Radionuclide Release Investigation

Indian Point Energy Center (IPEC)

Buchanan, New York

As a part of the Independent Spent Fuel Storage Installation (ISFSI) Dry Cask Storage Project at IPEC, certain modifications were required within the Indian Point Unit 2 Fuel Storage Building (IP2-FSB). Among these was the installation of a new crane to assist with the transfer of spent fuel into the dry casks. The installation of this crane required the construction of new foundations for the crane supports and a sub-surface counterweight. It was necessary to excavate to bedrock through the floor of the IP2-FSB adjacent to the IP2-Fuel Storage Pool (FSP) to construct the crane foundations and counterweight. 

During excavation, the south wall of the IP2-SFP was exposed. On September 1, 2005 and thereafter, two horizontal hairline shrinkage cracks were observed which exhibited signs of moisture. One crack was found to be actively discharging water at an initial rate of up to approximately 1.5 liters per day. Radiological testing by Entergy indicated constituents found in the discharge water to be generally consistent with water typically associated with the IP2-FSP; although radionuclide analysis appeared to show that the water may have exited the pool liner eight to nine years in the past. 

Following review of all available information concerning the Systems Structures and Components (SSCs) at the facility and the hydrogeology of the Site, GZA prepared a Site Conceptual Model (SCM). The initial SCM consisted of groundwater flow in bedrock governed by natural anisotropies and anthropogenic influences such as additional blasting-induced fracturing in the foundation bedrock, and a number of actively flowing foundation drains, as well as the overall impact of changes to the natural flow system as a result of mass excavation into the natural bedrock bank of the Hudson River. Our initial SCM anticipated groundwater flow into the site from the North, East and South, with an overall westerly groundwater discharge path to the river. Backfill material along the western wall of the cooling water discharge canal, excavated approximately 35 feet into the bedrock, was expected to intercept the tritium laden groundwater, with preferential flow to the river thereafter .

To assess the leak from the IP2-FSB and validate our Site Conceptual Model, GZA installed 41 monitoring installations, in addition to the 18 existing monitoring wells at the Site. Prior to boring installation, GZA conducted a review of existing utility plans, performed surface geophysical surveys, and employed vacuum excavation techniques to provide a very high level of certainty pursuant to avoiding potentially miss-located underground utilities or SSCs. GZA conducted downhole borehole geophysics, including ATV/OTV, on 22 bedrock borings to evaluate fracture orientations and their degree of interconnectivity. In addition, the geophysics data was correlated to actual subsurface conditions through inspections of rock cores by GZA geologists. We conducted 229 hydraulic conductivity tests using pneumatic slug testing as wells as straddle zone packer tests. Twelve bedrock monitoring installations were completed with Solinst Waterloo Multilevel Sampling instruments and 18 well installations were completed as nested piezometers. Pressure transducers were installed in the existing wells and newly installed wells to evaluate groundwater flow, tidal effects, effects of precipitation on groundwater flow, and interconnectivity of fractures. 

The results of the investigation were used to establish the source of radionuclide contamination in the groundwater and establish the contaminant fate and transport mechanisms. We were able to delineate two plumes on the Site. The first plume is composed primarily of tritium which emanated from the Unit 2 spent fuel pool. The second plume is composed predominantly of Strontium, which emanated from the Unit 1 spent fuel pool complex. GZA used the radiological activity in these plumes along with hydrogeologic data to help compute the dose impact oftheradionuclide release tothe Hudson River. The results indicated that the dose was less than 1/100 of the permitted levels. In addition, we prepared a long term groundwater monitoring program consistent with the NEI groundwater protection initiative to monitor the existing groundwater plumes as well as monitor potential releases from other SSCs.

GZA participated with and on behalf of Entergy Nuclear Northeast in several NEI and EPRI presentations on the Groundwater Protection Initiative, as well as public hearings, public meetings, and community outreach events with representatives from  the public and the NRC in attendance.