ML20215D822
| ML20215D822 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/08/1987 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | NORTHEAST NUCLEAR ENERGY CO. |
| Shared Package | |
| ML20215D790 | List: |
| References | |
| NUDOCS 8706190156 | |
| Download: ML20215D822 (11) | |
Text
'
l 7590-01 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of )
)
NORTHEAST NUCLEAR ENERGY ) Docket No. 50-245 COMPANY,_ )
) 1 (Millstone Nuclear Power Sta tion, )
Unit No. 1) )
EXEMPTION I
1.
l Northeast Nuclear Energy Company (NNECO or the licensee) is the holder l of Facility Operating License No. DPR-21, which authorizes the operation of the Millstone Nuclear Power Station, Unit No. 1, (the facility) at the steady-l state power levels not in excess of 2011 megawatts thermal. The facility is a boiling water reactor (BWR) located at the licensee's site in New London County, Connecticut. The license provides, among other things, that it is subject to all rules, regulations and orders of the Nuclear Regulatory Commission (the Commission) now or hereafter in effect.
1 8706190156 870608 5 DR ADOCK 050
7590-01 l
11.
10 CFR 50.49, " Environmental qualification of electric equipment l important to safety for nuclear power plants," requires that the environ- 11 mental qualification program at Millstone Unit'No. I be completed at the end )
of the second refueling outage following March 31,1983(thesecondrefueling outage ended Decen'1ber 23,1985). . Approaching the December 1985 deadline, twenty-eight valve motor operators were the only components remaining to be qualified to-achieve full compliance with 10 CFR 50.49. By letters dated September 30, and October 16, 1985, the licensee reported that eleven of these valve operators would be replaced by the end of the 1985 refueling outage (the new qualified motor operators were installed during the October-December 1985 outage), exemption requests for six valves had been submitted and that the remaining eleven valves would require schedule extensions to complete on-going evaluations.
By letter dated December 18, 1985, the staff issued an evaluation that found the six valve motor operators for which a permanent exemption had been requested to be outside the scope of equipment required to be environmentally qualified and the staff concluded that an exemption for these six motor operators was not necessary. The Commission issued a Memorandum and Order to the licensee regarding the deadline for environmental qualification of the eleven valve motor operators at Millstone Unit No. 1, dated November 20, 1985, that granted an ex-tension of the schedule to the next outage of suff.icient duration after the staff has made a determination on whether an exemption to 10 CFR 50.49 could be granted, or to the next refueling outage, but in no case later than August 30, 1987.
s 7590-01 By letter dated January 17, 1986, the licensee submitted a request ,
1 for permanent exemption for the eleven valve motor operators based on the criteria of 10 CFR 50.12. Four of the eleven valves (1-LP-15A and B, 1-LP-16A and B) are the drywell spray valves that are located in the con-tainment spray.line outside the containment and provide isolation to prevent 4
inadvertent spraying of the drywell. Two valves (1-IC-2, 1-1C-4) are the iso-lation condenser steam inlet and condensate return isolation valves (the other two isolation condenser isolation valves are already qualified). 'Two valves (1-CV-2, 1-C0-3) are in the reactor water cleanup system (RWCU) and serve as the inboard and outboard isolation valves on the RWCU suction line. Two valves ,
(1-RR-2A and 2B) are used to isolate the low pressure coolant injection (LPCI) system from a break in the reactor coolant recirculation piping. The j l
last of the eleven valves (1-MW-96A) is an isolation valve between the main j condenser hotwell and the condensate storage tank (CST). By letter dated l March 12, 1987, the licensee withdrew its exemption request for valves 1-RR-2A and 2B based on discussions with the staff.
