ML20204C463

Safety Evaluation Supporting Amend 162 to License DPR-36

ML20204C463
Person / Time
Site:	Maine Yankee
Issue date:	03/16/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20204C453	List: ML20204C450 ML20204C456 ML20204C463
References
NUDOCS 9903230105
Download: ML20204C463 (5)

Text

. -. _ .= . . . . _ , .. - . - -.

- w

,/*""%

y *

'g UNITED STATES j l

;; NUCLEAR REGULATORY COMMISSION l o '8 WASHINGTON, D.C. 2056H001 l k 8 J

• • • • • ,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION 1 RELATED TO AMENDMENT NO.162 TO FACILITY OPERATING LICENSE NO. DPR- 36 ,

l l MAINE YANKEE ATOMIC POWER COMPANY MAINE YANKEE ATOMIC POWER STATION l DOCKET NO. 50-309

1.0 INTRODUCTION

By letter of April 13,1998, as supplemented by letter dated November 5,1998, Maine Yankee Atomic Power Company (MYAPC or the licensee) submitted a request for a change to the Maine Yankee Atomic Power Station (Maine Yankee) Facility Operating License No. DPR-36. Tht; requested change would revise the Appendix A Technical Specifications (TS) of License No. DPR-36 to change the Limiting Condition for Operation for the spent fuel storage pool water level based on a revised analysis of the fuel handling accident and on a new analysis for radiological shielding during movement of irradiated fuel. Specifically, the requested TS change would revise TS 3.1.1 " Fuel Storage Pool Water Level" to require a fuel storage pool water level greater than or equal to 21 feet above the spent fuel during movement of irradiated fuel assemblies in the fuel storage pool. Currently, the TS limit is 23 feet.

The supplemental information contained clarifying information that did not change the initial no significant hazards consideration and did not expand the scope of the original application.

2.0 BACKGROUND

On August 6,1997, the MYAPC Board of Directors decided to permanently cease further operation of the Maine Yankee Atomic Power Station. On August 7,1997, in accordance with 10 CFR 50.82(a)(1), MYAPC provided to the U.S. Nuclear Regulatory Commission (NRC) certifications of permanent cessation of operations and permanent removal of fuel from the reactor vessel.

In October 1997, MYAPC submitted a request to the NRC to revise the Appendix A TS of License No. DPR-36 to reflect the permanently shutdown and defueled status of the Maine Yankee facility. On March 30,1998, the NRC issued Amendment No.161 to License No.

DPR-36, which replaced the TS in their entirety. The revised TS, referred to as the Permanently Defueled Technical Specifications (PDTS), included a limiting condition for operation (LCO) and associated surveillance requirements for spent fuel pool (SFP) water l

9903230105 990316 PDR ADOCK 05000309 P PDR

\

O

~ ,

2- - .

level. This specification was determined to be necessary for inclusion in the TS because it is a limit that is an initial condition for a design basis accident, the fuel handling accident.

This specification requires that the SFP water level be maintained within limits during fuel movement and requires verification of compliance at a 24-hour frequency. The actions associated with this LCO require immediate suspension of movement of irradiated fuel assemblies in the SFP to minimize the potential for a fuel handling accident or a loss of shielding during fuel movement, in its October 1997 submittal, MYAPC stated that the minimum water level in the fuel storage pool requested in the PDTS met the assumptions of iodine decontamination factors following a fuel handling accident. Although the spent fuel fission products had actually decayed more than 9 months at the time of Maine Yankee's request, the licensee based the propossd LCO on an analysis which assumed a one week and/or 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> decay period. Thr resulting doses that were calculated for the fuel handling accident are below the values specified in 10 CFR Part 100. The specified water level also shields and minimizes the general area dose during fuel movement. In its safety evaluation of the PDTS, the NRC staff found the proposed LCO acceptable.

3.0 DISCUSSION AND STAFF EVALUATION The current TS minimum SFP level of 23 feet over the top of the irradiated fuel assemblies (44.2 feet elevation) corresponds approximately to the normal water level in the pool.

While it is possible for operators to maintain the fuel pool water level at the minimum required by the existing TS, it does not provide the operators with the desired operating margin for compliance without increasing the water to undesirable levels. Raising the water level too high interferes with the ability of the skimmers to function and floods certain electrical connections. In order to provide the operators with additional opcrating margin for compliance with the TS, Maine Yankee has requested a change to the TS that would lower the minimum level by 2 feet.  ;

The bases for the minimum water level in the SFP is to assure that the height of water available is sufficient to accommodate the radioactive iodine released following a fuel handling accident. In order to implement the proposed change, the licensee performed a revised analysis for the fuel handling accident in the SFP. The licensee's updated fuel handling accident analysis assumed an SFP water level of 19 feet and a reduced iodine decontamination factor (DF = 75) to account for the lower water level. Regulatory Guide (RG) 1.25, " Assumptions Used for Evaluating the Potential Radiological Consequences of a Fuel Handling Accident in the Fuel Handling and Storage Facility for Boiling and Pressurized Water Reactors," states in note 2, for water depths less than 23 feet (above spent fuel), the iodine decontamination factors will be less than those assumed in the guide (133 inorganic,1 organic, and 100 effective) and must be calculated on an individual case basis using assumptions comparable in conservatism to those of RG 1.25.

Standard Review Plan (SRP) Section 15.7.4, " Radiological Consequences of Fuel Handling Accidents," states that " Evaluation of Fission Product Release and Transport for a Fuel Handling Accident," G. Burley, October 5,1971, should be consulted to determine if there is an adequate basis for use of factors less conservative than those recommended in RG 1.25. The staff has determined that the licenseo assumed iodine decontamination factor of 75 is within the conservatism used in Burley (1971).

