Measurement of Moisture Storage Parameters of Building Materials

The moisture storage parameters of three different building materials: calcium silicate, ceramic brick and autoclaved aerated concrete, are determined in the hygroscopic range and overhygroscopic range. Measured sorption isotherms and moisture retention curves are then combined into moisture storage functions using the Kelvin equation. A comparison of measured results with global characteristics of the pore space obtained by mercury intrusion porosimetry shows a reasonable agreement; the median pore radii by volume are well within the interval given by the beginning and the end of the characteristic steep parts of the moisture retention curves

Measurement of Moisture Storage Parameters of Building Materials

The moisture storage parameters of three different building materials: calcium silicate, ceramic brick and autoclaved aerated concrete, are determined in the hygroscopic range and overhygroscopic range. Measured sorption isotherms and moisture retention curves are then combined into moisture storage functions using the Kelvin equation. A comparison of measured results with global characteristics of the pore space obtained by mercury intrusion porosimetry shows a reasonable agreement; the median pore radii by volume are well within the interval given by the beginning and the end of the characteristic steep parts of the moisture retention curves

Fixed neutron absorbers for improved nuclear safety and better economics in nuclear fuel storage, transport and disposal

Current designs of both large reactor units and small modular reactors utilize a nuclear fuel with increasing enrichment. This increasing demand for better nuclear fuel utilization is a challenge for nuclear fuel handling facilities. The operation with higher enriched fuels leads to reduced reserves to legislative and safety criticality limits of spent fuel transport, storage and final disposal facilities. Design changes in these facilities are restricted due to a boron content in steel and aluminum alloys that are limited by rolling, extrusion, welding and other manufacturing processes. One possible solution for spent fuel pools and casks is the burnup credit method that allows decreasing very high safety margins associated with the fresh fuel assumption in spent fuel facilities. This solution can be supplemented or replaced by an alternative solution based on placing the neutron absorber material directly into the fuel assembly, where its efficiency is higher than between fuel assemblies. A neutron absorber permanently fixed in guide tubes decreases system reactivity more efficiently than absorber sheets between the fuel assemblies. The paper summarizes possibilities of fixed neutron absorbers for various nuclear fuel and fuel handling facilities. Moreover, an absorber material was optimized to propose alternative options to boron. Multiple effective absorbers that do not require steel or aluminum alloy compatibility are discussed because fixed absorbers are placed inside zirconium or steel cladding

Performance of ENDF/B-VIII.0 library for VVER reactors criticality safety, fuel depletion and reactor dosimetry applications

The latest ENDF/B nuclear data library released in 2018 is the result of a new international approach to develop evaluated nuclear data for general purpose applications. In order to use the latest ENDF/B-VIII.0 nuclear data library in safety analyses, validation calculations for available benchmark experiments and comparison calculations for previous library versions are required. Validation of this new library for three important reactor areas, criticality safety, fuel depletion and reactor dosimetry, was performed with MCNP6, KENO-VI and Serpent 2 codes for VVER application. Criticality safety and fuel depletion results show better agreement with ICSBEP and SFCOMPO benchmark database cases for the ENDF/B-VIII.0 library when compared with previous libraries including ENDF/B-VII.1. On the other hand, using the latest VIII.0 library for VVER reactor dosimetry applications including neutron fluence on reactor pressure vessel and ex-vessel neutron fluence activation monitors is not recommended since the library gives significantly lower neutron fluence and detector activities when comparing to number of alternative nuclear data libraries. Two nuclides that are dominantly responsible for the discrepancies between the latest ENDF/B library and other libraries were identified as O-16 and Fe-56. The conclusions are limited to VVER application where the water gap between the reactor core and the pressure vessel is significantly decreased compared to PWR