ML20140E112
| ML20140E112 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 04/10/1997 |
| From: | OAK RIDGE ASSOCIATED UNIVERSITIES |
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| Shared Package | |
| ML20140E110 | List: |
| References | |
| NUDOCS 9704250083 | |
| Download: ML20140E112 (9) | |
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CONFIRMATORY SURVEY 4
OFTHE GROUP E EFFLUENT DISCHARGE PATHWAY AREAS l
FORT ST. VRAIN NUCLEAR STATION PLATTEVILLE COLORADO INTRODUCTION The Public Service Company of Colorado (PSC) operated a 330 MWe High Temperature Gas Cooled Reactor (HTGR) from July 1979 until August 1989. The plant, designated as the Fort St.
Vrain Nuclear Station (FSV), was authorized for cor struction on September 17,1969 when the U.S.
Nuclear Regulatory Conunission (NRC) issued a prc visional construction permit. Construction was completed in December 1973 and a facility operating license, License No. DPR-34, Docket No.
50-267, was granted on December 21,1973. Initial fuel loading commenced on December 26,1973 and initial criticality was achieved January 31,1974. After a prolonged period of startup testing, low-power operation and plant modifications, the plant was committed for commercial operation on July 1,1979. Full power was achieved November 6,1981 (PSC 1995a).
In the nuclear steam supply system for FSV, heat was produced by fission in the HTGR utilizing a uranium-thorium fuel cycle. Graphite was used for the moderator, core structure, and reflector.
High temperature helium was used as the primary coolant to produce superheated and reheated steam at a temperature of 1,000 degrees F to match conventional thermal station conditions. The entire nuclear steam supply system, including the reactor core, graphite moderator and reflector, steam generators and helium circulators, was contained within a Prestressed Concrete Reactor Vessel (PCRV).
During the operational period, FSV operated for approximately 890 effective full-power days; FSV was shut down on August 18,1989. The PSC Board of Directors reviewed and confirmed the Executive Management decision that FSV would not be restarted, and that PSC would pursue decommissioning of FSV. The decision to permanently shut down and decommission FSV was based on related technical and financial considerations. Problems were identified with the control rod drive assemblies and the steam generator steam ring headers that presented significant technical obstacles which could be overcome, but at a significant financial cost and time commitment. In 4./d42560'e5 W641'o #
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addition, due to the uniqueness of the HGTR fuel cycle, the cost to purchase new fuel was
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prohibitive. This, in conjunction with low plant availability and correspondingly high operating costs, made continued operation of FSV impractical.
l In May 1991, the NRC granted PSC a 10 CFR 50 Possession Only License. On November 23, 1992, the NRC issued the Order to Authorize Decommissioning of Fort St. Vrain and Amendment i
No. 85 to Possession Only License No. DPR-34 (PSC 1995b). PSC's objective was the dismantlement and decommissioning of FSV to release all site areas for unrestricted use. To 4
accomplish this, a portion of the PCRV structure and the radioactive balance-of-plant equipment that 3
exceeded the limits for unrestricted use were decontaminated or removed as described in the Fort i
St. Vrain decommissioning plan.
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The radiological status of the FSV environs was evaluated in the FSV Initial Radiological Site Characterization Report in order to provide information pertinent to the decommissioning and final survey of FSV (PSC 1992). There were no spills or accidents during operation of FSV which had the potential of contaminating the site. The Radiological Environmental Monitoring Program (REMP) was continued throughout the decommissioning to ensure that any contamination of the site environs which could have occurred as a result of decommissioning activities was detected.
The FSV facility was largely left intact following decommissioning; dismantlement of structures was confined to the PCRV, and portions of the Reactor Building, Turbine Building, and Liquid Waste System. Following defueling, the PCRV contained the majority of the remaining radioactive inventory. The radioactive source term at FSV was primarily a result of neutron activation of both metallic and concrete components, and impurities contained in graphite components of the PCRV.
These activation products included beta-gamma emitters such as Co-60, Eu-152, and Eu-154, and low-energy beta and x-ray emitters such as H-3, C-14, and Fe-55, with H-3 and Fe-55 the largest contributors to the total radionuclide inventory (PSC 1995a).
FSV's final survey included all pertinent structures, surfaces, and systems and components, concentrating on those previously identified as contaminated or potentially contaminated during the Fort St. Vram Nuclear Station (687). April 10.1997 2
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dismantlement / decommissioning phases.
