ML20198Q403
| ML20198Q403 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 10/28/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20198Q384 | List: |
| References | |
| NUDOCS 9711120202 | |
| Download: ML20198Q403 (4) | |
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WASHINGTON, D.C. 30M6-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO CONTROL ROOM HABITABILITY RE0VIREMENTS OMAHA PUBLIC POWER DISTRICT FORT CALHOUN STATION. UNIT.NO. 1 DOCKET NO. 50 285
1.0 INTRODUCTION
By letter dated August 19, 1994, Omaha Public Power District (the licensee),
submitted an evaluation of the effects of an accidental release of toxic chemicals stored in the newly constructed Cargill Corn Milling and Processing Facility (Cargill) or transported on the highway or by the ra11 road (Reference 1),
lhe licensee responded to staff requests for additional information by letters dated January 17, 1995, and April 5, 1995.
The Cargill facility was constructed in the vicinity of the Fort Calhoun nuclear plant and there is a concern that the accidentally released toxic chemicals can infiltrate into the control room and incapacitate the operators.
The plant toxic gas monitoring system (TGMS) can monitor the following six toxic chemicals: ammonia, hydrazine, hydrochloric acid, hydrofluoric acid, sulfuric acid and chlorine.
However, operation of the Cargill facility involves use of some toxic chemicals, which cannot be monitored by the TGMS.
The licensee has demonstrated that there is no need to monitor them, because they will never pose any significant safety hazard. The chemical concentrations will either be below the levels at which the control room operators could be incapacitated, or the probability of their release is so low that the resulting hazards need not to be considered.
2.0 EVALUATION 2.1 Identification and Evaluation of Toxic Chemicals OPPD has determined that the corn milling and processing facility (Cargill) near the Fort Calhoun Station (FCS) contains potentially toxic chemicals which were not previously aodressed. The licensee stated that the Cargill facility uses seven chemicals which have been classified as toxic per Regulatory Guide (RG) 1.78, " Assumptions for Evaluating the Habitability of a Nuclear Power Plant Control Room During a Postulated Hazardous Chemical Release," as well as by the EPA's Extremely Hazardous Materials Lists,. Those chemicals are:
sulfur dioxide, ammonia, carbon dioxide, hydrochloric acid, sulfuric acid, gasoline and ethanol.
The Cargill facility is located 1.3 miles due north of FCS, and therefore any spills of a toxic material which occur at the Cargill
' Journal of Applied Toxicology, Volune 3. No. 6 (1983), pp. 272-290.
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2 facility were considered. Cargill ships toxic materials on a railroad spur, located on the FCS site, that passes within 0.4 mile of the plant.
The im)act of a rail car spill was considered.
Four different chemicals are ship)ed )y rail: gasoline, ethanol, carbon dioxide and sulfur dioxide.
Cargill slips toxic material on U. S. H10hway 75 which is a closest point) from the control room intake. p>roximately 0.7 miles (at its Tive different chemicals are transported on the highway:
ethanol, carbon dioxide, hydrochloric acid.
sulfuric acid and gasoline. The postulated explosion of a rail car is considered to be more severe than a possible explosion on the highway with respect to structural safety.
The TGMS can monitor only three of these seven chemicals:
ammonia, hydrochloric acid and sulfuric acid. The licensee is, therefore, required to submit evaluations of the effects that the rGease of the remaining chemicals (sulfur dioxide, carbon dioxide, gasoline and ethanol) will have on the control room habitability.
The licensee chose not to take credit for chemicals monitored by the TGMS and evaluated all the chemicals in the Cargill facility.
The staff finds that the licensee's site description of the Cargill facility in relation to FCS and the identification of the toxic chemical materials are acceptable since they are consistent with Sections 2.2.1 - 2.2.2 of the Standard Review Plan (SRP) and RG 1.78.
2.1 Deterministic Analysis The licensee performed two types of analyses: deterministic and 3robabilistic.
In the deterministic analyses the licensee calculated a
)uildup of toxic chemicals inside the control room, after an accidental release either from the Cargill facility or during transportation.
The licensee did these calculations using the T0XIC 5.2-computer code and following the guidance of RG 1.78.
The T0XIC 5.2 code is a dispersion modeling code based on the Pasquill-Gifford equations.
By including different parameters characterizing toxic chemical releases, the code can predict the movement of toxic clouds from accident sites and can calculate buildup of toxic chemical concentrations within the control room. A toxic chemical is considered not to cause any safety hazards when, either its concentration in the control room never reached toxicity limit or at least two minutes elapse between the time the o>erating crew smells the chemical and the time when the toxicity limit is reacled.
For the odor threshold values, the concentrations
- of toxic chemicals specified in Reference 2 were used.
Except for carbon dioxide. "immediately dangerous to life and health" (IDLHi values were used as the toxicity limits.
Since the IDLH is defined as a maximum concentration of toxic substances, which could be tolerated by humans for 30 minutes, its use as toxicity liinits for a two-minute exposure is a conservative assumption.
