Radiation damage and simulated fission product effects on the properties of inert matrix materials

Candidate inert matrix materials for actinide transmutation (MgAl₂O₄, CeO₂) or immobilization (ZrSiO₄) containing ²⁴¹Am were characterized. The currently most considered material, ZrO₂, was produced, with La₂O₃ as stand-in for Am, and with and without simulated fission products to investigate burnup effects. The oxygen potential was measured using an EMF cell. The accumulation of radiation damage due to Am decay was investigated by periodically measuring lattice parameters and hardness. Sequential leaching tests in deionized water, aimed at correlating the leaching behaviour of Am and of the matrix with radiation damage, showed significant release of Am and of some matrix components.     

Influence of evaluated data of fission product poisons on criticality

The main objective of this research is to study the influence of cross-section differences of fission product poisons among various newly released evaluated cross-section libraries ENDFB-VI.8, JENDL3.2, JEF2.2, IAEA, ENDFB-VII and JEFF3.1 on criticality of an MTR type research reactor. The effect of cross-sections of poisons on the reactivity was studied with the help of WIMSD and CITATION codes. Various cross-section libraries were used in SARC (System for Analysis of Reactor Core) code for the fuel cycle analysis. It was found that the negative reactivity induced due to ¹³⁵Xe for the equilibrium core is around 36.00 mk whereas for ¹⁴⁹Sm it ranges from 6.65 to 7.06 mk. The three libraries (JENDL3.2, IAEA and ENDFB-VII) resulted in small increase in the Xenon worth as compared to the other three libraries. For Samarium, JEFF3.1 gives the highest worth whereas ENDFB-VI.8 gives the least worth among the six libraries.     

Influence of corium oxidation on fission product release from molten pool

Qualitative and quantitative determination of the release of low-volatile fission products and core materials from molten oxidic corium was investigated in the EVAN project under the auspices of ISTC. The experiments carried out in a cold crucible with induction heating and RASPLAV test facility are described. The results are discussed in terms of reactor application; in particular, pool configuration, melt oxidation kinetics, critical influence of melt surface temperature and oxidation index on the fission product release rate, aerosol particle composition and size distribution. The relevance of measured high release of Sr from the molten pool for the reactor application is highlighted. Comparisons of the experimental data with those from the COLIMA CA-U3 test and the VERCORS tests, as well as with predictions from IVTANTHERMO and GEMINI/NUCLEA codes are made. Recommendations for further investigations are proposed following the major observations and discussions.     

~(147)Pm对小鼠生殖细胞的遗传毒理效应

本文研究观察了小鼠静脉摄入重核裂变产物~(147)Pm后不同间隔时间对生殖细胞染色体畸变和精子(主要是无钩精子)畸形的诱变效应,实验结果发现~(147)Pm可诱发精原细胞染色体结构畸变;随着机体受内污染时间的延长,染色体畸变率和多倍体细胞也有所增加,同时~(147)Pm也可诱发初级精母细胞产生染色体断片和易位,形成多价体。染色体断片率随~(147)Pm辐照时间的延长而升高。而多价体只在内污染10天后的实验组中出现。     

Volatile fission product and sodium release from liquids

For the improvement of radioactive source term calculations the computer code revols has been developed for the mechanistic modeling of the evaporative release of volatible species (e.g. water, sodium and volatile fission products as NaJ, Cs and Rb) from different hosts into an inert gas atmosphere. The code, showing a modular structure, has been developed to be coupled with reactor containment safety analysis codes as the contain / lmr and lmfbr version. In substituting existing constant-retention-factor formulations by introducing a geometry and state dependent, instationary retention factor, an improved aerosol and fission product source calculation can be obtained. The comparison of theoretical predictions with experimental results performed at the Karlsruhe Research Center shows good agreement.     

Diffusion behavior of fission product in pyrolytic silicon carbide

The concentration distributions of ¹³³Xe, ¹⁴⁰Ba, ⁸⁹Sr, ¹⁴¹Ce, ¹⁰³Ru and ⁹⁵Zr-⁹⁵Nb in a SiC layer and releases of these fission products from SiC coated fuel particles were measured in a temperature range from 1650° to 1850°C, to obtain the diffusion parameters and to investigate the diffusion behaviors in SiC. Temperature dependences of the diffusion coefficients of these fission products except ⁹⁵Zr-⁹⁵Nb were obtained. In diffusion behaviors of the alkali earth fission product, volume diffusion occured considerably besides grain boundary above 1650°C. ¹⁴¹Ce and ¹⁰³Ru diffusions were almost through grain boundaries in the temperature range. ⁹⁵Zr-⁹⁵Nb showed volume diffusion besides boundaries diffusion in their distribution annealed at 1850°C for 35 h, but those for the shorter time or at the lower temperature would be due to boundary diffusion. In comparison of the diffusion coefficients in SiC and PyC, it was proved that SiC was effective for retention of the solid fission products.     

Experimental study on the effect of fission product gas release into blockage wake region using a simulated LMFBR fuel subassembly

The objective of this study is to evaluate temperature rise due to gas release in the wake region of LMFBR fuel subassemblies. The experiments were conducted in two sets of grid-spacer-type 37-pin bundles simulating LMFBR fuel subassemblies. In Test section 37GC, the central 24 subchannels were blocked by a stainless steel plate and in Test section 37GE one-half edge part (39 subchannels) of the total flow area was blocked by the same material. The experimental results were compared with data obtained in similar tests using a spacer wire-type pin bundle, designated 37WC. The temperature rises in 37GE and 37WC were nearly identical in value and effect of gas release rate. The marked agreement seems to imply that there is a limit in the content of released gas in the wake region. On the other hand, the temperature rise behind the central blockage in the grid-type bundle, where gas might easily flow out to the core flow region, was far less than in the other geometries.     