At the request of the NRC's Division of Waste j
Management, ESSAP performed un iridependent confirmatory survey of the repower area in March j-1995 at the Fort St. Vrain site (OltISE 1995a). Subsequent independent survey activities at FSV
- included licensee survey package reviews, confirmatory surface scans, and comparison surface activity measurements (e.g., side-by-side measurements) performed from September 25 through 27, 1995 (ORISE 1996a). During the period January 22 through 25,1996, ESSAP performed instrument comparison activities---including side-by-side surface activity measurements and surface scans-and i
reviews of the licensee's embedded piping program and use ofin situ gamma spectrometry for j
determining the licensed material contribution to exposure rate (ORISE 1996b). Most recently, ESSAP performed independent confirmatory surveys during the period September 30 through October 3,1996. Specifically, ESSAP performed surface scans, surface activity measurements, and exposure rate measurements; and reviews of the licensee's hard to detect nuclide (HTDN) assessment program. A draft report describing these activities was prepared c.nd submitted to the NRC for comment on January 30,1997 (ORISE 1997).
J In October 1996, PSC completed final survey activities for the Group E Effluent Discharge Pathway areas at FSV and issued Volume 6 of the Final Survey Report (PSC 1996). The effluent discharge h
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-pat way cons sts o open and areas, storage and evaporation ponds and basins, concrete-lined ditches, unlined ditches, and the 10.1 hectare (25 acre) Farm Pond. Water from both ditches was routinely used for irrigation of the surrounding fields and pastures. It is also known that water would leak from the Goose Quill Ditch providing a means of transport of radioactive materials to the surrounding soil. Additionally, the ditches were periodically dredged to maintain flow rates and avoid overflaw. The removed vegetation and sediment was routinely deposited on the banks adjacent to the ditches (PSC 1996).
The NRC's Division af Waste Management requested that ESSAP perform independent confirmation survey activities of the Liquid Effluent Pathway areas at Fort St. Vrain.
Fort St. Vrain Nuclear Station (687). April 10.1997 3
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SITE DESCRIPTION The FSV facility is located approximately 56 kilometers [km(35 miles)] north of Denver and 5.6 km
, northwest of the town of Platteville, in Weld County, Colorado. The site is located in an agricultural area oi gently rolling hills. Grade elevation at the plant is 1,460 meters (4,790 feet) above sea level.
The site consists of 6995 hectares (ha) owned by PSC, identified as the Owner-Controlled Area, of which approximately 260 ha were designated as the exclusion area during plant operation. Farming has been continued on Owner-Controlled areas of the site, but there are no farming operations or permanent residences located within the Restricted Area. The Restricted Area is surrounded by a security fence, and access is controlled for purposes of protection ofindividuals from exposure to radiation.
1 The station is located on the east side of county road 19% approximately 3.2 km south of the confluence of the South Platte River and the St. Vrain River. Neither of the rivers is considered navigable. Cooling for the plant was provided by mechanical draft cooling towers. Make-up to the 3
cooling towers was provided from the rivers, and supplemented by shallow well water. Nineteen shallow wells are located on the site. The licensee also owns rights to surface water in four irrigation ditches which traverse portions of the site.
Effluent from the plant was discharged to a point west of the plant and County Road 19 %, where it entered the concrete-lined Goose Quill Ditch. The Goose Quill Ditch runs north and east approximately 2,135 meters (m) before terminating at the Jay Thomas Ditch. The Jay Thomas Ditch flows north approximately 700 m from the confluence with the Goose Quill Ditch where it empties into the Farm Pond. Outfall from the pond eventually terminated at the South Platte River.
l PSC divided the Liquid Effluent Pathway areas into fourteen survey units, designated E001 through E014, and classified the units into two categories based on the potential for residual contamination.
