1 Independent Spent Fuel Storage Installation; ISFSI at Yankee Rowe David A. Montt, CHP Yankee Rowe Fuel Storage Facility Associate & Senior Health Physicist

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Independent Spent Fuel Storage Installation;ISFSI at Yankee Rowe

David A. Montt, CHP Yankee Rowe Fuel Storage FacilityAssociate & Senior Health PhysicistDade Moeller and Associates, Inc.1 Acton Place, Suite 201Acton, Massachusetts 01720

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•Achieved Initial Criticality—1960•Began Commercial Operation—1961•Upgrade to 600 MWt—1963•Decision to Cease Operations—2/1992•Possession Only Status—8/1992•Decommissioning Activities—1992 - 2006•ISFSI Monitoring Pre-Transfer (Begin)—7/2001•Fuel Movement to ISFSI (Begin)—6/2002•Fuel Movement to ISFSI Completed—6/2003•Decommissioning Complete---10/2006•ISFSI Monitoring Post-Transfer (Continues)—Present

YNPS History

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• Project Objectives in 2001

– Demonstrate Compliance with 10CFR72.104 and 10CFR72.106

– Use Modeling to Predict Dose Rates at Various Locations on Site.

– Assess Impact on FSS Effort Scheduled to Start in 2004

– Fine Tune Computer Model Predictions with Empirical Data

– Transfer Knowledge Gained to Connecticut Yankee ISFSI Efforts .

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• http://www.yankeerowe.com/decommissioning_dismantle.html - web page for video of demolition progression from March 2003 to December 2003

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Yankee Nuclear Power Station (YNPS) Decommissioning Activities Complete

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Independent Spent Fuel Storage Installation;ISFSI at Yankee Rowe(Site in December 2006)

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• Investigation Components

– Stationary TLD’s• TLDs (Gamma & Neutron) Stationed at Pre-determined Locations in July 2001.

• 2-ISFSI TLDs Co-Located with Existing REMP TLDs

• Normal change out is Quarterly and coordinated with REMP TLDs change outs; July 2001 (3rd Qtr) change out is merged with 4th quarter 2001

– In Situ Monitoring• June 2002 in-situ survey with Ion Chamber, REM 500, Hawk, and portable

Canberra Gamma Spectroscopy System.

• Data collected on three separate occasions – pre, during and post transfer

– Computer Modeling • NAC Computer Model

• NRC Computer Model

• and Duke/FANPL Model

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• Stationary TLD’s

– GM# : REMP TLDs• Gamma only

– IF# : ISFSI TLDs• Gamma TLDs• Neutron TLDs

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Independent Spent Fuel Storage Installation;

ISFSI at Yankee Rowe

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• Measurable Impacts from Site Activities – Example

– ISFSI & REMP TLD Locations within 100 meters of the ISFSI Pad show an increase in Gamma activity, and then Drop between the 3rd Qtr 2003 and 1st Qtr 2004.

– During the 3rd quarter 2003, the 2 high specific activity particulate filters used in the hydrolasing and drain down of the SFP were craned out of the SFP building.

– Filter 1 was stored behind a 1” thick steel plate to shield from work activities to the north of the site, but left the south unshielded, initially. Contact DR < 100 mr/hr

– Later, temporary concrete shield walls were used to enclose both filters and the area was secured & locked.

– They were then placed in a concrete shipping cask behind the Safe Shutdown Building until shipment in February 04

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• Numerical data is tabulated for Gamma and Neutron

– This is raw data – no adjustments– Permits observation over time and results trending,

particularly for off site, unaffected locations– Fairly good correlation between co-located REMP and

ISFSI Gamma TLDs.– Appears to be neutron event in 4th Qtr 2003 at three

neutron TLD locations; IF 40, IF 2, and IF 11. The 2 offsite locations and the on site TLD located at the highest elevation on site.

– Not all TLDs affected. Checked Web for solar flares in this period – no correlation – to date this is unexplained

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• Next Table – first look at what we had

– Raw Data collected and averaged over each location for period post fuel transfer to ISFSI pad

– Indicates Exponential Decay Curve– Out to about 200 meters, neutron results indicate neutron

dose is significant – neutron dose ~50-80% of neutron dose

– Significant drop in dose for both components at the 100-125 meter distance and starts to level off

– Dramatic Dip in Neutron dose at 200-215 meters, then climbs back up to 100-125 meter dose at off site locations to 800 meters or ~1/2 mile; dip an anomaly.

