ML20210K709
| ML20210K709 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 08/13/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20210K705 | List: |
| References | |
| NUDOCS 9708200049 | |
| Download: ML20210K709 (7) | |
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t UNITED STATES j
j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20666 0001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
.3 RELATED TO AMENDMENT N0. 91 TO FACILITY OPERATING LICENSE NO. NPF-66,
_J AND AMENDMENT NO. 84 TO FACILITY OPERATING LICENSE NO. NPF-77 COMMONWEALTH EDISON COMPANY BYRON STATION. UNIT NO 2 BRAIDWOOD STATION. UNIT N0 2 DOCKET NOS STN 50-455 AND STN 50-457
1.0 INTRODUCTION
By letter dated May 24, 1997, as supplemented on May 31, June 20, June 24, and July 18, 1997, Commonwealth Edison Company (Comed, the licensee) requested an exigent license amendment regarding technical specification {TS) surveillance requirement (SR) 4.5.2.b.1, emergency core cooling system (ECCS) subsystem pump casing and high point venting. The May 31, June 20, June 24, and July 18, 1997, submittals provided additional clarifying information that did not change the proposed initial no significant hazards consideration determination.
During discussions with the NRC on May 22 and 23, 1997, concerning a plugged ECCS pump vent line at Byron, Unit 2, the licensee was made aware that their practices for venting chemical and volume (CV) control system (CVCS) discharge piping high points did not reflect precise compliance with TS 4.5.2.b.1.
The purpose of venting is to verify that the piping is full of water. The-CVCS high point vent is in a section of piping that is pressurized by the CV pump (s) and should not be opened during plant operation. On May 23, 1997, the staff issued an emergency license amendment for Braidwood, Unit 1 and a Notice of Enforcemer.t Discretion (NOED) for Byron, Units 1 and 2, and Braidwood Unit 2.
The NOED stated NRC's intention to exercise discretion not to enforce compliance with TS 4.5.2.b.1 for the period from 7:00 p.m. (CDT) on May 23, 1997, until issuance of a license amendment. The NRC confirmed issuance of the N0ED by letter dated May 28, 1997. As specified in NRC Administrative Letter 95-05, Revision to Staff Guidance for Implementing NRC Policy on Notice of Enforcement Discretion, the licensee submitted a request for an exigent license amendment on May 24, 1997.
On May 31, 1997, Byron, Unit 1, was shut down due to an inoperable channel of the steam line isolation system. On that day, Comed requested that the license amendment submittal be processed as an emergency license amendment for 3yron Unit 1.
On June 1,1997, the NRC issued amendment No. 90, for Byron, Unit 1.
9708200049 970813 PDR ADOCK 05000455 P
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[ l By letter dated June 20, 1997, the licensee responded to NRC's request for additional information (RAI) and provided isometric drawings of the ECCS system. On June 24, 1997, the lictnsee submitted a revised exigent amendment request for Byron, Unit 2, and Braidwood, Unit ?, which reflected the changes that were developed based on discussions with the NRC staff. The revision removed the cycle-based limitation on the applicability of TS SR 4.5.2.b.1 and its associated Bases.
In addition, UT inspection of CV 206 valve when the B train of the C1 pump is not operating, is added to the ECCS Subsystems TSs and Bases.
Finally, the revision removes the reference to the system pressure proposed in the May 24, 1997 ECCS Subsystems Bases.
In their letter dated July 18, 1997, the licensee provided the ultrasonic testing procedure number and the method used to demonstrate its qualification.
The exigent amendment revises the venting requirement to encompass the non-operating ECCS pumps and discharge piping, which are provided with high point vent valves.
Those portions of the ECCS systems which are in communication with operating system flow will not be required to be vented. This would normally encompass the operating High Head Safety Injection (CV) subsystem during Modes 1-4 operation, and the operating Low Head Safety Injection Subsystem (RH) durinc
'iods when shutdown cooling is in operation.
Additionally, the we.
of the surveillance will be revised to clearly s
indicate that the installed high point vent valves ad pump casing vent valves will be utilized to ace)mplish the venting operation. The Intermediate Head Safety Injection (SI) Subsystem and the RH subsystem are equipped with pump casing vents. The centrifugal CV pumps are not equipped with pump casing vent valves due to the configuration of the suction and discharge piping. The licensee considers the pumps to be self-venting because the suction and discharge piping enter the pump casing from the top. A new requirement is added to ultrasonically examine the discharge piping of the idle centrifugal pump and the portion of the piping upstream of the High Head Safety Injection isolation valves adjacent to the vent valve every 31 days.
These changes are required to align the SR with the physical construction of the installed piping, and accommodate operating conditions which preclude cycling the installed high point vent valves during system operation, while continuing to provide assurance that the ECCS piping remains water solid.
2.0 EVALUATION The purpose cf venting a piping system is to ensure that the piping is full of water. TS 4.5.2.b.1 requires that the ECCS pump casings and discharge piping high points outside of containment be vented at least once per 31 days. With the exception of the operating centrifugal charging pump, the ECCS pumps are normally in a standby, nonoperating mode. As such, flow path piping has the potential to develop voids and pockets of entrained gases. Maintaining the piping full of water ensures that the system will perform properly, injecting its full capacity into the RCS upon demand.
