ML20071A607
| ML20071A607 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 04/06/1991 |
| From: | Creel G BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9104160336 | |
| Download: ML20071A607 (5) | |
Text
.....
i A
B Al.TIMORE GAS AND ELECTRIC CHARLES CENTER e P.O. DOX 1475
- DALTIMORE, MARYLAND 21203 1475 NUCLE AR BMETY & PL ANNING DEPARTMrNT r.antat (-ures weit An coath Pmt April 6,1991 wm u =mn mu U. S. Nuclear Regulatory Commission Washington,DC 20555 NITENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No. 2: Docke' No. 50 318 Reauest for Regionni A'aiver of Comnlinnce
REFERENCE:
(a) Letter from hir. G.C. Creel (BO&E) to Document Control Desk, dated April 5,1991, same subject Gentlemen:
This letter replaces Reference (a) in its entirety. Reference (n)is hereby withdrawn.
Baltimore Gas & Electric (BO&E) Company requests a Regional waiver of compliance from certain requirements of Calvert Cliffs Unit 2 Tc;hnical Specification 3.6.1.7,' Containment Purge System."
That Specification requires, in hiODES 1,2,3, and 4, that "The containment purge supply and exhaust isolation valves shall be closed by isolating air to the air operator and maintaining the solenoid air supply valve deenergized." We request a waiver to allow operating the containment purge supply and exhaust isolation valves in hiode 3 (llot standby) aad hiode 4 (llot shutdown) for the purpose of purging the Unit 2 containment, and to conduct local leak rate testing (and repairs, if required) of the containment purge valves upon completion of the purge. If any of the four containment isolation valves falls its local leak rate test, that failed valve will be re 3 aired within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or the unit will be in cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. This a so constitutes a waiver from Technical Specifications.t6.1.1, " Containment integrity," inasmuch as containment purge applies to that Specification.
ClitCUhtSTANCES Unit 2 is in hiODE 3, in the process of starting up for Cycle 9 operation following shutdown in hiarch,1989. During the refueling outage, new insulation was installed on the Unit 2 Reactor Coolant System piping. In addition, substantial maintenance involving penetrants and lubricants in the plant has been conducted. As the plant has been heated up from cold shutdown, off gassing from the new insulation and heat up of fluid residues has unexpectedly resulted in high levels of carbon monoxide inside the containment building. While some work can be completed wearing breathing equipment, in order to allow for personnel access to complete all necessary maintenance and gh 9104160336 910406
/
1*
PDR ADOCK 05000318 1
105 P
PDR I O
' Document Control Desk April 6,1991
, Page 2 surveillance items the containment must be purged. If the containment is not purged in MODE 3 or 4, the unit will have to be cooled down to MODE S (cold shutdown) then heated back up, causing an unnecessary transient on the plant. This would also delay starting up Unit 2.
The situation could not be avoided. Similar insulation was installed on Unit 1, but far las new insulation was necessary and the phenomenon did not occur Previous outages resulted in lower concentrations of contaminants, but it was impractical to quantify the expected concentrations or to eliminate them before plant heatup. Therefore, no basis existed for expecting this phenomenon during this startup.
l SAlYlY SIGNIFICANCE ANI) POTENTI Al, CONSEOUENCES The contaktment purge system includes a sup31y acnetration with a supply fan and two 48 irnh butterfly valves for containment isolation, one lnsk e and one outside containment, and an exhaust 3enetration with an exhaust fan and two 48 inch butter 0y valves for containment isolation, again one nside and one outside containment.
Purging the Unit 2 containment will!nvolve opening these 481nch air. operated butter 0y valves at the supply and the exhaust containment penetrations. These are openings that are normally shut in MODES 1 through 4 due to Loss of Coolant Accident (LOCA) considerations. If a LOCA occurs while purging, a release of a portion of the wntainment atmosphere would be possible before the valves are thut.
I Unit 2 has been shut down for over two years. The decay heat of the reactor is very low. Therefore the chances of overheating of the fuel, fuel failure, and introduction of fission products into the reactor coolant are also low. The activity in the reactor coolant is also low. If a LOCA did occur, the overall activity concentrations of any released containment atmosphere would be very low relative to l
previous accident analysis conditions. Also, the actual time of purging will be minimlied, further reducing the chance that the worst case of a LOCA while purging could occur, An evaluation was performed to assess the consequences of a LOCA while purging containment for the present decay heat and Reactor Coolant System conditions. The source term considered to leak from the containment in the current LOCA analysis consisted of 100% of noble gases and 50% of halogen fission product gases contained in the fuel. These fission products were decayed the appropriate amount to reflect current conditions and conservatively assumed to be totally released to the environment in analyzing the effects of a potential LOCA during purge. The results for whole body dose were 4.2 rem, which is greater than the present accident analysis result of 2.2 rem but is far below the 10 CFR Part 100 limit of 25 rem. The thyroid dose result was lower than the prescat analysis result due to the decay ofiodine, the primary contributor to that dose.
