ML20046B539

Submits leak-before-break Analysis to Allow Licensees to Exclude Rupture of Primary Reactor Coolant Piping from Design Basis.Description of Permanent Neutron Shield/Pool Seal Encl

ML20046B539
Person / Time
Site:	Calvert Cliffs
Issue date:	07/29/1993
From:	Denton R BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9308050096
Download: ML20046B539 (10)

Text

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6 BALTIMORE GAS AND ELECTRIC ,

1650 CALVERT CLIFFS PARKWAY . LUSBY, MARYLAND 20657-4702 ROBERT E DENTON VsCE PRE 51 DENT NUCLE AR ENERGY (4so)200-4455 July 29,1993 U. S. Nuclear Regulatory Commission Washington,DC 20555 ATTENTION: Document Ccmtrol Desk i

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 ,

Installation of a Neutron Shield / Pool Seal at Calvert Cliffs Units 1 and 2 ,

REFERENCES:

(a) Topical Report CEN-367-A, " Leak Before Break Evaluation of l Primary Coolant Piping in Combustion Engineering Designed Nuclear Steam Supply Systems, February 1991 7

(b) Letter from Mr. J. E. Richardson (NRC) to Mr. E. C. Sterling l (CEOG), dated October 30, 1990, Acceptance for Referencing of  !

Topical Report CEN-367,

• Leak-Before-Break Evaluation of Primary l Coolant Imop Piping in Combustion Engineering Designed Nuclear  :

Steam Supply Systems" l

Baltimore Gas and Electric Company (BG&E) plans to install a permanent neutron shield / pool seal over the reactor vessel annulus in both Calvert Cliffs Units 1 and 2. We expect the new shield to ,

reduce BG&E's personnel radiation exposure rates long term by reducing the time and the number  ;

of personnel required to install and remove the existing neutron shield and pool seal. We also expect to decrease our outage times by reducing the time it takes to establish a good seal and restore the reactor vessel annulus to its normal operating condition. The shield deJgn and installation requires a change to our compliance with General Design Criteria (GDC) 4. As required by GDC 4, we are submitting our leak-before-break analysis to allow us to exclude a rupture of the primary reactor i coolant piping from our design basis. This will allow us to close off the top of the reactor vessel annulus with the neutron shield / pool seal. A description of the permanent neutron shield / pool sealis provided in Attachment (1).

Reference (a) is a description of the leak-before-break analysis performed by Combustion Engineering for their nuclear steam supply systems. The report is applicable to Calvert Cliffs. This topical report has been approved for our use by the NRC (Reference b). We wish to reference the topical report in support of the neutron shield installation. A brief discussion of the applicability of the report to Calvert Cliffs is provided in Attachment (2). In addi' ion to the leak-before-break analysis, the report requires that we submit a description of our leakage detection system to ensure it has the necessary sensitivity. This information is provided in Attachment (3). , i 9308050096 930729 PDR n e. ~ .--

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Document Control Desk July 29,1993 Page 2 By this letter, we are informing the NRC that we intend to use CEN-367-A as 9 technical basis for

] applying leak-before-break to the primary coolant piping. In addition, we are providing a description of the leakage detection system at Calvert Cliffs. We request NRC concurrence that installation of a

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permanent neutron shield over our reactor vessel annulus is consistent with GDC 4. We anticipate installing the new neutron shield / pool seal in Unit I during the scheduled refueling outage in the opring 1994. Therefore, we request NRC concurrence by January 15, 1994. The new neutron shield / pool seal is scheduled to be installed in Unit 2 in the spring 1995 refueling outage.

L Should you have any questions regarding this matter, we will be pleased to discuss them with you.

i Very truly yours,

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[ C RED / PSF / psf! dim Attachments: (1) Permanent Neutron Shield / Pool Seal Description ,

(2) Leak-Before-Break Analysis (3) Description of Leakage Detection System l

l cc: D. A. Brune, Esquire J. E. Silberg, Esquire R. A. Capra, NRC D. G. Mcdonald, Jr., NRC T. T. Martin, NRC P. R. Wilson, NRC R. I. McLean, DNR J. IL Walter. PSC l

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'. : I ATTACIIMENT (1) j PERMANENT NEUTRON SIIIELD/ POOL SEAL DESCRIPTION 1

The bottom of the refueling pool surrounds the upper part of the reactor vessel in the vicinity of the )

reactor vessel head flange for both Calvert Cliffs Units 1 and 2. During operation, a gap exists '

between the reactor vessel and the refueling pool floor. This gap is partially covered by a neutron shield, which consists of water bags supported by a steel frame. The neutron shielding is arranged so that adequate ventilation is maintained in the reactor vessel cavity. The forced ventilation cools the concrete and instrumentation in the cavity. During refueling operations, it is necessary to remove i the existing neutron shielding and seal this gap to prevent entry of the refueling pool water into the reactor vessel cavity. The hardware used to close this gap is a removable circular seal ring made of stainless steel plate with rubber gaskets attached. After refueling is completed and the refueling pool is drained, the seal ring is removed and the neutron shield is re-installed.

in an effort to minimize personnel exposure and decrease the potential for leakage into the reactor vessel c:.vity, a permanent neutron shield / refueling pool seal ring will be installed. The attached sketch (Figure 1) shows the top view of the proposed permanent neutron shield and seal ring. The removable hatches in the seal ring provide a pathway for ventilation air, a pathway for containment spray water to reach the sump, and provide access to excore instrumentation.

