Fast Neutron Spectrum

Testing of Heterogeneity Methods Used In Fast Reactor Critical Analyses by Comparison with Theoretical (GEDANKEN) Experiments, R. G. Palmer, J. P, Plummer, R. B. Nicholson (ANL-Idaho) 

The results of bivariate, real-flux, and volume-weighting procedures for normal, half sodium-voided and fully sodium-voided cores are shown in Table I where they are compared to the exact values. The fluxes for the weighting procedures were obtained from TESS calculations on the unit cells with added pseudo-absorption D-Bi cross sections. Also shown in Table I are the calcu M worths of thin central slabs of and C. 

ResttU ot Various WsishUiig Procedures on Experiments In GEDANKEN 1 

Other GEDANKEN cores are now being stadied in particular, a two-zoned-core simulation of a power-flattened reactor in infinite slab geometry. A cylindrical 2D core with radial plane plate structure identical to GEDANKEN 1 is being calculated to study the effect of leakage parallel to the plates. 

A One-Dimensional 8 Transport Theory Code for the CDC-3600, ANL Report, to be published (1970). 

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These neutron threshold detectors and the thermal neutron detectors, presented in Table 5.3-5, can be used to monitor the thermal and fast neutron spectra incident on the test specimens. These detectors possess reasonably long half-lives and activation cross sections covering the desired neutron energy range. 

G. D. Joanou and J. S. Dudek, GAM-I A Consistant P-1 Multigroup Code for the Calculation of Fast Neutron Spectra and Multigroup Constants, GA-1850 (June, 1961). 

Integral Measurements of Fast-Neutron Spectra in Some Uranium- and Plutonium-Fueled Fast Reactor Cores, R. Sher (Stanford)... 

Fast-neutron spectra in several uranium— and plutonium-fueled cores in the Swedish FRO critical assembly have been studied using the threshold reactions... 

J. A. GRUNDL and G. B. HiUtSEN, Measurement of Average Cross-Section Ratios in Fundamental Fast-Neutron Spectra, NttcUar Data for Reactors, VoL I, IAEA, Vienna (1967). 

G. D. JOANOU and J. S. DUDEK, GAM-H, A B, Code for the calculation of Fast-Neutron Spectra and Associated Multigroup Constants," GA-426S, General Atomic (Sep. 1963). 

The international group has identified six Generation rV reactor systems for development. All of these reactors should be ready for deployment by 2030. The fast neutron spectrum reactors can use the fuel values of all of the fissile and fertile transuranic isotopes in reprocessed fuel. This does not occur in the current thermal spectrum reactors. Producing energy... 

AOYAMA, T., ITO, C., Integral Test on Activation Cross Section of Tag Gas Nuclides Using Fast Neutron Spectrum Fields, Proc. Int. Conf. on Nuclear Data (ND2001), Ibaraki, Japan, 7-12 October 2001, JAERI, published as Journal of Nuclear Science and Technology, Supplement 2 (2002). 

The guidance given in this publication is applicable to research reactors with limited hazard potential to the public and typical characteristics. For addressing the topic in research reactors with several tens of megawatts of power, fast neutron spectrum research reactors or small prototype power reactors, etc., other similar IAEA publications prepared for power reactors may be more appropriate for a number of aspects (see References). No specifications for such a transition to other guidance are presented. 

Stainless-steel-clad UOj-PuO fuel elements have been assumed for the reference design of the gas-cooled fast reactor cores, although comparative evaluations of stainless-steel-clad carbide fuel elements have been made 14). In either case, the type of fuel element envisioned for the gas-cooled fast reactors is an assembly of approximately 1-cm-diam, stainless-steel-clad fuel rods. The subdivision of the fuel must be very great in order to achieve the high core power densities and fuel ratings required for reasonable performance with a fast-neutron-spectrum reactor. 

Conventional LWRs alone cannot be used to transmute minor actinides because thermal neutrons are not as effective for inducing the fission reaction. As a result, nfinor actinides (especially, non-fissile even isotopes of plutonium) build up as a function of time. Therefore, thermal reactors tend to preferentially produce minor actinides. Fast reactors or fast neutron spectrum devices on the other hand tend to more effectively destroy the minor actinides because the probability of fission for both the even and odd isotopes of plutonium fission with fast neutrons is considerably higher than with thermal neutrons. Thus, last reactors are heavily preferred for the recycle of plutonium and the ultimate complete destruction of all of the minor actinides. 

For the AFC to be most effective and reduce the inventory of minor actinides at a reasonable rate, dedicated devices that produce a hard or fast neutron spectrum will be required. Such devices include the advanced liquid metal reactors (ALMRs), a fast reactor configured to operate as an actinide incinerator rather than breeder and accelerator-driven systems (ADSs). Fast reactor technology discussed earlier in this chapter is relatively mature whereas the development of ADS is in its infancy. Accelerator-based waste transmutation programs are ongoing in France, Japan, USA, and CERN. 

A fast neutron spectrum allows production of more fissile material than that consumed for heat generation. In a fast reactor liquid metal such as sodium is normally used to remove the heat, and it has a minimum effect on the moderation of fission neutrons. Sodium as a coolant has an excellent heat capacity, low operating pressure and natural convection capability. 

H. Bohl, Jr., MUFT-5—A Fast Neutron Spectrum Program for the Philco-2000," WAPD-TM-218 0une 1960). 

H. Bohl, Jr., E. M. Gelbard, and G. H. Ifyan, MUFT-4, Fast Neutron Spectrum Code for the IBM-704, WAPO-TM-72 (July 1957). 