The two categories, referred to as affected or unaffected are defined as follows: Affected areas are those areas that have potential radie.ctive contamination or known radioactive contamination; unaffected areas are all areas not classificci as affected and are not expected to contain residual Fort St. Vrain Nuclear Station (687)
- Apdl 10,1997 4
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radioactivity. Area classification was determined by plant operating history and the results of previous radiological surveys. PSC designated eleven of the survey units as affected. These survey J
units included the Goose Quill Ditch and its brks (E001 and 002), the Farm Pond and its outfall (E003), the Jay Thomas Ditch and its banks (E004 and 006), Irrigation Ditches 1 through 6 and the North and South Marshes (E008 and 010), permanent pasture and farmland both east and west of County Road 19 % (E011 through 013), and a sediment storage area (E014). All of these affected j
survey units are outside the FSV restricted area. Three survey units within the restricted area were classified unaffected and included the East and West Settling Basins and Storage Basins (E005),
i Sewage Lagoons 1 and 2 and East and West Evaporation Ponds (E007), and the South Evaporation i
Pond (E009).
SURVEY PROCEDURES On March 31 and April 1,1997, ESSAP, with support from the NRC, performed a confirmatory survey of the Effluent Discharge Pathway at the Fort St. Vrain Nuclear Station. The survey consisted of visual inspections, gamma surface scans and surface soil sampling of selected portions of the discharge pathway, that included Sections A, C, and D of the Goose Quill ditch banks, Irrigation Ditches 3 and 5, the adjacent pasture land north of the Goose Quill ditch and east and west i
l ofIrrigation Ditch 3, the South Marsh, and the sediment storage pile. The survey was conducted in
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- accordance to a survey plan dated March 26,1997 (ORISE 1997) which was submitted to and j
approved by the NRC's Division of Waste Management. Survey and laboratory procedures were performed in accordance with the ORISE/ESSAP Survey Procedures, Laboratory Procedures, and Quality Assurance Manuals (ORISE 1995a, b, and c). This report summarizes the procedures and results of the survey, Surface scans for gamma activity were performed over 100 % of the South Marsh and Sections A, C, and D of the Goose Quill Ditch banks out to three meters. Gamma scans were performed over 75 to 100% of the unlined bottoms ofIrrigation Ditches 3 and 5 and along the adjacent land out to one meter. The pasture land both east and west ofIrrigation Ditch 3 was randomly scanned over I
approximately 25% of the area.
Fort St Vrain Nuclear Station (687). April 10,194/
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A total of 19 surface soil samples (0-15 cm) were collected from the Goose Quill ditch banks and Irrigation Ditch 5 at locations of slightly elevated gamma activity identified by surface scans or at locations selected based on the licensee's documentation. Nine of these samples were collected in a 10 meter by 10 meter grid block established by the licensee as a result ofinvestigation sampling, in order to perform analytical comparison with the licensee's results. Additionally,4 surface samples were collected from random locations in the sediment storage area, also for comparison purposes.
FINDINGS AND RESULTS Surface scans identified eight locations of slightly elevated gamma activity on the banks of the Goose Quill Ditch and three locations in Irrigation Ditch 5.
Radionuclide concentrations and the sum of the ratios in ESSAP biased soil samples are presented
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in Table 1. Soil samples were analyzed by gamma spectrometry and the spectra were evaluated for the primary radionuclides of interest-Co-60 and Cs-137, as well as any other identifiable photopeaks. The results of the 9 samples collected from the 10 meter by 10 meter grid in Section A of the Goose Quill ditch and the 4 samples collected from the sediment storage area were directly compared to the licensee's results and are presented in Table 2.
Radionuclide concentrations for ESSAP biased soil samples ranged from less than 0.1 to 8.8 pCi/g for Co-60 and from less than 0.1 to 6.3 pCi/g for Cs-137. The highest concentrations of both Co-60 and Cs-137 were from the soil sample collected near Flag 157 in Section D of the Goose Quilt ditch banks. The site guidelines for Co-60 and Cs-137 are 5.59 and 7.87 pCi/g, respectively, and together must meet the sum of the ratios criteria (i.e., less than unity). The sum of the ratios for these samples ranged from less than 0.1 to 2.4.
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Radionuclide concentrations in comparison soil samples ranged from less than 0.1 to 3.2 pCi/g for i
j Co-60 and from 0.1 to 1.6 pCi/g for Cs-137. PSC samples collected from the same locations ranged '
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from 0 to 5.72 pCi/g for Co-60 and from 0 to 3.27 pCi/g for Cs-137. Both ESSAP's and PSC's highest concentrations were from the same sampling location.
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SUMMARY
On March 31 and April 1,1997, at the request of the NRC's Division of Waste Management, ESS AP l
performed a confirmatory survey of the Effluent Discharge Pathway at the Fort St. Vrain Nuclear Station. Survey activities included surface scans and soil sampling.