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• Corrections to Data– Neutron

– It was at this point, following last in situ survey (1st Qtr 2004) and final report on in situ monitoring that DESEL warns against using neutron spectral data, exposure rate data, and neutron TLD data.

– Counts too low, bad statistics. TLDs not designed for use in environment. Moisture adversely affects crystal lattice, and produces erroneous results.

– DESEL recommendation; use neutron data within 100 meters, and preferably within 100 feet, for trending only.

– Beyond 100 meters, terminate use of neutron TLDs.– See Table 1 (next slide) for pre and post transfer results

– Gamma– It was at this point we evaluated gamma background levels– Used what was now outer ring TLDs (formerly inner ring) to

calculate an average background level for gamma radiation.

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• In the Rowe, Massachusetts area, NORM is 66 millirem per year. These are normal exposures and variations for this component of background radiation because the characteristics of the locations vary. In fact, background radiation varies by more than 35 millirem per year in the Rowe, Massachusetts area. These background radiation readings were measured by Yankee using a Pressurized Ion Chamber instrument on Tuesday, January 6, 1998. The millirem per year calculation was based on this measurement.

– Franklin County Courthouse Conference room (Greenfield, MA) 99 millirem/yr– Hope Street Entrance to Courthouse (Greenfield, MA) 94 millirem/yr– Franklin County Courthouse Council Gov't Rm. (Greenfield Ma.) 87 millirem/yr– Residential Basement (Greenfield Ma.) 86 millirem/yr– Yankee Rowe Air Monitoring Station (Heartwellville VT.) 82 millirem/yr– Whitcomb Summit (Forida Ma.) 82 millirem/yr– Mohawk Regional School Parking Lot (Buckland, Ma.) 79 millirem/yr– St. Joachim's Church (Readsboro, VT.) 77 millirem/yr– Bridge of Flowers Entrance (Buckland, Ma.) 77 millirem/yr– Residential Garage (Greenfield, Ma.) 77 millirem/yr– Yankee Rowe Training Center (Rowe, Ma.) 76 millirem/yr– North Adams Regional Hospital (No. Adams, Ma.) 70 millirem/yr– Wilson's Parking Lot (Greenfeild, Ma.) 70 millirem/yr– Landing at Pot Holes (Shelburne, Ma.) 68 millirem/yr– Rowe School Parking Lot (Rowe, Ma.) 64 millirem/yr– Entrance to Poet Seat's Tower (Greenfield, Ma.) 59 millirem/yr

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Independent Spent Fuel Storage Installation;

ISFSI at Yankee Rowe

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• FSS Survey Results

– The FSS survey group conducted a survey of the site using Bicron Meters to quantify the impact of the ISFSI on the FSS areas to be surveyed, the results of which were used to determine the number of soil samples to be collected.

– The results were in thousands of counts per minute (kcpm) and then converted to mrem/hour.

– These results are raw data and not corrected for background (NORM).

– When corrected for NORM, the results agree well with the TLD and in situ gamma results.

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N 9

N576N 288

N144N E576

N E288N E144

N E72N E72

N E144

N E144

N E 72

N E 36

N E 18

N E 13

E 36

E 18

E 9

S 144

S 72 S 36

S 18

S 9

S W 144

S W 72

S W 36

S W 18

S W 9

W 36

W 18

W 9

N W288

NW

144

N W 18

N W 9

N E 9

N N W 72

N N W 36

N N W 18

N W 36

N 72N N E 80

N N E 80N 100

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• In Situ Surveys– Three in situ radiation surveys were performed [5, 6, 7].

• The first survey, which was conducted in April 2002, provided background radiation measurements for the ISFSI.

• The second, which was conducted June 2002, provided radiation measurements associated with the first spent fuel canister after it was transferred to the ISFSI.

• The third survey, which was conducted December 2003, provided radiation measurements after the transfer of all of the canisters to the ISFSI pad.

– Instruments Used• the laboratory used a portable gamma spectrometry system (HPGe

detector) for in situ gamma measurements, • a pressurized ion chamber (PIC) for exposure rate measurements, • and environmental radiation monitors (HAWK and Rem-500 survey

meters) capable of mixed field (gamma and neutron) measurements.

