ML041890364
| ML041890364 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 06/29/2004 |
| From: | Jamil D Duke Power Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML041890364 (6) | |
Text
'N D Duke D.M. JAMIL 1DPowere Vice President A Duke Energy Company Duke Power Catawba Nuclear Station 4800 Concord Rd. / CNOI VP York, SC 29745-9635 803 831 4251 803 831 3221 fax June 29, 2004 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555
Subject:
Duke Energy Corporation Catawba Nuclear Station, Units 1 and 2 Docket Numbers 50-413 and 50-414 Replacement of Hydrogen Ignitor Glow Plugs
References:
- 1. NUREG-0954, "Safety Evaluation Report related to the operation of Catawba Nuclear Station, Units 1 and 2,"
Supplements Nos. 5 and 6, dated February 1986 and May 1986, respectively.
- 2. Letter from NRC to Duke Power Company, "Safety Evaluation - Closure of the Hydrogen Control Issue Pursuant to 10 CFR 50.44 for Catawba and McGuire Nuclear Stations (TAC Nos. M63034, M63035, M63032, M63033)," dated May 26, 1993.
The purpose of this letter is to inform the NRC regarding Catawba's plans to replace the hydrogen ignitor glow plugs with glow coils. This letter is.being provided for information only and no NRC action is being requested.
Background
10 CFR 50.44 requires units with ice condenser containments to install suitable hydrogen control systems that would accommodate an amount of hydrogen equivalent to that generated from the reaction of 75% of the fuel cladding with water. The Hydrogen Ignition System (HIS) provides this required capability. This requirement was placed on ice condenser units because of their small containment volume and low design pressure (compared with pressurized water reactor dry containments). Calculations indicate that if hydrogen equivalent to that generated from the reaction of www.duke-energy.com
- U.S. Nuclear Regulatory Commission Page 2 June 29, 2004 75% of the fuel cladding with water were to collect in the primary containment, the resulting hydrogen concentration would be far above the lower flammability limit such that, if ignited from a random ignition source, the resulting hydrogen burn would seriously challenge the containment and safety systems in the containment.
The HIS is based on the concept of controlled ignition using thermal ignitors, designed to be capable of functioning in a post accident environment, seismically supported, and capable of actuation from the control room. A total of 70 ignitors are distributed throughout the various regions of containment in which hydrogen could be released or to which it could flow in significant quantities. The ignitors are arranged in two independent trains such that each containment region has at least two ignitors, one from each train, controlled and powered redundantly so that ignition would occur in each region even if one train failed to energize.
When the HIS is initiated, the ignitor elements are energized and heat up to a surface temperature 2 1700 0 F. At this temperature, they ignite the hydrogen gas that is present in the airspace in the vicinity of the ignitor. The HIS depends on the dispersed location of the ignitors so that local pockets of hydrogen at increased concentrations would burn before reaching a hydrogen concentration significantly higher than the lower flammability limit.
Hydrogen ignition in the vicinity of the ignitors is assumed to occur when the local hydrogen concentration reaches 8.5 volume percent (v/o) and results in 100% of the hydrogen present being consumed.
Catawba currently utilizes diesel engine glow plugs as the hydrogen ignitors. The currently installed glow plugs in Units 1 and 2 are obsolete and can no longer be purchased from current suppliers or from the manufacturers. Only two methods of hydrogen ignition have been demonstrated and accepted by the NRC; the diesel engine glow plug (obsolete) and the Tayco glow coil. The only acceptable replacement for the glow plug is the Tayco manufactured ignitors, which have been proven reliable in other ice condenser plants in the nuclear industry.
The Tayco ignitors were specifically designed for nuclear applications and have long-term support from the manufacturer. The Tayco ignitors were tested and analyzed in a joint effort by Duke Energy Corporation and other
U.S. Nuclear Regulatory Commission Page 3 June 29, 2004 utilities with ice condenser plants. They have proven to be a viable method for hydrogen mitigation. 6ther plants (e.g., Sequoyah, Watts Bar) have been utilizing Tayco ignitors for many years with very reliable results.