This will also prevent water hammer and pumoing of noncondensible gas (e.g., air, nitrogen, or hydrogen) into the reactar vessel following an SI signal or during shutdown cooling.
The 31 day fremency for the surveillance which ensures that the system is full of water ii as into consideration the gradual nature of gas accumulation
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- in the ECCS piping. According to the. licensee, the intent of the TS requirement can be achieved by showing that the CV pumps do not require venting (because they are self-venting), and the piping can be shown-to be full by an alternative testing method (Ultrasonic Testing).
2.1 Pumn Casina and liiah Point Ventina The ECCS is comprised of the high head CV pumps, SI system pumps, RH pumps and associated piping. The SI and RH pumps are povided with pump casing vents.
The ECCS discharge piping for Byron, Unit 2, and Braidwood, Unit 2, are provided with vents located at high points throughout the systems outside their respective containments.
During power operations at each plant,.one CV pump is in operation and the other > ump'is in standby. The operating pump is continuously vented via flow throug1 the system.- The pumps (operating and non-operating) are designed and installed to be virtually self-venting, and are not provided with casing vent valves.
The design of the pump places the suction and discharge piping at the top of the pump casing.
The CV suction piping is in communication with either the Refueling Water Storage Tank (RWST) or the Volume Control Tank-(VCT).
Both of these sources provide a net positive suction pressure for the pumps.
The non-operating subsystems which will not be manually vented are in communication with an operating system and subject to system flow and/or pressure.
For the CV subsystem, the non-active portion of piping upstream of the injection line isolation valves is subjected to CV pump discharge praissure of approximately 2500 psia._ The discharge piping containing the high point vent-(SIO45) is at full CV pump discharge pressure and, therefore, it-is not appropriate from an equipment reliability and personnel safety standpoint to
.open the valve for venting purposes..
By letters dated March 17. 1989, August 25, 1989, March 12, 1990, and June 10, 1991, Comed submitted a TS amendment request to discontinue-the performance of the venting-SR for the ECCS piping inside containment for both Byron and Braidwood units.
However, Byron, Unit 2, and Braidwood, Unit 2, do not have high points inside containment for the ECCS pump casings and discharge piping.
systems. The staff reviewed and approved the request in the Safety Evaluation (SE) relating to Amendment-No. 47 for Byron, Unit 1, and No.-36 for Braidwood, Unit 1,- dated June 22, 1992.
In support of the TS amendment request, Comed stated that it had performed an engineering analysis and concluded that in the unlikely event of air voids entering the discharge side 'of the ECCS pumps, the piping would be capable of withstanding a water hammer event caused by the maximum credible air void 'in the piping. With respect to the engineering analysis, the-staff reaffirms its conclusion stated in the SE supporting the amendments; that, in general,- the calculations and analytical methods used in
. determining the effects of water hammer for any system are uncertain in nature
-due to computer code-limitations and therefore,-the staff did not consider the water hammer analysis in evaluating Comed's request.
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For the RH subsystem in operation during shutdown cooling, the piping which is excluded from manual venting is' subjected to a pressure of approximately 360 -
psia and flows which vary from approximately 1000 gpm to 3000 gpm.
The licensee believes that operating RH pump and piping will not be subject to gas i
accumulation under these conditions. The staff finds the licensee's t
assessment acceptable.
The design of the CV pumps is such that significant gas does not collect in the pumps, whether they are running or not. The suction and discharge lines are on the top of the CV pumps and the internal cavities in the pump are small enough that significant gas accumulation in the pump casing would not occur.
2.2 Ultrasonic Testino Examinations Although the licensee has concluded that the probability of significant gas formation was low and transient loads associated with the gas woJ1d be small, the licensee will l
'orm surveillance using UT inspections to verify that the piping is full of u.r.
This is consistant with the intent of the original TS as described in Section 2.0 of this SE. The UT inspections will be on selected portions of piping involving the idle CV pump discharge piping up to the first check valve on the pump discharge and miniflow lines, the stagnant water segments of piping upstream of CV isolation valves SI8801 A and B adjacent to vent valve SIO45, and the piping at the CV206 valve if the BCV pump is idle, every 31 days.
The UT inspections will be performed using a pulse-echo, longitudinal sound wave technique. The technique consists of exciting a transducer to generate a sound wave that travels diametrically through dense materials.
If the pipe is full of water, the sound wave will travel through the water, bounce off the far wall of the pipe, and return to the transducer. The time it takes for the sound wave to travel round trip is converted into distance which equals the diameter of the pipe.
If the UT is performed from the high-point of a partially water filled pipe, the sound wave will not pass through the air gap, thus providing a go-no-go test.
The UT technique to be used is included as part of Comed's procedure NDT-C-46.
This procedure was written for the purpose of detecting sedimentation in piping. However, the procedure stipulates that all examinations shall be performed frem the outside diameter of a pipe filled with water. This procedure was qualified with pipes containing different levels of water ano sediment. The diameters and temperatures of the piping on which the UT surveillance will be performed are within the range for which the procedure was qualified.
