A 4,000-HP Reactor/Organic Rankine Cycle Power System for Undersea Oilfield Application
Authors: Mason D.G. , Vanosdol J.H. 
Published: October 2008

A small, compact, transportable nuclear power system for pumping crude oil from undersea wellheads is described. Such a system is economically attractive in arctic regions where sea ice precludes year-round operations from surface power sources or at great distances from the coastline. The system described is based upon reliable nuclear, organic Rankine power systems originally designed for unattended space operations. Systems up to 20 Mwe and 2 years' lifetime, between refurbishments, can be built with today's technology.

INTRODUCTION

Because of a growing demand for crude oil, offshore exploration is increasing rapidly. Estimates are that 20 percent of the world's oil supply now comes from offshore wells and that by 1980 that figure will have climbed to 50 percent. As exploration activities expand, the search will extend into deeper and deeper water at increasing distance from the shoreline. Many oil companies are investigating seafloor-mounted oil platforms as one approach to deep-water drilling and production. One version of this concept uses oil pumps attached to the platform to pump the crude oil tens or hundreds of miles to shore or shallow-water based depots. There are various means of providing power to these pumps, including (1) sea surface power ships or buoys that provide electrical power by cables to motors that drive the pumps, (2) power cables from shore-based power stations, and (3) nuclear power systems located on the platform. Because of large pumping distances and depths involved in some situations, large amounts of power are required; one case studied required approximately 4,000 hp, about 3 megawatts electrical. To deliver this power hundreds of miles from a shore-based power station is economically prohibitive. Use of a power ship is also costly approximately $50 thousand per day or $18 million annually. A power buoy has much more reasonable operating costs; however, it is vulnerable to surface storms and probably cannot be on station during winter months in the arctic because of sea ice. The seafloor-platform-based nuclear power system can operate under all weather and sea surface conditions with no loss of production and with competitive operating and capital expenditures.

The purpose of this paper is to describe the characteristics of a typical nuclear power system; its design, performance, cost, and operational features are presented in the following section

DESIGN AND PERFORMANCE

Description

Fig. 1 shows a simplified schematic of the reactor and power conversion system. The reactor is the zirconium hydride (ZrH) type developed by Atomics International for the United States Atomic Energy Commission. The concept was specifically designed to be inherently reliable because it was required to operate unattended without maintenance for years in the hostile environment of space. The primary loop coolant is NaK, a liquid metal, which is a eutectic mixture of sodium and potassium. NaK is used as the coolant because of its excellent heat transfer properties, low vapor pressure, low freezing point 0v120F), and compatibility with stainless steel piping. The NaK is heated in the reactor and flows through the piping to the heat exchanger where its heat is transferred to the organic working fluid.