- A

. s 1

l Maine Yankee was shut down on December 6,1996. The licensee dose calculations were evaluated at 1 year after shutdown. This allowed for a radiological decay period of 1 year for the most recently irradiated fuel assemblies, thereby reducing the source term considerably. This assumption is conservative compared to the actual decay period of more than 2 years for the newest fuel assemblies. The licensee-calculated offsite doses (0.195 millirem thyroid, and 0.224 millirem whole body at the Exclusion Area Boundary) are well within 10 CFR 100 acceptance criteria. Also, the licensee-calculated doses at the Control Room Intakes (4.3 millirem thyroid and 7.2 millirem whole body) se well within 10 CFR Part 50, General Design Criterion 19 acceptance criteria in consideration of the licensee's conservative assumptions of reduction of the iodine decontamination factor due to the reduced level of the SFP and a 1 year radiological decay period, the staff has found the licensee-calculated control room and offsite dose consequences to be acceptable.

The proposed change would allow the Fuel Storage Pool water level to be lowered by two feet from the existing TS requirement. This would decrease the amount of radiation shielding afforded by the overlying water. The licensee has performed a radiation shielding analysis to determine the maximum dose rate expected at the fuel handling platform and walkway around the pool. The calculations assumed a bounding water level of 19 feet and a raised fuel assembly at the maximum height of eighteen inches above the top of the stored fuel. The resulting calculated dose rate was 50 mrem /hr. The licensee's shielding calculations are acceptable. Although the radiation shielding of fuel assemblies does decrease, the staff's experience is that the activity in the spent fuel pool water, rather than shine from fuel assemblies, is the limiting contributor to the dose rate above the pool. The licensee's health physics program is designed to allow work processes at dose rates well above 50 mrem /hr and still control occupational exposure within the limits of 10 CFR Part 20. Therefore, the proposed change is acceptable. Moreover, the licensee plans to maintain the pool well above the requested TS level of 21 feet, at just a few inches below 23 feet. This plan would generally maintain the maximum level of water shielding consistent with the ALARA principle for occupational exposure.

The TS bases for minimum SFP water do not address decay heat removal capability of the SFP cooling system and the licensee has performed analyses that demonstrate that the fuel, storage racks, and SFP structural components are capable of withstanding sustained boiling. Nonetheless, the licensee evaluated the effect of the proposed SFP water change on the normal operating function of the spent fuel pool cooling system, the purpose of which is to remove oecay heat from the SFP water to maintain SFP temperature within a normal range. Pool temperature is normally maintained below 120*F. When the level decreases below 6 inches from the current normal operating level, the skimming function of the spent fuel pool purification system, if in operation, will be interrupted. However, the loss of skimming function does not impact the ability of the spent fuel pool cooling system to remove decay heat.

\

7 e .

The other effect the proposed water level change will have on the spent fuel pool cooling system is on the spent fuel pool cooling pumps. This effect is related to net positive suction head and the increased possibility of vortexing at the siphon protection piping (located at elevation 40 feet,11 inches) and potentialintroduction of air into the pumps.

The licensee performed calculations that determined that two spent fuel pool cooling pumps may be operated at a SFP water level that correspond f o 43-feet elevation or above without impacting the minimum net positive suction head and without vortex-induced air entrainment. At SFP levels below the 43-foot elevation, SFP cooling pump operation must be limited to one pump to prevent vortex-induced air entrainment. At high temperatures (above approximately 200*F) or SFP level below the 43-foot elevation, some throttling of SFP cooling flow is required to prevent vortex-induced air entrainment. The licensee has committed to maintain administrativc controls to restrict operation to one pump or throttled flow if these conditions exist. The effects on the 9FP cooling system are acceptable because, as discussed above, the licensee's analysis has demonstrated that the proposed water level change will not adversely affect the SFP cooling and cleaning system from performing its intended functions. Furthermore, an analysis of the SFP demonstrates that a loss of the SFP cooling system can be sustained indefinitely if adequate makeup is supplied to restore SFP water that is lost due to evaporation. Makeup water is available frcm multiple sources.

Although the licensee has requested to lower the minimum SFP water level, it does not intend to routinely operate at this level. Maine Yankee plans to operate the SFP at the current normal level to nreserve the function of the skimmers and will provide a large <

margin for compliance with the proposed TS minimum SFP water level, when applicable.

It is the NRC staff's assessment that the change proposed in this amendment does not pose any decrease in safety, or an increase in the probability of an analyzed or unanalyzed accident. Therefore, the staff finds the proposed TS change to the minimum SFP level to be acceptable.

4.0 STATE CONSULTATION

in accordance with the regulations of the Commission, on January 26,1999, Mr. Pat Dostie of the State of Maine, Department of Human Services, was notified of the proposed issuance of this amendment. The State official had concerns regarding the potential radiological dose to members of the public in the mud flats area of Bailey Cove.

The licensee provided its analysis to the State Official, who was satisfied that the impact of the proposed change was insignificant.

5.0 ;NVIRONMENTAL CONSIDERATION The amendment changes a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that

., 7

_ _ . _ _ _ _ _ __ _ _ - _ __ _ _ _ _ . - _._ ._...._ m _. . _ _ . . _ _ . - . _ _

.g *

+.

6 -

< 1 l

there is no significant increase in individual or cumulative occupational radiation exposure.

l -The Commission has previously issued a proposed finding that the amendment involves no  !

significant hazards consideration, and there has been no public comment on such finding l

(63 FR 27763). Accordingly, the amendment meets the eligibility criteria for categorical i exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

6.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that (1) there is reasonable 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 regulations of the Commission, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and i safety of the public.

Principal Contributor: Michelle Hart Michael Webb Date: March 16, 1999 i

l 1

l l

I i

I

, _ - _ , -, --