ML20154M738
| ML20154M738 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 05/31/1988 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML20154H964 | List: |
| References | |
| RTR-REGGD-01.078, RTR-REGGD-1.078 NUDOCS 8806020061 | |
| Download: ML20154M738 (9) | |
Text
- e i
r ASSESSMENT OF CONTROL ROOM HABITABILITY GIVEN A POSTULATED ONSITE RELEASE OF-20 WEIGHT PERCENT AQUE0US AfE0NIA Rancho Seco Nuclear Generating Station May 1988 r
8806020061 08051?ADOCK 05000312 PDR PDR P
S
1.0 ZNTRODUCTION This report describes the methodology and results of an analysis for the habitability of the Rancho Seco Nuclear Generating Station (RSNGS)
Control Room following a postulated catastrophic onsite release of 12,000 gallons of a 20 weight percent aqueous ammonia solution. A previous study submitted to the NRC (Reference 1) analyzed a similar accident involving a postulated 12,000 gallon spill of a 28 weight percent aqueous ammonia solution. Major differences between this analysis and the analysis in Reference 1 are:
1.
Use of a less concentrated aqueous ammonia solution (ie., 20 versus 28 percent by weight) increases the boiling point of the solution to a temperature (46.670C) which is unlikely to be exceeded at Rancho Seco. Thus, a postulated spill of the solution will result in a "continuous" mass release of the vapor only rather than both a continuous and puff release as is possible with a 28 percent aqueous ammonia solution at high ambient temperature.
2.
This analysis utilizes ',00 ppm of ammonia (the so-called 2-minute toxicity limit) as the concentration capable of incapacitating Control ooom opert. tors. The earlier analysis (Reference 1) had estimated the time of operator incapacitation using the analytical models in NUREG/CR-1741 (Models for the Estimation of Incapacitation Times Following Exposures tc Toxic Gases or Yapors).
3.
Ammonia concentrations reported in Reference 1 were based upon meteorological scenarios derived from an analgis of hourly data from the RSNGS onsite meteorological station covering calendar year 1987. The present analysis considers similar meteorological scenarios derived using the most recent 5 years of RSNGS onsite meteorological data.
2.0
SUMMARY
OF RESULTS Predicted ammonia concentrations inside and outside the RSNGS Control Room were calculated for four different meteorological scenarios:
Scenario A:
Lowest 5th percentile wind speed and corresponding "high" temperature - full site data Scenario B: Highest 95th percentile temperature and corresponding "low" wind speed - full site data Scenario C:
Lowest 5th percentile wind speed and corresponding "high" temperature - west winds only Scenario D: Highest 95th percentile temperature and corresponding "low" wind speed - west winds only 3.0 METHODOLOGY 3.1 MASS RELEASE AND ATMOSPHERIC DISPERSION MODELS The analytical models used to estimate the mass release rate of ammonia from a spilled 20 weight percent solution of aqueous ammonia, and the resulting concentration of ammonia occurring outside the RSNGS Control Room HVAC system outside air intake, and inside the Control Room are consistent with those described in NUREG-0570 (Reference 3). These models inc1'ide the following bases and assumptions:
1, 12,000 gallon-capacity storage tank totally filled with a 20 weight percent solution of aqueous ammonia is postulated to catastrgphically rupture.
The spilled liquid is confined within a 134 m' bermed area surrounding the storage tank (height of berm
= 2 feet).
2.
The boiling temperature of the spilled liquid (approximately 46.670C = 1160F) is higher than the ambient atmospheric temperature at the time of the postulated spill. [ Note:
the boiling temperature of 20 weight percent aqueous ammonia is higher than the highest unique maximum temperature recorded at Sacramento or Stockton, California, as reported in the RSNGS Updated Safety Analysis Report, Appendix 2B (Meteorology) Table V.] The evaporating liquid produces a continuous "plume" release of ammonia from the surfaces of the bermed area.
3.
Wind drives the released ammonia directly from the spill location to the Control Room normal HVAC system outside air intake.
