Crustal velocity and interseismic strain-rate on possible zones for large earthquakes in the Garhwal-Kumaun Himalaya.

The possibility of a major earthquake like 2015 Gorkha-Nepal or even greater is anticipated in the Garhwal-Kumaun region in the Central Seismic Gap of the NW Himalaya. The interseismic strain-rate from GPS derived crustal velocities show multifaceted strain-rate pattern in the region and are classified into four different strain-rate zones. Besides compressional, we identified two NE-SW orienting low strain rate (~ 20 nstrain/a) zones; namely, the Ramganga-Baijro and the Nainital-Almora, where large earthquakes can occur. These zones have surface locking widths of ~ 72 and ~ 75 km respectively from the Frontal to the Outer Lesser Himalaya, where no significant surface rupture and associated large earthquakes were observed for the last 100 years. However, strain reducing extensional deformation zone that appears sandwiched between the low strain-rate zones pose uncertainties on the occurences of large earthquakes in the locked zone. Nevertheless, such zone acts as a conduit to transfer strain from the compressional zone (> 100 nstrain/a) to the deforming frontal active fault systems. We also observed a curvilinear surface strain-rate pattern in the Chamoli cluster and explained how asymmetric crustal accommodation processes at the northwest and the southeast edges of the Almora Klippe, cause clockwise rotational couple on the upper crust moving over the MHT.

Investigation of flow dynamics of primary coolant in a delay tank of a swimming pool-type nuclear reactor using radiotracer technique.

Radiotracer investigations were carried out for tracing primary coolant in a delay tank of a swimming pool type nuclear reactor. The delay tank was designed to provide a certain delay or residence time to the primary coolant so that the short-lived radioisotopes such as (nitrogen-16 and oxygen-19) decay to a safer level before exiting from the delay tank. However, soon after commissioning of the reactor, the radiation levels at the exit of the reactor core and delay tank, in the working area were found to be higher than the permissible levels. Therefore, the main objectives of the investigations were to measure breakthrough and residence times and, to investigate flow dynamics of the coolant within the tank. Residence time distributions (RTDs) of the coolant were measured in the delay tank using technetium-99m as sodium pertechnatate as a radiotracer. The breakthrough time (BTT) and mean residence time (MRT) were determined from the measured RTD and the same were found to be inadequate to allow the decay of short-lived radioisotopes to the permissible levels. Axial dispersion model with two parallel flow streams was used to simulate the measured RTD curves. Results of the model simulation indicated bypassing of the coolant. Based on the results of the radiotracer investigations, necessary modifications were carried out in the design of the tank. After implementing the modifications, the radiotracer experiments were repeated and, the BTT and the MRT were found to increase sufficient enough to allow decay of the produced radioisotopes and thus to reduce the radiation levels at the exit of the delay tank and in the working area to the safer and permissible levels.