Khurram Mehboob

U.S.NRC Progress in Source Term Evaluation

In this paper progress in the source term evaluation has been presented. This paper presents the development of Source term evaluation of Nuclear Power Plants (NPPs) for Probabilistic Risk Assessment (PRA) for operation and licensing of the NPPs. Substantial research had been carried out by NRC, for this purpose. Nuclear Research and development (R&D) Agencies like ANL, NEA, ORNL, SNL, BCL and ANS incorporate with U.S. NRC, and by the time they had published research reports on progress in risk assessments and source term evaluation of different accidental consequences in Commercial NPPs.

IODINE REMOVAL EFFICIENCY IN NON-SUBMERGED AND SUBMERGED SELF-PRIMING VENTURI SCRUBBER

The objective of this conducted research is to study the iodine removal efficiency in a self-priming venturi scrubber for submerged and non-submerged operating conditions experimentally and theoretically. The alkaline solution is used as an absorbent, which is prepared by dissolving sodium hydroxide (NaOH) and sodium thiosulphate (Na2S2O3) in water to remove the gaseous iodine (I2) from the gas. Iodine removal efficiency is examined at various gas flow rates and inlet concentrations of iodine for submerged and non-submerged operating conditions. In the non-submerged venturi scrubber, only the droplets take part in iodine removal efficiency. However, in a submerged venturi scrubber condition, the iodine gas is absorbed from gas to droplets inside the venturi scrubber and from bubbles to surrounding liquid at the outlet of a venturi scrubber. Experimentally, it is observed that the iodine removal efficiency is greater in the submerged venturi scrubber as compare to a nonsubmerged venturi scrubber condition. The highest iodine removal efficiency of 0.99±0.001 has been achieved in a submerged self-priming venturi scrubber condition. A mathematical correlation is used to predict the theoretical iodine removal efficiency in submerged and non-submerged conditions, and it is compared against the experimental results. The Wilkinson et al. correlation is used to predict the bubble diameter theoretically whereas the Nukiyama and Tanasawa correlation is used for droplet diameter. The mass transfer coefficient for the gas phase is calculated from the Steinberger and Treybal correlation. The calculated results for a submerged venturi scrubber agree well with experimental results but underpredicts in the case of the nonsubmerged venturi scrubber.

Mitigation of PWR in-containment iodine source term under LOCA

Iodine is one of the most hazardous fission products from radiological consequences of LWR. In this paper, the iodine source term has been evaluated for two-loop PWR under severe accident initiated due LOCA. The TMI-2 reactor is considered as the reference reactor. The modelling and simulations of release of iodine have been carried out by developing a MATLAB code that uses the post-accident conditions and core inventory as its input. The containment response, in order to mitigate the environmental and incontainment iodine source term is studied in normal, emergency, and isolation states of containment. The in-containment iodine source term has been evaluated with, and without operation of Engineering Safety features (ESFs). The environmental iodine source term is calculated as the function of containment response. The containment retention factor (CRF) for iodine has also been studied in all confined states of containment. Results indicate the weak sensitivity of iodine towards exhaust rate with ESFs operation.

Numerical Simulation of Decontamination of Airborne Fission Products during In-Vessel Release Phase by Containment Spray

The containment spray system (CSS) has a significant role in limiting the risk of radioactive exposure to the environment. In this work, the optimal droplet size and pH value of spray water to prevent the fission product release have been evaluated to improve the performance of the spray system during in-vessel release phase. A semikinetic model has been developed and implemented in MATLAB. The sensitivity and removal rate of airborne isotopes with the spray system have been simulated versus the spray activation and failure time, droplet size, and pH value. The alkaline (Na2S2O3) spray solution and spray water with pH 9.5 have similar scrubbing properties for iodine. However, the removal rate from the CSS has been found to be an approximately inverse square of droplet diameter ( ) for Na2S2O3 and higher pH of spray water. The numerical results showed that 450 μm–850 μm droplet with 9.5 pH and higher or the alkaline (Na2S2O3) solution with 0.2 m3/s–0.35 m3/s flow rate is optimal for effective scrubbing of in-containment fission products. The proposed model has been validated with TOSQAN experimental data.