H. BOHL, Jr. etal., MUFT-5-A Fast Neutron Spectrum PrBettis Atomic Power Laboratory (1961). 

R D needs unique to the fast-spectrum GFR include development and demonstration of safety features, and decay heat removal systems to accommodate the high core power density and low thermal inertia of the core, optimization of fuel forms for the fast-neutron spectrum, development of materials that are resistant to fast-neutron influence under very high temperature conditions, efficient conversion without fertile blankets, and the demonstrated integration of an on-site spent fuel treatment and prefabrication process that is simple and compact. 

The balance-of-plant design (Figure 9.3) utilizes a relatively simple direct cycle power conversion system. The reference design for this concept is a 1700-MWe reactor operating at a pressure of 25 MPa with a reactor outlet temperature between 510°C and 550 C. This reactor can be designed as a fast neutron spectrum or thermal neutron spectrum reactor. The relatively simple design also allows for the incorporation of passive safety features. However, unlike the previously discussed concepts, the lower reactor outlet temperature... 

The SFR is a sodium-cooled fast-neutron-spectrum reactor designed primarily for the efficient management of actinides and conversion of fertile uranium in a closed fuel cycle. 

The LFR is a fast-neutron spectrum reactor cooled by molten lead or a lead-bismuth eutectic liquid metal. It is designed for the efficient conversion of fertile uranium and the management of actinides in a closed fuel cycle. 

The gas-cooled reactor (GCR) has a gas as the primary coolant, usually helium. With a fast-neutron spectrum, the GCR has the ability to breed fertile uranium and to consume actinides. 

Of all small reactors without on-site refuelling in this report, about half are liquid metal cooled reactors with fast neutron spectrum they include the following concepts (see Table 5) ... 

In the case of fast neutron spectrum reactors, the efficacy of inherent and passive safety features to anticipated transients without scram (ATWS) has been well established by testing in the EBR-II, FFTF, and Phoenix reactors [5 and 6], So too has passive decay heat removal. The severe accident hazard of reactivity addition upon core rearrangement in small fast reactors is addressed by a range of approaches including ... 

The higher specific in-core fissile inventory of small reactors with fast neutron spectrum may help ensure that not only the LWR legacy inventories already in temporary storage are worked down, but even uranium dioxide spent fuel from current and future LWR discharges is used up. As a result, minor actinide free HLW forms, which can be more tightly packed because of smaller heat loading, could be accommodated in less repository space. 

In the next phase of the 4S, when recovered plutonium and minor actinides (MA) would become politically and commercially available because of the shortage of natural fissile materials, fresh fuel consisting of the reprocessed fissile materials and depleted or natural uranium could be installed in the 4S. A fast neutron spectrum of the 4S avoids the degradation of fissile materials through burn-up therefore, the recovery process for the spent fuel of the 4S could be repeated many more times than for LWRs, resulting in a higher degree of natural uranium utilization. 

RAPID (Refuelling by All Pins, Integral Design) is the abbreviation for a small sodium cooled reactor of 10 000 kW(th) (1000 kW(e)) with U-Pu-Zr metal fuel and fast neutron spectrum [XVII-1 and XVII-2]. It is one of the successors of the RAPID-L [XVII-3 to XVII-7] - the operator-free fast reactor concept designed for a lunar based power system. 

For the first-of-a-kind BN GT unit, base load mode of operation was selected further BN GT units could be operated in load follow modes within electric output variation between 90 and 300 MW(e). The prerequisites for this are fast neutron spectrum (no effect of xenon poisoning in reactivity) and the use of a special gas turbine. To realize load follow operation modes, a demonstration of fuel element reliable performance under multiple power ramps and associated thermo-cycling would be needed, which could be accomplished during the operation of a first-of-a-kind plant. 

A fast neutron spectrum potentially allows the BN GT-based system with fuel recycling to produce energy consuming only depleted uranium, but such a system is currently less economically competitive than that employing spent PWRs MOX fuel as the initial fuel load. 

The strong coolant temperature-driven reactivity feedback in the fast neutron spectrum core enables autonomous load following whereby the reactor power self-adjusts itself to match heat removal from the primary coolant solely as a consequence of inherent physical phenomena. The system temperatures that are attained following an autonomous power change from the nominal steady state can be optimized through design of the core clamping... 

The strong reactivity feedback from the fast neutron spectrum core with transuranic nitride fuel and lead coolant results in passive core power reduction to decay heat power levels while system temperatures remain within structural limits, in the event of loss-of-normal heat removal to the secondary side through the in-reactor lead-to-C02 heat exchangers. 

The fast neutron spectrum with transuranic nitride fuel and lead coolant is fissile self sufficient with a core conversion ratio of unity. This enables a closed fuel cycle based upon a fertile feed stream of depleted or natural uranium and a minimal volume waste stream comprised only of fission products. All fissile material including minor actinides is recycled in the fabrication of new fuel cores and is burned as fuel in STAR reactors. 

From the outset, the design and safety philosophy of the STAR-LM has been to take advantage of the particular properties of lead coolant, nitride fuel, and a fast neutron spectrum core to achieve and ensure a strong reliance on inherent safety features and passive protection. One aspect of this philosophy is to eliminate the need for reliance upon any active systems. 

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