By letter dated October 17, 1985, the licensee submitted a probabilistic study summary of this issue derived from the Millstone 1 Probabilistic Safety Study (PSS). The PSS sumary investigated the reduction in core melt frequency and public risk if the modifications for environmental qualification for the eleven valves were implemented. For some of th'e valves, public safety was evaluated by performing sensitivity studies on the PSS interfacing system loss-of-coolant accident (LOCA) analysis. Other valves were not amenable to
S '
7950-01 direct numerical calculations and, therefore, engineering judgment based on insights from the PSS was utilized in assessing the benefit. The licensee's justification for each of the motor operator exemptions is briefly presented below:
(1) Valves 1-LP-15A and B, 1-LP-16A and B .
1 The licensee stated'that these valves are normally closed con-tainment spray valves located in the reactor building. For a LOCA in the reactor building, which may expose these valves to a harsh envi- j ronment, the valves are not required. For a design basis LOCA inside
^
containment, the valves are not required to change position, and their qualification is not needed to prevent or mitigate a design basis I
accident. ]
i (2) Valves 1-IC-2 and 1-IC-4 1 l
Valve 1-IC-2 is located in the reactor building on the inlet (steam) side piping of the isolation condenser (IC) system. Valve 1-IC-4 is i
located inside the drywell on the condensate (water) return line of )
i the IC. i 4
In the letter dated October 17, 1985, the licensee stated that 1-IC-2 is normally open and will receive a close signal if excessive '
steam flow is detected in the IC piping. If a break occurs in the.
IC piping in the drywell, closure of 1-IC-2 would not isolate.the break. If a break occurs in the IC piping in the reactor building, 1-IC-1 (a fully qualified valve in series with 1-1C-2, but inside containment) should close and thus isolate the break. For this scenario, 1-10-1 would not be exposed to a harsh environment. The !
r:
.. t .
1 7590-01 only benefit of environmentally qualifying 1-IC-2 is in case of 1 I
random failure of 1-1C-1. In that case, operation of 1-IC-2 would )
isolate the break. However, as estimated by the licensee, qualifi-cation of'l-IC-2 would only decrease the core melt probability by 2E-9 per year, f; Valve 1-1C-4 is normally open and will close if a high steam flow l 1
in the IC piping, is detected. For a break in the IC piping inside the j drywell, closure of 1-IC-4 will not isolate the break. If the break occurs in the IC piping outside the drywell,1-IC-3 (a fully qualified valve in series with 1-IC-4), which is normally closed, would isolate the break. Therefore, the closure of 1-IC-4 is not needed to isolate the break on the return line. The licensee stated that qualification Of 1-IC-4 will provide no benefit for core melt frequency.
(3) Valves 1-CU-2 and 1-CV-3 The RWCU valves 1-CV-2 and 1-CV-3 are normally open valves with both valves in series on the RWCU suction line. Valve 1-CU-2 is the inboard and 1-CV-3 is the outboard isolation valve. These valves will receive a close signal if excessive flow in the RWCU line is detected. I In the letter dated October 17, 1985, the licensee stated that if a break occurs inside the drywell, closing of these valves will have no !
l effect on isolating the break. If a break in the RWCU system occurs ]
l outside the drywell, valve 1-CV-2 can isolate the break. Since 1-CU-2 is located inside the drywell, it will not be exposed to a harsh en-vironment due to the break in the reactor building. The only benefit of environmentally qualifying valve 1-CV-3 is in the scenario where ,
i q
7590-01 valve 1-C0-2 randomly fails. The licensee estimated that qualifi- ,
cation of this valve would only reduce the core melt frequency by 4E-7 per year.
(4) Valves 1-RR-2A and 1-RR-2B The purpose of the reactor coolant recirculation piping valves 1-RR-2A and 1-RR-2B (normally open isolation valves) is to prevent spillage of LPCI flow following a break in either recirculation piping loop. This is achieved by closing the valve in the intact loop as part of LPCI loop selection logic. If the valve in the loop selected for LPCI injection fails to close, LPCI flow could flow through the recirculation pump and out through the break, thus bypassing the core.
In the letter dated March 12, 1987 the licensee withdrew its ex-emption request for these valves.