Before the refueling pool is flooded, hatches will be installed on each of the access holes. The covers contain a seal that will prevent leakage from the canal to t. reactor cavity. After the refueling pool is dromed, some of these hatches will be removed to provide a ventilation pathway during plant operatimns. The hatches are located so that access to the reactor cavity and reactor vessel nozzles is maintained for inspection purposes. Excore nuclear instrumentation can also be accessed through open hatches.

Under the permanent pool seal, neutron shield material will be installed. The shield ring consists of borated concrete, enclosed in a carbon steel assembly. This shield will ensure that neutron radiation leve' emain low in the containment. Figure 2 shows the proposed arrangement of the neutron sh' eld urer the pool seal.

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. ATTACINENT (2)

LEAK-BEFORE-BREAK ANALYSIS In October 1990, the N: J completed a review of Topical Report CEN-367-A, " Leak Before Break Evaluation of Primary Coolant Loop Piping in Combustion Engineering Designed Steam Supply Systems." This topical report forms the basis for ensuring that tl e probability of a pipe rupture in the primary system is sufficiently low that it no longer has to be considered in the design basis. This concept is allowed by General Design Criteria (GDC) 4.

The resised GDC 4 is based on the development of advanced fracture mechanics technology using i the leak-before-break concept. On October 27,1987, a final rule was published, amending GDC 4 of i Appendix A to 10 CFR 50. The revised GDC 4 allows the use of analyses to climinate from the design basis the dynamic effects of postulated pipe ruptures in the high energy piping. The new technology reflects an engineering advance which allows simultaneously an increase in safety, reduced worker radiation exposure, and lower maintenance costs. Implementation permits the ,

installation of a permanent neutron shield / pool seal. Although functional and performance  !

requirements for containments, emergency cor; cooling systems, and emironmental qualification of i equipment remain unchanged, local dynamic sffccts uniquely associated with postulated ruptures in piping which qualified for leak-before-break may be excluded from the design basis. The acceptable technical procedures and criteria are defined in NUREG-1061, Volume 3. t Using the criteria given in NUREG-1061, the Combustion Engineering Owners Group (CEOG)  !'

analyzed the primary coolant piping for Combustion Engineering plants and presented their results in Topical Report CEN-367-A. The report covers the primary coolant piping for Calvert Cliffs Units 1 and 2. The NRC reviewed and approved the report in a Safety Evaluation Report dated  :

October 30,1990. The NRC Staff found that the CEOG plants (which includes Calvert Cliffs) are in compliance with GDC 4, with a limitation. The NRC Staff did not review CEOG plants' leak detection systems for conformance to Regulatory Guide 1.45. Therefore, we ace submitting a description of our conformance with Regulatory Guide 1.45 in Attachment 3.

The CEOG Topical Report specifically included Calvert Cliffs' primary coolant piping, with the exception of the pressurizer surge line, in the scope of the analysis. We have reviewed the primary i coolant piping layout in our plant to ensure there are no additional lines which should have been included in the analysis. We have found no additionallines. Therefore, the conclusion of the CEOG Topical Report applies to Calvert Cliffs without modification.

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ATTACilMENT (3) i DESCRIPTION OF LEAKAGE DFTECTION SYSTEM 1

ne leakage detection system for the Reactor Coolant System is described in detail in Section 4.3 of our Updated Final Safety Analysis Report. This system complies with the guidance given in 4 Regulatory Guide 1.45 (May 1973) as described below.

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1. Requirement Leakage to the primary reactor containment from identified sources should be collected or otherwise isolated so that:

> the flow rates are monitored separately from unidentified leakage, and

> the total Ib' rate can be established and monitored.

Method of Compth.m i r

Identified leakage is defined as any leakage into a closed system, such as pump seal or valve packing leaks that are captured and conducted to a sump or collecting tank. Other sources of identified leakage includ. leakage into the containment atmosphere from sources that are both specifically known either not to interfere with the operation of the leakage detection systems or not to be pressure boundary leakage. Additionally, reactor coolant leakage through a steam generator to the secondary system is considered identified leakage.

Section 4.3.2.2 of the UFSAR describes the instrumentation available to determine the k> cation of identified leakuge. Methods exist for identifying leakage from the relief and ,

safety valves, the reactor vessel head closure seal, the reactor coolant pump seals, the steam generator tubes or tubesheets, and any miscellaneous Reactor Coolant System valve stem i leakage.  ;

2. Requirement leakage to the primary reactor containment from unidentified sources should be collected and the flow rate monitored with an accuracy of one gallon per minute (gpm) or better.

