[en] Underground facilities are being operated by several countries around the world for performing research and demonstration of the safety of deep radioactive waste repositories. The ''sp'' Hard Rock Laboratory is one such facility launched and operated by the Swedish Nuclear Fuel and Waste Management Company where various in situ experiments have been performed in fractured granites. One such experiment is the redox zone experiment, which aimed at evaluating the effects of the construction of an access tunnel on the hydrochemical conditions of a fracture zone. Dilution of the initially saline groundwater by fresh recharge water is the dominant process controlling the hydrochemical evolution of most chemical species, except for bicarbonate and sulfate, which unexpectedly increase with time. We present a numerical model of water flow, reactive transport, and microbial processes for the redox zone experiment. This model provides a plausible quantitatively based explanation for the unexpected evolution of bicarbonate and sulfate, reproduces the breakthrough curves of other reactive species, and is consistent with previous hydrogeological and solute transport models

[en] Underground facilities are being operated by several countries around the world for performing research and demonstration of the safety of deep radioactive waste repositories. The ''sp'' Hard Rock Laboratory is one such facility launched and operated by the Swedish Nuclear Fuel and Waste Management Company where various in situ experiments have been performed in fractured granites. One such experiment is the redox zone experiment, which aimed at evaluating the effects of the construction of an access tunnel on the hydrochemical conditions of a fracture zone. Dilution of the initially saline groundwater by fresh recharge water is the dominant process controlling the hydrochemical evolution of most chemical species, except for bicarbonate and sulfate, which unexpectedly increase with time. We present a numerical model of water flow, reactive transport, and microbial processes for the redox zone experiment. This model provides a plausible quantitatively based explanation for the unexpected evolution of bicarbonate and sulfate, reproduces the breakthrough curves of other reactive species, and is consistent with previous hydrogeological and solute transport models

[en] The control rods of the KRBI-I 250-MW(electric) boiling water reactor contain Vipac B₄C powder in Type 304 stainless steel tubes as a neutron-absorbing material. Because of an increase in the reactor coolant ³H activity, defective control rods were suspected. The hot cell examination of a highly exposed control rod revealed B₄C losses. The mechanism of failure was shown to be B₄C swelling and stress corrosion cracking of the absorber tubes, followed by B₄C washout. The B₄C volume swelling is ΔV(%) = 0.851x + 0.0449x² [x = ¹⁰B decays in 10²¹(n,α)/cm³]. The tube cracking starts at 30 to 35% and the B₄C washout at 50 to 55% local ¹⁰B burnup in the tubes

[en] Johnson noise thermometry is one of many important measurement techniques used to monitor the safety levels and stability in a nuclear reactor. However, this measurement is very dependent on the minimal electromagnetic environment. Properly removing unwanted electromagnetic interference (EMI) is critical for accurate drift-free temperature measurements. The two techniques developed by Oak Ridge National Laboratory (ORNL) to remove transient and periodic EMI are briefly discussed here. Spectral estimation is a key component in the signal processing algorithm used for EMI removal and temperature calculation. The cross-power spectral density is a key component in the Johnson noise temperature computation. Applying either technique requires the simple addition of electronics and signal processing to existing resistive thermometers. With minimal installation changes, the system discussed here can be installed on existing nuclear power plants. The Johnson noise system developed is tested at three locations: ORNL, Sandia National Laboratory, and the Tennessee Valley Authority’s Kingston Fossil Plant. Each of these locations enabled improvement on the EMI removal algorithm. Finally, the conclusions made from the results at each of these locations is discussed, as well as possible future work.