1 (5) Valve 1-MW-96A Valve 1-MW-96A is an isolation valve located on the discharge side of the emergency condensate transfer pump which allows transfer of in-ventory from the CST to the hotwell following initiation of feedwater ,
coolantinjection(FWCI)orfeedwater. The concern with this. valve is over the e'fect that high radiation that might occur following an accident and fuel damage. For any transient or LOCA, no fuel damage is expected if FWCI or.feedwater operation is successful. If there is fuel damage, it implies inoperability of FWCI/feedwater, then environmental qualification of 1-MW-96A is irrelevant. The licensee stated that qualifying this valve will offer no improvement in core melt frequency.
o 7590-01 III.
As stated above, the licensee has requested an exemption from 10 CFR 50.49,
" Environmental qualification of electric equipment important to safety for nuclear power plants," for nine valve motor operators and provided supportive justification for each motor operator. In this section, the. staff has evaluated I
the acceptability of these exemption requests based on the estimated risk re-duction benefits and system operations described in Section II. j (1) Drywell Spray Valves The staff has found the licensee's PSS to be generally acceptable.
No credit was taken for drywell spray valves 1-LP-15A and B, 1-LP-16A and B in the PSS analysis or in the design basis LOCA analysis. The f
staff concludes that repositioning of these valves is not required to prevent or mitigate design basis accidents and, therefore, the i environmental qualification of these valves would not serve the underlying purpose of 10 CFR 50.49. Also, the staff review in the Systematic Evaluation Program (SEP) found that the isolation pro-visions supplied by these valves to be acceptable. The staff finds that these valves need not be environmentally qualified, since they perform their safety function (containment isolation) before exposure to a harsh environment.
(2) Isolation Condenser Valves The staff review regarding 1-IC-4 concludes that environmental qualification of the associated motor operator would not reduce core I 1
melt frequency and would not serve the underlying purpose of the rule. '
I i
I
~
7590-01 1 The licensee's equipment qualification (10 CFR 50.49) exemption request for valve 1-IC-2 is based upon a probabilistic argument.
Valves 1-IC-1 (motor operator fully qualified) and 1-IC-2 (motor oper- 3 ator not environmentally qualified) are normally open, in series, and would receive a close signal on high flow in the IC system. If a LOCA l s
occurs in the piping between the reactor vessel'and 1-1C-1 (inside drywell), neither closure of 1-IC-1 nor 1-IC-2 will isolate the break. )
1
'If the LOCA were to occur outside containment between 1-1C-2 and l 1-1C-3 (NNEC0 estimates frequency-at 4E-7 per year),.by 10 CFR 50.49, ;
I-IC-2 must be assumed to go to its most adverse position (which is I "open") since its valve operator is not environmentally qualified and would be subject to a harsh environment. Valve 1-1C-1 is quali-fied, would not be subject to a harsh environment, and should close. l There is, however, a chance that 1-IC-1 would also fail to close (estimated at SE-3 per demand by the licensee). This would result in a non-isolable LOCA outside containment. NNECO's core melt frequency (CMF) estimate of a LOCA between these valves and 1-1C-1 not closing (which represents the maximum CMF reduction if.1-IC-2 is qualified) is 2E-9 per year. NNEC0 states that this value is'so small compared to the overall estimated core melt frequency at Millstone _1. that the i motor operator for 1-IC-2 need not be replaced in order to meet the underlying purpose of 10 CFR 50.49.
This argument's v'alidity is based in part on the reasonableness of the 4E-7 per year LOCA frequency used by NNEC0 (the staff originally _
used one about an order of magnitude. higher). However, the staff now a-
'i
4 7590-01 believes these LOCA frequencies may be lower bound numbers for Millstone Unit 1 since the isolation condenser line between 1-IC-2 and 1-10-3 has been subject to water hammer events and intergranular stress corrosion cracking (IGSCC) in the past. There is insufficient l assurance that these events will not reoccur. The staff finds the licensee's estimated core melt frequency reduction from replacing the motor operator on valve 1-10-2 to be too low and the uncertainty to be high as to what the frequency should be for a LOCA between valves 1-IC-2 and 1-1C-3.