Determination of fission product activities in graphite by gamma spectrometry

A non-destructive technique is described for the quantitative routine determination of radioactive fission and neutron activation products in graphite. The method is based on scintillation spectrometry and computer analysis of the y-spectra. Graphite samples from DRAGON loop experiments have been analysed and our results agree with figures obtained by radiochemical analysis of similar samples. The methods have been applied for the determination of axial and radial distributions of fission products in graphite fuel tubes.     

14.8 MeV中子诱发~(238)U裂变产物产额测量

裂变产物产额作为裂变过程的一个重要参数,其准确测量对有关裂变的很多方面都有重要意义。为了准确测量中子诱发~(238)U裂变产物产额,利用中国工程物理研究院PD-300加速器上的T(d,n)4He反应,产生14.8MeV的中子,诱发~(238)U裂变。辐照过程中,通过金硅面垒半导体探测器监测中子通量的变化。使用Al片作为监测片计算整个照射过程中样品的平均中子通量。辐照结束后,利用高纯锗(High-Purity Germanium,HPGe)探测器测得裂变产物特征γ射线计数,计算得到裂变产物的产额,使用MCNPX软件对中子的多次散射和自屏蔽效应进行修正,并通过计算得到样品和监测片的自吸收修正、中子通量波动因子。得到了95Zr、127Sb、140Ba、147Nd、131I、103Ru等长半衰期产物的累积产额值,并将结果与以前的文献值做了比对,研究结果有助于~(238)U裂变产物产额的分析和评价。     

The effect of irradiation-induced re-solution on fission gas release

A finite-difference technique is used to compute exact solutions to the diffusion equation describing fission gas release from UO₂ nuclear fuel during steady reactor operation. The resolution of gas atoms from grain-boundary bubbles is treated in two alternative ways, and the results of the parallel calculations compared. Predictions of gas release using simple analytical models are compared with the numerical results and are found in general to describe the process very accurately.     

用贫化铀裂变室测量绝对裂变率的影响因素研究

用贫化铀裂变室进行绝对裂变率测量。分析了裂变室记录裂变碎片的效率．对影响绝对裂变率测量的因素进行实验研究,包括探测器之间扰动影响,裂变室结构材料的影响等。     

Effect analysis of the intentional depressurization on fission product behavior during TMLB' severe accident

It has been found that the pressure in the reactor coolant system (RCS) remains high in some severe accident sequences at the time of reactor vessel failure, with the risk of causing direct containment heating (DCH).Intentional depressurization is an effective accident management strategy to prevent DCH or to mitigate its consequences. Fission product behavior is affected by intentional depressurization, especially for inert gas and volatile fission product. Because the pressurizer power-operated relief valves (PORVs) are latched open, fission product will transport into the containment directly. This may cause larger radiological consequences in containment before reactor vessel failure. Four cases are selected, including the TMLB' base case and the opening one, two and three pressurizer PORVs. The results show that inert gas transports into containment more quickly when opening one and two PORVs,but more slowly when opening three PORVs; more volatile fission product deposit in containment and less in reactor coolant system (RCS) for intentional depressurization cases. When opening one PORV, the phenomenon of revaporization is strong in the RCS.     

Fundamental aspects of defective nuclear fuel behaviour and fission product release

An in-reactor research program with individual, purposely defected, nuclear fuel elements has provided a fundamental understanding of the physical processes of fission product release from defective fuel. On the basis of these experiments, an analytical model has been developed to describe the release of radioactive iodine and noble gas from defective fuel into the primary coolant. An analytic treatment has also been used to model the low-temperature release of fission products from small particles of uranium-bearing compounds (uranium contamination) deposited on in-core surfaces. As a result of this study, a methodology is established whereby release from surface uranium contamination can be distinguished from that resulting from fuel pin failure. Application of this work to power reactor operation is discussed.     

Numerical prediction of the fission product plate-out for a VHTR application

In order to identify and quantify the key parameters affecting the predictions of fission product transport and plate-out behavior in the coolant circuits of a very high temperature reactor (VHTR) system, systematic and intensive analyses were performed based on numerical predictions as well as the existing experimental data. For the purpose, the computational module for modeling fission product transport phenomena was developed and incorporated into the system analysis code, GAMMA+ for an integrated analysis. This integration can provide more realistic boundary conditions such as velocity, temperature, etc., during off-normal conditions as well as normal operations in a given VHTR system.     

Initial results of investigations into fission product deposition in in-pile experiments

The safe operation of a high temperature reactor (HTR) depends to a decisive extent on the behaviour of the fission products released from the fuel elements into the primary loop and on the nuclides resulting from activation. To investigate the still little-explored mechanisms of transport and deposition for fission and activation products, a comprehensive program for the study of the deposition of fission products was undertaken at the KFA in collaboration with various industrial concerns and foreign project groups, which has in the meantime led to a preliminary knowledge of these processes. It is the aim of the experimental and theoretical efforts to develop a realistic model for deposition, which permits calculating the deposition onto components of the primary loop and thus also allows an assessment of the possibility for service and repair of the individual components. Beyond this, the model should serve as the basis for the realistic consideration of the consequences of a failure in the reactor. The initial results of the Saphir-Pégase and Vampyr-AVR in-pile experiments are discussed. It was found that deposition cannot be understood in terms of pure adsorption; on the contrary, irreversible processes, such as diffusion and chemical bonding, also have to be considered. A model which includes these mechanisms is explained and its correctness discussed in terms of the experimental results. The knowledge obtained to date supports the necessity for further intensive experimental and theoretical investigations directed to the understanding of the various factors affecting the deposition process and to the determination of their magnitudes.