ML20085M734
| ML20085M734 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 10/24/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20085M728 | List: |
| References | |
| NUDOCS 9111120127 | |
| Download: ML20085M734 (4) | |
Text
_ _ _ _ _ _ _ -
J
- pa arcg'e UNITED STATES I
'n NUCLEAR REGULATORY COMMISSION
,, c
$.g W ASHING TOP O C.20555 5AFETY EVALUATJON,,B,Y,_
0 F F 1 C E, O F, N,U,CL,E AR,,RE ACTO R, P E,GUL,ATJ ON e
SUPP00 TING At'ENDMENT NO.132 TO FACILITY OPERATING LICENSE NO. DPR-28 VERM0Ni Y4:KEE,NUCLEAf, P0yj,R COP,Ppf,A,TJpp VERMONT YANKEE NUCLEAR POWER STATION 00CKET t:0., 5,0,,2,71 l
1.0 It!TRODUCTION By letter dated January 15, 1991, as suppkmented May 16 and July 12, 1991, the Vermont Yankee Nuclear Power Corcoration (the licensee) submitted a request for changes to the Vermont Yankee Nuclear Power Station (VY or plant) Technical S-ecifications(TS). The requested changes would eld.
late the Technical Specification (15) requirements for the Toxic Gas Mori coring System. The tiay 16 and Jel.v 12, letters provided clarifying information that did not change the initial proposed no sipificant hazards consideration determination.
20 BACKGR0VHD The *.oxic gas monitoring system at the Vermont Yankee Nucleue Power Statior, was
' stalled to meet thi vntrol room habitab) tity requiremen'.s of item III.v.3.4 in NUPEG-0737, ' TM1 (tion Plan," Noveirber 1980. Technical Specification Sect'on 3.2J and 4.2J specify, respectively, the limiting conditions for operation and surveillan'ce requirements for the monitoring system.
Since the installation of the toxic gas monitoring systeni, the iictnsee, Vermont Yankee Nuclear Power Corporatit;n, has encountered several false alarms and spurious trips per operating cycle. The licensee has spent considerable amounts of resources on calibration, preventive maintenance, and corrective efforts to address these operating difficulties, by letters dated January '5 and July 12, 1991, the licensee proposed to eliminatt the toxic gas monitoring requirements and to delete Sections 3.2J and 4.2J from the Technical Specifications.
The licensee provided a probabilistic analysis to support the proposed change.
9111120127 911024 PDR ADOCK 05000271 p
PDR S
. 3.0 EVALUATION The licensee has identified chlorine as a potential hazard to control room habitability following a postulated accidental spill from a railroad shipment. The concentration of chlorine gas from an accidental release would oot meet the accepttoce criteria of Section 6.4, Control Room Habitability, in the NRC Standard Review Plan (NUREG-0800, July, 1981). Other toxic chemicals that are transported near tho plant site would not have significant impacts on control room habitability.
In the probabilistic analysis, the licensee assumes that the annual probability of chlorine gas reaching the air intake of the control room following an accidental release is the product of the annual train accident rate per mile, conditional probability that a significant release will occur (given an accident), annual number of railroad shipments within a five-mile radius of the plant, the length of railroad track within the five-mila radius of the plant, and the ar.nual distribution of wind speeds and meteorologict' stability of the plant site that could disperse the chlorine plume to the concrol room air intake. The analysis is performed over 17 discrete segmants along the railroad track, and the results of these 17 segments are sunned to give the overall probability.
Using the railroad shipment data and the site meteorological data, the licensee estimates that the annuil probability of a postulated accideatal spill of chlorine that results in ex aeding the toxicity level in the control room is 4E-7 (that is, four times ten raised to the minus seventh power).
This is the estimated probability of loss of control room habitability at the Vermont Yankee plant as a result of an offsite accidental release of chlorine cas.
The licensee also provides an estimate of the reactor core damage frequency following such a loss of control room habitability.
In this estimate, the reactor core damage frequency is calculated from an annual frequency of plant trips, the probability of reactor core cooling failure, and the probability of containment heat reno' val failure. Combined with the probability of loss of control room habitability, the frequency of reactor core damage following an accidental release of chlorine is estimated to be 1E-11 per year.
In the analysis of control room habitability, the licensee used the average accident rate for all
.oi..' ads during the period of 1984 to 1988 from the Federal Railroad Administration, Office of Safety, U. S. Department of Transportation, dated June 1989. The annual shipment data of chlorine gas was based on a 1990 survey of the Central Vermont Railroad and " -ingfield Track which are within five miles of the plant site. The orocabil'ty of a release, given an accident, was estinated from the accident data,nvolving all ha'ardous materials f;am the Federal Railroad Administration, Off.ce of Eurety.
The probability of a significant release, given a release, was determined from the actual chlorine incident data fram the U. S. Department of Transportation for the years 10,1 through 1989.
Known plant site meteor 71ogical data were used.
, The licenste has provided a discussion of the uncertainties of the parameters used in the analysis.
The staff has determined that the nethodology in the licensee's analysis of control rooto habitability is appropriate.
The assumptions are reasonable and conservative as the accident rate iicludes all accidents (thct is, derail-nents, fires, chemical spills, etc.). The data used in the analysis are reasonable, current, and based on reliable sources.
The staff has also determined that the probability of loss of control room habitability is small and meets the acceptance criteria of Section 2.2.3 of the NRC Standaro h i
an.
Powever, the staff notes that the estimated frequency of loss of control rcuin habitability, though small, is nevertheless close to the acceptance criteria of Section 2.7.3 in the Standard Review Plan. Therefore, since chlorine shipments via railroads nay change from time to time, and since the quantity of chlorine in each cargo may vary from shipment to shipment, the staff and licensee agreed to a repo-ting requirement as follows:
Every three years, starting in 1984, the licensee shall submit, a report providing the annuai frt;uency of railroad shipment: of bulk chlorine within five miles of the plant site in order to verify that the probability of loss of control room habitability meets the acceptance criteria of Section ?.2.3, of the NRC Standard Review Plan (NUREG-0800, July 1981).
The report will also consider any changes in the quantity of chlorine in each shipment. The report shall reference the number and date of this license amendment.
On the basis of the above e"aluation,
..ie staff concludes that the proposed deletion of Sections 3.2J and d.2J from the Technical Specifications of the Vermont Yankee Nuclear Power Station is acceptable, subject to the reporting requirement stated above.
4.0 STATECONSULTAJION In accordance with the Commission's regulations, the Vermont State official was notified of the proposed istuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL _CONSIDERATI[;
The amendment changes a requirement with respect to installation or use of e f acility component located within the restricted area as defined in 10 CFR Part 20.
The NRC staff has determined that the amendn.ent involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be reieased offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no pubi1c comment on such finding (56 FR 4873). Accordingly, the amendment meets the a
s
. eligibility criteria for categorical Exclusion set forth in 10 CFR 51.22(c)(9).
)
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental l
assessment need be prepared in connection with the issuance of the amendment.
a
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reascnable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will nct be inimical to the common defense and security or to the health and safety of the public.
Principal Cont.-ibutor: J. Wing Date: October 24, 1991 O
i t
i i
n
- _ _ - - _ _ _ - _ _ _ _ _ _ _ _ - -