The objective of this project is to develop a conceptual design of a particle-bed, gas-cooled fast reactor (PB-GCFR) core that meets the advanced reactor concept and enhanced proliferation-resistant goals of the US Department of Energy's NERI program. The key innovation of this project is the application of a fast neutron spectrum environment to enhance both the passive safety and transmutation characteristics of the advanced particle-bed and pebble-bed reactor designs. The PB-GCFR design is expected to produce a high-efficiency system with a low unit cost. It is anticipated that the fast neutron spectrum would permit small-sized units ({approx} 150 MWe) that can be built quickly and packaged into modular units, and whose production can be readily expanded as the demand grows. Such a system could be deployed globally. The goals of this two-year project are as follows: (1) design a reactor core that meets the future needs of the nuclear industry, by being passively safe with reduced need for engineered safety systems. This will entail an innovative core design incorporating new fuel form and type; (2) employ a proliferation-resistant fuel design and fuel cycle. This will be supported by a long-life core design that is refueled infrequently, and hence, reduces themore » potential for fuel diversion; (3) incorporate design features that permit use of the system as an efficient transmuter that could be employed for burning separated plutonium fuel or recycled LWR transuranic fuel, should the need arise; and (4) evaluate the fuel cycle for waste minimization and for the possibility of direct fuel disposal. The application of particle-bed fuel provides the promise of extremely high burnup and fission-product protection barriers that may permit direct disposal.« less

The issue of waste minimization in advanced reactor systems has been investigated using the Particle-Bed Gas-Cooled Fast Reactor (PB-GCFR) design being developed and funded under the U.S. Department of Energy Nuclear Energy Research Initiative (USDOE NERI) Program. Results indicate that for the given core power density and constraint on the maximum TRU enrichment allowable, the lowest amount of radiotoxic transuranics to be processed and hence sent to the repository is obtained for long-life core designs. Calculations were additionally done to investigate long-life core designs using LWR spent fuel TRU and recycle TRU, and different feed, matrix and reflector materials. The recycled TRU and LWR spent TRU fuels give similar core behaviors, because of the fast spectrum environment which does not significantly degrade the TRU composition. Using light elements as reflector material was found to be unattractive because of power peaking problems and large reactivity swings. The application of a lead reflector gave the longest cycle length and lowest TRU processing requirement. Materials compatibility and performance issues require additional investigation.

The present study was carried out in order to establish whether the concomitant treatment with somatostatin (SRIH) is capable of modifying gonadotrophin release in response to LH-RH administration in normal women during follicular, periovulatory, and luteal phases. SRIH was administered in a dose of 5.55 micrograms/min over 180 min and LH-RH (100 micrograms) was injected as a bolus at 90 min after the beginning of SRIH infusion. Within the dose used, SRIH significantly reduced LH response to LH-RH, whereas it did not alter FSH response to LH-RH. These results suggest that SRIH may play a part in the regulation of LH secretion in normal women.

To investigate the effect of metoclopramide (MET), a dopaminergic antagonist drug, on serum PRL concentration in maternal and cord blood (CB) serum, the drug was injected in 94 at term pregnant women whereas 28 mothers received saline. Maternal serum (MS) samples were obtained before MET injection and at the parturition time. According to the interval of time between MET administration and birth, MS specimens were grouped in 7 groups. CB was obtained from neonates whose mothers were injected with saline, group 0 and from newborns whose mothers were treated with MET, groups 1 to 7. In the 7 groups of women the mean PRL concentration before MET ranged between 307 and 439 ng/ml. After MET injection a significant increase has been observed in all groups with a minimum and maximal mean value of 639 and 931 ng/ml. The highest net increment of PRL has been measured in group 1 sampled at 5 to 30 minutes after MET. CB PRL concentration in group 0, saline treated, was not different from the values measured in group 1 to 7, treated groups, with a range between 504 and 703 ng/ml. These findings suggest that maternal lactotropes are still responsive to MET. On the opposite, fetal pituitary does not release PRL after MET injection probably because PRL secretory activity is maximal or because the dopaminergic receptors' system is still immature.

Metoclopramide (MET), a potent dopamine receptor-blocking drug, or saline was administered to 125 term pregnant women at various time intervals (5-412 min) before delivery. Maternal serum was obtained before and after MET injection. Cord blood was obtained at delivery in MET-treated and saline-treated (control group) women. No significant changes in serum TSH, T4, T3, or rT3 concentrations were observed in maternal or cord blood after MET administration. These results suggest that, in contrast to euthyroid nonpregnant women and men, MET administration does not induce a rise in serum TSH concentration in term pregnant women or in the term fetus. Thus, the dopaminergic inhibitory effect on anterior pituitary TSH secretion may not be an important factor in TSH regulation during pregnancy or in the fetus, or the dose of MET employed may be unable to overcome the dopamine inhibitory effect.

A Particle-Bed Gas-Cooled Fast Reactor (PB-GCFR) proposed and funded under the U.S. Department of Energy Nuclear Energy Research Initiative (USDOE NERI) Program is discussed, along with the preliminary physics results that have been obtained for a reference compact core (~50 W/cc) based on the pebble-bed system. Parametric studies are performed using homogeneous-cell and full-core physics models to investigate the impact of different fuel forms, pebble matrix material, temperature, fuel packing fraction, and core reflector material and dimension on the PB-GCFR design. One goal of this study is to assess the potential for a long-lived 300 MWt core design with a high conversion ratio that could sustain a cycle length of 15 to 30 years. The results of this study indicated that new fuel forms have to be considered in order to achieve a compact core design because the standard pebble-bed design has a significant material porosity that limits the core fuel volume fraction. The USDOE-sponsored NERI project on a Particle-Bed Gas-Cooled Fast Reactor (PB-GCFR) design will study different fuel forms and type, in order to meet the Generation-IV-systems goals of improved safety, enhanced proliferation resistance, nuclear waste minimization, and reduced system cost. The key innovation of this project is the application of a fast neutron spectrum environment to enhance both the passive safety and transmutation characteristics of the advanced particle-bed and pebble-bed reactor designs. The core design would meet the future needs of the nuclear industry, by being passively safe with reduced need for engineered safety systems. One of the major issues arising from previous gas-cooled fast reactor designs is the poor heat removal property of the helium coolant at low pressure. This issue was previously addressed by the use of highly reliable redundant coolant circulators. Passive-safety-in-the-design is however a major goal of this project. The ability to remove decay heat through conduction pathways, mainly, for station blackout and depressurization conditions and the capacity to tolerate failure to scram without reaching core disruption will be the focus of the design. The PB-GCFR design is supported by a long-life core concept that is refueled infrequently and hence reduces the potential for fuel diversion. The application of a fast neutron spectrum environment makes this design feasible since it permits compact core designs and fuel burnup characteristics that reduce the burnup reactivity control requirements. A low burnup reactivity swing also implies a low control rod worth requirement, which aids passive safety. The high neutron fluence inherent in the fast spectrum design coupled with the high operating temperature (for high efficiency) however provides challenges that have to be resolved. This would necessitate the investigation of materials that can withstand the high temperature and flux environments of the system. As a basis for quantifying the performance trade-off associated with long lifetime cores, a reference compact fast-spectrum core based on the pebble-bed system is being developed. This core is designed for a power rating of ~300 MWt (about 50 W/cc) and has no blanket zone, in order to make it unattractive for proliferation. Also for proliferation reasons, it is assumed that the fuel type would be based on the transuranics (TRU) component of spent nuclear fuel that has been extracted by a separation process. The rational in this scenario, is that by making use of the transuranics (Pu, Np,