In the case of carbon dioxide, which acts as an asphyxiant, control room habitability was assumed to be lost when its concentration reached the asphyxiation level specified in RG 1.78.
The results of the licensee's analyses have indicated that hydrochloric acid, gasoline and ethanol, stored at the Cargill facility meet the above safety criteria and sulfuric acid need not to be considered, because of its low volatility.
Similarly, carbon dioxide, sulfur dioxide, gasoline, and ethanol
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3 transported by the railroad and all the chemicals transported on the highway meet these criteria.
However, sulfur dioxide, ammonia, and carbon dioxioe i
stored in the Cargill facility and sulfur dioxide transported by rail failed to meet the deterministic safety criteria, because their accidental release would produce the conditions which could incapacitate control room o>erators.
4 For these chemicals the licensee performed probabilistic analyses (P%s).
2.2 Probabilistic Analysis The licensee's PRA review reported that the combined core damage frequency from all these four chemical releases would be 5x10'9 The Standard Review Plan (SRP). NUREG 0800 states that. "The ex>ected rate of occurrence of potential exposure in excess of the 10 CFR part 100 guidelines of approximately 10*6 per year is acceptable if, when combin6d with reasonable qualitative arguments, the realist 1C probability can be shown to be lower."
The staff has reviewed the licensee's deterministic and probabilistic analyses.
The staff independently verified the calculations of the toxic chemicals buildup in the control room using the NRC's H/ BIT computer code.
This review indicated that the licensee's 3redictions of the concentrations of toxic chemicals in the control room atmosplere are more conservative then the concentrations calculated by the HABIT code. The staff has also verified the detection and toxicity limits used by the licensee in its evaluation of different toxic chemicals.
The limits for detection of toxic chemicals b smell are not precisely defined quantities and sense of smell may vary "yom person to person. Although, the values-selected by the licensee are tL best presently available, the staff recommends that in order to ensure that the control room operators will be able to promptly detect the presence of toxic chemicals, the licensee institute a suitable training program.
The PRA methodology used by the licensee is sound: the licensee of Vermont Yankee Nuclear Power Plant used a similar methodology and NRC ap3 roved that submittal by a letter dated October 24, 1991. On the basis of tiese considerations the staff concludes that probabilistic evaluations in the licensee's submittal are acceptable.
2.3 Explosive Materials General Design Criterion 4 to 10 CFR Part 50 requires that nuclear power plant structures, systems, and components important to safety be appropriately protected against the dynamic effects resulting from equipment failures that may occur within the )lant as well as events and conditions that may occur outside the plant. T1ese latter events include the effects of the explosion of hazardous materials that may be carried on nearby transportation routes.
The licenste stated that it performed an evaluation of the explosion of the hazardous material in accordance with Regulatory Guide (RG) 1.91. " Evaluations of Explosions Postulated te Occur on Transportation Routes Near Nuclear Power Piants." Materials identified for the evaluation were gasoline and ethanol.
They are both supposed to be transported by rail cars with capacities of approximately 29.000 c"11ons. The ethanol will'be transported out of the
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>1 ant at the rate of approximately 6.5 rail cars per day.
The gasoline is to i
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>e trans)orted into the plant at the rate of approximately 2 rail cars per 1
week.
T1e minimum distance that the rail cars can be from the plant control room air intake is estimated to be 0.4 miles, The only potentially i
l explosive / flammable materials which were not considered in the analysis were
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small volumes of cleaning solvents, less than or equal to 2 gallons.
i The licensee also stated that two types of explosions were analyzed. One type assumed detonation of the entire contents of a rail car anywhere on the line or a tank at the Cargill site.
The other type considered detonation of a
-drift;ng vapor cloud. These were analyzed for the effects of over pressures 4
i and dynamic particle velocities and compared to site design criteria. The L
analysis is acceptable because it is in accordance with the guidelines i
prescribed-in RG 1.91.
The staff concludes that the licensee's analysis is adequate to assure the structural safety of the plant for )ostulated explosions of hazardous j
materials that are appropriate to tie Cargill site.
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3.0 CONCLUSION
l The staff concludes that the toxic chemicals stored in the Cargill facility or i
transported on the highway or by rail will not pose safety hazards to the Fort Calhoun plant. Although, the monitoring systm (TGMS) at Fort Calhoun will not have the capability to monitor all of these chemicals, the licensee i
submitted an acceptable proof that most of them would never reach the level at i
which they could incapacitate the control room operators.
For the few-toxic s
chemicals that could not meet this condition, the licensee has performed PRA l
analysis, that indicated that their accidental release and penetration into the control room is so unlikely that their prese..ce near the plant can be ignored. Based on these considerations, the staff finds the licensee's submittal acceptable.
Principal Contributors:
K. Parczewski S. Kim 4
L. Brown R. Wharton i
Date: October 28, 1997 1,
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