4 Atmospheric dispersion fac: ors are calcula+.ed using the dispersion models in NUREG-0570 for four different combinations of meteorological conditions (refer to Section 3.2 for a description of these scenarios and their derivation).
5.
The Control Room HVAC system contains no monitoring instrumentation to detect the presence of ammonia, alert the operators to its presence, or initiate automatic isolation of the Control Room from outside air.
Operators are assumed to rely on odor detection as the sole detection mechanism.
Their immediate action upon detection of the ammonia odor is to commence the donning of protective breathing equipment, which is assumed to require 2 minutes to complete.
No credit is taken for operators to effect manual isolation of the Control Room, although this capability does exist. The Control Room HVAC system is assumed to operate in the "normal" mode throughout the duration of the acci dent. -.. - -
3.2 tiETEOROLOGY Five years of meteorological data were recorded on an hourly basis from a tower at RSNGS. This data was analyzed to determine conservative meteorological conditions to assume for the RSNGS aqueous ammonia Control Room habitability study. Two basic approaches were utilized:
1.
Using either total site meteorological data (Scenario A) or data for winds blowing from the west (i.e., from the onsite ammonia tanks towards the Control Room HVAC system normal outside air intake, Scenario C), the lowest 5th percentile wind speed for the relevant wind rose sectors was determined.
Then, for those same sectors, a cumulative temperature distribution was constructed considering only those hours that the recorded wind speed was less than or equal to the 5th percentile wind speed. The highest 95th percentile value of the latter crmulative temperature distribution was then selected as the ambient atmospheric temperature to be used in association with the 5th percentile wind speed.
2.
Using either total site meteorological data (Scenario B) or data for winds blowing only from the west (Scenario D), the highest 95th percentile ambient temperature for the relevant wind rose sectors was determined.
Then, for those same sectors, a cumulative wind speed distribution was constructed considering only those hours that the recorded temperature was equal to or greater than the 95th percentile temperature. The lowest 5th percentile value of the cumulative wind speed distribution was then selected as the wind speed to be used in association with the highest 95th percentile temperature.
i Table 1 shows the wind speed, temperature, and ctmospheric stability associated with each scenario, as well as the predicted number of seconds between odor detection of ammonia inside the Control Room and the time that the concentration inside the Control Room reaches
(
100 ppm.
In all cases, Control Room operators would have in excess of 2 minutes from the time of odor detection to don protective breathing equipment before the ammonia concentration inside the Control Room reached 100 ppm. Two minutes is considered sufficient time for a trained operator to don protective breathing equipment (Reference 2). Thus, for meteorological scenarios involving credible "worst case" combinations of wind speed, ambient temperature, anJ Pasquill stability at Rancho Seco, the criteria of USNRC Regulatory Guide 1.78 and Standard Review Plan Section 6.4 are met. Control Room operators are adequately protected against a i
j postulated catastrophic rupture of the onsite 12,000 gallon-capacity aqueous ammonia tank filled with a 20 weight percent solution of l
aqueous ammonia. -
- a 3.3 OTHER INPUT DATA Table 2 summarizes physical, chemical, and toxicity parameters used to analyze the postulated 20 weight percent aqueous ammonia spill, as well as plant and Control Room parameters needed to calculate ammonia concentrations inside the Control Room.
4.0 RESULTS AND CONCLUSIONS The following four graphs, corresponding to Scenarios A, B, C, and D of Section 3.2, show time history plots of predicted ammonia concentrations outside and inside the Control Room based on the analytical models, input data, and assumptions described in Section 3.0.
Relevant data points extracted from these plots are summarized in Table 3.
For all four of the release scenarios (representing credible "worst case" combinations of ambient temperature, Pasquill stability, and wind speed) operators would have in excess of the 120 seconds recommended in USNRC Regulatory Guide 1.78 between odor detection of ammonia and the occurrence of 100 ppm ammonia inside the Control Room. Thus, operators are considered adequately protected against a postulated 12,000 gallon onsite release of 20 weight percent aqueous ammonia solution.