A walkdown of the plant's main ventilation system was conducted to evaluate the potential effects of its failure in the event of a LOCA steam pressure transient during purging. The location of the piping was determined to make any effect on the control of Unit 1, which is operating, unlikely. That
i
' Document Control Desk i
April 6,1991 Pagh3 equipment necessary to maintain reactor coolant inventory and decay heat removal for Unit 2 would aho be unlikely to be incapacitated.
COMPl NS ATOltY ACTIONS After the final purge and prior to Unit 2 entry into MODE 2, the containment purge sunply and exhaust isolation vahrs will be local leak rate tested.
Iloric acid concentration will be rnaintained greater than 20(K) ppm and all Control Element Assemblics will be fully inserted until satisfactory local leak rate testing of all purge valves.
1)URATION (R WAlVICR This weber is requested for as long as Unit 2 does not enter MODE 2 (Startup) or for seven days, whichever occurs first. Purging will be scheduled to optimize containment carton monoxide removal while minimizing purge time. The majority of the required purging is expected to be completed with the initial purge, but additional puiges may be necessary to address any delayed off gassing.
J.l ASIS l'OR NO SIGNil'ICANT ll AZARI)S CONSJJ)E)(ATIONS The proposed waiver has been evaluated against the standards in 10 CI R 50.92 and has been determined to not involve a significant hazards considerMion, in that operation of the facility in accordance with the proposed waiver:
(1) li'ould not imahe a significant increase in the probability or comequences of an accidentpreviously evaluated.
The probability of previously evaluated accidents is not affected by this waiser, because the change m containment ventilation does not impact any LOCA initiation scenano.
The consequences, however, are affected. An evaluation was performed to assess the consequences of a LOCA while purging containment for the present decay heat and Reactor Coolant System conditions. The source term considered to leak from the containment in the current LOCA analysis consisted of 100% of noble gases and 50%
of halogen fission product gases contained in the fuel. These fission products were decayed the appropriate amount to reflect current conditions and conservatively assumed to be totally released to the environment in analyzing the effects of a potential LOCA during purge. The results for whole body dose were 4.2 rern, which is greate, than the present accident analysis result of 2.2 rem but is far below the 10 1
' Document Control Desk April 6, tw1 i
Page 4 j
CFR Part 100 limit of 25 rem. The thyroid dose result was lower than the present analysis result due to the decay of iodine, the primary contributer to that dose.
Additionally, the likelihood of failure of the fuel assemblies which would result in the fission product release is substantially reduced because of the lower heat generation of the fission products in the fuel. Consideration of a similar case when analyzing long decayed fuel (3 years decayed) indicates that they would be sufficiently cooled in air to prevent fuel failure.
Therefore, there is not a significant increase in the probability or consequences of an accident previously evaluated.
Il'oidd not create the (2) previously svaluated. possibility of a new or different type of accident from This waiver would not result in a change to the plant itself and involves an operation that is routinely carried out in other MODES. Therefore it would not create the possibility of a new or different type of accident from any accident previously evaluated.
(3)
Il'aidd not invoh c a significant reduction in a margin ofsafety.
Containment integrity is essential for limiting the potential release of activity to the environment during a LOCA.
A LOCA dunng power operations results in pressurization of the containment with activated reactor coolant plus the potential for fuel cladding failure as decay heat is generated and reactor coolant pressure is reduced. Ciudding faCure could release fission products to the Reactor Coolant System, then possibly to the containment and then possibly to the environment as well.
Calvert Cliffs Unit 2 has not been operated at power for over two years. Therefore there is very little deca coolant system is low. y heat in the reactor and the level of activity in the r The amount of purging time will be limited and analysis has shown that the worst case LOCA while purging would not result in exceeding off site dose rate limits. Given these considerations the affect on margin of safety of purging containment while in Mode 3 or 4 is not significant.
ENVIRONMENTAL,CONSEOUENCES The purge operation will introduce fresh outside air into the upper containment, while drawing air from the lower levels and exhausting it through the plant's main vent, via high efficiency filtering and
' Document Control Desk April 6,1991
, Pag' 5 e
radiation monitoring devices. The effect of the release of the small amounts of carbon monoxide in question to the environment will be negligible and not irreversible.
S AFl!!Y CONQtl1 TEE REVIEW This proposed waiver of Technical Sp:cification 3.6.1.7 and 3.6.1.1 for Unit 2 and our discussion of significant hazards considerations have been reviewed by our Plant Operations and Safety Review Committee. They concur that utilization of this waiver will not result in an undue risk to the health and safety of the public.
Very truly yours, l
)
/
h.
O
/
GCC/DLS/ dis Attachment cc:
D. A. Brune, Esquire J. E. Silberg, Esquire R. A. Capra, NRC D. O. Mcdonald, Jr., NRC T. T. Martin, NRC L E. Nicholson, NRC R. I. Mclean, DNR J, IL Walter, PSC U
Li-l f