Method of Compliance .

Unidentified leakage is any leakage which cannot be classified as identified leakage as I defined above. leakage from the Reactor Ccalant System to the containment is collected in i the containment sump. The sump level is alarmed and the sump is drained when the wate j reaches a pre-set level. The frequency of draining the sump determines the leakage flow i rate. This m-thod has an accuracy of determining leakage of one gpm in less than one hour.

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ATTACllMENT (3)

DESCRIPTION OF LEAKAGE DFT. ECTION SYSTEM

3. Requirement At least three separate detection methods should be employed and two of these methods should be: (1) sump level and flow monitoring and; (2) airborne particulate radioactivity I monitoring. The third method may be selected from the following:

> monitoring of condensate flow rate from air coolers ,

e monitoring of airborne gaseous radioactivity.

Ilumidity, temperature, or pressure monitoring of the containment atmosphere should be considered as alarms or indirect indication of leakage to the containment.

Method of Compliance ,

We have three methods of leakage detection. Two of them are the required methods of monitoring the sump level and airborne particulate radioactivity. The third method we chose was to monitor airborne gaseous radioactivity. In addition, Section 4.3 of the UFSAR contains a discussion of the sensitivity of changes in containment humidity, temperature and pressure to the leakage size.

4. Requirement l Provisions should oc made to monitor systems connected to the reactor coolant pressure boundary (RCPB) for signs of intersystem leakage. Methods should include radioactivity monitoring and indicators to show abnormal water levels or flows in the affected areas.

'r Method of Comoliance The following systems are connected to the Reactor Coolant System:  ;

Chemical and Volume Control System - Leaks in the Reactor Coolant System may be detected while the plant is at power by performing an inventory balance calculation using parameters such as pressurizer level, volume control tank level, le:down flow, reactor coolant drain tank level, coolant temperature and charging flow rate. Process radiation monitors are i provided to continuously measure the activity of the reactor coolant.

Reactor Coolant Loop Drains. Ouench Tank Drains. Flance Leakace Detector Drains -

These drains are inside containment and drain to the containment sump. Both radiation and  !

level monitors are provided for the containment as described in (3).

Reactor Coolant Pumn Seal Leakage - A controlled bleedoff flow through the pump seals is j maintained to cool the seals and to equalize th:: pressure drop across each seal. The  !

controlled bleedoff is collected and processed by the Chemical and Volume Control System.

Any leakage past the vapor seal, the last mechanical seal is collected in the containment sump. A level alarm is provided for the sump. )

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ATTACIIMENT (3)

DESCRIPTION OF LEAKAGE DETECTION SYSTEM i

5. Reunirement The sensitivity and response time of each leakage detection system employed for unidentified  ;

leakage should be adequate to detect a leakage rate, or its equivalent, of one gpm in less than one hour.

Method of Compliance The frequency of monitoring the leakage detection systems is given in Technical Specification 4.4.6.2. The sensitivity of the monitoring systems is dependent on a large number of factors, such as leak location, fuel burnup, etc. The sensitivity of the systems is ,

discussed in Section 4.3.2.3 of the UFSAR.

6. Requirement r

The leakage detection systems should be capable of performing their function following seismic events that do not require plant shutdown. The airborne radioactivity monitoring ,

system should remain functional when subjected to the safe shutdown earthquake.

I Method of Compliance ,

The leakage detection systems described in the response to (3) above, are seismically (

qualified. Therefore, they will perform their function following a safe shutdown earthquake.  ;

7. Requireme_nt Indicators and alarms n.r each leakage detection system should be provided in the main  !

control room. Procedures for converting various indications to a common leakage equivalent should be available to the operators. The calibration of the indicators should account for needed independent variables.

L Method of Compliance Alarms for each method of leak detection are provided in the main control room. Reactor Coolant System leakage is evaluated by the operators using Surveillance Test Procedure 0-27. This surveillance test procedure is an inventory balance method ofleakage ,

detection. The containment sump level alarm system channels are calibrated every 18  !

months, and the containment gaseous and particulate monitoring system channels are [

calibrated every 24 months in accordance with Technical Specification 4.4.6.1. The  !

calibration accounts for the necessary independent variables.  :

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. ATTACIIMENT (3)

DESCRIPTION OF LEAKAGE DETECTION SYSTEM )

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8. Requirement The leakage detection systems should be equipped with provisions to readily permit testing  ;

for operability and calibration during plant operation.  ;

Method of Compliance  !

The three systems identified in the response to (3), above, are designed to permit channel checks and channel functional tests to be performed while the plant is at power. >

9. Requirement The technical specifications should include the limiting conditions for identified and unidentified leakage and address the availability if vario:ut types of instruments to assure adequate coverage at all times. t Method of Compliance Technical Specification 3.4.6.2 provides the limiting conditions for identified and unidentified reactor coolant leakage. Technical Specification 3.4.6.1 addresses the availability of the leakage detection systems and provides for grab samples if a system is out of service.  ;

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