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• A consistent measurement methodology was used. – Gamma Spectrum

• For the in situ gamma measurements, a gamma spectrum was collected at approximately 1 meter above the survey location with the unshielded detector orientated looking down and a second spectrum was collected with the unshielded detector in the horizontal position facing the ISFSI.

• Each gamma spectrum was acquired for 1800 seconds.

– Exposure Rate• Gamma exposure rates were collected with a PIC placed on a tripod

approximately 1 meter above the survey location.

• A series of 10 30-second measurements was recorded. The final exposure rate was produced from the mean and standard deviation of the data set.

– Neutron Exposure Rate & Spectrum• The neutron dose rate was measured using the Rem-500 mounted on a tripod

in the horizontal position at approximately 1-meter above the survey location. The spectra from integrated 2-hour measurements were obtained.

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• PIC Results from June 2002 and December 2003 one next slide.– Results within 100 -125 meters indicate measurable impact

from ISFSI– Results beyond 125 meters indicate seasonal influence

and possible lower ambient levels from remediation of licensed material completed to date.

– Results off site indicate seasonal variations may have resulted in lower post transfer final gamma survey results.

• REM 500 Results less decisive– Indicates slight increase in dose results on fence line.– Beyond ISFSI fence line, results inconclusive

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• Computer Modelling

– NAC Skyshine Codes• NAC Computer Model predicted the 10CFR72.104, 25

mrem/yr dose boundary, at 270 meters in all directions from the center of the pad.

• It included both direct and scatter components.• It assumed the most conservative canister array,

permitting other arrangements to be made without prior NRC approval, as all other potential array configurations were bounded by the initial model.

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• Computer Modelling (cont.)

– DESEL MCNP Code

• Duke Engineering & Services (DES)/Framatome-ANP (FANP) used the Monte Carlo N-Particle (MCNP) computer code, a 3-dimensional radiation simulation code to estimate the potential radiological impact from the Yankee ISFSI.

• The MCNP code is a more sophisticated code than the conservative, 2-dimensional Skyshine-III code.

– The first step determined dose from a single vertical concrete cask (VCC).

– The second step modeled the environment, 16 VCCs, soil, 22 detector locations, and 5 spectrum locations. YAEC provided the 22 detector locations, many of which corresponded to the ISFSI TLD locations. The individual burn-up and decay values for each of the 535 fuel assemblies were used to determine the source strengths.

• The MCNP effort terminated prior to the transfer of the first spent fuel canister to the ISFSI pad, and produced only preliminary neutron and gamma dose rate predictions – cost of development became limiting.

• The MCNP results identify the 10CFR72.104 dose boundary (25 mrem/y = 0.00285 mrem/h) at a distance of 406 meters (1320 ft) from the ISFSI.

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• Computer Modelling (cont.)– Both computer models assumed the original canister arrangement

as depicted in Figure 13

– TLD and in situ measurements were completed with the cannisters in the final arrangement as depicted in Figure 14.

– Both models also assumed an original decay heat value of 12.5 KW per canister, not the actual decay heats, which ranged from 6.5 KW to 8.5 KW and averaged approximately 7.5 KW

– This is a little more than half the original estimate. These factors most likely account for the difference between the computer model predicted locations for the 25 mrem/y dose boundary (270-406 meters) and the boundary location based on the interpolation of the measured data (approximately 140 meters - shown in Figure 15).

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• The following table compares the TLD results (adjusted for background), to the in situ results and the DESEL model results.

• The NAC model was run to predict the 25 mrem/year boundary only, and did not have enough data point to provide a meaningful comparison.

• Models are designed to be conservative for planning purposes.

• Direct surveys and TLDs provide more accurate assessments of actual conditions.

• A model reconciled with empirical data is still of value for situations where multiple sources exist and/or when methods to collapse the owner controlled boundaries need to be evaluated and compared.

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• If interested in a full copy of the report used to develop this presentation, forward your request by email to [email protected], and a .pdf file will be emailed to you.

• QUESTIONS?

Documents

1 Independent Spent Fuel Storage Installation; ISFSI at Yankee Rowe David A. Montt, CHP Yankee Rowe Fuel Storage Facility Associate & Senior Health Physicist