5.0 REFERENCES
[1] Letter from G. C. Andognini to F. J. Miraglia, Jr., (GCA 88-104), dated February 25, 1988, Attachment 4, "Control Room / Technical Support Center (TSC) Habitability Study: Aqueous Amnonia Concentrations."
[2] NRC Regulatory Guide 1.78, "Assumptions for Evaluating Habitability of a Nuclear Power Plant Control Room During a Postulated Hazardous Chemical Release," June,1974.
[3] Wing, J.1979, Toxic Vapor Concentrations in the Control Room Following a Postulated AccidonLat Release.
USNRC, Washington, DC, NUREG-0570 _ -
TABLE 1
SUMMARY
OF RSNGS CONTROL ROOM HABITABILITY FOLLOHING A POSTULATED 12,000 GALLON ONSITE SPILL OF 20% AQUE0US AMHONIA Meteorological Time Between Odor Canditions At Time Of Spill Detection And Occurrence Of 100 ppm Spill Hind Speed Pasquill Ambient Ammonia Inside The RSNGS Scenario (m/s)
Stability Temoerature (*C)
Control Room A
0.82 G
-23.15 14 min 59 sec B
1.70 E
29.86 6 min 49 see C
1.00 F
24.32 5 min 16 sec D
1.81 E
32.81 6 min 8 sec l
Page 1 of 2 TABLE 2 PARAMETERS USED FOR CALCULATING AMMONIA CONCENTRATIONS IN THE CONTROL ROOM Parameter Value Physical and Chemical Properties of 20% Ammonia Solution Molecular Weight 35.05 g/ mole Boiling Point, 20 Weight Percent Ammonia 46.670C in Water Density of Liquid 0 23.1500 (Scenario A) 0.9220 g/cm3 0 29.860C (Scenario B) 0.9190 g/cm3
@ 24.3200 (Scenario C) 0.9210 g/cm3 0 32.810C (Scenario D) 0.9178 g/cm3 Vapor Pressure of Solution 0 23.1500 (Scenario A) 287.0 mHg 0 29.860C (Scenario B) 384.67 mHg i
0 24.320C (Scenario C) 302.25 mHg 0 32.810C (Scenario D) 433.70 mHg l
l Flow Regime of Air Over Liquid Surface Scenario A Laminar Scenarios B, C, and D Turbulent Mass of Solution 4.2 x 107 g 1
i l
~
^
Page 2 of 2
. TABLE 2 Parameter Value Toxicity Parameters Odor Detection Threshol'd of Ammonia 46.8 ppm by volha Two-minute Toxicity Limit for Ammonia 100 ppm by (as defined in USNRC Regulatory Guide 1.78) volume Plant and Control Room Pararheters Straight Line Distance, Aqueous Ammonia 152m Tank to RSNGS Control Row Normal HVAC System Outside Air Intake Surface Area of Ammonia Tank 134m2 Containment Berm Length of Spill Area 11.6m Control Room Net Free Volume 55,300 ft3 3
Normal Control Room HVAC System -
810 ft / min Outside Air Makeup Rate 3
Normal Control Room HVAC System 810 ft / min Exhaust to Outside Air Height of Turbine Building (used for 18.3m i
particle building wake credit)
P
[
O' TA_B1L3 EFFECT OF A POSTULATED 12,000 GALLON, 20 HEIGHT PERCENT AQUEOUS AMMONIA SPILL ON CONTROL ROOM AND TSC PABITABILITY Time Available Predicted Peak Concentration Seconds After Release Seconds After Release For Control Room Of Ammonia At Control Room That Ammonia Odor That Control Room Operators To Accident Normal HVAC System Outside Is Detectable In Ammonia Concentration Don Protective
_Srenario Air Intake (opm)
Control Room Reaches 100 Dom Breathina Eauipment A
320.2 ppm 841 seconds 1740 seconds 899 seconds B
626.9 ppm 419 seconds 828 seconds 409 seconds C
774.0 ppm 413 seconds 729 seconds 316 seconds D
695.0 ppm 384 seconds 752 seconds 368 seconds 1
~~
'