Discussion of Technical and Licensing Issues The modification to install Tayco glow coils will require a number of physical changes to the HIS. The mounting boxes for each existing glow plug will be replaced to accommodate the installation of the glow coils. The installation of the glow coils will require a change to the circuit breakers, fuses, and transformers, as well as the addition of voltage regulators and the replacement of the cable from the motor control centers to the hydrogen ignitor control panels due to the additional current requirements of the glow coils.
All of the ignitor enclosures, transformers, and voltage regulators will be seismically mounted.
The Tayco Model 3442 glow coils that will be utilized will draw more current than the existing glow plugs. The glow coils are rated at 523 watts, 27.5 ohms, 120 volts AC. This equates to approximately 4.4 amps normal operating current per coil. By contrast, the glow plugs draw approximately 1.18 amps each. The increase in operating current necessitates the majority of the new design requirements.
Each cable coming from the inside of the containment penetration, that goes out to each ignitor group, has been determined to be adequate to handle the additional current loads of the new glow coils. Each of the six containment penetrations is sized to handle more than the load of a maximum group of six ignitors. In addition, the cabling from the hydrogen mitigation control panels to the containment penetrations is sufficient to accommodate the new current load. Therefore, all cables from the hydrogen ignitor control panels to each individual ignitor box are adequate to support the load requirements of the glow coils.
The emergency diesel generator loading calculation has been reviewed for impact from the proposed modification. The calculation has sufficient margin to add an additional 19.2 kW of load to both diesel generators on each unit as required by the new ignitors. The HIS loads are manually energized upon receiving a permissive after all other required loads have been sequenced on.
U.S. Nuclear Regulatory Commission Page 4 June 29, 2004 Catawba plans to perform the modification to utilize Tayco glow coils under the 10 CFR 50.59 process. Reference 1 contains a discussion relative to the performance of hydrogen ignitors in a containment spray environment.
During the initial licensing of Catawba, the NRC accepted the existing glow plug design on the basis of extensive testing that was being conducted at the time by Sandia National Laboratory. This testing demonstrated the adequacy of the ignitor performance under containment spray conditions. In Reference 2, the NRC indicated that by the time of preparation of Reference 1 (Supplement No. 6), the staff had completed its review of glow plug operability in a containment spray environment typical of that expected in the upper compartment. The NRC reported in Reference 2 that this issue had been resolved. Although the discussion in Reference 1 (Supplement No. 6) refers specifically to glow plugs and not to Tayco glow coils, the NRC has indicated the acceptability of Tayco glow coils for Sequoyah and Watts Bar. These plants have utilized Tayco glow coils for many years with good performance. The glow coil assemblies to be installed at Catawba will be identical to those installed at Sequoyah and Watts Bar relative to the dimensions of the ignitor assembly box and spray shield. Therefore, their performance in a containment spray environment will be comparable to that of the TVA plants.
The modification to install Tayco glow coils will be implemented on Unit 2 during the end-of-cycle 13 refueling outage. This outage is scheduled to begin in late summer of 2004. By that time, the glow plugs currently installed in Unit 2 will have reached the end of their service life and will require replacement. There are no alternatives other than Tayco glow coils.
No changes are required to the existing design bases for the HIS as a result of this modification. The Updated Final Safety Analysis Report, Technical Specification Bases for the HIS, and design basis documentation for the system will need to be revised to reflect the use of Tayco glow coils.
No actual Technical Specification changes will be required.
Conclusions Catawba needs to replace the existing glow plugs in the HIS as a result of obsolescence. The new Tayco glow coils will have continued system support with spare parts, and will have increased reliability over the glow plugs. The glow
U.S. Nuclear Regulatory Commission Page 5 June 29, 2004 coil performance will equal or exceed that of the glow plugs.
The purpose of this letter is to inform the NRC of Catawba's plans regarding this issue. No NRC action is being requested via this letter. Inquiries on this matter should be directed to L.J. Rudy at (803) 831-3084.
LJR/s
U.S. Nuclear Regulatory Commission Page 6 June 29, 2004 xc:
W.D. Travers U.S. Nuclear Regulatory Commission Regional Administrator, Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, GA 30303 E.F. Guthrie Senior Resident Inspector (CNS)
U.S. Nuclear Regulatory Commission Catawba Nuclear Station S.E. Peters (addressee only)
NRC Project Manager (CNS)
U.S. Nuclear Regulatory Commission Mail Stop 0-8 G9 Washington, D.C. 20555-0001