[en] Underground facilities are being operated by several countries around the world for performing research and demonstration of the safety of deep radioactive waste repositories. The ''sp'' Hard Rock Laboratory is one such facility launched and operated by the Swedish Nuclear Fuel and Waste Management Company where various in situ experiments have been performed in fractured granites. One such experiment is the redox zone experiment, which aimed at evaluating the effects of the construction of an access tunnel on the hydrochemical conditions of a fracture zone. Dilution of the initially saline groundwater by fresh recharge water is the dominant process controlling the hydrochemical evolution of most chemical species, except for bicarbonate and sulfate, which unexpectedly increase with time. We present a numerical model of water flow, reactive transport, and microbial processes for the redox zone experiment. This model provides a plausible quantitatively based explanation for the unexpected evolution of bicarbonate and sulfate, reproduces the breakthrough curves of other reactive species, and is consistent with previous hydrogeological and solute transport models

[en] The caustic precipitation of plutonium (Pu) and uranium (U) from Pu and U containing waste solutions has been investigated to determine whether gadolinium (Gd) could be used as a neutron poison for precipitation with greater than a fissile mass containing both Pu and enriched U. Precipitation experiments were performed using both actual samples and simulant solutions with a range of 2.6-5.16 g/L U and 0-4.3 to 1 U to Pu. Analyses were performed on solutions at intermediate pH to determine the partitioning of elements for accident scenarios. When both Pu and U were present in the solution, precipitation began at pH 4.5 and by pH 7, 99 percent of Pu and U had precipitated. When complete neutralization was achieved at pH greater than 14 with 1.2 M excess OH-, greater than 99 percent of Pu, U, and Gd had precipitated. At pH greater than 14, the particles sizes were larger and the distribution was a single mode. The ratio of hydrogen to fissile atoms in the precipitate was determined after both settling and centrifuging and indicates that sufficient water was associated with the precipitates to provide the needed neutron moderation for Gd to prevent a criticality in solutions containing up to 4.3 to 1 U to Pu and up to 5.16 g/L U

[en] The uranium neutron coincidence collar uses thermal neutron interrogation to verify the ²³⁵U mass in low-enriched uranium (LEU) fuel assemblies in fuel fabrication facilities. Burnable poisons are commonly added to nuclear fuel to increase the lifetime of the fuel. The high thermal neutron absorption by these poisons reduces the active neutron signal produced by the fuel. Burnable poison correction factors or fast-mode runs with Cd liners can help compensate for this effect, but the correction factors rely on operator declarations of burnable poison content, and fast-mode runs are time-consuming. Finally, this paper describes a new analysis method to measure the ²³⁵U mass and burnable poison content in LEU nuclear fuel simultaneously in a timely manner, without requiring additional hardware.

[en] Integrity and durability of solid radioactive wastes are related principally to rates at which waste constituents are leached into environmental water. This paper discusses a new and improved procedure which was developed for determining leachabilities of proposed radioactive waste forms. While no laboratory procedure can be expected to duplicate all possible environmental conditions, a single test is desirable to compare the leaching properties of solid waste forms produced in different laboratories

[en] The remodeling of the neutron irradiation facility of the Musashi Institute of Technology Reactor (TRIGA Mark II, 100 kW) was carried out for the purpose of boron neutron capture therapy. The gamma contamination was reduced by the bismuth scatterer technique, and the thermal-neutron intensity was enlarged by virtue of the cavity effect. A /sup 6/LiF sheet was used instead of a /sup 10/B sheet for neutron collimation to minimize production of the secondary gamma rays

[en] Monte Carlo simulations of nuclear instrumentation configurations generally need to be run in a full analog transport mode. Up to Version 9 of the Monte Carlo code TRIPOLI-4H, the transport between two consecutive neutron collisions is analog if no variance reduction technique is requested by the user, but the collision itself is sampled in a non analog way. This paper presents the first implementation of a full analog neutron transport mode in TRIPOLI-4. This option concerns only fixed source simulations. Details on the modifications implemented in the code are provided: The analog sampling of neutron interactions and the particular cases of fission and scattering reactions with multiple outgoing neutrons are addressed. Preliminary verification tests are provided, and results from non analog and analog neutron transport in a simple configuration of a pressurized water reactor fuel assembly are compared. An example of application to the simulation of the NUCIFER detector is also provided. This experiment, located in Saclay, France, next to the OSIRIS experimental reactor, is dedicated to reactor antineutrino detection, addressing both nonproliferation considerations and fundamental physics concerns. Antineutrinos emitted by fission reactions in OSIRIS are detected through the inverse beta decay reaction, producing a positron and a neutron. An analog TRIPOLI-4 simulation allowed us to calculate the distribution of neutron capture times on gadolinium nuclei. (authors)