand (1.4 g/cc) and. dry, packed sand (1.6 g/cc). The core is not flooded in this case, and the radial reflectors have been removed. While little moderation occurred in the sand and Si02 is an inferior scattering medium to BeO (and is also without the (n,2n) reaction), the reactor was going from somewhat reflected to essentially infinite reflection conditions. In a variety of cores this had led to a net increase in reactivity. This effect is highly dependent on the density of the sand. This core had a k-effective of 0.981 0.001 for this scenario. 

Wigner initiated and supervised the examination of as many combinations of fuel and moderator as the group could manage. By the end of 1945 he had explored lattices moderated with H2O, D2O, CO2, Be, BeO, and C, as well as homogenous mixtures of U, D2O and H2O. The constants such as diffusion length, resonance absorption, and cross-sections used in this exploration were based on experiments at Columbia, Princeton, and, later, on the exponential experiments in Chicago. 

Precaution Flamm. solid powd. mod. fire hazard as powd. or dust or when exposed to flame si. explosion hazard as dust incompat. with halocarbons reacts incandescently with fluorine and chlorine reacts with Li, P Hazardous Decomp. Prods. Heated to decomp, in air, emits very toxic fumes of BeO NFPA Health 3, Flammability 1, Reactivity 0 Uses Structural material in space technology moderator In nuclear reactors source of neutrons windows for x-ray tubes in gyroscopes, computer parts, inertial guidance systems additive in solid-propellant rocket fuels beryllium-copper alloys aircraft brakes neutron reflectors... 

A number of coolant gases can be used in direct contact with BeO at high temperatures in gas-cooled reactors using BeO as a moderator. Problems of erosion or volatility of BeO in such gases as He, CO2, or N2 are not significant if the water-vapor content of the coolant is sufficiently low. Corrosion of BeO by water vapor is not a serious problem below 850°C. At 1000°C and a Reynolds number of 10, a corrosion rate of only about 2.5 ju/year is reported in 30 atm CO2 with 330 ppm of water vapor (2i). Beryllium oxide is reported not to react with pure CO2, O2, or N2, and obviously helium, at temperatures in excess of 1200°C. 

The neutronic effectiveness of a moderator material can be expressed in terms of the conversion potential of a mixture of fuel and moderators in an infinite medium. This approach has been used in a relative comparison of HjO, BeO, and C with fuel which has appeared in a progress report on BeO reactor studies (26). In this evaluation, the excess production of neutrons per neutron absorbed in the fuel has been calculated for homogeneous mixtures of fuel and moderator having different moderator/ atom ratios, i.e.,... 

It can be seen in Table V that the excess production of neutrons per neutron absorbed in fuel increases with the moderator/U ratio to some optimum value, if the calculation is carried sufficiently far. On the basis of this comparison, it appears that the optimum conversion potential for BeO is about 11 % greater than that for C, and the optimum for C is about 8 % greater than for HjO. Although the results for DjO have not been included in the reference, it would be expected to lie between C and BeO. However, in the case of D2O and H2O, pressure tubes or calandria, as well as insulation, would be required in a gas-cooled reactor to separate the coolant and the moderator, and the neutron losses in the tubes would reduce the excess neutrons significantly. 

With the possible exception of BeO, graphite appears to be the most favorable moderator for gas-cooled reactors from a neutronics point of view. Because of limited irradiation experience with BeO and the current high cost of the material (largely because of its limited use), BeO has not been used extensively in nuclear reactors up to this time. 

Other factors, such as radiation damage, chemical stability, and structural requirements, can be important in the choice of the moderator material for a reactor concept. The radiation effects on graphite and BeO have received a great deal of attention. Detailed discussions of this subject can be found in the literature. Only a very brief review will be included here. 

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