ML20008G053
| ML20008G053 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 06/23/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20008G051 | List: |
| References | |
| NUDOCS 8107020071 | |
| Download: ML20008G053 (3) | |
Text
.
......,_-...m-s z.
p5x;;
~---
- . z, ;;u, ;.
v
.d
?
5::ETY E"ALUATIO" nY T"r 0FFICE OF HUCLEAR REACTOR REGULATIO4
- 0. ELATED TO AMENDMENT NO. 64 TO FACILITY OPERATING LICENSE NC. "?r '
PORTLA"O CC"ERf.L ELECTRIC COMPAMY THE CITY OF EUGENE. OREGON PACIFIC POWER AND LIGHT COMPANY TROJAN NUCLEAR PLANT DOCKET NO. 50-344 Introduction Guring a reanalysis of the Boron Dilution Event for hot and cold shutdown modes at the Millstone Unit 2 facility in early 1980, it was discovered that an incorrect assumption had been made, aference 1).
The analysis of this event while in Mode 5 (cold shutdown) had assumed a full reactor coolant system and a 1% shutdown margin.
The results of this analysis showed that it would take 20 minutes of uncontrolled boron dilution i
before the reactor returned to criticality. This satisfied the 15 minute minimum time interval assumed for the operators to recognize the situation and take appropriate action. However, the analysis had not considered the fact that Mode 5 operation is permitted with the reactor coolant system drained to the centerline of the hot leg.
Including this reduced volume of reactor coolant to be diluted in the analysis results in a time to rea-h criticality of less than 15 minutes.
The Millstone facility corrected this problem by revising their Technical Specifications to require a minimum 2% shutdown margin while in Mode 5.
By making this change, a time to criticality of greater than 15 minutes was established.
The staff requested the Trojan licensee to review their boron dilution event to verify that they had assumed a reduced reactor coolant system volume in their analysis' (Reference 2). The licensee's response (Reference 3 and 4) states that since Trojan's procedures have always required 100 ppm baron more than that needed for the nominal margin required by the Technical Specifications, no revisions to plant
?rocedures are necessary. However, since the Technical Specification rcquirem1nts alone do not guarantee an adequate shutdown margin during Mode 5, the licensee submitted a proposed Technical Specification change (Reference 4) to increase the Mode 5 shutdown margin.
81070 2 00M
c_
.velvatioq The licensee reanal.yzed the boron dilutten event assuming a draineu down reduced reacter ccchnt system volump ano tne most reactive contrcl red stuck out of the core. The maximum dilution capability is limited ::y the design flow of the Primary fiakeup Water pumps which total 300 gpa when both pumps are running.
The licensee's analysis concludes that the most limiting conditions with regard to reduction of shutdown margin occurs for the case of one RHR During Mode 5 operation, pump running and the maximum dilution flow.
the minimum Technical Specification requiremants do not guarantee an adequate shutdown margin during periods of FCS boron concentration greater than approximately 1250 ppm.
-The licensee has proposed revising Technical Specification 3/4.l.1.1, which requires a minimum shutdown margin of 1.6% Ak/k for plant operating Modes 1 through 4, to also include plant operating Mode 5.
Technical Specification 3/4.1.1.2, which requires a 1.0% ak/k for Mode 5 operation, would be deleted. The Technical Specification Bases has also been modified to state that the boron dilution event is the limiting condition for Mode 5 operation (Tavg6200*F).
We have reviewed the licensee's submittal and conclude that a conservative
. boron dilution event has been analyzed. Assuming a conservatively low value for the reactor coolant system volume and the maximum boron dilution rate, the licensee has shown that by increasing the Mode 5 shutdown margin to 1.6% ak/k, there will be at least 15 minutes (as required by SRP 15.4.6) before the reactor returns to criticality.
The Trojan operating precedures also calls for maintaining 100 ppm boron more than the minimum Technical Specification requirements so i
that additional margin will be available.
l Therefore, we conclude that the proposed Technical Specification changes are acceptable.
7 Environmental Consideration l
We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level sad will not result in any significant environmental impact. Having made l
this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 551.5(d)(4), that an envirormental impact statement or negative declaration and environ-I mental impact appraisal need not be prepared in connection with the issuance of 'this amendment.
y
.,.+rr
Conclusion Uc have concluded, casen na Ine cnnsiderations discussed above that; fli cecause the amendmeni dues not involve a significant ir.:r::::
in the p. ;bability or consequences of accidents previously consicereo and coes not involve a:significant decrease in a safety margir., tr.:
amendment does not invol,e a significant hazards consideration, (2) tnere i: reasonable assurance that the health and safety of the public will not be endangered by cg6 cation in the proposed manner, and '3) such activities will be conducted in compliance with the Commission's regulations and the issuar.cc e.~ this amendacnt will not be inimical to the common defense and security or to the health and safety of the public.
Date: June 23, 1981 References 1.
Millstone Unit 2 LER 80-05/1T-0
- 2. _ Letter from NRC to Portland General Electric Company, dated
~
September 30, 1980.
3.
Letter from Portland General Electric Company to NRC (B.D. Withers to Director, NRR) dated November 26, 1980.
4.
Letter from Portland General Electric Company to NRC (B.D. Withers to Director, NRR) dated March 16, 1981.
4 m_
y.-
.. ~ _ = _. _ -
...,,-~.
_