The LBB (Leak Before Break) project was a part of the OSA project activities for Medzamor NPP unit 2. The on site utility in Medzamor NPP during the project was Sogin. The Contractor of the LBB/LDS project was Ansaldo Energia in consortium with Empresarios Agrupados and KONEXP (Russia). The project was completed during the time period 2004 to mid 2005.

Lot 2, "Definition of new Leak Detection System (LDS) configuration" of the LBB project for Medzamor NPP, Unit 2 was implemented in parallel with Lot 1, "LBB Application to Armenia NPP Unit 2". According to general LBB concept a leak of 3,8 l/min (1 GPM) must be detected by the plant LDS within 1 hour of leakage occurrence with a location accuracy of 2m. At the same time it must be shown by calculation that the size of a hypothetical, so called "leakage crack" is by a factor of 2 smaller than a simultaneously calculated "critical crack" which would cause a pipe break. The "leakage crack" is defined as a through wall crack which gives a leak of 38 l/min (10 GPM). So there is a safety margin of 10 on the LDS and 2 on the "critical crack" size. If these LBB criteria are met no additional missile (high energy line break) protection is needed to protect essential components, piping and instrumentation next to the MCL (Main Coolant Line) and SL (Surge Line) in the confinement

Objectives

The objective of Lot 2 of the project was to define a LDS that meets the requirements for the application of the LBB methodology to the MCL and SL for Medzamor NPP, Unit 2. The overall objective was to define general conditions for LBB applicability at the ANPP approved by ANRA (Armenian Nuclear Regulatory Authority) and provide the technical background to ANPP for upgrading the layout of the Main Coolant Lines and Surge Line, as well as the inspection and surveillance practices, in order to ensure that those piping systems are compliant with the criteria for the qualification for Leak Before Break on the basis of available international methodology and practice.

Project Results

The selected LDS systems for an Integrated-Information LDS (II-LDS) has been described in detail in the results. The methods selected for the II-LDS are:

• Acoustic Leak Monitoring System (ALMS), which is deliberately devoted to detection of leaks in the primary piping.
• The Radiation Monitoring System (RMS) is an obligatory LDS in the LBB concept. RMS is a standard tool in Nuclear Power Plants (NPPs) for leak detection in the primary circuit in general.
• Monitoring air pressure and temperature can very well be incorporated into operation for leak detection and leak rate estimation.
• The floor drain sump is a good tool for leak monitoring and is recommended even in general in the U.S. Regulatory Guide 1.45.

Of the above methods the 3 first ones are direct leakage monitoring systems while the drain sump is an indirect LDS method.

Many other LDS methods have been briefly presented in the project reports. These methods are mainly functioning by indirect monitoring symptoms. The following LDS systems were discussed as potential candidates for the LBB concept in ANPP unit 2:

• Regular system for monitoring of Pressurizer (PRZ) and bubble tank parameters; adaptation recommended (AR).
• Regular system for monitoring of primary circuit parameters; (AR)
• Primary circuit make-up system; (AR)
• Reactor coolant pump intermediate circuit system; (AR)
• Regular system for monitoring condensate in the ventilation system; adaptation possible (AP)
• Control and protection system in control rod drive system; (AP)
• Humidity monitoring under the dome of the RPV; (AP)
• Monitoring system of live steam radioactivity; (AP)
• Monitoring system of blow-offs from main ejector activity; (AP)
• Monitoring system of the pressure in the inter-gasket space (drain) of steam generator collector heads; (AP)

In the reports it is indicated which of the above systems are recommended and which system could possible to apply as part of the LDS at ANPP unit 2.

The following additional systems have been proposed for improving the localization capability of leaks:

• Vision Based Monitoring System (VBMS) by infrared cameras for detecting hot spots on the piping or insulation surface
• Moisture tape humidity sensors (FL�SS) as is used e.g. in Bohunice NPP
• High sensitivity microphones as used in some RBMKs

Brief technical specifications of the VBMS and the microphones have also been presented as requested in the contract and TOR.

The following conclusions regarding results of the analyses of the LDS of the MCL and SL for leaks corresponding to the LBB concept and standard plant leaks were given:

• The existing ALMS equipment is capable of detecting leaks and determining uncontrolled leaks and locations. However, some additional sensors as well as replacement of some sensors are needed in order to fully meet the LBB requirements on leak detection.
• The RMS is capable to detect leaks in sealed compartments where all the relevant pipelines are located. The method can detect down to 1.9 l/min (0.5 GPM) which is good enough for detecting leaks in the MCL according to the LBB concept, but not in the SL. The time to trigger the RMS for leaks is less than 10 min, which also fulfils the LBB concept requests well (in <1 hour). The leak can, however, be located only in the compartment of leakage.
• The temperature and pressure measurements in the pipeline compartments can only be used as complementary methods because the sensitivity of leak detection just exceeds small unidentified leak rates. Location of leak is not possible.
• The drain sump level monitoring should be incorporated in the operation for leak detection and leak rate estimation. Necessary upgrading including instrumentation and verification was aslo described in the deliverables.

Conclusions

The main technical conclusions of this lot are briefly collected in the following:

• The LDS of ANPP Unit 2 does not meet the LBB concept requirements in present state and need upgrading.
• The ALMS can be upgraded by replacing some sensors and by installing new ones under the SG
• The RMS of the primary circuit is capable of detecting leaks in the confinement corresponding to 1.9 l/min within the requested time period but cannot locate the leak
• The floor drain sump is capable of detecting leaks but cannot locate the leak.
• For the MCL the LBB concept could be applied for leakage detection capacity of 1.9 l/min provided that the ALMS will be upgraded.
• For the SL the LBB concept could not be met for any of the specified loading conditions. For Normal Operating Conditions the LBB concept could be met if a LDS capacity of 1,9 l/min could be accepted. According to general rules the request on LDS is 3,8 l/min. According to contractor 1,9 l/min may be accepted if one can confirm the corresponding LDS capability. Nevertheless, for accident and earthquake conditions LBB concept cannot be met with the present SL piping support configuration and LDS capacity.