Surface scans identified eight locations of slightly elevated surface gamma activity along the banks of the Goose Quill ditch and three locations in Irrigation Ditch 5. Surface soil samples were collected from nine of these locations and from two additional locations selected after reviewing PSC documentation. Analytical results from these samples show that two samples collected in i
Section D at Flags 129 and 157, exceed the sum of ratios criteria at 1.2 and 2.4, respectively. The concentration of Co-60 in the sample from Flag 157 also exceeded the Co-60 guideline at 8.8 pCi/g.
Radionuclide concentrations in surface soil samples collected for comparison with PSC results were all within guideline limits and for most samples were comparable to the PSC results.
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TABLE 1 RADIONUCLIDE CONCENTRATIONS IN SOIL SAMPLES FROM ESSAP BIASED LOCATIONS EFFLUENT DISCIIARGE PATIIWAY FORT ST. VRAIN NUCLEAR STATION PLATTEVILLE, COLORADO Radionuclide Concentrations (pCi/g)*
Sample Location Co-60 Cs-137 Sum of Ratios 6 GOOSE QUILL DITCII BANKS Section A, Flag 15 0.5
- 0.1*
3.3 + 0.2 0.51 Section A, Flag 36 3.2 0.2 1.6
- 0.1 0.59 Section C, Flag 83
<0.1 0.1
- 0.1
<0.1 Section C, Flag 95
<0.1
<0.1
<0.1 I
Section C, Flag 101
<0.1
<0.1
<0.1 Section D, Flag 129 4.1 0.2 4.0
- 0.2 1.2, j
Section D, F1ag 135 1.6 + 0.1 1.1 0.1 0.43 Section D, Flag 157 8.8
- 0.3 6.3
- 0.3 2.4 IRRIGATION DITCH #5 PSC 25d 0.1
- 0.1 0.5
- 0.1 0.08 PSC 294 0.2 0.1 1.5
- 0.1 0.23 PSC 30d
<0.1 0.5
- 0.1
<0.1
- Background was not subtracted.
%e sum of ratios was calculated by dividing the reported concentrations by the site radionuclide guidelines and adding the ratios.
' Uncertainties represent the 95% confidence level, based only on counting statistics.
dRefers to the nearest PSC sampling location.
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O TABLE 2 RADIONUCLIDE CONCENTRATIONS IN SOIL ESSAP/PSC COMPARISON SAMPLES EFFLUENT DISCIIARGE PATIIWAY FORT ST. VRAIN NUCLEAR STATION PLATTEVILLE, COLORADO Radionuclide Concentrations (pCi/g)
Location
<1.0 0.3 + 0.1' O.00 (0.11) 0.2 (0.09) 95/109 3.2 0.2 1.6 0.1 5.72 (0.14) 3.27 (O.13) 110
<0.1 0.2 0.1 0.00(0.19) 1.11 (0.10) 111
<0.1 0.1
- 0.1 0.00(0.10) 0.00 (012) 112
<0.1 0.1 0.1 0.00 (0.12) 0.00 (0.15) 113
<0.1 0.1
- 0.1 0.00 (0.12) 0.06 (0.07) 114
<0.1 0.1
- 0.1 0.00 (0.12) 0.00 (0.12) 115
<0.1 0.1
- 0.1 0.00 (0,12) 0.00 (0.13) 116
<0.1 0.2 0.1 0.00 (0.12) 0.00 (0.15)
SEDIMENT STORAGE AREA 5
0.4
- 0.1 0.8
- 0.1 0.34 (0.07) 0.87 (0.07) 17 0.2
- 0.1 0.3 01 0.15 (0.05) 0.26 (0.05) 23 0.1 0.1 0.2 0.1 0.09 (0.05) 0.14 (0.04) 32 0.4
- 0.1 0.6
- 0.1 1.27 (0.08) 2.23 (0.09) l
' Refers to nearest PSC sample location.
6 Background was not subtracted from ESSAP results.
'%e two values indicate the net concentration and the (MDA) reported by PSC.
dUncertainties represent the 95% confidence level, based only on counting statistics.
0 Fort St. Vrain Nuclear Station (687). April 10,1997 essapWpo@st_nain' fort _vra 002