The staff concludes that the estimated reduction of core melt frequency associated with providing an environmentally qualified motor operator for 1-IC-2 is large enough and has enough uncertainty l
that the underlying purpose of 10 CFR 50.49 would not be met unless a qualified operator were provided. The staff, therefore, concludes that the 10 CFR 50.49 exemption request for 1-IC-2 should be denied. I (3) Reactor Water Cleanup System Valves The staff review of the PSS summary for these valves found the licensee's analysis method acceptable and agreed with the conclusions.
The staff estimates no reduction in core melt frequency if 1-CV-2 and 1-CV-3 are qualified for high radiation / aging. The staff believes that an RWCU system LOCA will not prevent valves 1-CV-2 and 1-CV-3 from performing their containment isolation functions. The licensee conservatively assumed 1-CV-3 will always fail in the open position in the event of an RWCU LOCA outside containment. Estimating an RWCU
7590-01 LOCA frequency of 2E-6 per year and a demand failure probability of 0.11 and 0.07 for 1-CV-2 and 1-CV-3, respectively..the licensee l l
estimates that qualifying 1-CV-3 will reduce the estimated core melt j frequency by 3E-7 per year. The staff concludes that qualifying these )
valves for a high radiation environment is not necessary to ensure the equipment will function to mitigate a design basis event since i the valves will automatically isolate before the core can be uncovered. j i'
Therefore, environmental qualification would not serve the underlying purpose of 10 CFR 50.49.
(4) LPCI loop Selection Valves The licensee has withdrawn its exemption request from 10 CFR 50.49 for valves 1-RR-2A and 1-RR-2B following discussions with the staff.
(5) , Condensate Transfer Valve The staff finds that valve 1-MW-96A is not required to perform any safety function for a design basis event. On this basis, 10 CFR 50.49 does not require qualification of this valve for a radiation (or any other harsh) environment. The staff finds valve 1-MW-96A to be outside the scope of equipment required to be environmentally quali-fied and, therefore, no exemption from 10 CFR 50.49 is necessary.
IV.
Accordingly, the Commission has determined that, except for valve 1-1C-2 and valve 1-MW-96A pursuant to 10 CFR 50.12(a)(i), the exemption requested by the licensee's letter of January 17, 1986, as modified by licensee's letter dated March 17, 1987, is authorized by law, will not present an undue risk to
7590-01 the public health and safety, and is consistent with the common defense and security. In addition, the Commission has determined that, pursuant to 10 CFR- I 50.12(a)(2)(ii), special circumstances are present for this exemption in that I application of the regulation in the particular circumstances .is not necessary l
to achieve the underlying purposes of the rule as set forth above. The Commission hereby grants to the licensee an exemption from the qualification )
i requirements of 10 CFR 50.49 with respect to seven of the requested nine valve ;
motor operators identified above. The request with respect to' valve 1-MW-96A is unnecessary and the request with respect to valve 1-1C-2 is denied.
Pursuant to 10 CFR 51.32, the Commission has determined that the issuance of the exemption will have no significant impact on the environment (May26,1987 52 FR 19612).
A copy of the Safety Evaluation, dated June 8, 1987, related to this
{
action is available for public inspection at the Conrnision's Public Document Room, 1717 H Street, N.W., Washington, D.C. and at the local public document room located at the Waterford Public Library. 49 Rope ~ Ferry Road, Waterford, Connecticut 06385. A copy may be obtained upon written request addressed to the U. S. Nuclear Regulatory Commission, Washington, D.C. 20555. Attention:
Director Division of Reactor Projects III/IV/V and Special Projects.
This Exemption is effective upon issuance.
FOR THE NUCLEAR REGULATORY COMMISSION
]/ $
Denn s M. Crutchfield, Di ector-Division of Reactor Projects III/IV/V and Special Projects Office of Nuclear Reactor Regulation Dated at Bethesda, Maryland !
this 8th. day of June 1987.