US NRC progress in source term evaluation

In this paper progress in the source term evaluation is presented. This paper presents the development of source term evaluation of Nuclear Power Plants (NPPs) for Probabilistic Risk Assessment (PRA) for operation and licensing of the NPPs. Substantial research had been carried out by NRC, for this purpose. Nuclear Research and Development (R&D) agencies like ANL, NEA, ORNL, SNL, BCL and ANS incorporate with US NRC, and have published research reports on progress in risk assessments and source term evaluation of different accidental consequences in commercial NPPs.

CFD Simulation of Prediction of Pressure Drop in Venturi Scrubber

Venturi Scrubbers are used in filtered vented containment system (FVCS) for collection of aerosols produced in NPP in severe accidents. Therefore, venturi scrubber (VS) needs an attention to design it properly and improved in all aspects. In this research, CFD simulations of prediction of pressure drop in venturi scrubber has been carried out. ANSYS CFX tool is used to obtain the simulation results. k-ε turbulence model is employed to study the fluid dynamics of the venturi scrubber. Mesh size plays an important role for convergence and accuracy of results. Therefore, the mesh independency is checked for optimized mesh size.

Study on the Effect of Containment Performance on Lodine Source Term

In this paper, the iodine source term is studied with the containment performance in normal, isolation, and emergency state of containment. For this study, a MATLAB computer-based program is developed, which simulates the iodine source term with time. The environmental iodine source term is determined with time normal, isolation and emergency state of containment. With the operation of Engineering Safety Features ESFs the effect on the iodine source term has been observed. From the results, it is observed that the iodine is strongly dependent on the exhaust rate and significantly reduced with ESFs operation.

Evaluation of Iodine Source Term in PWR under Loss of Coolant Accident

During the severe accident in nuclear power plant (NPP), large amounts of fission products are released with accident progression, including In-vessel and Ex-vessel release. Thus, the Source term evaluation is essential for the probability risk assessment (PRA) and is still imperative for the licensing and operation of NPPs. Iodine is one of the most reactive fission products emitting in a large amount to containment and have a severe impact on health and sounding environment. Therefore, the iodine source term has been evaluated for 1000MW Reactor, by considering the TMI-2 as the reference reactor. The modeling and simulation of released radioactivity have been carried out by developing a MATLAB computer-based program. For post 1100 operation days, with the instantaneous release of radioactivity to the containment has been studied under LOCA. The dependency of radioiodine on ventilation exhaust rates has been studied in normal, emergency and isolation mode of containment. Moreover, the containment retention factor is also evaluated in said states of containment.

Kinetic Study of Containment Retention Factor (CRF) for Large Dry Containment Under Radiation Load

The Nuclear Power Plants (NPPs) have been built on the concept of Defense in depth. The severe accident causes the failure of fission product barriers and let the fission products to escape into environment. The containment is the last barrier to the fission products. Thus, the containment is installed with engineering safety features (ESFs) i.e. spray system, heat removal system, recirculation filtration system; containment filtered venting system (CFVS), and containment exhaust filtration system. In this work, kinetic study of the containment retention factor (CRF) has been carried out for a large dry PWR containment considering 1000 MWe PWR. The computational modeling and simulation have been carried out by developing a kinetic code in MATLAB, which uses the fractions of activity airborne into the containment after the accident. The Kinetic dependency of CRF on containment filtration systems, spray system with caustic and boric acid spray has been carried out. For noble gases, iodine and aerosols, the CRF increases with the increase in exhaust rate. While, CRF for iodine first increases then start reducing with containment spray flow rate. The Kinetic dependency of CRF has also been studied for boric and caustic spray.Copyright

REMOVAL EFFICIENCY OF IODINE AT SATURATED STEAM IN SUBMERGED VENTURI SCRUBBER

Sever accident due to molten core of Nuclear Power Plant causes the production of steam which carries the radioactive iodine. It is important to retain the radioactive iodine from contaminated gas and steam before it is released into the environment. The purpose of this research is to investigate the removal efficiency of iodine in a submerged venturi scrubber for saturated steam at 100°C. Venturi Scrubber is submerged in a venturi tank filled with liquid which is alkaline by adding sodium hydroxide (NaOH) and sodium thiosulphate (Na2S2O3) in scrubbing water. Saturated Steam of 100 °C is injected into an experimental loop. Iodine removal efficiency is investigated for saturated steam at various compressed gas flow rate 330, 420, and 510 kg/s. Inlet and outlet concentration are measured at the sampling points of an experimental loop to calculate the iodine removal efficiency. The maximum removal efficiency of 99.4% is achieved at gas mass flow rate of 510 kg/s.Copyright