The licensee indicated that a revised procedure was developed, using the same UT techniques from NDT-C-46, but including performance qualifications, additional acceptance critaria, and actions to satisfy the SR to be incorporated in the TS.
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._ Byron and Braidwood have performed UT inspections of the CV piping system.
Specifically, the piping on the discharge side of the standby:CV pump up to the downstream check valves for both units was UT inspected along with the stagnant piping around the $1045 vent valves. No voids were identified in either section of piping.
Based upon the testing performed, to ensure that the intent of the SR has been satisfied the staff concluded that the proposed change is acceptable. -This is consistent with the-Standard Technical-Specifications Westinghouse Plants, NUREG-1431 Revision 1, issued April 1995, which includes SR 3.5.2.3 to
" Verify ECCS piping is full of water." Both the SR and the basis for the SR are performance-based and not prescriptive on how the licensee is to perform the verification.
2.3 Technical Snecification Chanaes TS 4.5.2.b.1 is revised to require that each ECCS subsystem be demonstrated operable at least once per 31 days by venting the ECCS pump castings and discharge piping high points outside of containment that are equipped with high point vent valves for subsystems not in direct communication with operating systems. An expanded bases discussion-is added to clarify that only
- the RH and SI pumps are equipped with pump casing vent valves. Additionally, the bases notes that the CV subsystem will not normally be vented, and the operating train of_RH will not be vented while shutdown cooling is in-operation. Additionally, a new TS requirement is added to ultrasonically.
examine, on a monthly basis, the discharge piping of the idle centrifugal pump and the portion of the piping upstream of_the High Head Safety Injection isolation valves The staff finds these changes acce(2SI8801A&B) adjacent to vent valve 2SIO45.
ptable as discussed in Sections 2.0, 2.1 and 2.2, above.
2.4
-Summary The licensee has proposed TS changes based on the self venting characteristics of the CV pumps and UT examination of the portions of the piping where gas could accumulate. The staff has evaluated the licensee's description of the CV pumps and agrees that the design of-the pumps is such that significant-
_ quantities of gas will.not collect in the pumps whether they are running or
. idle. The staff also agrees that the use of UT as proposed by ~the licensee is an acceptable method to d2tect gas that may accumulate at high points in the lines. Further, the TS_ changes proposed by the licensee to incorporate the UT examinations are accuptable.
3.0-EXIGENT CIRCUMSTANCES On May.22, 1997, the licensee was informed that Byron and Braidwood were not in literal compliance with the wording-of TS SR 4.5.2.b.l. -- The-licensee considered Byron and Braidwood to be in compliance with the TS requirements by crediting the dynamic venting action of the operating system as the means of ensuring that the ECCS piping is full of water and by considering the idle centrifugal charging pump to be self venting due to system design and piping l
b-configuration. - After being informed that they were not in compliance with the
-TS.Tthe licensee submitted a request for enforcement discretion. On May 23, 1997, the NRC issued a NOED for the period from 7:00 p.m. on May 23, 1997, until issuance of a license amendment. By letter dated May 24, 1997, the
-licensee promptly requested:an exigent license amendment regarding TS 4.5.2.b.1. -The exigent amendment request was in accordance with the NRC Administrative Letter 95-05," Revision to Staff Guidance for_ Implementing NRC Policy on Notice of Enforcement Discretion." The exigent amendment was-
- requested because the licensee did not have the opportunity to make a timely non-exigent. application prior to May 22, 1997. The Comission finds that the exigent situation existed pursuant 10 CFR 50.91(a)(6).
Notice of-the staff's proposed determination that this proposed amendment involves no significant hazards consideration was published-in the Federal Reaister on June 10, 1997 (62 FR 31633).
Given that this notice has provided 30 days-notice as required by 10 CFR 90.91(a)(2), there is no need for the Commission to make a final: determination that the proposed amendment does not
-involve a significant hazards. consideration.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official
.was notified of the proposed issuance of the amendments. The State official had no coments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendments change surveillance requirements. The NRC staff has determined that the. amendments involve no-significant increase in the amounts, and no significant change in the types, of any effluents that my be released offsite, and that there is no si,nificant increase in individual or cumulative occupational radiation exposure.i -The Comission-has previously issued a-proposed finding that the amendments-involve no significant hazards consideration, and there has been no public coment on such finding (62 FR 31633). Accordingly. the amendments meet the eligibility criteria for categorical exclusion-set forth in 10 CFR 51.22(c)(9)
Pursuant to 10 CFR 51.22 be pre (b) no environmental impact statement or environmental assessment need pared in connection with the issuance of the amendments.
6.0 CONCLUSION
. Based on its review as discussed-above, the staff finds the proposed revisions to the TS regarding ECCS pumps, piping venting requirements _and the use of_ UT
-is' acceptable for. assuring that ECCS water filled piping'is void free.
Furthermore,.the Comission has concluded 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
-7 compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
3 Principal Contributors:
J. Rajan D. Naujock M. Shualbi Date:
August 13, 1997 k
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